Wavetek 4920 User manual

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Page 1

SER'S HANDBOOK

Model 4920

Alternating Voltage Measurement Standard

Final Width = 175mm

Page 2

Final Width = 175mm

USER'S HANDBOOK

for

THE MODEL 4920

ALTERNATING VOLTAGE

MEASUREMENT STANDARD

(for servicing procedures

refer to the Maintenance Handbook)

850264 Issue 2.0 (December 1998)

ISO 9002

Wavetek Ltd

CERTIFICATE No. FM 29700

For any assistance contact your nearest Wavetek Sales and Service Center. Addresses can be found at the back of this handbook.

Due to our policy of continuously updating our products, this handbook may contain minor differences in specification, components and circuit design to the instrument actually supplied. Amendment sheets precisely matched to your instrument serial number are available on request.

is a US registered trademark of Wavetek Corporation.

Page 3

Wavetek Corporation

Standard Warranty Policy

Wavetek warrants that all Products manufactured or procured by Wavetek conform to Wavetek's published specifications and are free from defects in materials and workmanship for a period of one (1) year from the date of delivery to the original Buyer, when used under normal operating conditions and within the service conditions for which they were designed. This warranty is not transferrable and does not apply to used or demonstration products.

The obligation of Wavetek arising from a Warranty claim shall be limited to repairing, or at its option, replacing without charge, any assembly or component (except batteries) which in Wavetek's sole opinion proves to be defective within the scope of the Warranty. In the event Wavetek is not able to modify, repair or replace nonconforming defective parts or components to a condition as warranted within a reasonable time after receipt thereof, Buyers shall receive credit in the amount of the original invoiced price of the product.

Wavetek must be notified in writing of the defect or nonconformity within the Warranty period and the affected Product returned to Wavetek's factory, designated Service Provider, or Authorized Service Center within thirty (30) days after discovery of such defect or nonconformity. Buyer shall prepay shipping charges and insurance for Products returned to Wavetek or its designated Service Provider for warranty service. Wavetek or its designated Service Provider shall pay costs for return of Products to Buyer.

Wavetek shall have no responsibility for any defect or damage caused by improper storage, improper installation, unauthorized modification, misuse, neglect, inadequate maintenance, accident or for any Product which has been repaired or altered by anyone other than Wavetek or its authorized representative or not in accordance with instructions furnished by Wavetek.

The Warranty described above is Buyer's sole and exclusive remedy and no other warranty, whether written or oral, expressed or implied by statute or course of dealing shall apply. Wavetek specifically disclaims the implied warranties of merchantability and fitness for a particular purpose. No statement, representation, agreement, or understanding, oral or written, made by an agent, distributor, or employee of Wavetek, which is not contained in the foregoing Warranty will be binding upon Wavetek, unless made in writing and executed by an authorized representative of Wavetek. Under no circumstances shall Wavetek be liable for any direct, indirect, special, incidental, or consequential damages, expenses, or losses, including loss of profits, based on contract, tort, or any other legal theory.

April 1, 1994

Final Width = 175mm

Wavetek Corporation reserves the right to amend specifications without notice.

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4920 User’s Handbook

Final Width = 175mm

CONTENTS

Page

SAFETY ISSUES READ THIS ENTIRE SECTION THOROUGHLY BEFORE ATTEMPTING TO INSTALL, OPERATE OR SERVICE THE MODEL 4920 ALTERNATING VOLTAGE MEASUREMENT STANDARD v

SECTION 1 INTRODUCTION AND GENERAL DESCRIPTION

Standard and Optional Measurement Facilities 1-1 Accessories 1-4 Additional Documentation 1-4 Outline of 4920 Applications 1-5 Principles of Operation 1-7

SECTION 2 INSTALLATION AND OPERATING CONTROLS

Unpacking and Inspection 2-1 Calibration Enable Switch S2 2-1 Introduction to the Front Panel 2-2 Introduction to the Rear Panel 2-3

Preparation for Operation

Power Cable 2-4 IEEE 488 Bus Connector 2-4

Line Power Fuse 2-5 Line Voltage 2-5 Bench Mounting 2-6 Rack Mounting 2-6 Rack Slide Mounting 2-8 Connectors and Pin Designations 2-12

