Fluke PM6690 Operator's Manual

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Tim er/Counter/ Analyzer

PM6690

Operators Manual

PN 4822 872 20301

April 2005 - First Edition

Printed in Sweden.

GENERAL INFORMATION .............VI

About this Manual .................VI

Warranty........................VI

DeclarationofConformity ...........VI

1 Preparation for Use

Preface ....................... 1-2

Introduction ........................1-2

PowerfulandVersatileFunctions ....1-2

NoMistakes.....................1-3

Design Innovations ..................1-3

State of the Art Technology Gives

DurableUse ....................1-3

HighResolution..................1-3

Remote Control .....................1-4

FastGPIBBus...................1-4

Safety ........................1-5

Introduction ........................1-5

Safety Precautions ..................1-5

CautionandWarningStatements ....1-6

Symbols........................1-6

If in Doubt about Safety ............1-6

Unpacking ....................1-7

Check List .........................1-7

Identification .......................1-7

Installation .........................1-7

Supply Voltage...................1-7

Grounding.........................

1-8

OrientationandCooling............1-8

Fold-Down Support ...............1-8

Rackmount Adapter...............1-9

2 Using the Controls

Basic Controls ......................2-2

Secondary Controls ..................2-4

Connectors & Indicators ...........2-4

Rear Panel .....................2-5

Description of Keys ..................2-6

Power .........................2-6

SelectFunction ..................2-6

Autoset/Preset...................2-6

MoveCursor ....................2-6

DisplayContrast .................2-7

Enter..........................2-7

Save&Exit.....................2-7

Don'tSave&Exit.................2-7

Presentation Modes...............2-7

EnteringNumericValues...........2-8

HardMenuKeys .................2-9

Default Settings ....................2-15

3 Input Signal Conditioning

Input Amplifier ......................3-2

Impedance......................3-2

Attenuation .....................3-2

Coupling .......................3-3

Filter ..........................3-3

Man/Auto.......................3-4

Trig ...........................3-5

How to Reduce or Ignore Noise and

Interference ......................3-6

Trigger Hysteresis ................3-6

How to use Trigger Level Setting.....3-7

III

4 Measuring Functions

Introduction to This Chapter .....4-2

Selecting Function ...................4-2

Frequency Measurements .......4-3

FREQ A, B.........................4-3

FREQ C ...........................4-3

RATIO A/B, B/A, C/A, C/B .............4-4

BURST A, B, C .....................4-4

Triggering ......................4-4

Burst Measurements using Manual

Presetting ......................4-5

Frequency Modulated Signals ..........4-6

Carrier Wave Frequency f f

...........................4-7

max

............................4-7

min

...........................4-8

p-p

Errors in f

max,fmin

, and Df

AM Signals ........................4-8

Carrier Wave Frequency ...........4-8

Modulating Frequency .............4-9

Theory of Measurement ..............4-9

Reciprocal Counting ..............4-9

Sample-Hold...................4-10

Time-Out......................4-10

Measuring Speed ...............4-10

PERIOD..........................4-12

SingleA,B.....................4-12

AverageA,B,C.................4-12

Time Measurements ...........4-13

Introduction .......................4-13

Triggering .....................4-13

Time Interval ......................4-14

TimeIntervalAtoB..............4-14

TimeIntervalBtoA..............4-14

TimeIntervalAtoA,BtoB........4-14

Rise/Fall Time A/B..................4-14

Pulse Width A/B ...................4-15

Duty Factor A/B ....................4-15

Measurement Errors ................4-15

Hysteresis.....................4-15

Overdrive and Pulse Rounding .....4-16

Auto Trigger....................4-16

Phase .......................4-17

What is Phase? ....................4-17

Resolution ........................4-17

Possible Errors ....................4-18

.........4-6

.........4-8

p-p

Inaccuracies ...................4-18

Voltage ...................... 4-22

MAX,VMIN,VPP

............................4-23

RMS

....................4-22

5 Measurement Control

About This Chapter ..................5-2

MeasurementTime...............5-2

GateIndicator ...................5-2

SingleMeasurements .............5-2

Hold/Run&Restart...............5-2

Arming.........................5-2

StartArming.....................5-3

StopArming.....................5-3

Controlling Measurement Timing . 5-4

The Measurement Process ............5-4

Resolution as Function of

MeasurementTime...............5-4

MeasurementTimeandRates ......5-5

WhatisArming? .................5-5

Arming Setup Time ..................5-9

Arming Examples ...................5-9

Introduction to Arming Examples.....5-9

#1 Measuring the First Burst Pulse . . . 5-9

#2 Measuring the Second

BurstPulse ....................5-11

#3 Measuring the Time Between

BurstPulse#1and#4............5-12

#4 Profiling ....................5-13

6 Process

Introduction ........................6-2

Averaging ......................6-2

Mathematics .......................6-2

Example:.......................6-2

Statistics ..........................6-3

Allan Deviation vs. Standard Deviation 6-3

SelectingSamplingParameters .....6-3

Measuring Speed ................6-4

Determining Long or Short Time

Instability .......................6-4

StatisticsandMathematics .........6-5

Confidence Limits ................6-5

JitterMeasurements ..............6-5

Limits .............................6-6

Limit Behavior ...................6-6

LimitMode......................6-7

Limits and Graphics..................6-7

7 Performance Check

General Information..................7-2

Preparations .......................7-2

Test Equipment .....................7-2

Front Panel Controls .................7-3

InternalSelf-Tests ................7-3

Keyboard Test ...................7-3

Short Form Specification Test ..........7-5

Sensitivity and Frequency Range ....7-5

Voltage ........................7-6

Trigger Indicators and Input Controls. . 7-7

Trigger Level Check ..............7-8

Reference Oscillators .............7-8

ResolutionTest..................7-9

Rear Inputs/Outputs .................7-9

10MHzOUT....................7-9

EXTREFFREQINPUT............7-9

EXTARMINPUT.................7-9

Measuring Functions ................7-10

Check of HOLD OFF Function ........7-10

Options ..........................7-11

Input C Check ..................7-11

8 Specifications

Introduction ........................8-2

Measurement Functions ..............8-2

Frequency A, B, C ................8-2

Frequency Burst A, B, C ...........8-2

PeriodA,B,CAverage............8-2

PeriodA,BSingle................8-3

RatioA/B,B/A,C/A,C/B...........8-3

Time Interval A to B, B to A, A to A,

BtoB..........................8-3

PulseWidthA,B.................8-3

RiseandFallTimeA,B............8-3

PhaseARel.B,BRel.A...........8-4

DutyFactorA,B .................8-4

max,Vmin,Vp-p

TimestampingA,B ...............8-4

Auto Set / Manual Set .............8-5

Input and Output Specifications ........8-5

Inputs A and B...................8-5

Input C (PM6690/6xx) .............8-6

Input C (PM6690/7xx) .............8-6

Rear Panel Inputs & Outputs ........8-6

Auxiliary Functions ..................8-7

Trigger Hold-Off..................8-7

ExternalStart/StopArming .........8-7

A,B ...............8-4

Statistics .......................8-7

Mathematics ....................8-7

OtherFunctions..................8-7

Display.........................8-8

GPIBInterface...................8-8

USBInterface ...................8-8

TimeView™.....................8-8

Measurement Uncertainties ...........8-9

Random Uncertainties .............8-9

SystematicUncertainties...........8-9

Time Interval, Pulse Width,

Rise/FallTime..................8-10

Frequency & Period..............8-10

Ratio f

Phase ........................8-10

DutyFactor ....................8-10

Calibration ........................8-11

DefinitionofTerms...............8-11

General Specifications ..............8-11

EnvironmentalData..............8-11

Power Requirements .............8-11

Explanations ...................8-12

Timebase Options ...............8-12

Dimensions&Weight ............8-13

Ordering Information ................8-13

......................8-10

1/f2

9 Index

10 Service

Sales and Service office .............10-2

GENERAL INFORMATION

About this Manual

This manual contains directions for use that apply to the Timer/Counter/Analyzer PM6690.

In order to simplify the references, the PM6690 is further referred to throughout this manual as the '90'.

Warranty

The Warranty Statement is part of the Getting Started Manual that is included with the shipment.

Declaration of Conformity

The complete text with formal statements concerning product identification, manufacturer and standards used for type testing is available on request.

Chapter 1

Preparation for Use

Preface

Introduction

Congratulations on your choice of instrument. It will serve you well for many years to come.

Your Timer/Counter/Analyzer is designed to bring you a new dimension to bench-top and system counting. It offers significantly increased performance compared to traditional Timer/Counters. The '90' offers the following advantages:

–

12 digits of frequency resolution per second and 100 ps resolution, as a result of high-resolution interpolating reciprocal counting.

–

A variety of HF prescaler options with up per frequency limits ranging from 3 GHz to 8 GHz.

–

Integrated high performance GPIB inter face using SCPI commands.

–

A fast USB interface that replaces the tra ditional but slower RS-232 serial interface.

–

Timestamping; the counter records exactly when a measurement is made.

–

A high measurement rate of up to 250 k readings/s to internal memory.

Powerful and Versatile Functions

A unique performance feature in your new instrument is the comprehensive arming possibilities, which allow you to characterize virtually any type of complex signal concerning frequency and time.

For instance, you can insert a delay between the external arming condition and the actual arming of the counter. Read more about Arming in Chapter 5, “Measurement Control”.

In addition to the traditional measurement functions of a timer/counter, these instruments have a multitude of other functions such as

phase, duty factor, rise/fall-time and peak

voltage. The counter can perform all measurement functions on both main inputs (A & B). Most measurement functions can be armed, either via one of the main inputs or via

a separate arming channel (E).

By using the built-in mathematics and statis tics functions, the instrument can process the measurement results on your benchtop, with out the need for a controller. Math functions include inversion, scaling and offset. Statistics functions include Max, Min and Mean as well

1-2 Preface

Preparation for Use

as Standard and Allan Deviation on sample sizes up to 2*10

No Mistakes

You will soon find that your instrument is more or less self-explanatory with an intuitive user interface. A menu tree with few levels makes the timer/counter easy to operate. The large backlit graphic LCD is the center of in formation and can show you several signal pa rameters at the same time as well as setting status and operator messages.

Statistics based on measurement samples can easily be presented as histograms or trend plots in addition to standard numerical mea surement results like max, min, mean and standard deviation.

The AUTO function triggers automatically on any input waveform. A bus-learn mode simplifies GPIB programming. With bus-learn mode, manual counter settings can be transferred to the controller for later reprogramming. There is no need to learn code and syntax for each individual counter setting if you are an occasional bus user.

Design Innovations

State of the Art Technology Gives Durable Use

These counters are designed for quality and durability. The design is highly integrated. The digital counting circuitry consists of just one custom-developed FPGA and a 32-bit

microcontroller. The high integration and low

component count reduces power consumption and results in an MTBF of 30,000 hours. Modern surface-mount technology ensures high production quality. A rugged mechanical construction, including a metal cabinet that withstands mechanical shocks and protects against EMI, is also a valuable feature.

High Resolution

The use of reciprocal interpolating counting in this new counter results in excellent relative resolution: 12 digits/s for all frequencies.

The measurement is synchronized with the input cycles instead of the timebase. Simultaneously with the normal “digital” counting, the counter makes analog measurements of the time between the start/stop trigger events and the next following clock pulse. This is done in four identical circuits by charging an integrating capacitor with a constant current, starting at the trigger event. Charging is stopped at the leading edge of the first follow ing clock pulse. The stored charge in the inte grating capacitor represents the time differ ence between the start trigger event and the leading edge of the first following clock pulse. A similar charge integration is made for the stop trigger event.

When the “digital” part of the measurement is ready, the stored charges in the capacitors are

Preface 1-3

Preparation for Use

measured by means of Analog/Digital Converters.

The counter’s microprocessor calculates the result after completing all measurements, i.e. the digital time measurement and the analog interpolation measurements.

The result is that the basic “digital resolution” of ± 1 clock pulse (10 ns) is reduced to 100 ps for the '90'.

Since the measurement is synchronized with the input signal, the resolution for frequency measurements is very high and independent of frequency.

The counters have 14 display digits to ensure that the display itself does not restrict the resolution.

Remote Control

This instrument is programmable via two interfaces, GPIB and USB.

The GPIB interface offers full general func tionality and compliance with the latest stan dards in use, the IEEE 488.2 1987 for HW and the SCPI 1999 for SW.

In addition to this 'native' mode of operation there is also a second mode that emulates the Agilent 53131/132 command set for easy ex change of instruments in operational ATE systems.

Fast GPIB Bus

These counters are not only extremely power ful and versatile bench-top instruments, they also feature extraordinary bus properties.

The bus transfer rate is up to 2000 triggered measurements/s. Array measurements to the internal memory can reach 250 k measure ments/s.

This very high measurement rate makes new measurements possible. For example, you can perform jitter analysis on several tens of thou sands of pulse width measurements and cap ture them in a second.

An extensive programming manual helps you understand SCPI and counter programming.

The counter is easy to use in GPIB environments. A built-in bus-learn mode enables you to make all counter settings manually and transfer them to the controller. The response can later be used to reprogram the counter to the same settings. This eliminates the need for the occasional user to learn all individual programming codes.

Complete (manually set) counter settings can also be stored in 20 internal memory locations and can easily be recalled on a later occasion. Ten of them can be user protected.

The USB interface is mainly intended for the lab environment in conjunction with the op tional TimeView™ analysis software. The communication protocol is a proprietary ver sion of SCPI.

1-4 Preface

Safety

Preparation for Use

Introduction

Even though we know that you are eager to get going, we urge you to take a few minutes to read through this part of the introductory chapter carefully before plugging the line connector into the wall outlet.

This instrument has been designed and tested for Measurement Category I, Pollution Degree 2, in accordance with EN/IEC 61010-1:2001 and CAN/CSA-C22.2 No. 61010-1-04 (including approval). It has been supplied in a safe condition.

Study this manual thoroughly to acquire ade quate knowledge of the instrument, especially the section on Safety Precautions hereafter and the section on Installation on page 1-7.

Safety Precautions

All equipment that can be connected to line power is a potential danger to life. Handling restrictions imposed on such equipment should be observed.

To ensure the correct and safe operation of the instrument, it is essential that you follow generally accepted safety procedures in addition to the safety precautions specified in this manual.

The instrument is designed to be used by trained personnel only. Removing the cover for repair, maintenance, and adjustment of the instrument must be done by qualified person nel who are aware of the hazards involved.

The warranty commitments are rendered void if unauthorized access to the interior of the instrument has taken place during the given warranty period.

Safety 1-5

Preparation for Use

Caution and Warning Statements

CAUTION: Shows where incorrect

procedures can cause damage to, or destruction of equipment or other property.

WARNING: Shows a potential danger

that requires correct procedures or practices to prevent personal in jury.

Symbols

Shows where the protective ground terminal is connected inside the instrument. Never remove or loosen this screw.

This symbol is used for identifying the functional ground of an I/O signal. It is always connected to the instrument chassis.

Fig. 1-1 Do not overlook the safety in

Inform your Fluke representative.

–

For example, the instrument is likely to be unsafe if it is visibly damaged.

structions!

Indicates that the operator should

consult the manual.

One such symbol is printed on the instrument, below the A and B inputs. It points out that the damage level for the input voltage decreases from 350 V input impedance from 1 MW to 50 W.

to 12V

whenyouswitchthe

rms

If in Doubt about Safety

Whenever you suspect that it is unsafe to use the instrument, you must make it inoperative by doing the following:

–

Disconnect the line cord

–

Clearly mark the instrument to prevent its further operation

1-6 Safety

Unpacking

Preparation for Use

Check that the shipment is complete and that no damage has occurred during transportation. If the contents are incomplete or damaged, file a claim with the carrier immediately. Also notify your local Fluke sales or service organization in case repair or replacement may be required.

Check List

The shipment should contain the following:

–

Counter/Timer/Analyzer, Model 90

–

Line cord

–

N-to-BNC Adapter (only if one of the

prescaler options has been ordered)

–

Printed version of the Getting Started

Manual.

–

Brochure with Important Information

–

Certificate of Calibration

–

Options you ordered should be installed.

See Identification below.

–

CD including the following documentation

in PDF:

•

Getting Started Manual

•

Operators Manual

•

Programming Manual

Identification

The type plate on the rear panel shows type number and serial number. See illustration on page 2-5. Installed options are listed under the menu User Options - About, where you can also find information on firmware version and calibration date. See page 2-12.

Installation

Supply Voltage

Setting

The Counter may be connected to any AC supply with a voltage rating of 90 to 265

, 45 to 440 Hz. The counter automati

rms

cally adjusts itself to the input line voltage.

Fuse

The secondary supply voltages are electroni cally protected against overload or short cir cuit. The primary line voltage side is protected by a fuse located on the power supply unit. The fuse rating covers the full voltage range. Consequently there is no need for the user to replace the fuse under any operating condi tions, nor is it accessible from the outside.

Unpacking 1-7

Preparation for Use

CAUTION: If this fuse is blown, it is

likely that the power supply is badly damaged. Do not replace the fuse. Send the counter to the local Service Center.

Removing the cover for repair, maintenance and adjustment must be done by qualified and trained personnel only, who are fully aware of the hazards involved.

The warranty commitments are rendered void if unauthorized access to the interior of the instrument has taken place during the given warranty period.

Grounding

Grounding faults in the line voltage supply will make any instrument connected to it dangerous. Before connecting any unit to the power line, you must make sure that the protective ground functions correctly. Only then can a unit be connected to the power line and only by using a three-wire line cord. No other method of grounding is permitted. Extension cords must always have a protective ground conductor.

Orientation and Cooling

The counter can be operated in any position desired. Make sure that the air flow through the ventilation slots at the top, and side panels is not obstructed. Leave 5 centimeters (2 inches) of space around the counter.

Fold-Down Support

Fig. 1-2 Fold-down support for comfort

able bench-top use.

For bench-top use, a fold-down support is available for use underneath the counter. This support can also be used as a handle to carry the instrument.

CAUTION: If a unit is moved from a

cold to a warm environment, con densation may cause a shock hazard. Ensure, therefore, that the grounding requirements are strictly met.