SECTION 3 BASIC MEASUREMENTS

The Measurement Task 3-1 Introduction to the Front Panel 3-1 Menu Keys 3-2 Major Function Keys 3-4 Initial State at Power On 3-5 Soft Key Conventions 3-6 Quick Tour of the Major Function Menus 3-7 ACV Menu 3-7 mV Menu 3-10 AC/DC Menu 3-12 Input and Status Keys 3-14 Conclusion 3-24

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4920 User’s Handbook

Page

SECTION 4 USING THE 4920

Preliminaries 4-1 Safety 4-1 Interconnections - General Guidelines 4-2

Connection of Current Shunt Adaptor Model 4921 4-3

Functions 4-4

Measurement of AC Voltage 4-4 mV Function - AC Millivolt Ranges (Option 10) 4-6 AC/DC Function - AC to DC Transfer 4-9

Facilities 4-12

Input Channels A and B 4-12 Digital Filter 4-13 RMS Computation - Low Frequency Limits 4-14 Spot Frequency Operation 4-15 Status Reporting 4-17 Monitoring 4-17

Math 4-19 Direct Action Keys 4-22 Numeric Keyboard Keys 4-23 Test Facilities 4-24 Calibration Operations 4-27

Section 4 Appendices:

A Error Detection/Error Messages 4-A1

Final Width = 175mm

SECTION 5 SYSTEMS APPLICATION VIA THE IEEE 488 INTERFACE

Section 5 Contents List 5-0-1 Classified Alphabetical List of IEEE 488.2 Codes used in the 4920 5-0-2 Introduction 5-1 4920 Commands and Queries - Syntax Diagrams 5-28

Section 5 Appendices:

A IEEE 488.2 Device Documentation Requirements 5-A1 B 4920 Device Settings at Power On 5-B1

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Final Width = 175mm

4920 User’s Handbook

CONTENTS (Continued)

Page

SECTION 6 SPECIFICATIONS

Mechanical and Environmental 6-1 Electrical 6-2 Maximum Inputs 6-3 Accuracy Specifications 6-4

ACV Accuracy 6-4 mV Accuracy 6-6 AC/DC Accuracy 6-8

SECTION 7 SPECIFICATION VERIFICATION

Introduction 7-1 Equipment Requirements 7-1 Preparation 7-2 ACV Performance Verification 7-3 Spot Frequency Verification 7-4 User's Uncertainty Calculations 7-6 Verification Report Sheet 7-7

SECTION 8 ROUTINE CALIBRATION

Introduction 8-1 Autocal 8-1 The CAL Menu 8-2 Equipment Requirements 8-4 Preparation 8-5 ACV 100mV Calibration 8-6 ACV Calibration 8-7 ACV Spot Calibration 8-8 Calibration at other than Nominal Values 8-10 Setting a New Calibration Due Date 8-10

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4920 User’s Handbook

SAFETY ISSUES

READ THIS ENTIRE SECTION THOROUGHLY BEFORE ATTEMPTING TO INSTALL, OPERATE OR SERVICE THE MODEL 4920 ALTERNATING VOLTAGE MEASUREMENT STANDARD

General Safety Summary

Explanation of safety related

This instrument has been designed and tested in accordance with the British and European standard publication EN61010:1993/A2:1995, and has been supplied in a safe condition.

This manual contains information and warnings that must be observed to keep the instrument in a safe condition and ensure safe operation. Operation or service in conditions or in a manner other than specified could compromise safety. For the correct and safe use of this instrument, operating and service personnel must follow generally accepted safety procedures, in addition to the safety precautions specified.

To avoid injury or fire hazard, do not switch on the instrument if it is damaged or suspected to be faulty. Do not use the instrument in damp, wet, condensing, dusty, or explosive gas environments.

Whenever it is likely that safety protection has been impaired, make the instrument inoperative and secure it against any inintended operation. Inform qualified maintenance or repair personnel. Safety protection is likely to be impaired if, for example, the instrument shows visible damage, or fails to operate normally.

symbols and terms

DANGER electric shock risk

The product is marked with this symbol to indicate that hazardous voltages (>30 VDC or AC peak) may be present.

CAUTION refer to

documentation

The product is marked with this symbol when the user must refer to the instruction manual.