WARNING: Never interrupt the

grounding cord. Any interruption of the protective ground connection inside or outside the instrument or disconnection of the protective ground terminal is likely to make the instrument dangerous.

1-8 Unpacking

Preparation for Use

Rackmount Adapter

Fig. 1-3 Dimensions for rackmounting

If you have ordered a 19-inch rack-mount kit for your instrument, it has to be assembled af ter delivery of the instrument. The rackmount kit consists of the following:

2 brackets, (short, left; long, right)

–

4 screws, M5 x 8

–

4 screws, M6 x 8

–

Fig. 1-4 Fitting the rack mount brackets

hardware.

on the counter.

WARNING: Do not perform any inter

nal service or adjustment of this instrument unless you are qualified to do so.

Before you remove the cover, dis connect mains cord and wait for one minute.

Capacitors inside the instrument can hold their charge even if the in strument has been separated from all voltage sources.

Assembling the Rackmount Kit

Make sure the power cord is disconnected

–

from the instrument.

Turn the instrument upside down.

–

See Fig. 1-5.

Undo the two screws (A) and remove

–

them from the cover.

–

Remove the rear feet by undoing the two screws (B).

–

Remove the four decorative plugs (C) that cover the screw holes on the right and left side of the front panel.

–

Grip the front panel and gently push at the rear.

–

Pull the instrument out of the cover.

Fig. 1-5 Remove the screws and push the

counter out of the cover.

Unpacking 1-9

Preparation for Use

Remove the four feet from the cover.

–

Use a screwdriver as shown in the following illustration or a pair of pliers to remove the springs holding each foot, then push out the feet.

Fig. 1-6 Removing feet from the cover.

Push the instrument back into the cover.

–

See Fig. 1-5.

Mount the two rear feet with the screws

–

(B) to the rear panel.

Put the two screws (A) back.

– –

Fasten the brackets at the left and right side with the screws included as illustrated in Fig. 1-3.

–

Fasten the instrument in the rack via screws in the four rack-mounting holes

The long bracket has an opening so that cables for Input A, B, and C can be routed inside the rack.

Reversing the Rackmount Kit

The instrument may also be mounted to the right in the rack. To do so, swap the position of the two brackets.

1-10 Unpacking

Chapter 2

Using the Controls

Basic Controls

A more elaborate description of the front and rear panels including the user interface with its menu system follows after this introductory

INPUT A

Opens the menu from

which you can adjust all

settings for Input A like

Coupling, Impedance

and Attenuation.

INPUT B

Opens the menu from

which you can adjust all

settings for Input B like

Coupling, Impedance

and Attenuation.

survey, the purpose of which is to make you familiar with the layout of the instrument.

SETTINGS

Select measurement pa

rameters such as mea surement time, number

of measurements, and

so on.

STANDBY LED

The LED lights up when the

counter is in STANDBY

mode, indicating that power

is still applied to an internal

optional OCXO, if one has

been installed.

2-2 Basic Controls

STANDBY/ON

Toggling secondary

power switch.

Pressing this button

in standby mode turns the counter

ON and restores the

settings as they

were at

power-down.

MATH/LIMIT

Menu for selecting one of a set of for

mulas for modifying

the measurement result. Three con stants can be en

tered from the

keyboard.

Numerical limits

canalsobeen

tered for status re

porting and

recording

USER OPT.

Controls the follow

ing items:

1. Settings memory

2. Interface

3. Calibration

4. Self-test

5. About

Using the Controls

STAT/PLOT

Enters one of

three statistics

presentation

modes.

Switching be

tween the modes

is done by

toggling the key.

VALUE

Enters the nor

mal numerical

presentation

mode with one

main parameter

and a number of

auxiliary parame

ters.

MEAS FUNC

Menu tree for

selecting mea

surement func

You can use the

seven softkeys

below the dis

play for confir

tion.

mation.

AUTO SET

Adjusts input

trigger voltages

automatically to

the optimum lev

els for the cho

sen measure

ment function.

Double-click for

default settings.

CURSOR

CONTROL

The cursor

position, marked

by text inversion

on the display,

canbemovedin

four directions.

HOLD/RUN

Toggles between HOLD (one-shot)

mode and RUN

(continuous)

mode. Freezes

the result after completion of a measurement if HOLD is active.

RESTART

Initiates one

new measure

ment if HOLD is

active.

EXIT/OK

Confirms menu

selections and

moves up one

level in the menu

tree.

CANCEL

Moves up one

menu level with

out confirming

selections made.

Exits REMOTE

mode if not

LOCAL

LOCKOUT.

Basic Controls 2-3

Confirms menu selections with

out leaving the

menu level.

ENTER

Using the Controls

Secondary Controls

Connectors & Indicators

GRAPHIC DISPLAY

320 x 97 pixels LCD with backlight for show

ing measurement results in numerical as well

as graphical format. The display is also the

center of the dynamic user interface, compris

ing menu trees, indicators and information

boxes.

TRIGGER IN

DICATORS

Blinking LED in

dicates correct

triggering.

GATE INDI

CATOR

A pending mea

surement

causes the

LED to light up.

NUMERIC INPUT KEYS

Sometimes you may want to enter numeric values like the

constants and limits asked for when you are utilizing the

postprocessing features in MATH/LIMIT mode. These

twelve keys are to be used for this purpose.

SOFTKEYS

The function of these seven keys is menu de

pendent. Actual function is indicated on the

Depressing a softkey is often a faster alterna

tive to moving the cursor to the desired posi

coupled channels A &

ments, either one at a

tion and then pressing OK.

MAIN INPUTS

The two identical DC

B are used for all

types of measure

time or both together.

LCD.

(Optional Input C)

available, covering different frequency

ranges. These units

are fully automatic and no controls af

mance. The Type N connector is fit

RF INPUT

A number of RF

prescalers are

fect the perfor

ted only if a prescaler is

installed.

2-4 Secondary Controls

Rear Panel

Using the Controls

Indicates instrument type and serial number.

Optional Main Input

Connectors

The front panel inputs can be moved to the rear panel by means of an optional ca ble kit. Note that the input capacitance will be higher.

Type Plate

Fan

A temp. sensor controls the speed of the fan. Normal bench-top use means low speed, whereas rack-mount ing and/or options may result in higher speed.

Protective Ground

This is where the pro tective ground wire is connected inside the in strument. Never tamper with this screw!

Line Power Inlet

AC 90-265 V

45-440 Hz, no range

switching needed.

191125

Terminal

RMS

Reference Output

10 MHz derived from the internal or, if present, the external reference.

External Reference

Input

Can be automatically se lected if a signal is pres ent and approved as timebase source, see Chapter 9.

External Arming Input

See page 5-7.

GPIB Connector

Address set via User Op tions Menu.

USB Connector

Universal Serial Bus (USB) for data commu nication with PC.

Secondary Controls 2-5

Using the Controls

Description of Keys

Power

The ON/OFF key is a toggling secondary power switch. Part of the instrument is always ON as long as power is applied, and this standby condition is indicated by a red LED above the key. This indicator is consequently not lit while the instrument is in operation.

Select Function

This hard key is marked MEAS FUNC. When you depress it, the menu below will open.

Fig. 2-1 Select measurement function.

The current selection is indicated by text inversion that is also indicating the cursor position. Select the measurement function you want by depressing the corresponding softkey right below the display.

Alternatively you can move the cursor to the wanted position with the RIGHT/LEFT arrow keys. Confirm by pressing ENTER.

A new menu will appear where the contents depend on the function. If you for instance have selected Frequency, you can then select between Frequency, Frequency Ratio and Frequency Burst. Finally you have to decide which input channel(s) to use.

Autoset/Preset

By depressing this key once after selecting the wanted measurement function and input chan

nel, you will most probably get a measure ment result. The AUTOSET system ensures that the trigger levels are set optimally for each combination of measurement function and input signal amplitude, provided rela tively normal signal waveforms are applied. If Manual Trigger has been selected before pressing the AUTOSET key, the system will make the necessary adjustments once (Auto Once) and then return to its inactive condition.

AUTOSET performs the following functions:

Set automatic trigger levels

•

Switch attenuators to 1x

•

Turn on the display

•

By depressing this key twice within two seconds, you will enter the Preset mode, and a more extensive automatic setting will take place. In addition to the functions above, the following functions will be performed:

•

Set Meas Time to 200 ms

•

Switch off Hold-Off

•

Set HOLD/RUN to RUN

•

Switch off MATH/LIM

•

Switch off Analog and Digital Filters

•

Set Timebase Ref to Internal

•

Switch off Arming

Default Settings

An even more comprehensive preset function can be performed by recalling the factory de fault settings. See page 2-13.

Move Cursor

There are four arrow keys for moving the cur sor, normally marked by text inversion, around the menu trees in two dimensions.

2-6 Description of Keys

Using the Controls

Display Contrast

When no cursor is visible (no active menu se lected), the UP/DOWN arrows are used for adjusting the LCD display contrast ratio.

Enter

The key marked ENTER enables you to con firm a choice without leaving your menu posi tion.

Save & Exit

This hard key is marked EXIT/OK. You will confirm your selection by depressing it, and at the same time you will leave the current menu level for the next higher level.

Don't Save & Exit

This hard key is marked CANCEL.Bydepressing it you will enter the preceding menu level without confirming any selections made at the current level.

If the instrument is in REMOTE mode, this key is used for returning to LOCAL mode, unless LOCAL LOCKOUT has been pro grammed.

Presentation Modes

VALUE

full resolution together with a number of aux iliary parameters in small characters with lim

ited resolution.

Fig. 2-3 Limits presentation.

If Limits Alarm is enabled you can visualize the deviation of your measurements in relation to the set limits. The numerical readout is now combined with a traditional analog pointer-type instrument, where the current value is represented by a "smiley". The limits are presented as numerical values below the main parameter, and their positions are marked with vertical bars labelled LL (lower limit) and UL (upper limit) on the autoscaled graph.

If one of the limits has been exceeded, the limit indicator at the top of the display will be flashing. In case the current measurement is out of the visible graph area, it is indicated by means of a left or a right arrowhead.

STAT/PLOT

If you want to treat a number of measure ments with statistical methods, this is the key to operate. There are three display modes available by toggling the key:

•

Numerical

•

Histogram

•

Trend Plot

Fig. 2-2 Main and aux. parameters.

Value mode gives single line numerical pre sentation of individual results, where the main parameter is displayed in large characters with

Description of Keys 2-7

Using the Controls

Numerical

Fig. 2-4 Statistics presented numerically.

In this mode the statistical information is dis played as numerical data containing the fol lowing elements:

Mean: mean value

•

Max: maximum value

•

Min: minimum value

•

P-P: peak-to-peak deviation

•

Adev: Allan deviation

•

Std: Standard deviation

•

Histogram

Fig. 2-5 Statistics presented as a histo

gram.

The bins in the histogram are always autoscaled based on the measured data. Lim its, if enabled, and center of graph are shown as vertical dotted lines. Data outside the limits are not used for autoscaling but are replaced by an arrow indicating the direction where non-displayed values have been recorded.

Trend Plot

Fig. 2-6 Running trend plot.

This mode is used for observing periodic fluc tuations or possible trends. Each plot termi nates (if HOLD is activated) or restarts (if RUN is activated) after the set number of samples. The trend plot is always autoscaled based on the measured data, starting with 0 at restart. Limits are shown as horizontal lines if enabled.

Remote

When the instrument is controlled from the GPIB bus, and the remote line is asserted, the presentation mode changes to Remote, indicated by the label Remote on the display. The main measurement result and the input settings are displayed in this mode.

Entering Numeric Values

Sometimes you may want to enter constants and limits in a value input menu, for instance one of those that you can reach when you

press the MATH/LIMIT key.

You may also want to select a value that is not in the list of fixed values available by pressing the UP/DOWN arrow keys. One example is Meas Time under SETTINGS.

2-8 Description of Keys

A similar situation arises when the desired value is too far away to reach conveniently by incrementing or decrementing the original value with the UP/DOWN arrow keys. One example is the Trig Lvl setting as part of the INPUT A (B) settings.

Using the Controls

Whenever it is possible to enter numeric val ues, the keys marked with 0-9; . (decimal point) and

± (stands for Change Sign)takeon

their alternative numeric meaning.

It is often convenient to enter values using the scientific format. For that purpose, the rightmost softkey is marked EE (stands for Enter Exponent), making it easy to switch be tween the mantissa and the exponent.

Press EXIT/OK to store the new value or

CANCEL to keep the old one.

Hard Menu Keys

These keys are mainly used for opening fixed menus from which further selections can be made by means of the softkeys or the cursor/select keys.

Input A (B)

Impedance: 50 W or1MW

•

Attenuation: 1x or 10x

•

Trigger:1Manual or Auto

•

Trigger Level:2numerical input via front

•

panel keyboard. If Auto Trigger is active, you can change the default trigger level manually as a percentage of the amplitude.

Filter:3On or Of

•

Notes: 1 Always

Auto when measuring

risetime or falltime

2 The absolute level can either be

adjusted using the up/down arrow keys or by pressing ENTER to reach the numerical input menu.

3 Pressing the corresponding

softkey or ENTER opens the Filter Settings menu. See Fig. 2-8. You can select a fixed 100 kHz analog filter or an adjustable digital filter. The equivalent cutoff frequency is set via the value input menu that opens if you select Digital LP Frequency from the menu.

Fig. 2-7 Input settings menu.

By depressing this key, the bottom part of the display will show the settings for Input A (B).

The active settings are in bold characters and can be changed by depressing the correspond ing softkey below the display. You can also move the cursor, indicated by text inversion, to the desired position with the RIGHT/LEFT arrow keys and then change the active setting with the ENTER key.

The selections that can be made using this menu are:

•

Trigger Slope: positive or negative, indi cated by corresponding symbols

•

Coupling: AC or DC

Fig. 2-8 Selecting analog or digital filter.

Input B

The settings under Input B are equal to those under Input A.

Description of Keys 2-9

Using the Controls

Settings

Arm

Fig. 2-9 The main settings menu.

This key accesses a host of menus that affect the measurement. The figure above is valid af ter changing the default measuring time to 10 ms.

Meas Time

Fig. 2-10 Submenu for entering measur-

ing time.

This value input menu is active if you select a frequency function. Longer measuring time means fewer measurements per second and gives higher resolution.

Burst

Fig. 2-11 Entering burst parameters.

Fig. 2-12 Setting arming conditions.

Arming is the general term used for the means

to control the actual start/stop of a measure ment. The normal free-running mode is inhib ited and triggering takes place when certain pretrigger conditions are fulfilled.

The signal or signals used for initiating the arming can be applied to three channels (A, B, E), and the start channel can be different from the stop channel. All conditions can be set via the menu below.

Trigger Hold-Off

Fig. 2-13 The trigger hold-off submenu.

A value input menu is opened where you can set the delay during which the stop trigger conditions are ignored after the measurement start. A typical use is to clean up signals gen erated by bouncing relay contacts.

Statistics

This settings menu is active if the selected measurement function is BURST – a special case of FREQUENCY – and facilitates mea surements on pulse-modulated signals. Both the carrier frequency and the modulating fre quency – the pulse repetition frequency (PRF) – can be measured, often without the support of an external arming signal.

2-10 Description of Keys

Fig. 2-14 Entering statistics parameters.

Using the Controls

In this menu you can do the following:

Set the number of samples used for cal

•

culation of various statistical measures.

Set the number of bins in the histogram

•

view.

Pacing

•

The delay between measurements, called pacing, can be set to ON or OFF, and the time can be set within the range 2 ms – 1000 s.

Timebase Reference

Fig. 2-15 Selecting timebase reference

Here you can decide if the counter is to use an Internal or an External timebase. A third alternative is Auto. Then the external timebase will be selected if a valid signal is present at the reference input. The EXT REF indicator at the upper right corner of the display shows that the instrument is using an external timebase reference.

source.

timestamping which measurement

channel precedes the other.

Auto Trig Low Freq

•

In a value input menu you can set the lower frequency limit for automatic trig gering and voltage measurements within the range 1 Hz – 100 kHz. A higher limit means faster settling time and consequently faster measurements.

Timeout

•

Switch the Timeout function ON or OFF (see below).

Timeout Time

•

Set the maximum time the instrument will wait for a pending measurement to finish before outputting a zero result. The range is 10 ms to 1000 s.

Math/Limit

Fig. 2-17 Selecting 'Math' or 'Limits' pa-

rameters.

You enter a menu where you can choose between inputting data for the Mathematics or the Limits postprocessing unit.

Miscellaneous

Fig. 2-16 The 'Misc' submenu.

The options in this menu are:

•

Smart Time Interval (valid only if the se lected measurement function is Time In terval)

The counter decides by means of

Fig. 2-18 The 'Math' submenu.

The Math branch is used for modifying the measurement result mathematically before presentation on the display. Thus you can make the counter show directly what you

want without tedious recalculations, e.g. revo

lutions/min instead of Hz.

Description of Keys 2-11

Using the Controls

The Limits branch is used for setting numeri cal limits and selecting the way the instrument will report the measurement results in relation to them.

Let us explore the Math submenu by pressing the corresponding softkey below the display.

The display tells you that the Math function is not active, so press the Math Off key once to open the formula selection menu.

Fig. 2-19 Selecting 'Math' formula for

postprocessing.

Select one of the four different formulas, where K, L and M are constants that the user can set to any value. X stands for the current non-modified measurement result.

marked X

is used for entering the display

reading as the value of the constant.

The Limit submenu is treated in a similar way, and its features are explored beginning on page 6-6.

User Options

Fig. 2-22 The User Options menu.

From this menu you can reach a number of submenus that do not directly affect the measurement.

You can choose between a number of modes by pressing the corresponding softkey.

Save/Recall Menu

Fig. 2-20 Selecting formula constants.

Each of the softkeys below the constant labels opens a value input menu like the one below.

Fig. 2-21 Entering numeric values for

constants.

Use the numeric input keys to enter the man tissa and the exponent, and use the EE key to toggle between the input fields. The key

2-12 Description of Keys

Fig. 2-23 The memory management

menu.

Twenty complete front panel setups can be stored in non-volatile memory. Access to the first ten memory positions is prohibited when

Setup Protect is ON. Switching OFF Setup Protect releases all ten memory positions si

multaneously. The different setups can be in dividually labeled to make it easier for the op erator to remember the application.

Using the Controls

The following can be done:

Save current setup

•

Fig. 2-24 Selecting memory position for

•

Fig. 2-25 Selecting memory position for

saving a measurement setup.

Browse through the available memory positions by using the

arrow keys. For faster browsing, press

Next to skip to the next memory

the key bank. Press the softkey below the num ber (1-20) where you want to save the setting.

Recall setup

recalling a measurement setup.

RIGHT/LEFT

Setup protection

•

Toggle the softkey to switch between

ON/OFF modes. When ON is ac

the tive, the memory positions 1-10 are all protected against accidental overwriting.

Fig. 2-26 Entering alphanumeric charac

ters.

Calibrate Menu

This menu entry is accessible only for calibration purposes and is password-protected.

Interface Menu

Select the memory position from which you want to retrieve the contents in the same way as under Save current setup above. You can also choose Default to restore the preprogrammed factory set tings. See the table on page 2-15 for a complete list of these settings.

•

Modify labels

Select a memory position to which you want to assign a label. See the descrip tions under Save/Recall setup above. Now you can enter alphanumeric char acters from the front panel. See the fig ure below. The seven softkeys below the display are used for entering letters and digits in the same way as you write SMS mes sages on a cell phone.

Fig. 2-27 Selecting active bus interface.

Bus Type

Select the active bus interface. The alterna

tives are GPIB and USB. If you select GPIB, you are also supposed to select the GPIB Mode and the GPIB Address. See the next two paragraphs.

Description of Keys 2-13

Using the Controls

GPIB Mode

There are two command systems to choose from.

Native

•

The SCPI command set used in this mode fully exploits all the features of this instru ment series.

Compatible

•

The SCPI command set used in this mode is adapted to be compatible with Agilent 53131/132/181.

GPIB Address

Value input menu for setting the GPIB ad dress.

Test

A general self-test is always performed every time you power-up the instrument, but you can order a specific test from this menu at any time.

calibration date

•

firmware versions for:

•

basic instrument

interfaces

optional factory-installed hardware

•

Hold/Run

This key serves the purpose of manual arm ing. A pending measurement will be finished and the result will remain on the display until a new measurement is triggered by pressing the RESTART key.

Restart

Often this key is operated in conjunction with the HOLD/RUN key (see above), but it can also be used in free-running mode, especially when long measuring times are being used, e.g. to initiate a new measurement after a change in the input signal. RESTART will not affect any front panel settings.

Fig. 2-28 Self-test menu.

Press Test Mode to open the menu with available choices.

Fig. 2-29 Selecting a specific test.

Select one of them and press Start Test to run it.

About

Here you can find information on:

2-14 Description of Keys

Default Settings

Using the Controls

See page 2-13 to see how the following prepro grammed settings are recalled by a few key

strokes.

PARAMETER VALUE/SETTING

Input A & B

Trigger Level AUTO

Trigger Slope POS (A), NEG (B)

Impedance 1 MW

Attenuator 1x

Coupling AC

Filter OFF

Arming

Start OFF

Start Slope POS

Start Arm Delay 200 ms

Stop OFF

Stop Slope POS

Hold-Off

Hold-Off State OFF

Hold-Off Time 200 ms

Time-Out

Time-Out State OFF

Time-Out Time 100 ms

Statistics

Statistics OFF

No. of Samples 100

No.ofBins 20

PARAMETER VALUE/SETTING

Pacing State OFF

Pacing Time 20 ms

Mathematics

Mathematics OFF

Math Constants K=1, L=0, M=1

Limits

Limit State OFF

Limit Mode ABOVE

Lower Limit 0

Upper Limit 0

Burst

Sync Delay 200 ms

Start Delay 200 ms

Meas. Time 200 ms

Freq. Limit 300 MHz

Miscellaneous

Function FREQ A

Meas. Time 200 ms

Smart Time Interval OFF

Auto Trig Low Freq 100 Hz

Timebase Reference INT

Default Settings 2-15

Using the Controls

This page is intentionally left blank.

2-16 Default Settings

Chapter 3

Input Signal

Conditioning

Input Signal Conditioning

Input Amplifier

The input amplifiers are used for adapting the widely varying signals in the ambient world to the measuring logic of the timer/counter.

These amplifiers have many controls, and it is essential to understand how these controls work together and affect the signal.

The block diagram below shows the order in which the different controls are connected. It is not a complete technical diagram but in tended to help understanding the controls.

The menus from which you can adjust the set tings for the two main measurement channels are reached by pressing INPUT A respectively INPUT B. See Figure 3-2. The active choices are shown in boldface on the bottom line.

Impedance

The input impedance can be set to 1 MW or 50 W by toggling the corresponding softkey.

Fig. 3-2 Input settings menu.

CAUTION: Switching the impedance

to 50 W when the input voltage is above 12 V nent damage to the input circuitry.

may cause perma

RMS

Attenuation

The input signal's amplitude can be attenuated

by 1 or 10 by toggling the softkey marked

1x/10x.

Use attenuation whenever the input signal exceeds the dynamic input voltage range ±5 V or else when attenuation can reduce the influence of noise and interference. See the section dealing with these matters at the end of this chapter.

Fig. 3-1 Block diagram of the signal conditioning.

3-2 Input Amplifier

Input Signal Conditioning

Coupling

Switch between AC coupling and DC cou pling by toggling the softkey AC/DC.

DC Coupling

Fig. 3-3 AC coupling a symmetrical sig

nal.

AC Coupling

Use the AC coupling feature to eliminate un wanted DC signal components. Always use AC coupling when the AC signal is superim posed on a DC voltage that is higher than the trigger level setting range. However, we recommend AC coupling in many other measurement situations as well.

When you measure symmetrical signals, such as sine and square/triangle waves, AC coupling filters out all DC components. This means that a 0 V trigger level is always centered around the middle of the signal where triggering is most stable.

NOTE: For explanation of the hysteresis band,

see page 4-3.

Fig. 3-5 No triggering due to AC coupling

of signal with low duty cycle.

Filter

If you cannot obtain a stable reading, the sig nal-to-noise ratio (often designated S/N or SNR) might be too low, probably less than 6 to 10 dB. Then you should use a filter. Certain conditions call for special solutions like highpass, bandpass or notch filters, but usually the unwanted noise signals have higher frequency than the signal you are interested in. In that case you can utilize the built-in lowpass filters. There are both analog and digital filters, and they can also work together.

Fig. 3-4 Missing trigger events due to AC

coupling of signal with varying duty cycle.

Signals with changing duty cycle or with a very low or high duty cycle do require DC coupling. Fig. 3-4shows how pulses can be missed, while Fig. 3-5shows that triggering does not occur at all because the signal ampli tude and the hysteresis band are not centered.

Fig. 3-6 The menu choices after selecting

Analog Lowpass Filter

FILTER.

The counter has analog LP filters of RC type, one in each of the channels A and B, with a cutoff frequency of approximately 100 kHz, and a signal rejection of 20 dB at 1 MHz.

Accurate frequency measurements of noisy LF signals (up to 200 kHz) can be made when

the noise components have significantly

Input Amplifier 3-3

Input Signal Conditioning

higher frequencies than the fundamental sig

nal.

Digital Lowpass Filter

The digital LP filter utilizes the Hold-Off function described below.

With trigger Hold-Off it is possible to insert a deadtime in the input trigger circuit. This means that the input of the counter ignores all hysteresis band crossings by the input signal during a preset time after the first trigger event.

When you set the Hold-Off time to approx. 75% of the cycle time of the signal, erroneous triggering is inhibited around the point where the input signal returns through the hysteresis band. When the signal reaches the trigger point of the next cycle, the set Hold-Off time has elapsed and a new and correct trigger will be initiated.

Instead of letting you calculate a suitable Hold-Off time, the counter will do the job for you by converting the filter cutoff frequency you enter via the value input menu below to an equivalent Hold-Off time.

Fig. 3-7 Value input menu for setting the

cutoff frequency of the digital fil ter.

You should be aware of a few limitations to be able to use the digital filter feature effectively and unambiguously. First you must have a rough idea of the frequency to be measured. A cutoff frequency that is too low might give a perfectly stable reading that is too low. In such a case, triggering occurs only on every 2nd,

3rd or 4th cycle. A cutoff frequency that is too high (>2 times the input frequency) also leads to a stable reading. Here one noise pulse is counted for each half-cycle.

Use an oscilloscope for verification if you are in doubt about the frequency and waveform of your input signal..

The cutoff frequency setting range is very wide: 1 Hz - 50 MHz

Hold-off time

Correct

measurement

Fig. 3-8 Digital LP filter operates in the

measuring logic, not in the input amplifier.

Man/Auto

Toggle between manual and automatic trigger ing with this softkey. When Auto is active the counter automatically measures the peak-to-peak levels of the input signal and sets the trigger level to 50% of that value. The attenuation is also set automatically.

At rise/fall time measurements the trigger lev els are automatically set to 10% and 90% of the peak values.

When Manual is active the trigger level is set in the value input menu designated Tri g.See below. The current value can be read on the display before entering the menu.

3-4 Input Amplifier

Input Signal Conditioning

Speed

The Auto-function measures amplitude and calculates trigger level rapidly, but if you aim at higher measurement speed without having to sacrifice the benefits of automatic trigger

ing, then use the Auto Trig Low Freq func tion to set the lower frequency limit for volt

age measurement.

If you know that the signal you are interested in always has a frequency higher than a cer tain value f

, then you can enter this value

low

from a value input menu. The range for f

low

1 Hz to 100 kHz, and the default value is 100 Hz. The higher value, the faster measure ment speed due to more rapid trigger level voltage detection.

Even faster measurement speed can be reached by setting the trigger levels manually. See Tri g below.

Follow the instructions here to change the low-frequency limit:

–

Press SETTINGS ® Misc ® Auto Trig Low Freq.

–

Use the UP/DOWN arrow keys or the numeric input keys to change the low fre

quency limit to be used during the trigger level calculation, (default 100 Hz).

–

Confirm your choice and leave the SET

TINGS menu by pressing EXIT/OK three

times.

Trig

Value input menu for entering the trigger level manually.

deleting the position preceding the current cursor position.

Fig. 3-9 Value input menu for setting the

NOTE: It is probably easier to make small ad

NOTE: Switching over from AUTO to MAN Trig

Auto Once

trigger level.

justments around a fixed value by us ing the arrow keys for incrementation or decrementation. Keep the keys de pressed for faster response

ger Level is automatic if you enter a trigger level manually.

Converting “Auto” to “Fixed”

The trigger levels used by the auto trigger can be frozen and turned into fixed trigger levels simply by toggling the MAN/AUTO key. The current calculated trigger level that is visible on the display under Tri g will be the new fixed manual level. Subsequent measurements will be considerably faster since the signal levels are no longer monitored by the instru ment. You should not use this method if the signal levels are unstable.

NOTE: You can use auto trigger on one input

and fixed trigger levels on the other.

Use the UP/DOWN arrow keys or the nu

meric input keys to set the trigger level.

A blinking underscore indicates the cursor po sition where the next digit will appear. The LEFT arrow key is used for correction, i.e.

Input Amplifier 3-5

Input Signal Conditioning

How to Reduce or Ignore Noise and Interference

Sensitive counter input circuits are of course also sensitive to noise. By matching the signal amplitude to the counter’s input sensitivity, you reduce the risk of erroneous counts from noise and interference. These could otherwise ruin a measurement.

Fig. 3-10 Narrow hysteresis gives errone-

ous triggering on noisy signals.

To ensure reliable measuring results, the coun ter has the following functions to reduce or eliminate the effect of noise:

10x input attenuator

–

Continuously variable trigger level

–

Continuously variable hysteresis for some

–

functions

Analog low-pass noise suppression filter

–

Digital low-pass filter (Trigger Hold-Off)

–

To make reliable measurements possible on very noisy signals, you may use several of the above features simultaneously.

Optimizing the input amplitude and the trigger level, using the attenuator and the trigger con trol, is independent of input frequency and useful over the entire frequency range. LP filters, on the other hand, function selectively over a limited frequency range.

Trigger Hysteresis

The signal needs to cross the 20 mV input hysteresis band before triggering occurs. This hysteresis prevents the input from self-oscillating and reduces its sensitivity to noise. Other names for trigger hysteresis are “trigger sensitivity” and “noise immunity”. They ex plain the various characteristics of the hyster esis.

Fig. 3-11 Wide trigger hysteresis gives

correct triggering.

Fig. 3-12 Erroneous counts when noise

Fig. 3-10 and Fig. 3-12 show how spurious signals can cause the input signal to cross the

3-6 How to Reduce or Ignore Noise and Interference

passes hysteresis window.

Input Signal Conditioning

trigger or hysteresis window more than once per input cycle and give erroneous counts.

Fig. 3-13 Trigger uncertainty due to noise.

Fig. 3-13 shows that less noise still affects the trigger point by advancing or delaying it, but it does not cause erroneous counts. This trigger uncertainty is of particular importance when measuring low frequency signals, since the signal slew rate (in V/s) is low for LF signals. To reduce the trigger uncertainty, it is desirable to cross the hysteresis band as fast as possible.

do not attenuate the signal too much, and set the sensitivity of the counter high.

In practice however, trigger errors caused by erroneous counts (Fig. 3-10 and Fig. 3-12) are much more important and require just the op posite measures to be taken.

To avoid erroneous counting caused by spuri ous signals, you need to avoid excessive input signal amplitudes. This is particularly valid when measuring on high impedance circuitry and when using 1MW input impedance. Under these conditions, the cables easily pick up noise.

External attenuation and the internal 10x attenuator reduce the signal amplitude, includ ing the noise, while the internal sensitivity control in the counter reduces the counter’s sensitivity, including sensitivity to noise. Reduce excessive signal amplitudes with the 10x attenuator, or with an external coaxial attenuator, or a 10:1 probe.

How to use Trigger Level Setting

For most frequency measurements, the optimal triggering is obtained by positioning the mean trigger level at mid amplitude, using either a narrow or a wide hysteresis band, de pending on the signal characteristics.

Fig. 3-14 Low amplitude delays the trig

ger point

Fig. 3-14 shows that a high amplitude signal passes the hysteresis faster than a low ampli tude signal. For low frequency measurements where the trigger uncertainty is of importance,

How to Reduce or Ignore Noise and Interference 3-7

Fig. 3-15 Timing error due to slew rate.

When measuring LF sine wave signals with little noise, you may want to measure with a

Input Signal Conditioning

high sensitivity (narrow hysteresis band) to re duce the trigger uncertainty. Triggering at or close to the middle of the signal leads to the smallest trigger (timing) error since the signal slope is steepest at the sine wave center, see Fig. 3-15.

When you have to avoid erroneous counts due to noisy signals, see Fig. 3-12, expanding the hysteresis window gives the best result if you still center the window around the middle of the input signal. The input signal excursions beyond the hysteresis band should be equally large.

Auto Trigger

For normal frequency measurements, i.e. without arming, the Auto Trigger function changes to Auto (Wide) Hysteresis, thus widening the hysteresis window to lie between 70 % and. 30 % of the peak-to-peak amplitude. This is done with a successive approximation method, by which the signal’s MIN. and MAX. levels are identified, i.e., the levels where triggering just stops. After this MIN./MAX. probing, the counter sets the trigger levels to the calculated values. The default relative trigger levels are indicated by 70 % on Input A and 30 % on Input B. These values can be manually adjusted between 50 % and 100 % on Input A and between 0 % and 50 % on Input B. The signal, however, is only ap

plied to one channel.

tem makes many measurements per second. Here you can increase the measuring rate by switching off this probing if the signal amplitude is con stant. One single command and the AUTO trigger function determines the trigger level once and enters it as a fixed trigger level.

Manual Trigger

Switching to Man Trig also means Narrow Hysteresis at the last Auto Level. Pressing

AUTOSET once starts a single automatic trigger level calculation (Auto Once). This cal culated value, 50 % of the peak-to-peak am plitude, will be the new fixed trigger level, from which you can make manual adjustments if need be.

Harmonic Distortion

As rule of thumb, stable readings are free from noise or interference.

However, stable readings are not necessarily correct; harmonic distortion can cause erroneous yet stable readings.

Sine wave signals with much harmonic distortion, see Fig. 3-17, can be measured correctly by shifting the trigger point to a suitable level or by using continuously variable sensitivity, see Fig. 3-16. You can also use Trigger Hold-Off, in case the measurement result is not in line with your expectations.

Before each frequency measurement the coun ter repeats this signal probing to identify new MIN/MAX values. A prerequisite to enable

GOOD

AUTO triggering is therefore that the input signal is repetitive, i.e., ³100 Hz (default).

Another condition is that the signal amplitude does not change significantly after the mea

Fig. 3-16 Variable sensitivity.

surement has started.

NOTE: AUTO trigger limits the maximum mea

suring rate when an automatic test sys

Fig. 3-17 Harmonic distortion.

3-8 How to Reduce or Ignore Noise and Interference

BAD

Chapter 4

Measuring Functions

Introduction to This Chapter

This chapter describes the different measuring functions of the counter. They have been grouped as follows:

Frequency measurements

Frequency

–

Period

– – Ratio –

Burst frequency and PRF.

–

Time measurements

–

Time interval.

–

Pulse width.

–

Duty factor.

–

Rise/Fall time.

Phase measurements

Voltage measurements

–

MAX,VMIN

–

VPP.

Selecting Function

See also the front panel layout on page 2-3 to find the keys mentioned in this section together with short descriptions.

Press MEAS FUNC to open the main menu for selecting measuring function. The two basic methods to select a specific function and its subsequent parameters are described on page 2-6.

4-2 Selecting Function

Measuring Functions

Frequency Measurements

FREQ A, B

The counter measures frequency between 0 Hz and 300 MHz on Input A and Input B.

Frequencies above 100 Hz are best measured using the Default Setup. See page 2-13. Then Freq A will be selected automatically. Other important automatic settings are AC Cou- pling, Auto Trig and Meas Time 200 ms. See below for an explanation. You are now ready to start using the most common function with a fair chance to get a result without further adjustments.