Earth (Ground) terminal

Functional Earth (Ground) only must not be used as a Protective Earth.

WARNING WARNING STATEMENTS

IDENTIFY CONDITIONS OR PRACTICES THAT COULD RESULT IN INJURY OR DEATH.

Final Width = 175mm

WARNING THIS INSTRUMENT CAN

DELIVER A LETHAL ELECTRIC SHOCK. NEVER TOUCH ANY LEAD OR TERMINAL UNLESS YOU ARE ABSOLUTELY CERTAIN THAT NO DANGEROUS

VOLTAGE IS PRESENT.

CAUTION CAUTION STATEMENTS

IDENTIFY CONDITIONS OR PRACTICES THAT COULD RESULT IN DAMAGE TO THIS OR OTHER PROPERTY.

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4920 User’s Handbook

Protective Earth (Ground)

Final Width = 175mm

Protection Class I:

The instrument must be operated with a Protective Earth/Ground connected via the power cable's protective earth/ground conductor. The Protective Earth/Ground connects to the instrument before the line & neutral connections when the supply plug is inserted into the power socket on the back of the instrument.

WARNING ANY INTERRUPTION OF THE

PROTECTIVE GROUND CONDUCTOR INSIDE OR OUTSIDE THE INSTRUMENT IS LIKELY TO MAKE THE INSTRUMENT DANGEROUS.

To avoid electric shock hazard, make signal connections to the instrument after making the protective ground connection. Remove signal connections before removing the protective ground connection, i.e. the power cable must be connected whenever signal leads are connected.

Do Not Operate Without Covers

To avoid electric shock or fire hazard, do not operate the instrument with its covers removed. The covers protect users from live parts, and unless otherwise stated, must only be removed by qualified service personnel for maintenance and repair purposes.

WARNING REMOVING THE COVERS

MAY EXPOSE VOLTAGES IN EXCESS OF 1.5KV PEAK (MORE UNDER FAULT CONDITIONS).

Safe Operating Conditions

Only operate the instrument within the manufacturer's specified operating conditions. Specification examples that must be considered include:

ambient temperature ambient humidity power supply voltage & frequency maximum terminal voltages or currents altitude ambient pollution level exposure to shock and vibration

To avoid electric shock or fire hazard, do not apply to or subject the instrument to any condition that is outside specified range. See Section 6 of this manual for detailed instrument specifications and operating

conditions.

CAUTION CONSIDER DIRECT

SUNLIGHT, RADIATORS AND OTHER HEAT SOURCES WHEN ASSESSING AMBIENT

TEMPERATURE.

CAUTION BEFORE CONNECTING THE

INSTRUMENT TO THE SUPPLY, MAKE SURE THAT THE REAR PANEL AC SUPPLY VOLTAGE CONNECTOR IS SET TO THE CORRECT VOLTAGE AND THAT THE CORRECT FUSES ARE FITTED.

Page 9

Fuse Requirements

To avoid fire hazard, use only the fuse arrangements that appear in the fuse specification table below. Additionally, the supply network must be fused at a maximum of 16A, and in the UK, a 5A fuse must be fitted in the power cable plug.

Power Input Fuse

4920 User’s Handbook

Supply (Line)

Voltage Selection

115 VAC

230 VAC

Rear panel detail

115V

(100-130V)

POWER VOLTAGE

SELECTOR

Fuse Action

Time delay

Time delay HBC

SAFETY WARNING

1. DISCONNECT POWER AND SIGNAL LEADS

230V

BEFORE REMOVING COVERS.

(200-260V)

2. FOR CONTINUED PROTECTION AGAINST ELECTRIC SHOCK THE POWER CORD PROTECTIVE CONDUCTOR MUST BE CONNECTED TO SAFETY EARTH (GROUND).

3. FOR CONTINUED PROTECTION AGAINST FIRE FIT A 250V FUSE OF THE CORRECT RATING.

4. READ THE OPERATORS HANDBOOK BEFORE USE. NOTE NO USER SERVICEABLE PARTS CONTAINED. DO NOT REMOVE THE COVERS. HAZARDOUS VOLTAGES PRESENT. REFER SERVICE TO QUALIFIED PERSONNEL.

Fuse Rating

IEC (UL/CSA)

1 A (1.4 A)

500 mA (700 mA)

PL10

Wavetek

Part No.

920116

920084

POWER INPUT

37 VA max. 47 - 63Hz

Manufacturer

& Type No.

Littlefuse 215001

Littlefuse 215.500

F1 FUSE

POWER INPUT

115V - T1.0 A

230V-T500 mA H

5x20mm IEC127

Final Width = 175mm

vii

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4920 User’s Handbook

Final Width = 175mm

The Power Cable and Power Supply Disconnection

The intended power supply disconnect device is the ON/OFF switch that is located on the instrument's front panel. The ON/OFF switch must be readily accessible while the instrument is operating. If this operating condition cannot be met, the power cable plug or other power disconnecting device must be readily accessible to the operator.

To avoid electric shock and fire hazard, make sure that the power cable is not damaged, and that it is adequately rated against power supply network fusing.

If the power cable plug is to be the accessible disconnect device, the power cable must not be longer than 3 metres.

Instrument Terminal Connections

Make sure that the instrument is correctly protectively earthed (safety grounded) via the power cable before and while any other connection is made. When not in use, cover INPUT A with its protective cap.

Installation Category I:

Measurement and/or guard terminals are designed for connection at Installation (Overvoltage) Category I. To avoid electric shock or fire hazard, the instrument terminals must not be directly connected to the AC line power supply, or to any other voltage or current source that may (even temporarily) exceed the instrument's peak ratings.

WARNING TO AVOID INJURY OR

DEATH, DO NOT CONNECT OR DISCONNECT SIGNAL LEADS WHILE THEY ARE CONNECTED TO A HAZARDOUS VOLTAGE OR

CURRENT SOURCE.

MAKE SURE THAT SIGNAL LEADS ARE IN A SAFE CONDITION BEFORE YOU HANDLE THEM ANY WAY.

WHEN NOT IN USE, COVER INPUT A USING ITS PROTECTIVE CAP.

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Maintenance and Repair

Observe all applicable local and/or national safety regulations and rules while performing any work. First disconnect the instrument from all signal sources, then from the AC line supply before removing any cover. Any adjustment, parts replacement, maintenance or repair should be carried out only by authorised Wavetek technical personnel.

WARNING FOR PROTECTION AGAINST

INJURY AND FIRE HAZARD, USE ONLY MANUFACTURER SUPPLIED PARTS THAT ARE RELEVANT TO SAFETY. PERFORM SAFETY TESTS AFTER REPLACING ANY PART THAT IS RELEVANT TO SAFETY.

Moving and Cleaning

First disconnect the instrument from all signal sources, then from the AC line supply before moving or cleaning.Use only a damp, lint-free cloth to clean fascia and case parts.

Final Width = 175mm

Observe any additional safety instructions or warnings given in this manual.

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Final Width = 175mm

Page 13

Section 1 - Introduction and General Description

SECTION 1 Introduction and General Description

Cat I

290V

max

OPTION

1420V pk

max

10V pk

max

Store

CaltrigSRQLocalSampleExt'trigReset

Status Config

ACV

+/-4210

938765

mV AC/DC Input

Exp Enter Quit

Last rdg

Monitor Test Math

Designed with Standards and Calibration laboratories in mind, the 4920 provides extremely high performance in AC Voltage measurement, combined with ease of use.

Standard and Optional Measurement Facilities

Basic Configuration

The 4920 is a high-quality Alternating Voltage Measurement Standard. Its basic configuration offers the following measurement capabilities:

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Cal Power

Final Width = 175mm

• High Accuracy mode - RMS AC Voltage measurement in eight ranges from

90mV to 1100V; 1Hz to 1MHz; 1-year specifications to ±30ppm. Input Impedance > 200Ω/V. Display resolution to 100nV maximum.

• Transfer mode - Ranges and resolution as ACV. AC/DC or AC/AC transfers

performed faster and more easily than with normal thermal transfer devices..

• Millivolt Ranges (Option 10) - Measurements from 0.9mV to 110mV in four

ranges.

• Menu Control - flexible and easy to use.

• Calibration - Autocal external calibration.

• Remote Control - Fully IEEE-488.2 programmable.