Summary of Settings for Good

Frequency Measurements

–

AC Coupling, because possible DC offset is normally undesirable.

–

Auto Trig means Auto Hysteresis in this case, (comparable to AGC) because super imposed noise exceeding the normal nar row hysteresis window will be suppressed.

–

Meas Time 200 ms to get a reasonable tradeoff between measurement speed and resolution.

Some of the settings made above by recalling the Default Setup can also be made by activat ing the AUTOSET key. Pressing it once means:

Auto Trig. Note that this setting will be

–

made once only if Man Trig has been se lected earlier.

Pressing AUTOSET twice within two seconds also adds the following setting:

Meas Time 200 ms.

–

FREQ C

With an optional prescaler the counter can measure up to 3 GHz or 8 GHz on Input C. These RF inputs are fully automatic and no setup is required.

H y s t e r e s i s b a n d ( S E N S )

T r i g g e r l e v e l o f f s e t

T r i g g e r p o i n t s

0 V

Fig. 4-1 Frequency is measured as the

inverse of the time between one trigger point and the next;

ft=

R e s e t p o i n t s

FREQ A, B 4-3

Measuring Functions

RATIOA/B,B/A, C/A, C/B

To find the ratio between two input frequen cies, the counter counts the cycles on two channels simultaneously and divides the result on the primary channel by the result on the secondary channel.

Ratio can be measured between Input A and Input B, where either channnel can be the pri mary or the secondary channel. Ratio can also be measured between Input C and Input A or between Input C and Input B. Here Input C is the primary channel.

Note that the resolution calcula

tions are very different as compared to frequency measurements. See page 8-9 for details.

BURST A, B, C

A burst signal as in Fig. 4-2has a carrier wave (CW) frequency and a modulation frequency, also called the pulse repetition frequency (PRF), that switches the CW signal on and off.

Both the CW frequency, the PRF, and the number of cycles in a burst are measured without external arming signals and with or without selectable start arming delay. See Chapter 5 “Measurement Control” for a fun damental discussion of arming and arming de lay.

The general frequency limitations for the re spective measuring channel also apply to burst measurements. The minimum number of cy cles in a burst on Input A or Input B is 3 be low 160 MHz and 6 between 160 MHz and 300 MHz. Burst measurements on Input C in volve prescaling, so the minimum number of

cycles will be 3 x prescaling factor.The 3 GHz option, for example, has a prescaling factor of 16 and requires at least 48 cycles in each burst.

The minimum burst duration is 40 ns below and 80 ns above 160 MHz.

Triggering

Bursts with a PRF above 50 Hz can be mea sured with auto triggering on.

The out-of-sync error described under heading

“Possible errors” on page 4-6may occur more frequently when using Auto Trigger.

When PRF is below 50 Hz and when the gap between the bursts is very small, use manual triggering.

Always try using AUTOSET first. Then the Auto Trigger and the Auto Sync functions in combination will give satisfactory results without further tweaking in most cases. Sometimes switching from AUTO to MANual triggering in the INPUT A/B menus is enough to get stable readings. The continually calculated trigger levels will then be fixed.

Input C has always automatic triggering and AUTOSET only affects the burst synchroni zation.

C W

B u r s t S i g n a l

P R F

Fig. 4-2 Burst signal.

4-4 RATIO A/B, B/A, C/A, C/B

Burst Measurements using

Manual Presetting

You can measure the frequency on Input A and Input B to 300 MHz and on Input C with limited specifications to the upper frequency limit of the prescaler with the internally syn chronized BURST function as follows:

Select Freq Burst under the Freq menu

–

Select A, B,orC as measurement input.

–

Press SETTINGS and Burst. Select a

–

Meas Time that is shorter than the burst duration minus two CW cycles.

If you do not know the approximate burst pa rameters of your signal, always start with a short measurement time and increase it gradu ally until the readout gets unstable.

Press Sync Delay and enter a value lon-

–

ger than the burst duration and shorter than the inverse of the PRF. See Fig. 4-3.

B u r s t S i g n a l

Fig. 4-3 Set the sync delay so that it ex

–

Press Start Delay and enter a value lon ger than the transient part of the burst pulse.

–

Select Frequency Limit (160/300 MHz) if Input A or Input B is to be used. Use the low limit if possible to minimize the number of cycles necessary to make a measurement.

–

Press EXIT/OK to measure.

All relevant burst parameters can be read on the display simultaneously.

pires in the gap between the bursts.

S y n c . d e l a

Measuring Functions

Selecting Measurement Time

Fig. 4-4 Three time values must be set to

The measurement time must be shorter than

the duration of the burst. If the measurement continues during part of the burst gap, no matter how small a period of time, then the measurement is ruined. Choosing a measurement time that is too short is better since it only reduces the resolution. Making burst frequency measurements on short bursts means using short measurement times, giving a poorer resolution than normally achieved with the counter.

How Does the Sync Delay

measure the correct part of a burst

Work?

The sync delay works as an internal start arm

ing delay: it prevents the start of a new mea

surement until the set sync delay has expired. See Fig. 4-5.

After the set measurement time has started, the counter synchronizes the start of the mea surement with the second trigger event in the burst. This means that the measurement does

BURST A, B, C 4-5

Measuring Functions

not start erroneously during the Burst Off du ration or inside the burst.

M e a s u r e

S y n c - d e l a y

G a t e T i m e

Fig. 4-5 Measuring the frequency of the

Possible Errors

Before the measurement has been synchronized with the burst signal, the first measurement(s) could start accidentally during the presence of a burst. If this would happen and if the remaining burst duration is shorter than the set measurement time, the readout of the first measurement will be wrong. However, after this first measurement, a properly set start-arming sync delay time will synchronize the next measurements.

In manually operated applications, this is not a problem. In automated test systems where the result of a single measurement sample must be reliable, at least two measurements must be made, the first to synchronize the measure ment and the second from which the measure ment result can be read out.

carrier wave signal in a burst.

Frequency Modulated Signals

A frequency modulated signal is a carrier

max–f0

) that changes

wave signal (CW frequency = f in frequency to values higher and lower than the frequency f that changes the frequency of the carrier wave.

The counter can measure:

= Carrier frequency.

= Maximum frequency.

max

= Minimum frequency.

min

Df = Frequency swing = f

. It is the modulation signal

Carrier Wave Frequency f

To determine the carrier wave frequency, measure f f

Press STAT/PLOT to get an overview of all the statistical parameters.

Select the measurement time so that the coun ter measures an integral number of modulation periods. This way the positive frequency devi ations will compensate the negative deviations during the measurement.

Example: If the modulation frequency is

50 Hz, the measurement time 200 ms will make the counter measure 10 complete modu lation cycles.

which is a close approximation of

mean

4-6 Frequency Modulated Signals

If the modulation is non-continuous, like a voice signal, it is not possible to fully com pensate positive deviations with negative deviations. Here, part of a modulation swing

Measuring Functions

may remain uncompensated for, and lead to a measuring result that is too high or too low.

W o r s t C a s e M e a s u r i n g T i m e

D u r a t i o n , w h e r e

= f

m e a n

m a x

{

m o d u l a t i o n

m i n

Fig. 4-6 Frequency modulation

M o d u l a t i o n s i g n a l

In the worst case, exactly half a modulation cycle would be uncompensated for, giving a maximum uncertainty of:

-=±

mean

measuring ulation

max

´´

mod

For very accurate measurements of the carrier wave frequency f

, measure on the

unmodulated signal if it is accessible.

Modulation Frequencies

above 1 kHz

–

Turn off SINGLE.

–

Set a long measurement time that is an even multiple of the inverse of the modu lation frequency.

You will obtain a good approximation when you select a long measurement time, for in stance 10 s, and when the modulation fre quency is high, above 1000 Hz.

Low Modulation Frequencies

Press SETTINGS ® STAT and make the No. of samples parameter as large as possi

ble considering the maximum allowed mea surement time. Press STAT/PLOT and let the

counter calculate the mean value of the sam ples.

You will usually get good results with 0.1 s measurement time per sample and more than 30 samples (n ³ 30). You can try out the opti mal combination of sample size and measure ment time for specific cases. It depends on the actual f

and Df

max

Here the sampling frequency of the measure ment (1/measurement time) is asynchronous with the modulation frequency. This leads to individual measurement results which are ran domly higher and lower than f

. The statisti

cally averaged value of the frequency f approaches f0when the number of averaged samples is sufficiently large.

When the counter measures instantaneous frequency values (when you select a very short measurement time), the RMS measurement uncertainty of the measured value of f

-=±´D

mean0

max

where n is the number of averaged samples of f.

max

–

Press SETTINGS ® STAT and set No.of

samples to 1000 or more.

–

Press Meas Time and select a low value.

–

Press STAT/PLOT and watch f

min

–

Press SETTINGS ® STAT and set No.of samples to 1000 or more.

–

Press Meas Time and select a low value.

–

Press STAT/PLOT and watch f

max

min

mean

is:

Frequency Modulated Signals 4-7

Measuring Functions

p-p

Press SETTINGS ® STAT and set No.of

–

samples to 1000 or more.

Press Meas Time and select a low value.

–

Press STAT/PLOT and watch Df

=-=´

DDfff f

pp-

max min

Errors in f

max,fmin

A measurement time corresponding to

p-p

, and Df

p-p

cle, or 36° of the modulation signal, leads to an error of approx 1.5%.

Select the measurement time:

measure

M o d u l a t i o n s i g n a l

Fig. 4-7 Error when determining f

´110

A / 1 0

modulation

< 0 . 0 0 7 B

max

To be confident that the captured maximal fre quency really is f

, you must select a suffi

max

ciently large number of samples, for instance n ³ 1000.

AM Signals

The counter can usually measure both the car rier wave frequency and modulation fre quency of AM signals. These measurements

are much like the burst measurements de scribed earlier in this manual.

Carrier Wave Frequency

The carrier wave (CW) is only continuously present in a narrow amplitude band in the middle of the signal if the modulation depth is high. If the sensitivity of the counter is too low, cycles will be lost, and the measurement ruined.

Fig. 4-8 Effects of different sensitivity

To measure the CW frequency:

–

Enter the INPUT A menu.

–

Select a measurement time that gives you the resolution you want.

–

Turn on Manual trigger.

–

Press Trig level and enter 0 V trigger level (press the numeric key 0 and EXIT/OK).

–

Select AC coupling.

–

Select 1x attenuation to get a narrow hys teresis band.

–

If the counter triggers on noise, widen the hysteresis band with the ‘variable hyster

esis’ function, i.e. enter a trigger level

>0 V but <V

when measuring the CW Frequency of an AM signal.

. See Fig. 4-8.

P-Pmin

4-8 AM Signals

Measuring Functions

Modulating Frequency

The easiest way to measure the modulating frequency is after demodulation, for instance by means of a so-called RF-detector probe (also known as a demodulator probe, e.g. Pomona type 5815) used with AC-coupling of the input channel. If no suitable demodulator is available, use the Freq Burst function to measure the modulation frequency in the same way as when measuring Burst PRF.

S y n c . d e l a y

M e a s u r e d c y c l e s

Fig. 4-9 Measuring the modulating fre-

–

Press MEAS FUNC and select Freq Burst A.

–

Press SETTINGS ® Burst ® Meas Time and enter a measurement time that

is approximately 25 % of the modulating period.

–

Press Sync Delay and enter a value that is approximately 75 % of the modulating period. See Fig. 4-3.

–

Press INPUT A and turn on Manual trig ger.

–

Press Trig and enter a trigger level that makes the counter trigger according to Fig. 4-9.

Even though the main frequency reading may now be unstable, the PRF value on the display will represent the modulating frequency.

quency.

Theory of Measurement

Reciprocal Counting

Simple frequency counters count the number of input cycles during a preset gate time, for instance one second. This leads to a ± 1 input cycle count error that, at least for low-fre quency measurements, is a major contribution to uncertainty.

However, the counters described here use a high-resolution, reciprocal counting tech nique, synchronizing the measurement start with the input signal. In this way an exact number of integral input cycles will be counted, thereby omitting the ± 1 input cycle error.

S e t M e a s u r i n g T i m e

t 1

t g

A c t u a l G a t e T i m e

Fig. 4-10 Synchronization of a measure

ment.

After the start of the set measurement time, the counter synchronizes the beginning of the actual gate time with the first trigger event (t of the input signal. See also Fig. 4-10.

In the same way, the counter synchronizes the stop of the actual gate time with the input sig nal, after the set measurement time has elapsed. The multi-register counting technique allows you to simultaneously measure the ac

t 2

)

Theory of Measurement 4-9

Measuring Functions

tual gate time (tg) and the number of cycles (n) that occurred during this gate time.

Thereafter, the counter calculates the fre

quency according to Mr. Hertz’s definition:

The '90' measures the gate time, tg, with a res olution of 100 ps, independent of the mea

sured frequency. Consequently the use of prescalers does not influence the quantization error. Therefore, the relative quantization error is: 100 ps/tg.

For a 1-second measurement time, this value is:

100

100 10 1 10

=´ =´

12 10

Except for very low frequencies, tgand the set measurement time are nearly identical.

Sample-Hold

If the input signal disappears during the measurement, the counter will behave like a voltmeter with a sample-and-hold feature and will freeze the result of the previous measurement.

Time-Out

Mainly for GPIB use, you can manually select a fixed time-out in the menu reached by press ing SETTINGS ® Misc ® Timeout Time. The range of the fixed timeout is 10 ms to 1000 s, and the default setting is Off.

Select a time that is longer than the cycle time of the lowest frequency you are going to mea sure; multiply the time by the prescaling fac tor of the input channel and enter that time as time-out.

When no triggering has occurred during the time-out, the counter will show NO SIGNAL.

Measuring Speed

The set measurement time determines the measuring speed for those functions that uti lize averaging – Frequency and Period Avg. For continuous signals,

Speed

when Auto trigger is on and can be increased to:

Speed

when Manual trigger is on, or via GPIB:

Speed

Average and Single Cycle

Measurements

To reduce the actual gate time or measuring aperture, the counters have very short measurement times and a mode called Single for period measurements. The latter means that the counter measures during only one cycle of the input signal. In applications where the counter uses an input channel with a prescaler, the Single measurement will last as many cy cles as the division factor. If you want to mea sure with a very short aperture, use an input with a low division factor.

Averaging is the normal mode for frequency

and period measurements when you want to reach maximum resolution. There is always a tradeoff between time and precision, however, so decide how many digits you need and use

as short a measurement time as possible to ar rive at your objective.

+102.

+10 001.

+10 00012.

readings/s

4-10 Theory of Measurement

Prescaling May Influence

Measurement Time

Prescalers do affect the minimum measure ment time, inasmuch as short bursts have to contain a minimum number of carrier wave periods. This number depends on the prescaling factor.

I n p u t s i g n a l

f t e r

p r e s c a l e r

1 6 p e r i o d s

Fig. 4-11 Divide-by-16 Prescaler

f / 1 6

Fig. 4-11 shows the effect of the 3 GHz prescaler. For 16 input cycles, the prescaler gives one square wave output cycle. When the counter uses a prescaler, it counts the number of prescaled output cycles, here f/16. The display shows the correct input frequency since the microcomputer compensates for the effect of the division factor d as follows:

Measuring Functions

Function Prescaling

Factor

FREQ A/B (300 MHz) 2

BURST A/B (<160 MHz) 1

BURST A/B (>160 MHz 2

PERIOD A/B AVG (300 MHz) 2

PERIOD A/B SGL (300 MHz) 1

FREQ C (3 GHz) 16

FREQ C (8 GHz) 256

All other functions 1

Table 4-1 Prescaling factors.

When measuring pulses with a low repetition rate, for example a 0.1 Hz pulse with a non-prescaled function like PERIOD SGL, the measurement will require at least the duration of one cycle, that is 10 seconds, and at worst nearly 20 seconds. The worst case is when a trigger event took place just before the beginning of a measurement time (Fig. 4-12). Measuring the frequency of the same signal will take twice as long, since this function involves prescaling by a factor two.

Prescalers do not reduce resolution in recipro

P o s s i b l e t r i g g e r e v e n t s

cal counters. The relative quantization error is

100 ps

still:

See Table 4-1 to find the prescaling factors used in different operating modes.

LF Signals

Signals below 100 Hz should be measured with manual triggering, unless the default set

S e t m e a s u r i n g

t i m e

T i m e f o r o n e m e a s u r e m e n t

Fig. 4-12 Measurement Time

G a t e t i m e

ting (100 Hz) is changed. See page 2-11. The low limit can be set to 1 Hz, but the measure ment process will be slowed down consider ably if auto triggering is used in conjunction with very low frequencies.

Even if you have chosen a short measurement

time, this measurement will require between

20 and 40 seconds (for this example).

Theory of Measurement 4-11

Measuring Functions

RF Signals

As mentioned before, a prescaler in the C-in put divides the input frequency before it is counted by the normal digital counting logic. The division factor is called prescaler factor and can have different values depending on the prescaler type. The 3 GHz prescaler is de signed for a prescaling factor of 16. This means that an input C frequency of, e.g.,

1.024 GHz is transformed to 64 MHz.

Prescalers are designed for optimum perfor mance when measuring stable continuous RF. Most prescalers are inherently unstable and would self-oscillate without an input signal. To prevent a prescaler from oscillating, a “go-detector” is incorporated. See Fig. 4-13.

The go-detector continuously measures the level of the input signal and simply blocks the prescaler output when no signal, or a signal that is too weak, is present.

+ N

G o - d e t e c t o r

Fig. 4-13 Go-detector in the prescaler

T o c o u n t i n g

l o g i

PERIOD

Single A, B

Average A, B, C

From a measuring point of view, the period

function is identical to the frequency function. This is because the period of a cyclic signal has the reciprocal value of the frequency (

In practice there are two minor differences.

1. The counter calculates FREQUENCY

(always AVG) as:

number of cycles

actual gate time

while it calculates PERIOD AVG as:

actual gate time

number of cycles

2. In the PERIOD SINGLE mode, the coun-

ter uses no prescaler.

All other functions and features as described earlier under “Frequency” apply to Period measurements.