1-1

Page 14

Section 1 - Introduction and General Description

‘Hard’ and ‘Soft’ Keys - Menus

Final Width = 175mm

The use of hard keys (labels printed on the keys themselves) and soft keys (labels appear on the separate menu display) allows programming of the instrument into a wide range of configurations. Pressing the hard key of one of the main functions (ACV, mV option or AC/DC transfer) alters the instrument circuitry to the selected function, at the same time displaying its own menu. Alternatively, once a main function is active, the Config hard key can be used to alter the configuration. Each soft key, marked with an arrowhead (∧), is labelled by the legend above it on the display.

The Status hard key allows a check of configured parameters. Once Status is selected, the Config hard key can be used to check or alter the IEEE488 bus address, to check on the instrument identification, or view significant dates.

The Monitor key permits access to such information as the signal frequency of an AC input signal being measured; and to calculations of the deviation between two measurements.

The menus are arranged in tree structures, leading the user through their branches to an end node, at which the physical circuitry or software selections of the instrument can be changed to suit the required parameters. For ease of use, each track from main function to end node involves the minimum number of user selections.

When the instrument power is switched on, all functions are forced into a safety default state. Once a function is configured to a required state it remains in that state, regardless of subsequent configurations in other functions, until either the state is changed or the instrument power is switched off.

As an easy introduction to the main function keys and their associated menus, users can follow a guided tour through the main tree structures, sequenced in Section 3. The full range of facilities, together with access information, is detailed in Section 4.

System Use

The 4920 is designed as standard to form part of a remote control system, conforming to IEEE 488.2 Standard Digital Interface. Remote control information is given in Section 5. This fulfils the Device Documentation Requirements of the standard (summary in Section 5 Appendix A).

Self Test

The Test key displays a menu which provides access to a comprehensive series of self-tests. Among these are:

• An operational selftest;

• A diagnostic selftest;

• A test of the displays;

• A test of the front panel keys; Details of these selftests can be found in Section 4

of this handbook.

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Section 1 - Introduction and General Description

Calibration

Autocal

The 4920 is an ‘Autocal’ instrument, providing full external calibration of all ranges and functions from the front panel; thus making the removal of covers unnecessary.

Periodically, the 4920 is electronically calibrated against traceable external standards, where any differences in the instrument’s readings compared to the value of the external calibration sources can be used to derive calibration constants, which are stored by the instrument in non-volatile memory. These external calibration corrections later serve to correct all readings taken by the 4920.

Calibration can also be carried out under remote control via the IEEE 488 interface.

Calibration Security

A recessed Calibration Enable/Disable switch on the rear panel prevents accidental use of Autocal. For remote operation; in addition to operating the Enable/Disable switch, an 'enable' code is required to gain access to calibration operations.

Calibration Routines

The Routine Calibration procedures are described in Section 8 of this handbook.

Message Readout

Generally, the selections offered in the menus reflect the availability of facilities, incompatible combinations being excluded. Nevertheless, the menu display doubles as a message screen, giving a clear readout of information to the user such as unsuitable attempts at configuration, test failures and some other conditions which would need to be reported to a Datron service center.

Processor

The instrument is internally controlled by a 68000 series microprocessor. It ultimately translates all information, either from the front panel keys or from remote control, according to its program in firmware, into control signals which determine the instrument’s operation.

Computing

As measurements are taken they can be compared with an earlier 'reference', or several measurements can be combined to obtain statistical data. Some of the keys under the Menu display double as a keyboard for setting the bus address, math constants etc.

Full details of the computing facilities are given in Section 4.

Final Width = 175mm

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Page 16

Section 1 - Introduction and General Description

Accessories

The instrument is supplied with the following accessories:

Description Part Number

Power Connector Cable (L1949) 920012 Power Fuse (230V use) T500mA 920084 Power Fuse (115V use) T1.0AH 920116 Hex Key 1.5mm AF (Handle removal) 630284 User’s Handbook 850264 User’s Quick Reference Guide 850912

N-Connector Protection Cap 630537

Optional Accessories

Final Width = 175mm

The following accessories can be purchased for use with the 4920:

Description

Model 1512: High Quality 2/4-Wire AC Lead Kit Model 1513: General Purpose AC Lead Kit (Dual 4mm Plug) Model 1514: High Quality 4-Wire DC Lead (Separate 4mm Plugs) Model 4921: Shunt Adaptor

Description Part Number

4920 Maintenance Handbook 850265 4920 Reference Handbook 850266

Additional Documentation

The Maintenance Handbook contains information required to adjust and maintain the 4920, including mechanical data, routine servicing, remedial adjustments, diagnostic guides and circuit descriptions.

The Reference Handbook contains component lists, layout drawings and circuit diagrams.

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Page 17

Outline of 4920 Applications

Section 1 - Introduction and General Description

Thermal Transfer Standards - Difficulties

The 4920 has been designed primarily to overcome some of the inefficiencies, costs and complications of calibrating and verifying traceable accuracy of the alternating voltage outputs from AC or multifunction calibrators.

Thermal transfer standards have for many years been the backbone of AC measurement in these and other applications, but their operational requirements are increasingly impeding improvements in productivity. Considerable care is needed due to the electrical and mechanical fragility of thermal elements, and skilled operators are diverted by the tedium of long settling times. Maintenance, support and operating costs of the TTS remain significant overheads, stimulating a search for faster, more rugged and cost-effective alternatives.

At millivolt levels, because of the insensitivity of the TTS, it needs to be supplemented at low frequencies by such devices as the inductive voltage divider (IVD), and at higher frequencies by 'tenth of range' transfer methods, both of which add significant uncertainties to the process.

With the advent of the IEEE 488 and other instrumentation interfaces, measurement and calibration processes are increasingly being programmed for remote and automatic control, to improve their cost-effectiveness. Because of long settling times and the frequency of skilled operator intervention, the TTS is intrinsically unsuitable for automation.

All of these factors motivated the evolution of the 4920 AVMS.

Anticipated Applications for the 4920

There are six main areas where it is envisaged that the 4920 will operate, while improving on the performance of thermal transfer standards:

• Speed up the operation of high-accuracy AC measurement processes.

• Fully support calibration and verification of the AC voltage functions in Datron's 4200A and 4700 series calibrators.

• In multi-function calibrators, transfer the traceability of their previously-calibrated DC voltage ranges to the calibration of their highaccuracy AC voltage ranges.

• Internally transfer the traceability of its own AC voltage ranges to the measurement of AC millivolts (a stable, but not necessarily accurate, source of 100mV at the measurement frequency is all that is required).

• Perform all its functions within an automated measurement system, under remote control via the IEEE 488.1 interface, conforming to IEEE

488.2 protocols.

• Using Model 4921 Shunt Adaptor; adapts specifically to Fluke A40 and A40A current shunts, for AC current measurements between

2.5mA and 20A.

The means by which the 4920 carries out its tasks are outlined under 'Principles of Operation' in the following pages.

Final Width = 175mm

1-5

Page 18

Section 1 - Introduction and General Description

Input

290V

Option

1420V pk

max

10V pk

max

Millivolt

Preamp

x30

Option 10 - Millivolts

High Accuracy

AC-DC Electronic Converter

Analog

to Digital

Conversion

Analog

Subsystem

Final Width = 175mm

1-6

Keyboard

Control

Application

Program

Digital

Processing

and

Control

IEEE 488

Remote

Controller

Interface

FIG. 1.1 4920 BLOCK DIAGRAM

Front Panel

Displays

Local

Operation

Remote

Operation

Page 19

Section 1 - Introduction and General Description

Principles of Operation

Figure 1.1 (opposite) shows the instrument's basic measurement functions.

Basics

Precision Design

The 4920 AVMS is designed for calibration and standards laboratory applications, taking full advantage of the inherent qualities of critical accuracy-defining components and advanced measurement techniques to achieve its high performance. It is suited to all applications where a thermal transfer standard would presently be used, with the exception of some highly-developed specialities. It employs a method of calibration which is designed to maintain performance across the entire range of its functions.

Three-Reading Measurement Cycle

In all modes, each displayed measurement consists of three separate internal readings in which the RMS value of the input is detected and processed via the A-D and microprocessor system, then fed back to calibrate the measurement process. The final result is transferred to the instrument’s microprocessor for calibration, further processing and display.

ACV Function

AC voltages input via the front panel are conditioned by a DC-coupled AC preamp, and presented to an electronic RMS detector. The DC ‘RMS’ level output from the detector acts as reference for the generation of a ‘Calculable AC Reference’. This represents the processed RMS value of the applied signal in an AC-AC transfer, during the three-reading measurement cycle mentioned above.