The presence of a burst signal to be measured makes certain demands upon the signal itself. Regardless of the basic counter’s ability to measure during very short measurement times, the burst duration must meet the fol

lowing minimum conditions:

Burst presc factor inp cycle time

(. )(. )>´ ´3

min

or at least 80 ns

Normally the real minimum limit is set by other factors, like the speed of the GO-detec tor. This speed depends on the specific input option used.

4-12 PERIOD

Measuring Functions

Time Measurements

Introduction

Measuring the time between a start and a stop condition on two separate channels is the basis for all time interval measurements. In addition to the fundamental function Time Interval A to B, the counters also offer other channel combinations and derived functions like Pulse Width and Rise/Fall Time.

H y s t e r e s i s b a n d ( S E N S )

T r i g g e r l e v e l o f f s e t

T r i g g e r p o i n t s

0 V

R e s e t p o i n t s

Fig. 4-14 Time is measured be

tween the trigger point and the reset point. Accurate measurements are possible only if the hysteresis band is narrow.

Triggering

The set trigger level and trigger slope define the start and stop triggering.

If Auto is on, the counter sets the trigger level to 50% of the signal amplitude, which is ideal for most time measurements.

Summary of Conditions for

Reliable Time Measurements:

–

Auto Once, that is freezing the levels determined by Auto Trig, is normally the best choice when making time measure ments. Choose Man Trig and press AUTOSET once.

–

DC coupling.

–

1x Attenuation. Selected automatically if AUTOSET was used before to set the

trigger levels.

–

High signal level.

–

Steep signal edges.

Even though the input amplifiers have high sensitivity, the hysteresis band has a finite value that would introduce a small timing er ror for signals with different rise and fall times, for instance asymmetrical pulse signals like the one in Fig. 4-14. This timing error is taken care of by using hysteresis compensa

Introduction 4-13

Measuring Functions

tion that virtually moves the trigger points by half the hysteresis band.

Time Interval

All time interval functions can be found under the function menu Time.

The toggling SLOPE keys (marked with a positive or negative edge symbol) un der the menus INPUT A/B decide which edge of the signal will start resp. stop the measure ment.

Time Interval A to B

The counter measures the time between a start condition on input A and a stop condition on input B.

Time Interval B to A

The counter measures the time between a start condition on input B and a stop condition on input A.

Time Interval A to A, B to B

When the same (common) signal source sup plies both start and stop trigger events, con nect the signal to either input A or input B.

These functions can be used for measuring rise and fall times between arbitrary trigger levels.

Rise/Fall Time A/B

These functions can be found under the func tion menu Time.

Rise and fall time can be measured on both in put A and input B.

By convention, rise/fall time measurements are made with the trigger levels set to 10 % (start) and 90 % (stop) of the maximum pulse amplitude, see Figure 4-15.

The counter measures the time from when the signal passes 10 % of its amplitude to when it passes 90 % of its amplitude. The trigger lev els are calculated and set automatically.

Auxiliary parameters shown simultaneously

are Slew Rate (V/s), V

T r i g g e r L e v e l B

I n p u t A / C o m m o n B

T r i g g e r L e v e l A

Fig. 4-15 Trigger levels for rise/fall mea-

surements.

max

and V

For ECL circuits, the reference levels are 20 % (start) and 80 % (stop). In this case you can use either of two methods:

1. Select the general Time Interval function de

scribed above and set the trigger levels man ually after calculating them from the abso lute peak values. Then you can benefit from the auxiliary parameters V

max

measurements made on input A, use the fol lowing settings:

Rise Time:

Trig Level A = V Trig Level B = V

min

+0.2(V +0.8(V

max-Vmin

Fall Time:

Trig Level A = V

Trig Level B = V

2. Select one of the dedicated Rise/Fall Time

min

+0.8(V +0.2(V

max-Vmin

functions, and exploit the possibility to man

min

1 0 0 %

9 0 %

1 0 %

and V

0 %

.For

min

) )

4-14 Time Interval

Measuring Functions

ually adjust the relative trigger levels (in %) when Auto Trigger is active. Both input channel menus are used for entering the lev els, but only one channel is the active signal input.

See the paragraph on Auto Trigger (page 4-16) to find out how overshoot or ringing may af fect your measurement.

Pulse Width A/B

The function menu designation is Pulse.Ei ther input A or input B can be used for mea suring, and both positive and negative pulse width can be selected.

Positive pulse width means the time be-

–

tween a rising edge and the next falling edge.

– Negative pulse width means the time be-

tween a falling edge and the next rising edge.

The selected trigger slope is the start trigger slope. The counter automatically selects the inverse polarity as stop slope.

Duty factor

Pulse width

Period

The total measurement time will be doubled compared to a single measurement, because "Duty" requires 2 measurement steps.

Measurement Errors

Hysteresis

The trigger hysteresis, among other things, causes measuring errors, see Figure 4-16. Actual triggering does not occur when the input signal crosses the trigger level at 50 percent of the amplitude, but when the input signal has crossed the entire hysteresis band.

S t a r t C h a n n e l A

T r i g g e r l e v e l

Duty Factor A/B

The function menu designation is Duty.Ei ther input A or input B can be used for mea suring, and both positive and negative duty factor can be selected. See the preceding para graph for a definition of positive and negative in this context.

Duty factor (or duty cycle) is the ratio be tween pulse width and period time. The coun ter determines this ratio by first making a pulse width measurement, then a period mea surement, and calculates the duty factor as:

S t o p C h a n n e l B

Fig. 4-16 Trigger hysteresis

The hysteresis band is about 20 mV with at tenuation 1x, and 200 mV with attenuation

10x.

To keep this hysteresis trigger error low, the attenuator setting should be 1x when possible. Use the 10x position only when input signals

have excessively large amplitudes, or when

you need to set trigger levels higher than 5 V.

M e a s u r e d T i m e I n t e r v a l

Pulse Width A/B 4-15

Measuring Functions

Overdrive and Pulse Rounding

Additional timing errors may be caused by triggering with insufficient overdrive, see Fig ure 4-17. When triggering occurs too close to the maximum voltage of a pulse, two phenom ena may influence your measurement uncer tainty: overdrive and rounding.

T r i g g e r l e v e l

A c t u a l t r i g g e r i n g

C r o s s i n g t r i g g e r l e v e l

Fig. 4-17 Insufficient overdrive causes

Trigger Error.

Overdrive: When the input signal crosses

the hysteresis band with only a marginal overdrive, triggering may take some 100 ps longer than usual. The specified worst case 500 ps systematic trigger error includes this error, but you can avoid it by having adequate overdrive.

Rounding: Very fast pulses may suffer

from pulse rounding, overshoot, or other aberrations. Pulse rounding can cause significant trigger errors, partic ularly when measuring on fast cir cuitry.

Auto Trigger

Auto Trigger is a great help especially when you measure on unknown signals. However, overshoot and ringing may cause Auto to

choose slightly wrong MIN and MAX signal

levels. This does not affect measurements like

frequency, but transition time measurements

may be affected.

Therefore, when working with known signals such as logic circuitry, set the trigger levels manually.

Always use manual trigger levels if the signal repetition rate drops below 100 Hz (default), or below the low frequency limit set by enter ing a value between 1 Hz and 50 kHz in the menu Auto Trig Low Freq. You can reach it by pressing SETTINGS ® Misc.

4-16 Measurement Errors

Phase

Measuring Functions

What is Phase?

Phase is the time difference between two signals of the same frequency, expressed as an angle.

Phase?

Fig. 4-18 Phase delay.

The traditional method to measure phase de lay with a timer/counter is a two-step process consisting of two consecutive measurements, first a period measurement and immediately after that a time interval measurement. The phase delay is then mathematically calculated as:

360°´ -()Time Interval A B

Period

or in other words:

Phase A B Time Delay FREQ-= °´ ´360

A somewhat more elaborate method is used in these counters. It allows the necessary mea surements to be performed in one pass by us ing time-stamping. Two consecutive time-stamps from trigger events on channel A and two corresponding time-stamps from channel B are enough to calculate the result, including sign.

Resolution

P e r i o d ( T )

T i m e d e l a y (

Fig. 4-19 Traditional phase definition.

The frequency range for phase is up to 160 MHz and the resolution depends on the frequency. For frequencies below 100 kHz the resolution is 0.001° and for frequencies above 10 MHz it is 1°. It can be further improved by averaging through the built-in statistics func tions.

t )

f=Dt *

3 6 0

What is Phase? 4-17

Measuring Functions

Possible Errors

Phase can be measured on input signal fre quencies up to 160 MHz. However, at these very high frequencies the phase resolution is reduced to:

100 360ps FREQ´´

Random Errors

The phase quantization error algorithm is:

100 360ps FREQ´´°

For example, the quantization error for a 1 MHz input signal is thus:

ps ´´ ´ °» °.

100 1 10 360 004

Inaccuracies

The inaccuracy of Phase A-B measurements depends on several external parameters:

Input signal frequency

–

Peak amplitude and slew rate for input sig

–

nals A and B

Input signal S/N-ratio

–

Some internal parameters are also important:

Internal time delay between channel A and

–

B signal paths

– Variations in the hysteresis window be-

tween channel A and B

Let us look deeper into the restrictions and possibilities of using phase measurements.

Inaccuracy: The measurement errors are of two kinds:

–

Random errors

–

Systematic errors

The random errors consist of resolution (quantization) and noise trigger error.

Systematic errors consist of “inter-channel de lay difference” and “trigger level timing” er rors. Systematic errors are constant for a given set of input signals, and in general, you can compensate for them in the controller (GPIB-systems) or locally via the MATH/LIM menu (manual operation) after making cali bration measurements. See Methods of Com pensation on page 4-20.

The trigger noise error consists of start and stop trigger errors that should be added. For

sinusoidal input signals each error is:

3602°

ratio

´p

Let’s use the example above and add some noise so that the S/N ratio will be 40 dB. This corresponds to an amplitude ratio of 100 times (and power ratio of 10000 times). Then the trigger noise will contribute to the random error with:

360

»°

2 100

The sum of random errors should not be added linearly, but in an “RMS way”, because of their random nature. Let’s do so for our exam ples above.

4-18 Possible Errors

Measuring Functions

Random error =

quant err start trg err stop trg err.. .. ..

222

The total random errors are thus:

22 2

0040606085

....++»°

(single-shot)

What about random errors caused by internal amplifier noise? Internal noise contribution is normally negligible. The phase error caused by noise on the signal, whether internal or ex ternal, is:

3602°

´p

ratio

For an input signal of 250 mV cal internal noise figure of 250 mV

and the typi

rms

gives us a S/N-ratio of a minimum of 60 dB (1000 times). This gives us a worst case error of

0.06°. Increasing the input signal to 1.5 V

rms

decreases the error to 0.01°.

Another way to decrease random errors is to use the statistics features of the instrument and calculate the mean value from a number of samples.

Systematic Errors in Phase

Measurements

Systematic errors consist of 3 elements:

–

Inter-channel propagation delay difference.

–

Trigger level timing errors (start and stop), due to trigger level uncertainty.

The inter-channel propagation delay differ ence is typically 500 ps at identical trigger conditions in both input channels. Therefore, the corresponding Phase difference is:

<0.5 ns ´360°´ FREQ

See the following table.

Trigger level timing error

160 MHz

100 MHz

10 MHz

1MHz

100 kHz

10 kHz and below

Table 4-2 Phase difference caused by

inter-channel propagation delay difference

The “trigger level timing error” is depending on two factors:

The actual trigger point is not exactly

–

zero, due to trigger level DAC uncertainty and comparator offset error.

The two signals have different slew rates

–

at the zero-crossing.

Every counter has input hysteresis. This is necessary to prevent noise to cause erroneous input triggering. The width of the hysteresis band determines the maximum sensitivity of the counter. It is approximately 30 mV, so when you set a trigger level of 0 V, the actual trigger point would normally be +15 mV and the recovery point –15 mV. This kind of tim ing error is cancelled out by using hysteresis compensation.

Hysteresis compensation means that the mi crocomputer can offset the trigger level so that actual triggering (after offset) equals the set trigger level (before offset). This general hys teresis compensation is active in phase as well as in time interval and rise/fall time measure ments. There is a certain residual uncertainty of a few mV and there is also a certain tem perature drift of the trigger point.

28.8°

18.0°

1.8°

0.18°

0.018°

0.002°

Possible Errors 4-19

Measuring Functions

The nominal trigger point is 0 V with an un

certainty of ± 10 mV.

Asinewaveexpressedas

Vt V ft

() sin( )=´ 2p

close to the zero-crosssing. That gives

´ 2p

, has a slew rate

DDV

us the systematic time error when crossing 10 mV, instead of crossing 0 mV.

102mV

()

´´p

V FREQ

()

And the corresponding phase error in degrees is:

10 360

mV FREQ

´°´

V FREQ

´´p

which can be reduced to:

06.

()

This error can occur on both inputs, so the worst case systematic error is thus:

06 06.

+°

().()

VA VB

Vpeak (A)

150 mV 150 mV

1.5 V 150 mV

1.5 V 1.5 V

Table 4-3 Systematic trigger level timing

Methods of Compensation

The calculations above show the typical un

()

Vpeak (B)

error (examples).

Worst case systematic error

4°+4° =8°

0.4°+4° =4.4°

0.4°+0.4°=0.8°

certainties in the constituents that make up the total systematic error. For a given set of input signals you can compensate for this error more or less completely by making calibration

measurements. Depending on the acceptable residual error, you can use one of the methods described below. The first one is very simple but does not take the inter-channel propaga

tion delay difference into account. The second one includes all systematic errors, if it is car ried out meticulously, but it is often not practi cable.

Common settings for the two inputs are:

Slope: Coupling: Impedance:

Trigger: Trigger Level: Filter:

Pos or Neg AC 1MW or 50 W depending on source and frequency Man 0V Off

Method 1:

Connect the test signals to Input A and Input B. Select the function Phase A rel A to find the initial error. Use the MATH/LIM menu to enter this value as the constant L in the formula K*X+L by pressing X

Now the current measurement result (X

and change sign.

) will

be subtracted from the future phase measure ments made by selecting Phase A rel B.A considerable part of the systematic phase er

rors will thus be cancelled out. Note that this calibration has to be repeated if the frequency or the amplitude changes.

Method 2:

Connect one of the signals to be measured to both Input A and Input B via a 50 W power splitter or a BNC T-piece, depending on the source impedance. Make sure the cable lengths between power splitter / T-piece and instrument inputs are equal. Select the func tion Phase A rel B and read the result. Enter this value as a correction factor in the same way as described above for Method 1.

4-20 Possible Errors

In order to minimize the errors you should also maintain the signal amplitudes at the in puts, so that the deviation between calibration and measurement is kept as small as possible.

Measuring Functions

The same restrictions as for Method 1 regard ing frequency and amplitude apply to this method, i.e. you should recalibrate whenever one of these signal parameters changes.

Residual Systematic Error:

By mathematically (on the bench or in the controller) applying corrections according to one of the methods mentioned above, the sys tematic error will be reduced, but not fully eliminated. The residual time delay error will most probably be negligible, but a trigger level error will always remain to a certain extent, especially if the temperature conditions are not constant.

Possible Errors 4-21

Measuring Functions

Voltage

MAX

Press MEAS FUNC ® Vol t. The counter can measure the input voltage levels V and VPPon DC-input voltages and on repetitive signals between 1 Hz and 300 MHz.

The default low frequency limit is 20 Hz but can be changed via the SETTINGS ® Miscellaneous menu between 1 Hz and 50 kHz. A higher low-frequency limit means faster measurements.

The voltage capacity is –50 V to +50 V in two automatically selected ranges.

For LF signals the measurement has “voltme ter performance”, i.e. an accuracy of about 1 % of the reading.

You can select any one of the parameters to be the main parameter that is displayed in large digits and with full resolution, while the others are displayed simultaneously at the bottom of the display in smaller characters.

MIN

MAX,VMIN

5 : t h

4 : t h

3 : r d

2 : n d

1 : s t

Fig. 4-20 The voltage is determined by

making a series of trigger level settings and sensing when the counter triggers.

+ V

p e a k

0 V

4-22 V

MAX,VMIN,VPP

RMS

Measuring Functions

When the waveform (e.g. sinusoidal, triangu lar, square) of the input signal is known, its crest factor, defined as the quotient(Q the peak (V

)andRMS(V

) values, can be

rms

)of

used to set the constant K in the mathematical function K*X+L. The display will then show the actual V suming that V

rms

EXAMPLE: A sine wave has a crest factor of

value of the input signal, as

rms

is the main parameter.

1.414 ( mula above will be 0.354.

Press

), so the constant in the for

MATH/LIM and after that

Math®Math(Off)®K*X+L Press K=

and enter 0.354 via the

ENTRY

stant is set to its default setting 0. Confirm your choices with the softkeys below the display. If the input is AC cou-

pled and now show the RMS value of any sine wave input.

keys. Check that the L con-

selected, the display will

NUMERIC

If the sine wave is superimposed on a DC voltage, the RMS value is found as:

0.354*V

pp+VDC

.IfVDCis not known it can

be found as:

MAX MIN

To display the rms value of a sine wave super imposed on a DC voltage, follow the example above, but set L = V

4-23

RMS

Measuring Functions

This page is intentionally left blank.

4-24 V

RMS

Chapter 5

Measurement Control

About This Chapter

This chapter explains how you can control the start and stop of measurements and what you can obtain by doing so. The chapter starts by explaining the keys and the functions behind them, then gives some theory, and ends with actual measurement examples.

Measurement Time

This parameter is only applicable to the func tions Frequency and Period Average.In creasing the measurement time gives more digits, i.e. higher resolution, but fewer mea surements per second. The default value is 200 ms but can be changed via SETTINGS ® Meas Time between 20 ns and 1000 s.

The default value gives 11 digits on the display and 4 to 5 measurements each second. Varying the measurement time is a hardwarebased averaging method in contrast to the software-based mean value function that can be found in the STAT/PLOT menu.

The measurement time changes in 1/2/5 steps if you use the arrow keys for stepping. By us ing the numeric entry keys you can set any value within the specified range with a resolu tionof20ns.

To quickly select the lowest mea

surement time, enter 0. The counter will select 20 ns auto matically.

Gate Indicator

The GATE LED is on when the counter is busy counting input cycles.

Single Measurements

SINGLE is implicitly the normal measure

ment mode, which means that the counter

shows the results from a single input cycle. The exceptions are Frequency and Period

Average.

Single or Average is not relevant for V

or Vppmeasurements.

min

Hold/Run & Restart

Pressing HOLD completes the current mea surement and freezes the result on the display.

Pressing RESTART initiates a new measure

ment.

If you are performing a statistics measurement and press HOLD, the pending sample will be finished. Then the measurement will stop, and you can, for instance, watch the graphic representation of the samples taken so far.

Pressing RESTART starts a new measurement from sample 1, and the measurement will stop when the preset number of samples has been taken.

Arming

Arming gives you the opportunity to start and

stop a measurement when an external qualifier

event occurs.

Start and stop of the arming function can inde pendently be set to positive slope, negative

slope, or it can be turned off. A delay between 10 ns and 2 s can be applied to the start arm ing channel to facilitate certain measurements. Theresolutionis10ns.

Input E on the rear panel is the normal arming input, but also input A and input B can be used. The frequency range for input E is 80 MHz, whereas it is 160 MHz for the other inputs.

All the versatile arming functions can be reached under SETTINGS ® Arm.

max

5-2 About This Chapter

Arming is somewhat complicated yet gives the flexibility to perform a measurement on a specific portion of a complex signal, like a frequency measurement on the colorburst con tained in a composite video signal.

Other examples of arming can be found later in this chapter, starting on page 5-9.

Start Arming

Start arming acts like an ExternalTrigger on an oscilloscope. It allows the start of the ac tual measurement to be synchronized to an ex ternal trigger event.

In a complex signal, you may want to select a certain part to perform measurements on. For this purpose, there is an arming delay function, which delays the actual start of measurement with respect to the arming pulse, similar to a “delayed timebase” in an oscilloscope.

You can choose to delay start arming by a preset time.

Measurement Control

Start arming can be used for all functions except Frequency Burst, Ratio and Vol t.If you use start arming to arm an average measurement, it only controls the start of the first sample.

Stop Arming

Stop arming prevents the stop of a measure ment until the counter detects a level shift on the arming input. Combining Start and Stop Arming results in an “external gate” function which determines the duration of the measure ment.

Stop arming can be used for all functions ex cept Frequency Burst, Ratio, Vol t and Rise/Fall Time.

About This Chapter 5-3

Measurement Control

Controlling Measurement

Timing

The Measurement Process

Basic Free-running Measurements

Since these counters use the reciprocal counting technique, they always synchronize the start and stop of the actual measuring period to the input signal trigger events. A new measurement automatically starts when the previous measurement is finished (unless HOLD is on). This is ideal for continuous wave signals.

The start of a measurement takes place when the following conditions have been met (in or der):

–

The counter has fully processed the previ ous measurement.

–

All preparations for a new measurement are made.

–

The input signal triggers the counter’s measuring input.

The measurement ends when the input signal meets the stop trigger conditions. That hap pens directly after the following events:

The set measurement time has expired (ap-

–

plies to Frequency and Period Average measurements only).

The input signal fulfils the stop trigger

–

conditions, normally when it passes the trigger window the second time.

Resolution as Function of Measurement Time

The quantization error and the number of dig its on the display mainly define the resolution of the counter, that is the least-significant digit displayed.

As explained on page 4-10 under Reciprocal Counting, the calculated frequency f is:

while the relative rms quantization error

= ±100ps/t

The counter truncates irrelevant digits so that the rms quantization resolution cannot change the LSD (least-significant digit) more than ± 5 units. This occurs when the displayed value is

5-4 The Measurement Process

Measurement Control

99999999, and the quantization error is worst case. The best case is when the displayed value is 10000000. Then the quantization res olution corresponds to ± 0.5 LSD units.

± 1 unit in 99999999 (=1E8)

A gradual increase of the measurement time reduces the instability in the LSD caused by the quantization uncertainty. At a specific measurement time setting, the counter is justi fied to display one more digit. That one addi tional digit suddenly gives ten times more dis play resolution, but not a ten times less quantization uncertainty. Consequently, a measurement time that gives just one more display digit shows more visual uncertainty in the last digit.

For a stable LSD readout, the maximum measurement time selected should be one that still gives the required number of digits. Such optimization of the measurement time enables the total resolution to be equal to the quantization resolution.

means 10 times more relative resolution than ± 1 unit in 10000000 (=1E7), despite the same number of digits.

Measurement Time and Rates

The set measurement time decides the length of a measurement if Frequency or Period Average is selected.

This is important to know when you want to make fast measurements, for example when you are using the statistics features, or when you are collecting data over the GPIB bus.

The so-called “dead time”, that is the time be tween the stop of one measurement and the start of the next one in the course of a block measurement, can be below 2 ms.

A block is a collection of consecutive mea surements, the results of which are stored in local memory for statistics or plotting pur

poses (STAT/PLOT menu) or for later trans fer to a controller over one of the data com munication links (GPIB, USB or ETHERNET).

Additional controls over start and stop of measurements

Free-running measurements may be easy to understand, but measurements can get more complex.

Besides input signal triggering, the start of a

measurement is further controlled by the fol lowing elements:

Manual RESTART,ifHOLD is selected.

–

GPIB triggering (<GET> or *TRG), if bus

–

triggering is selected.

External arming signal, if Start Arming

–

is selected.

–

Expired start arming delay, if Arming Delay is selected.

In addition to expired measurement time and stop signal triggering, the stop of measurement is further controlled by:

–

External arming signal triggering, if Stop Arming is selected.

GPIB triggering is described in the Program ming manual.

Now let’s look deeper into the concept of arming.

What is Arming?

Arming is a pretrigger condition (“qualifier”) that must be fulfilled before the counter al

lows a measurement to start.

Arming can also be used to qualify the stop of a measurement. This is called “stop arming”

The Measurement Process 5-5

Measurement Control

as opposed to the more common “start arm ing”.

When you use arming, you disable the normal free-run mode, i.e. individual measurements must be preceded by a valid start arming sig nal transition.

If you use start arming and stop arming to gether you get an externally controlled mea surement time, a so-called “External Gate”.

Manual Arming

The counters have a manual start arming func tion called HOLD. Here you manually arm the start of each individual measurement by pressing the RESTART key.

Use this manual arming mode to measure single-shot phenomena, which are either triggered manually or occur at long intervals. Another reason for using this manual arming could simply be to allow sufficient time to write down individual results.

When Do I Use Start Arming?

Sync

Pulse

nal

Fig. 5-1 A synchronization signal starts

Start arming is useful for measurements of fre quency in signals, such as the following:

–

Single-shot events or non-cyclic signals.

–

Pulse signals where pulse width or pulse positions can vary.

–

Signals with frequency variations versus time (“profiling”).

the measurement when start arming is used.

A selected part of a complex waveform

–

signal.

Signal sources that generate complex wave forms like pulsed RF, pulse bursts, TV line signals, or sweep signals, usually also produce

a sync signal that coincides with the start of a

sweep, length of an RF burst, or the start of a TV line. These sync signals can be used to arm the counter. See Fig. 5-1.

When Do I Use Stop Arming?

You normally use stop arming together with

start arming. That means that the external gating signal controls both the start and the stop of the measurement. Such a gating signal can be used to force the counter to measure the frequency of a pulsed RF signal. Here the position of the external gate must be inside a burst. See Fig. 5-2.

E x t G a t e

B u r s t S i g n a l

Fig. 5-2 Start and stop arming together is

Note that burst measurements with access to an external sync signal are performed in the normal Frequency mode, whereas burst measurements without an external sync signal are performed in the self-synchronizing Fre

quency Burst mode.

In time interval measurements, you can use the stop arming signal as a sort of “external trigger Hold Off signal.” Here you block stop

used for burst signal gating.

S t o p A r mS t a r t A r m

5-6 The Measurement Process

Measurement Control

triggering during the external period. See Fig. 5-3.

S t a r t A r m

Fig. 5-3 Using arming as an external Hold

The Arming Input

Input E is the normal arming input. It is

–

Off.

S t o p A r m

suitable for arming (sync) signals that have TTL levels. The trigger level is fixed at 1.4V and cannot be changed. The trigger slope can be set to positive or negative. The Input E connector can be found on the rear panel of the instrument.

–

Input A or Input B can also be used as arming input for all single channel measurements and dual channel measurements where the arming signal is one of the mea suring signals. This input is more suitable if your arming signal does not have TTL levels. All input controls such as AC/DC, Trigger Level, 50 W/1MW etc. can be used to condition the arming signal.

Using the measuring signal as arming signal

When performing time or frequency measure ments on complex signals having a unique trigger point, input B arming can be used to make the measuring signal itself “auto-arm” the counter, e.g. to measure the frequency of a signal after it has reached a specified voltage limit (= set trigger level), see Fig. 5-4.

–

Connect the signal to input A.

Press INPUT A and adjust the settings to

–

suit the interesting part of the signal.

Press INPUT B and adjust the settings so

–

that the unique trigger point can be de tected. Normally DC coupling and Manual trigger level should be preferred.

Activate start arming with or without de

–

lay on input B via the SETTINGS menu.

The signal on input A will be internally con nected to input B, so no external signal tap is necessary.

When Do I Use Arming With

Delay?

You can delay the start arming point with re spect to the arming signal. Use this function when the external arming signal does not coincide with the part of the signal that you are interested in.

The time delay range is 20 ns to 2 s with a setting resolution of 10 ns.

Getting The Whole Picture

The flowchart in Fig. 5-5 illustrates how arming a trigger hold off enables precise control

of the start and stop of the actual measurement when you operate the counter from the front panel. If you control the counter via the GPIB or USB, read more about bus arming and trig gering under the heading “How to use the trig ger system” in the Programming Manual.

FREQ A

Uniqu e Trigger Point B

Input signal

Set Measuring Ti me Trigger Level A B

Fig. 5-4 Auto-arming using the trigger

level on B as qualifier.

The Measurement Process 5-7

Measurement Control

DI SPLAY

HOLD?

START

ARMING?

WAIT F OR I NP UT

SI GNAL TO TRI GGER

START OF

MEASUREMENT

TRI GGE R

HOLD- OFF?

STOP

ARMING?

END OF PRESET

MEASURI NG TI ME

yes

PRESS

RESTART

WAI T FOR

EXT. SI GNAL

WAIT PRESET TI ME

WAI T FOR

EXT. SI GNAL

DELAY?

yes

WAIT PRESET TI ME

WAIT F OR I NP UT

SI GNAL TO TRI GGER

STOP

MEASUREMENT

PROCESS RESULT

&DISPLAY

Fig. 5-5 Measurement control flow diagram.

5-8 The Measurement Process

Measurement Control

Arming Setup Time

The arming logic needs a setup time of about 5 nanoseconds before the counter is really armed; see Fig. 5-6.

A r m i n g S i g n a l

M e a s u r e d S i g n a l

S e t u p T i m e

Fig. 5-6 Time from active external control

When arming delay is selected, the setup time is different; see Fig. 5-7. It illustrates the effect of the 100 ns delay resolution.

A r m i n g S i g n a l

M e a s u r e d S i g n a l

Fig. 5-7 Time from expired time delay un

edge until measurement is armed:

P r o g r a m m e d D e l a y

S e t u p T i m e : r a n

e f r o m - 6 0 t o + 4 0 n s

til measurement is armed: . –60 to +40 ns.

Arming Examples

Introduction to Arming Examples

The following arming examples are available:

#1 Measuring the first pulse in a burst

#2 Measuring the second pulse in a burst

#3 Measuring the time between pulse #1

and #4 in a burst

#4 Profiling

Examples 1 and 2 measure the pulse width of a selected positive pulse in a burst. You can, however, also measure the period, rise time, or duty factor by changing FUNCTION, and you can measure on a negative pulse by changing trigger slope.

If you do not know the basic parameters of the signal to be measured, we recommend to use an oscilloscope for monitoring. Then you can estimate roughly how to set trigger slope, arming slope and arming delay.

#1 Measuring the First Burst Pulse

S y n c E

Fig. 5-7 shows that a start trigger signal may be detected although it appears 60 nanosec onds before the programmed time delay has expired. The start trigger signal must come 40 nanoseconds after the programmed time delay has expired to guarantee correct start of the measurement.

I n p u t A

Fig. 5-8 Synchronizing the measurement

Inthefirstexamplewewillmeasurethewidth of pulse #1 in a repetitive pulse burst. In this example, a synchronization signal (SYNC) with TTL levels is also available. See Fig. 5-8. However, the quick and simple method de

so that the pulse width of the first pulse is measured.

Arming Setup Time 5-9

Measurement Control

scribed first does not employ arming at all but rather draws on the fact that a counter of this type tends to self-synchronize its internal pro cesses to the input signal.

Our task is to synchronize the start of the mea surement (start trigger) to the leading edge of the first pulse. Depending on the signal tim ing, this can be easy, difficult, or very diffi

cult.

A. Auto Synchronization Without

Arming

If we are lucky, we can manage without using the arming function at all. Often, the counter can automatically synchronize the measure ment start to the triggering of the first pulse. The conditions for success are that the PRF is not too high, preferably below 50 Hz and certainly not above 150 Hz. The duration of a pulse burst (between first and last pulse) should be substantially less than the distance to the next burst, and the number of pulses in the burst should be more than 100 to avoid occasional miscounts.

Do the following steps to perform auto synchronization without arming:

–

Connect the burst signal to input A.

–

Adjust the manual sensitivity and trigger level until the burst signal triggers the counter correctly.

–

Use the MEAS/FUNC key to select Pulse Width A.

–

Use Pacing Time to select a value that approaches the time between the bursts.

Absolute synchronization will not be guaran teed in this way, but there is a high probability that auto-synchronization will work anyway. However, occasional erroneous values will be displayed. To achieve guaranteed synchroni zation, use the Start Arming function.

B. Synchronization Using Start

Arming

The SYNC signal can be directly used to arm

the measurement. This requires that the lead ing edge of the SYNC signal occurs more than

5 nanoseconds before the leading edge of the first pulse in the burst. See Fig. 5-9.

S y n c E

I n p u t A

Fig. 5-9 Synchronization using start arm

S t a r t A r m i n g

> 5 n s

ing.

Do the following steps to perform synchronization using start arming:

– Connect SYNC to input E. –

Connect the burst signal to input A.

–

Adjust the trigger level to match the burst signal under study.

–

Press SETTINGS ® Arm

–

Select Start Arm Delay = 0 and Start Chan E.

–

Use MEAS/FUNC to select Pulse Width A.

If there is no (or too little) time difference be tween the arming signal and the first pulse in the pulse burst, arming must be combined with a delay. See example C.

C. Synchronization Using Start Arming With Time Delay

If the pulse bursts have a stable repetition fre quency, you synchronize the measurement us ing Start Arming with Time Delay. Here you use the SYNC pulse belonging to a preceding burst to synchronize the start of measurement.

5-10 Arming Examples

Measurement Control

Set the time delay to a time longer than the duration of a pulse burst and shorter than the repetition time of the pulse bursts. See Fig. 5-10.

S y n c E

D e l a y

I n p u t A

Fig. 5-10 Synchronization using start

arming with time delay.

Use the same test setup as in the preceding ex ample but enter a suitable Start Arm Delay.

#2 Measuring the Second Burst Pulse

The next task is to measure the width of the second pulse in the pulse train from example

1. How can we now synchronize the measurement start to the start of the second pulse? In this case auto-synchronization, without the use of the arming function, cannot work. Auto-synchronization can be used only to synchronize on the first trigger event in a burst.

Depending on the SYNC signal’s position rel ative to the burst, and the duration of the SYNC signal, the measurement can be per formed with or without using arming delay.

If the SYNC-pulse timing is not so suitable as in the above measurement example, then arm

S y n c E

S t a r t A r m i n g

I n p u t A

Fig. 5-11 If the trailing edge of the sync

signal appears before the sec ond pulse, use arming without delay.

ing must be used combined with a time delay; see the following figure:

S y n c E

S t a r t A r m i n g

D e l a y

I n p u t A

Fig. 5-12 Use arming with delay if the

trailing edge of the sync signal appears too late to be useful.

Use the same test setup as in the preceding ex

ample but enter a suitable Start Arm Delay.

The set delay time must be set to expire in the gap between pulse #1 and #2.

If the trailing edge of the SYNC signal occurs

after the leading edge of the first pulse but be fore the second pulse in the pulse burst, then

normal start arming without delay can be used. Select triggering on positive slope on in put A and negative slope on input E. The slope for the active arming channel is set in the SETTINGS ® Arm ®Start Slope menu.This example is shown in the following figure:

Arming Examples 5-11

Measurement Control

#3 Measuring the Time Between Burst Pulse #1 and #4

In the previous examples, the synchronization task has been to identify the start of a mea surement and to perform a single-shot time in terval measurement. Now, we will complicate the picture even more. In our next example we will not only arm the start, but also the stop of a measurement. We will measure the time be tween the first and the fourth pulse in the pulse burst. We still have the SYNC signal available, see Fig. 5-13.

S y n c E

I n p u t A

1 2 3 4

Fig. 5-13 Measuring a time interval inside

The measurement function is not Pulse Width A but Time Interval A to A where the set- tings for input B are used for controlling the stop conditions. The desired start and stop trigger points are marked in the preceding il lustration. Our task is now to arm both the start and the stop of this measurement. The start arming is already described in example #1, i.e., synchronize measurement start to the leading edge of the first pulse. The challenge is to synchronize the stop of the measurement, i.e., to arm the stop. If we do nothing, the time interval measured will be the time between the first and the second pulse. We must thus delay the stop. This can be done in different ways.

A. Using Trigger Hold Off to

a burst.

Delay the Stop a Certain Time

Trigger Hold Off is used to inhibit stop trig gering during a preset time. The Hold Off pe

riod starts synchronously with the start trigger event. The Hold Off time should be set to ex pire somewhere between pulse number 3 and 4, see Fig. 5-14.

S t a r t A r m

T r i g g e r H o l d O f f

I n p u t A

Fig. 5-14 If Hold Off expires between

Use the same test setup as in the preceding examples. Then proceed as follows:

Use the MEAS/FUNC key to select

–

Time Interval A to A.

–

Press INPUT B and choose positive slope and a suitable trigger level.