Millivolts (mV) - Option 10

An external 100mV signal, at within ±1% of the frequency of the AC voltage to be measured, is input via the front panel. The 4920 uses this input to characterize the gain of an internal x30 amplifier. This 100mV characterization signal needs to be stable for the duration of the amplifier characterization operation - its absolute value is unimportant. In subsequent use the amplifier is placed in cascade with traceable ACV ranges to measure millivolt inputs from 0.9mV to 110mV.

AC/DC Transfer Mode

The RMS value of an AC voltage is compared with the combined RMS value of two DC reference voltages of equal value and opposite polarity.

The DC reference signals are applied in sequence and their individual values are measured and stored. The system digitally computes the RMS of these two stored values to form the 'DCRMS equivalent', which is also stored.

The system then measures the RMS value of the applied AC signal, and digitally computes its deviation from the 'DCRMS equivalent'. The deviation is displayed in ppm.

Final Width = 175mm

1-7

Page 20

Section 1 - Introduction and General Description

ACV Operation

Input

290V

max

Option

1420V pk

max

Input

Precision

Attenuator

10V pk

max

& Preamp

Vsig

Detector

Vbias

RMS

Current-to-Voltage

Converter

Iout

Vbias = Vout

Bessel

Filter

2.8 Gain Buffer

Vout

Sample

and Hold

Vref

Final Width = 175mm

Quasi-Sinewave

Measurement

Range

Switching

Sequence

Switching

(S1 - S5)

FIG. 1.2 4920 ACV OPERATION

Attenuators and Preamp

Basic Design (Fig. 1.2)

The basic design incorporates a DC-coupled preamplifier, which has relatively high input impedance (124kΩ//150pF on the 3V to 100V ranges; otherwise 404kΩ//90pF). The gaindefining resistor chains are guarded, and the remaining time constants are set above 1MHz so that hardware trims are not required.

Range Selection

There are three main attenuators:

1. A permanent 1kV/300V attenuator for overload sensing;

2. A 100V/30V/10V/3V attenuator, switched in parallel with the 1kV/300V attenuator;

3. A 1V/300mV attenuator in the unity gain buffer, in series with the 1kV/300V attenuator.

DC Reference for

Quasi-Sinewave

Timing

Measurement

Data

A-D

Control

A - D

Converter

Filter

Switching

Calculable

Source

Generator

Processor

System

Attenuator Elements

The attenuators, which configure the amplifier gain to define the high-accuracy AC Voltage ranges, consist of extremely stable metal foil resistors, packaged in large hermetic-seal cases. Similar types are used in the 1V range protection chain.

To ensure that no spurious leakage currents cause linearity, temperature-coefficient or drift problems in the attenuator chains, the sealed cases form a guard at HF, driven by a capacitor chain. Within the cases of the attenuator elements, the resistor values are split and the junctions guarded to effect a high degree of frequency flatness.

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Page 21

Section 1 - Introduction and General Description

RMS Converter

DC Coupled Preamp

In order to minimize the input capacitance to the preamp, reed relays are used to select the signal paths for the various ranges. The preamp bootstraps extensive pcb tracking to guard the attenuators, input tracking and reed relays; it also drives a bootstrap buffer which forces the preamp power supplies to follow the input signal level by reference to bootstrap. The preamp thus sees no change in input signal relative to its supplies, again minimizing its input capacitance and achieving very high common mode rejection.

Separate PCB

The whole attenuator and preamp circuit is mounted on a separate sub-assembly, fabricated with PTFE board, and mounted above the main High Accuracy ACV printed circuit assembly.

The preamp is run at unity or X3 gain depending on range selection, with corresponding compensation switching. Its output voltage is fed to the RMS Converter on the High Accuracy ACV printed circuit assembly, from which the compensation current for the preamp signal current into the signal ground (0V-4) is derived.

Protection

The instrument can measure up to 1100VRMS and can withstand a continuous overload of 1100VRMS or 1556V peak. Overload is sensed by a resistor at the low end of the 1000V/300V attenuator; and protection is activated from the HIACC_AC pcb. Two series resistors, referred to two zener diodes, absorb the overload energy for up to 1 second, by which time the protection system will have disconnected the instrument input from both the 100V/30V/10V attenuator and the preamp input.