–

Press SETTINGS ®Trigger Hold Off (On) and enter a suitable Hold Off time.

–

Make sure the start arming conditions from example #1 are maintained, i.e. no arming delay.

–

Measure.

B. Using Stop Arming (i.e.,

pulses three and four, the cor rect time interval is measured.

External Hold Off) to Delay the Stop

So far in our examples, the sync signal has been used exclusively as a start arming signal; i.e., we have been concerned only about the leading edge of the sync signal, and not its du ration. However, the sync signal can also be used as an External Trigger Hold Off when you select stop arming on the trailing edge of the sync signal. If the duration of the sync pulses can be externally varied, we can select

5-12 Arming Examples

Measurement Control

a duration that expires in the gap between pulse #3 and #4.

S y n c E

S t a r t A r m i n g

I n p u t A

Fig. 5-15 Using both start and stop arm

Use the same test setup as in the preceding ex ample. Then proceed as follows:

Press SETTINGS ® Arm and select

–

Stop Chan E and negative Stop Slope.

Measure.

–

ing to select the part of the burst that is of interest.

S t o p A r m i n g

#4 Profiling

Profiling means measuring frequency versus time. Examples are measuring warm-up drift in signal sources over hours, measuring the linearity of a frequency sweep during seconds, VCO switching characteristics during milli seconds, or the frequency changes inside a “chirp radar” pulse during microseconds. These counters can handle many profiling measurement situations with some limitations. Profiling can theoretically be done manually, i.e., by reading individual measurement re sults and plotting in a graph. However, to avoid getting bored long before reaching your 800th or so measurement result, you must use some computing power and a bus interface. In profiling applications, the counter acts as a fast, high-resolution sampling front end, stor ing results in its internal memory. These re sults are later transferred to the controller for analysis and graphical presentation. The TimeView™ software package greatly simpli fies profiling.

You must distinguish between two different types of measurements called free-running and repetitive sampling.

Free-Running Measurements

Free-running measurements are performed over a longer period, e.g., to measure the sta bility over 24 hours of oscillators, to measure initial drift of a generator during a 30-minute warm-up time, or to measure short-term sta bility during 1 or 10s. In these cases, measure ments are performed at user-selected intervals in the range 2 ms to 1000 s. There are several different ways of performing the measure

ments at regular intervals.

Measurements using the statistics features for setting the “pacing time”

By setting the pacing time to 10 s for example, measurements are automatically made at 10 s intervals until the set number of samples has been taken. The range is 2 - 2*10 HOLD/RUN and RESTART if you want to stop after one full cycle. You can watch the trend or spread on the graphic display while the measurement is proceeding.

Using a controller as a “pacer”

As an alternative, the timer in the controller can be used for pacing the individual measure ments. This allows for synchronization with external events, for instance a change of DUT when checking a series of components.

Using external arming signals

External arming signals can also be used for “pacing.” For example with an arming signal consisting of 10 Hz pulses, individual mea surements are armed at 100 ms intervals.

Letting the counter run free

When the counter is free-running, the shortest delay between measurements is approximately

4 ms (internal calibration OFF) or 8 ms (inter

.Use

Arming Examples 5-13

Measurement Control

nal calibration ON) plus set measurement time. For example, with a measurement time of 0.1 ms, the time between each sample is ap proximately 104-108 ms.

Repetitive Sampling Profiling

The measurement setup just described will not work when the profiling demands less than 4 ms intervals between samples.

How to do a VCO step response profil ing with 100 samples during a time of 10 ms.

This measurement scenario requires a repe ti tive input step signal, and you have to repeat

your measurement 100 times, taking one new sample per cycle. And every new sample should be delayed 100 ms with respect to the previous one.

The easiest way to do this is by means of a controller, e.g. a PC, although it is possible but tedious to manually set and perform all 100 measurements.

The following are required to setup a measurement:

–

A repetitive input signal (e.g., frequency output of VCO).

–

An external SYNC signal (e.g., step volt age input to VCO).

–

Use of arming delayed by a preset time (e.g., 100, 200, 300 ms).

See Fig. 5-16 and Fig. 5-17.

When all 100 measurements have been made, the results can be used to plot frequency ver sus time. Note that the absolute accuracy of

the time scale is dependent on the input signal itself. Although the measurements are armed at 100 ms ± 100 ns intervals, the actual start of measurement is always synchronized to the first input signal trigger event after arming.

The TimeView™ software package will do this measurement quickly and easily.

Voltage step

generator

Fig. 5-16 Setup for transient profiling of a

VCO.

VCO

Input E, Ext Arm

Input A

5-14 Arming Examples

Fig. 5-17 Results from a transient profiling

measurement.

Chapter 6

Process

Introduction

Three different ways to process a measuring result are available: Averaging, Mathematics and Statistics. They can be used separately or all together.

In addition to postprocessing you can also monitor the measurement results in real time by setting limits and deciding how to react when they are crossed.

Averaging

Hardware averaging by means of counting clock pulses during several full input signal cycles is only used for the measurement func tions Frequency and Period Average.The parameter to be set by the operator in this case is Meas Time under SETTINGS,andthe range is 20 ns to 1000 s. Longer measuring times mean higher resolution.

The other functions employ single cycle measuring, and the method to get average results is to utilize the statistics features described later.

Mathematics

The counter can use four mathematical ex pressions to process the measurement result before it is displayed:

1. K*X+L

2. K/X+L

3. K*X/M+L

4. (K/X+L)/M

Press MATH/LIM ® Math to enter the first mathematics submenu. See page 2-12how to enter the constants K, L and M and how to se lect the formula that best suits your need.

The default values of K, L and M are chosen so that the measurement result is not affected directly after activating Math. Recalling the default setting will restore these values as well.

Example:

If you want to observe the deviation from a certain initial frequency instead of the abso lute frequency itself, you can do like this:

Recall the default settings by pressing

–

USER OPT ® Save/Recall ® Recall Setup ® Default.

Connect the signal to be measured to input

–

Press AUTO SET to let the counter find

–

the optimum trigger conditions on its own.

Press MATH/LIM ® Math ® L

–

If the current display value is suitable for

–

your purpose, then press X be transferred to the constant L. You can repeat pressing X The constant will be updated with the latest measurement result.

–

Instead of using X0you can enter any nu merical value from the front panel. Let's assume that 10 MHz is your reference fre quency. The mantissa is marked by text in version for immediate editing. Press 1 ® 0 ® ± ® EE ® 6.

–

Confirm by pressing EXIT/OK. Now the constant L is updated and displayed as

-10E6.

–

Press Math and choose the expression K*X+L by pressing the softkey below it.

–

Now the display will show the deviation from the value you have just entered.

By changing the constant K you can scale the result instead.

until you are satisfied.

. It will then

6-2 Introduction

Process

Statistics

Statistics can be applied to all measuring func tions and can also be applied to the result from Mathematics.

The available statistics functions are as fol lows:

X MAX: Displays the maximum value

within a sampled population of N

-values.

X MIN: Displays the minimum value within

a sampled population of N x

X P-P: Displays the peak-to-peak deviation

within a sampled population of N

-values.

MEAN: Displays the arithmetic mean

value (x x

) of a sampled population of N

-values and is calculated as:

ST DEV: Displays the standard deviation

(s) of a sampled population of N x ues and is calculated as:

()

It is defined as the square root of the variance.

A DEV: Displays the Allan deviation (s)ofa

sampled population of N x

is calculated as:

()

It is defined as the square root of the Allan variance.

The number N in the expressions above can assume any value between 2 and 2*10

-values.

-val-

-values and

Allan Deviation vs. Standard Deviation

The Allan Deviation is a statistic used for characterizing short-term instability (e.g. caused by jitter and flutter) by means of sam ples (measurements) taken at short intervals. The fundamental idea is to eliminate the influ ence of long-term drift due to aging, tempera ture or wander. This is done by making con secutive comparisons of adjacent samples.

The Standard Deviation, which is probably a more familiar statistic, considers the effects of all types of deviation, as all samples in the population are compared with the total mean value.

As you can see, both the Allan Deviation and the Standard Deviation are expressed in the same units as the main parameter, e.g. Hz or s.

Selecting Sampling Parameters

–

Press SETTINGS ® Stat..

–

Press No. of samples and enter a new value by means of the numerical keys or the UP/DOWN arrow keys, if you want to change the default value of 100.

–

Proceed in the same way for No. of bins, if you want to present the measurement re sults graphically in a histogram.

Note that the six statistic

measures are calculated and dis played simultaneously only in the non-graphic presentation mode under STAT/PLOT.

Use the same key for toggling between the three modes Nu merical - Histogram - Trend.

Statistics 6-3

Process

Press Pacing time and enter a new value

–

if you want to change the default value 20 ms. The range is 2 ms - 1000 s. The pacing parameter sets the sampling inter val.

Activate the set pacing time by pressing

–

Pacing Off. The status is changed to Pacing On. Status Pacing Off means that

the set number of samples will be taken with minimum delay.

Press HOLD/RUN to stop the measuring

–

process.

Press RESTART to initiate one data cap

–

ture

Toggle STAT/PLOT to view the measure

–

ment result as it is displayed in the different presentation modes.

Note that you can watch the in-

termediate results update the display continually until the complete data capture is ready.

This is particularly valuable if the collection of data is lengthy.

Measuring Speed

When using statistics, you must take care that the measurements do not take too long time to perform. Statistics based on 1000 samples does not give a complete measurement result until all 1000 measurements have been made, although it is true that intermediate results are displayed in the course of the data capture. Thus it can take quite some time if the setting of the counter is not optimal.

trigger levels, and 1000 or 10000 times a fraction of a second is a long time.

Do not use a longer measuring time than

–

necessary for the required resolution.

Remember to use a short pacing time, if

–

your application does not require data col lection over a long period of time.

Determining Long or Short Time Instability

When making statistical measurements, you must select measuring time in accordance

with what you want to obtain:

Jitter or very short time (cycle to cycle) varia

tions require that the samples be taken as Sin gle measurements.

If average is used (Freq or Period Average only), the samples used for the statistical calculations are already averaged, unless the set measuring time is less than the period time of the input signal (up to 160 MHz). Above this frequency prescaling by two is introduced anyhow, and as a consequence a certain amount of averaging. This can be a great advantage when you measure medium or long time instabilities. Here averaging works as a smoothing function, eliminating the effect of jitter.

T i m e I n t e r v a l o r F r e q u e n c y

D r i f t

J i t t e r

Here are a few tips to speed up the process:

–

Do not use AUTO trigger. It is convenient, but it takes a fraction of a second each time the timer/counter determines new

6-4 Statistics

T i m e

Fig. 6-1 Jitter and drift.

The signal in Fig. 6-1contains a slower varia tion as well as jitter. When measuring jitter

Process

you should use a limited number of samples so that the slow variation does not become no ticeable or alternatively use the dedicated sta tistic measure for this kind of measurement, the Allan deviation.

To measure the slower variation you calculate Max, Min or Mean on a long series of aver aged samples. Here averaging eliminates the jitter in each sample and the long measuring time and large number of samples means that the measurement can record very slow varia tions. The maximum pacing time equals the maximum measuring time for each sample and is 1000 s, and the maximum number of samplesis2*10 single data capture could theoretically span up to 2*10

, which in effect means that a

s or more than 60000 years.

Statistics and Mathematics

The counter allows you to perform mathematical operations on the measured value before it is presented to the display or to the bus. See Page 6-2to get an overview of the four available equations.

Any systematic measurement uncertainty can be measured for a particular measurement setup, and the needed correction constants can be entered into these equations. Statistics will then be applied to the corrected measured value.

Confidence Limits

The standard deviation can be used to calcu late the confidence limits of a measurement.

Confidence limits = ± ks

Where:

= standard deviation

k = 1 for a confidence level of 68.3% (1s - limits) k = 2 for a confidence level of 95.5% (2s - limits)

k = 3 for a confidence level of 99.7%

(3s - limits)

Example

A measurement of a time interval of 100 msis used to illustrate how the confidence limits are calculated from the measurement result.

Use the statistics to determine the mean value and standard deviation of the time interval. Take sufficient samples to get a stable reading. Assume further that the start and stop trigger transitions are fast and do not contribute to the measurement uncertainties. The counter dis plays:

MEAN value = 100.020 msandaSTDDEV= 50 ns, then the 95.5% confidence limits =

=±2*50 ns = ±100 ns.

±2s

The 3s - limit will then be ±3*50 ns = ±150 ns

Jitter Measurements

Statistics provides an easy method of determining the short term timing instability, (jitter) of pulse parameters. The jitter is usually specified with its rms value, which is equal to the standard deviation based on single mea surements. The counter can then directly mea sure and display the rms jitter.

Otherwise, the standard deviation of mean values can be measured. The rms value is a good measure to quantify the jitter, but it gives no information about the distribution of the measurement values.

To improve a design, it might be necessary to analyze the distribution. Such measurements as well as trend analysis can be performed by means of the built in graphic capability - tog gle the STAT/PLOT key to see the two graphic presentation modes.

Statistics 6-5

Process

Even higher versatility can be exploited with a controller and the optional TimeView™Fre quency and Time Analyzing Software Pack

age.

Limits

The Limits Mode makes the counter an effi cient alarm condition monitor with high flexi bility as to the report possibilities.

Press MATH/LIM ® Limits to enter the first Limits Menu. See below.

Fig. 6-2 The Limit Menu, level 1

You can set two levels by entering the submenus named Lower Limit resp. Upper Limit. Any numerical value can be entered using scientific notation. The active keys are the digits 0-9, the decimal point, the change sign (±) and the softkey designated EE for toggling between the mantissa and the exponent.

Typos are erased by pressing the left arrow key. Confirm by pressing ENTER.

Limit Behavior

Press Limit Behavior to set how the counter will react on limit crossings. The following choices exist:

•

Off

No action taken. LIM indicator is OFF. In all other behavior modes, the

dicator is ON and non-flashing, unless the limits set in the

have been crossed.

Limit Mode menu

LIM in

Capture

•

The measurements are compared with the limits set under

Lower Limit and

Upper Limit, and the LIM symbol will

be flashing when the active

Limit Mode has set the LIM flag.

Only samples meeting the test criterion will be part of the population in statistics presentations.

Alarm

•

The measurements are compared with the limits set under

Lower Limit and

Upper Limit, and the LIM symbol will

be flashing when the active

Limit Mode has set the LIM flag.

All samples, i.e. also those outside the limits, will be part of the population in statistics presentations.

Alarm_stop

•

The measurements are compared with the limits set under

Lower Limit and

Upper Limit, and the LIM symbol will

be flashing when the active

Limit Mode has set the LIM flag.

The measurement process will stop, and the value that caused the limit detector to trigger can be read on the dis play.

Only samples taken before the alarm condition will be part of the population in statistics presentations.

The alarm conditions can also be detected via the SRQ function on the GPIB. See the Pro gramming Manual.

6-6 Limits

Process

Limit Mode

The Limit Mode offers three choices:

Above

•

Results above the set lower limit will pass. A flashing

play reports that the measurement re sult has been below the lower limit at least once since the measurement

started. Use

LIM symbol to its non-flashing state. Below

•

Results below the set upper limit will pass. A flashing

play reports that the measurement re sult has been above the upper limit at least once since the measurement

started. Use

LIM symbol to its non-flashing state. Range

•

Results inside the set limits will pass. A flashing

ports that the measurement result has been below the lower limit or above the upper limit at least once since the mea-

surement started. Use reset the

state.

LIM symbol on the dis

RESTART to reset the

LIM symbol on the dis

RESTART to reset the

LIM symbol on the display re-

RESTART to

LIM symbol to its non-flashing

This type of graphic resembles a classic ana log pointer instrument, where the pointer is a "happy smiley" as long as it is positioned inside the limits and a "sad smiley" when it gets outside the limits but is still within the

display area. Values that fall outside the dis

play area are represented by a "<"attheleft edge or a ">" at the right edge.

The location of the bars is fixed, so the "in side" range takes up the mid third of the dis play area. This means that the resolution and the scale length are set by the limits that have

been entered by the operator.

Limits and Graphics

Limits can also be applied to the two-dimensional graphics, the trend plot and the histogram. By introducing limits you can inhibit the auto-scaling and indirectly set the scale length and the resolution.

Fig. 6-3 The analog limit monitor.

If Range is selected and the presentation mode is VAL UES , a one-dimensional graphic representation of the current measurement value in relation to the limits can be seen at the same time as the numerical value.

The upper limit (UL) and the lower limit (LL) are vertical bars below the main numerical display, and their numerical values are dis played in small digits adjacent to the bars. See Fig. 6-3.

Fig. 6-4 Limits in a trend plot.

Fig. 6-5 Limits in a histogram.

Limits and Graphics 6-7

Process

This page is intentionally left blank.

6-8 Limits and Graphics

Chapter 7

P erf ormance Check

Performance Check

General Information

WARNING: Before turning on the in

strument, ensure that it has been installed in accordance with the In stallation Instructions outlined in Chapter 1 of the User's Manual.

NOTE: The procedure does not check every

facet of the instrument’s calibration; rather, it is concerned primarily with those parts of the instrument which are essential for determining the function of

the instrument.

It is not necessary to remove the instrument cover to perform this procedure.

This performance procedure is intended for:

checking the instrument’s specification.

–

incoming inspection to determine the ac

–

ceptability of newly purchased instruments and recently recalibrated instruments.

checking the necessity of recalibration af-

–

ter the specified recalibration intervals.

Preparations

steps not meeting equipment specifications.

Power up your instrument at least 30 minutes before check ing to let it reach normal oper ating temperature. Failure to do so may result in certain test

Test Equipment

Type of Equipment Required Specifications

–8

Reference Oscillator

Voltage Calibrator

LF Synthesizer Square/ Sine up to 10 MHz, 10 V

Pulse Generator 2 ns rise time, 5 V peak, >10 MHz, continuous & one-shot trigger

Oscilloscope 350 MHz, <3% voltage uncertainty

RF Signal Generator 100 MHz to 3 or 8 GHz dep. on prescaler option, 10 MHz ext.ref.

Power Splitter 50 W 6dBBNC

T-piece BNC

Termination 50 W feedthrough BNC

Lowpass Filter 50 kHz (for 1 MW)

BNC Cables 5 to 7 pcs of suitable lengths

10 MHz, 1*10

DC -50 V to +50 V (e.g. 5500) for calibrating the built-in voltage ref erence, alternatively corresponding DC power supply + DVM with uncertainty <0.1 %

(e.g. 908) for calibrating the standard oscillator

–9

(e.g. 909) for calibrating PM6690/_5_ & PM6690/_6_

RMS

Table 7-1 Recommended equipment for calibration and performance check.

7-2 General Information

Performance Check

Front Panel Controls

Internal Self-Tests

The test programs forming the self-diagnosis can be activated from the front panel as fol lows:

Press USER OPT

–

Press Test.

–

Press Test Mode.

–

Select one of the six tests available by

–

pressing the softkey below the label with the name of the test function. Five of the tests (RAM, ROM, Logic, Display, and Interface) are individual. They are briefly described below. The sixth, named All, performs all five individual tests in sequence.

• All - all tests performed in sequence

•

RAM - test of RAM memory

•

ROM - test of ROM memory

•

Logic - test of counter ASIC and other

logic circuits.

•

Display - test of graphic display

module

•

Interface - test of GPIB and USB

–

Press Start Test.

–

If a fault is detected, an error message ap pears on the display and the program halts. Note any error messages.

–

If no faults are detected, the instrument re turns to the normal measurement mode.

that something changes on the display when you press a key. Consequently you can press the keys in almost any order without paying attention to the exact response, but for those who want to be more systematic there is a ta ble overleaf, where all keys are exercised at least once.

Press the keys as described in the first column and look at the display for the text in the sec ond column. Some keys change more text on the display than described here. The display text mentioned here is the one mostly associ ated with the selected key.

NOTE: For the instrument to respond correctly,

this test must be carried out in se quence, and you must start with the DEFAULT setting. See page 2-13. No signals should be applied to the input connectors

Keyboard Test

This test verifies that the timer/counter re sponds when you press any key. It is not a functional test. Such tests are performed later in this chapter. The important thing here is

Front Panel Controls 7-3

Performance Check

Key(s) Display Notes P/F

STANDBY Off

ON Backlight On

INPUT A Input A:

Man

Trig Trig: xy mV

0.123V Trig: 0.123 V

t (5 times) Trig: _ V

4.567 Trig: 4.567 V

t (5 times) Trig: _ V

8.9 Trig: 8.9 V

± Trig: -8.9 V

mV Trig: -8.9 mV

V Trig: -8.9 V

AUTOSET Menu disappears

INPUT B Input B:

SETTINGS Settings:

ENTER Meas Time: 200 ms

p Meas Time: 500 ms

q Meas Time: 200 ms

EXIT/OK Settings:

EXIT/OK Menu disappears

MATH/LIM Math/Limit:

USER OPT User options:

CANCEL Menu disappears

HOLD/RUN Hold

HOLD/RUN Hold disappears

MEAS FUNC Measure function:

Red standby LED On (Key common to ON)

Red standby LED Off (Key common to

STANDBY)

Menu for setting Slope, Coupling, Impedance

etc.

Menu for entering numeric values in V or mV

Menu for setting Slope, Coupling, Impedance

etc.

Menu for setting Meas Time, Hold-Off, Ref.

Source etc.

Menu for setting Meas Time, Hold-Off, Ref.

Source etc.

Menu for selecting post-processing formula and

alarm limit

Menu for Calibration, Memory Management, In

terface etc.

At upper right corner

Menu for selecting measurement function

7-4 Front Panel Controls

Performance Check

Key(s) Display Notes P/F

u Period

ENTER Single A

EXIT/OK Menu disappears

STAT/PLOT Period Single A

MEAN:

VALUE Stat parameters dis

appear

Table 7-2 Keyboard test

Short Form Specification Test

Sensitivity and Frequency Range

Recall the DEFAULT settings.

– –

Press INPUT A.

–

Select 50 W input impedance, 1x attenuation, MANual trigger and Trigger level 0V.

–

Connect a signal from a HF generator to a BNC power splitter.

–

Connect the power splitter to Input A of your counter and an oscilloscope.

Cursor position marked by text inversion

Period Single A: at upper left corner

Aux parameters: Max, Min, P-P, Adev, Std

Set the input impedance to 50 W on the

–

oscilloscope.

Adjust the amplitude according to the fol

–

lowing table. Read the level on the oscilloscope. The timer/counter should display the correct frequency.

Connect the signal to Input B.

– – Press INPUT B. –

Select 50 W input impedance, 1x attenuation, MANual trigger and Trigger level 0V.

–

Press MEAS FUNC ® Freq ® Freq A ®B

–

Repeat the measurements above for Input B.

Frequency

(MHz)

10 15 –23

50 15 –23

100 15 –23

200 15 –23

300 25 –19

Table 7-3 Sensitivity for inputs A & B at various frequencies

Level Pass

rms

dBm Input A Input B

Short Form Specification Test 7-5

Performance Check

Voltage

Recall the DEFAULT settings.

–

Press INPUT A and select DC coupling.

–

Do not apply an input signal to Input A yet.

Press EXIT/OK.

–

The counter should now indicate:

–

=0± 0.01 V and

MAX

=0± 0.01 V.

MIN

Connect 4.00 VDCto channel A, using an

–

external low pass filter on the input.

The readings should be:

–

= 4.00 ± 0.05 V and

MAX

= 4.00 ± 0.05 V.

MIN

Repeat the measurement with inverted po-

–

larity

Press INPUT A and select 10x.

–

Press EXIT/OK.

– – Change the DC level to 40 V. –

The counter should indicate: V

= 40.0 ± 0.5 V and

MAX

VMIN = 40.0 ± 0.5 V

–

Repeat the measurement with inverted polarity.

–

Press INPUT A and select 1x.

–

Press EXIT/OK.

–

Connect a sinusoidal signal to Input A with an amplitude of 4.00 Vpp and a fre quency of 100 kHz.

–

The indication should be 4.00 ± 0.27 VPP.

–

Press INPUT A and select 10x.

–

Press EXIT/OK.

–

Change the amplitude to 18 VPP.

–

The display should read 18.0 ± 2.1 VPP.

–

Press INPUT B and select DC coupling. Do not apply an input signal to Input B yet.

Press EXIT/OK.

–

Press MEAS FUNC ® Freq ® Freq A

–

®B.

The counter should now indicate:

–

=0± 0.01 V and

MAX

=0± 0.01 V

MIN

Repeat the measurements for Input B as

–

described above for Input A.

7-6 Short Form Specification Test

Trigger Indicators and Input Controls

Performance Check

Trigger Level

Trigger Indicator Pass

(manually set)

+1 V off

-1 V on

0.0 V blinking

Table 7-4 Trigger indicator check.

NOTE: This test must be performed in the se

quence given.

Recall the DEFAULT settings.

–

Press INPUT A and select MANual trigger

–

level.

Connect the LF synthesizer to Input A.

–

Use the following settings (into 50 W): Sine, 10 kHz, 0.9 V

, and +0.50 V DC

offset.

–

Verify that the three modes for the trigger indicator are working properly by changing the trigger level:

–

Press the Trig key and enter 1 V via the keyboard, then verify by pressing EXIT/OK. Check the trigger indicator according to Table 7-4.

–

Press the Trig key and enter –1 V via the keyboard by pressing the ± key, then

Input A Input B

verify by pressing EXIT/OK. Check the trigger indicator according to Table 7-4.

Press the Trig key and enter 0 via the

–

keyboard, then verify by pressing EXIT/OK. Check the trigger indicator according to Table 7-4.

Apply the signal to Input B instead.

–

Press MEAS FUNC ® Freq ® Freq A

–

® B

–

Press INPUT B and select MANual trigger level.

–

Repeat the trigger level settings above to verify the three trigger indicator modes for Input B.

Settings V

INPUT A, DC, 50 W

10X

1MW

Table 7-5 Input controls check.

max

+950 mV +50 mV

+450 mV -450 mV

+0.45 V -0.45 V

> +0.45 V < -0.45 V

min

Pass/Fail

Input A Input B

Short Form Specification Test 7-7

Performance Check

Trigger Level Check

Recall the DEFAULT settings.

–

Connect the LF synthesizer to Input A.

–

Use the same settings as in the previous test.

Press INPUT A and select DC and 50 W.

–

Check the first V

–

els on the display according to Table 7-5.

Perform the rest of the settings in se

–

quence, and read the corresponding V and V ues are approximate and serve only as in dicators of state changes.

Connect the generator to Input B.

–

Press MEAS FUNC ® Freq ® Freq A

–

® B

Press INPUT B and select DC and 50 W

–

Perform the settings and check the Vmax

–

and Vmin values for Input B according to Table 7-5.

values. Remember that these val

min

max

and V

voltage lev

min

max

Reference Oscillators

X-tal oscillators are affected by a number of external conditions like ambient temperature and supply voltage. Aging is also an important factor. Therefore it is hard to give limits for the allowed frequency deviation. The user himself must decide the limits depending on his application, and recalibrate the oscillator accordingly.

To check the accuracy of the oscillator you must have a calibrated reference signal that is at least five times more stable than the oscilla tor that you are testing. See Table 7-6 and the list of test equipment on page 7-2. If you use a non-10 MHz reference, you can use the math ematics in the timer/counter to multiply the reading.

Recall the DEFAULT settings.

–

Connect the reference to input A

–

Check the readout against the accuracy re

–

quirements of your application.

Acceptance Test

Table 7-6 can serve as an acceptance test and gives a worst case figure after 30 minutes warm-up time. All deviations that can occur in a year are added together.

Oscillator Frequency Readout Suitable Reference P/F

PM6690/_1_ (Standard)

PM6690/_5_(OCXO)

PM6690/_6_(OCXO)

Table 7-6 Acceptance test for oscillators.

10.00000000 MHz ± 150 Hz

10.00000000 MHz ± 1Hz

10.00000000 MHz ± 0.25 Hz

7-8 Short Form Specification Test

908

909

Performance Check

Resolution Test

Connect the pulse generator to a power

–

splitter.

Connect one side of the power splitter to

–

Input A on the counter using a coaxial ca ble.

Connect the other side of the power split

–

ter to Input B on the counter.

Settings for the pulse generator:

Amplitude = 2 VPP, (high level +2 V and

–

low level 0 V)

Period = approx. 1 ms

–

Duration = approx. 50 ns

–

Rise time = 2 ns

–

Restore the timer/counter's default settings and make the following changes:

Function = Time A-B

–

Press STAT/PLOT key to the right of the

–

display.

–

Settings for INPUT A and INPUT B:

–

50 W input impedance

–

MANual trigger level

–

Trig level = 0.5 V

–

DC coupling

–

POS slope

The standard deviation (Std) should be <100 ps.

Rear Inputs/Outputs

10 MHz OUT

Connect an oscilloscope to the 10 MHz

–

output on the rear of the counter. Use a coaxial cable and 50 W termination.

The output voltage should be sinusoidal

–

and above 1 V

RMS

(2.8 V

p-p

EXT REF FREQ INPUT

Recall the DEFAULT settings.

–

Connect a stable 10 MHz signal (e.g REF

–

OUT from another counter) to input A.

Connect a 10 MHz, 100 mV

–

(0.28 V to EXT REF IN.

) signal from the LF synthesizer

P-P

– Select Ext Ref. by keying in the following

sequence:

SETTINGS ® Meas Ref ® External

–

The display should show 10 MHz.

–

Change the external reference frequency to 5 and 1 MHz.

–

The counting should continue, and the dis play should still show 10 MHz.

EXT ARM INPUT

–

Proceed from the test above.

–

Select MANual trigger.

–

Connect the pulse generator to Ext Arm Input.

–

Settings for the pulse generator: single shot pulse, manual trigger, amplitude TTL = 0 - 2 V duration = 10 ns.

, and

RMS

Rear Inputs/Outputs 7-9

Performance Check

Activate start arming by keying in the fol

–

lowing sequence:

SETTINGS ® Start Chan ® E

The counter does not measure.

–

Apply one single pulse to Ext Arm Input.

–

The counter measures once and shows

–

10 MHz on the display.

Measuring Functions

Connect a 10 MHz sine wave signal with

–

approx. 1 V power splitter to Input A and Input B, e.g. from 10 MHz Out on the rear panel. Use equal cable lengths from the power splitter to the inputs.

– Recall the DEFAULT settings.

Select the following settings for the timer/counter via INPUT A and INPUT B:

–

50 W impedance for A and B.

–

MANual trigger.

–

POS slope.

–

Check that the timer/counter performs the correct measurement by displaying the re sult as shown under the “Display” column in Table 7-7.

–

Select function via MEAS FUNC.

amplitude into 50 W via a

RMS

Check of HOLD OFF Function

Recall the DEFAULT settings.

–

Select the following common timer/counter settings for both Input A and Input B via the hard menu keys INPUT A and INPUT B:

50 W impedance.

–

DC coupling.

–

MANual trigger, x1 attenuation.

–

Trigger level = 0.5 V.

–

Press SETTINGS and activate Hold Off.

–

Select Hold Off On and set the Trigger Hold Off time to 1 ms.

Connect the pulse generator with the fol-

–

lowing settings to Input A :

Period = 100 ms.

– – Duration 10 ns. –

Double pulse.

–

Delay = 1 ms.

–

Amplitude = 1.0 VPP, (high level +1V and low level 0V).

–

Rise time 2 ns.

–

Check the following results:

–

Freq A with Hold Off On = 10 kHz.

–

Freq A with Hold Off Off = 20 kHz.

–

Connect the signal to Input B, select Freq B and repeat the tests above.

7-10 Measuring Functions

Performance Check

Connect the output of a signal generator

Options

Input C Check

To verify the specification of the different RF prescalers (Input C), use the following basic test setup:

Selected Function Action Display P/F

FREQ A

FREQ B

FREQ C

FREQ RATIO A/B

FREQ RATIO C/B

PER SINGLE A

PER SINGLE B

PER AVERAGE A

PER AVERAGE B

TIME INT A to B

PULSE POS A

PULSE NEG A

RISE TIME A

FALL TIME A

PHASE A rel B

PHASE B rel A

PHASE A rel A

DUTY POS A

DUTY NEG A

VOLT MAX A

VOLT MIN A

500 MHz, -15 dBm to Inp. C 500 MHz

POS SLOPE A, NEG SLOPE B 50 ns

NEG SLOPE A, POS SLOPE B 50 ns

POS SLOPE A, NEG SLOPE B 180° or -180°

POS SLOPE A, POS SLOPE B 0° or 360°

–

covering the specified frequency range to the RF input of the counter.

Connect the 10 MHz REF OUT from the

–

generator to the EXT REF IN on the rear panel of the counter.

2) 3)

100 ns

50 ns

30 ns

0.5

-0.75 V

10 MHz

180° or -180°

+0.75 V

Table 7-7 Measuring functions check

1) Value depends on the symmetry of the signal.

2) Exact value depends on input signal.

3) If an RF option is installed.

Options 7-11

Performance Check

Choose Meas Ref from the SETTINGS

–

menu and select External.

Choose Freq C from the MEAS FUNC

–

menu.

Generate a sine wave in accordance with

–

the tables.

Verify that the counter is counting cor

–

rectly. (The last digit will be unstable)

Frequency Amplitude P/F

MHz mV

100-300 20 -21

300-2500 10 -27

2500-2700 20 -21

2700-3000 40 -15

RMS

dBm

Table 7-8 RF input sensitivity,

3 GHz Option.

Frequency Amplitude P/F

MHz mV

200-500 20 -21

500-3000 10 -27

3000-4500 20 -21

4500-6000 40 -15

6000-8000 80 -9

Table 7-9 RF input sensitivity,

8 GHz Option.

RMS

dBm

7-12 Options

Chapter 8

Specifications

Introduction

Only values with tolerances or limits are guar anteed data. Values without tolerances are in

formative data, without guarantee.

Measurement Functions

Refer to page 8-9 for uncertainty information.

Inputs A and B can be swapped in all modes except Rise Time and Fall Time.

Display: All measurements are displayed with a large main parameter value and smaller auxiliary parameter values (with less resolution). Some measurements are only available as auxiliary parameters.

Frequency A, B, C

Range:

Frequency Burst A, B, C

Frequency and PRF of repetitive burst signals can be measured without external control sig

nal and with selectable start arming delay.

Functions: Frequency in burst (Hz)

Range A, B, C: See Frequency A, B, C

Min. Burst Duration: 40 ns (80 ns > 160 MHz)

Min. No. of Pulses in Burst (Inp A, B):

PRF Range (see also Inp C spec): 0.5 Hz - 1 MHz

Start Delay Range: 10 ns - 2 s, resolution

n Display:

Main Parameter: Aux. Parameters:

PRF (Hz) Number of cycles in burst

3 (6 above 160 MHz)

(Inp C):

3 x prescaler factor

10 ns

Frequency in burst PRF & number of cycles in burst

Input A: 0.001 Hz - 300 MHz

Input B: 0.001 Hz - 300 MHz

Input C: 100 MHz - 3 GHz

Resolution: 12 digits/s

Display:

Main Parameter:

Aux. Parameters:

(PM6690/6__) 200 MHz - 8 GHz (PM6690/7__)

Frequency

max,Vmin,Vp-p

8-2 Introduction

Period A, B, C Average

Range:

Input A, B: Input C (3 GHz):

(8 GHz):

Resolution:

Display:

Main Parameter: Aux. Parameters:

3.3 ns - 1000 s 370 ps - 10 ns 125 ps - 5 ns 12 digits/s

Period V

max,Vmin,Vp-p

Fluke PM6690 Operator's Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Table of Contents

Preparation for Use

Safety 1-5

Unpacking 1-7

Default Settings 2-15

Measuring Functions

FREQ A, B 4-3

Theory of Measurement 4-9

Introduction 4-13

Pulse Width A/B 4-15

What is Phase? 4-17

Measurement Control

Arming Setup Time 5-9

Process

Statistics 6-3

Limits and Graphics 6-7

P erf ormance Check

Front Panel Controls 7-3

Short Form Specification Test 7-5

Rear Inputs/Outputs 7-9

Options 7-11

Specifications