Conversion Process

RMS conversion is based on a modified analog multiplier, consisting of a ‘squaring’ logarithmic amplifier whose output is buffered into a balanced exponential amplifier.

The DC current output of the squaring circuit ‘Iout’ is proportional to ‘Vin2’ if a fixed sourcecurrent bias is applied to the logging and antilogging elements. The transfer function is

Iout ∝ Vin2 / (R2 x Ibias)

where R is the common value of balanced source resistors and Ibias is the common source-bias current for the logging and antilogging circuits.

Iout is converted into a DC voltage Vout which ultimately becomes the RMS Converter output. However, in order to apply the ‘square-root’ element of the computation, this voltage is fed back to provide a current bias whose amplitude follows Iout, and this forces Iout to a value proportional to √(Vin2).

The transfer function now becomes

Iout ∝ Vin2 / (R2 x Iout)

as R is constant this leads to Iout2 ∝ Vin2, and to Iout ∝ √Vin2. After current-to-voltage conversion

and filtering, this gives Vout ∝ √Vin2 as the DC output voltage fed to the A/D, subject only to calibration.

Final Width = 175mm

1-9

Page 22

Section 1 - Introduction and General Description

Transfer Loop

Final Width = 175mm

Transfer Process (Fig. 1.2)

Three internal measurements are made to determine the precise RMS value of the signal. The first is an estimate (to about 1%) which is also a function of the gain of the RMS Converter. The other two are used to determine that gain and then apply corrections to the first measurement.

Calculable Source Generator

The Sample-and-Hold circuit provides a memory of Vout, to be used as reference for the Calculable Source Generator. This in turn constructs a ‘quasisinewave’ whose amplitude and form factor are known, in order to ensure that the transfer is a true AC to AC process.

Transfer Sequence Switching

Figure 1.2 shows the arrangement of the elements in the loop. The positions of switches S1-S5 are altered by firmware to generate the threemeasurement sequence:

First Measurement (M1): The uncorrected RMS value of the input signal (Vsig) is measured directly by the A-D and processor. The DC analog value of Vout (Vref) is memorized in the Sample-and-Hold circuit:

S1 closed drives the RMS Converter from

Vsig;

S2 open prevents the quasi-sinewave from

interfering with the measurement;

S3 closed the A-D and processor evaluate

the first estimate;

S4 closed Vout is sampled; S5 open removes Vref from the direct

measurement of the input.

Second Measurement (M2): Vref from the previous measurement (M1) is measured by the A-D and processor. Meanwhile, the quasi-sinewave (resulting from Vref) is applied to the RMS converter to allow settling for the next measurement (M3).

S1 open Vsig is removed; S2 closed drives the RMS Converter from

the the quasi-sinewave (settling only);

S3 open removes Vout from the

measurement;

S4 open freezes Vref; S5 closed the A-D and processor measure

Vref.

1-10

Page 23

Third Measurement (M3) : The quasi-sinewave is measured by the RMS converter, A-D and processor.

S1 open Vsig is not applied; S2 closed drives the RMS Converter from

the quasi-sinewave for the measurement;

S3 closed applies Vout for the quasi-

sinewave to the A-D and processor for measurement;

S4 open Vref remains frozen; S5 open prevents Vref from interfering

with the RMS measurement of the quasi-sinewave;

Final RMS Computation

If the gain of the RMS Detector, Filter and Buffer is G (not precisely known), then:

M1 = G.Vsig(RMS);

so Vsig(RMS) = M1 / G. M2 and M3 are combined to determine G very

precisely: G = Transfer Measurement / Transfer

Reference = M3 / M2.

This is used to eliminate G:

Vsig(RMS) = M1.M2 / M3.

Section 1 - Introduction and General Description

Final Width = 175mm

1-11

Page 24

Section 1 - Introduction and General Description

Millivolt (mV) Operation (Option 10)

Input

Channel A

Input

Channel B

AC MILLIVOLT AMPLIFIER

FIG. 1.3 4920 MILLIVOLT OPERATION

x 30

ACV

300mV - 1kV

Ranges

Final Width = 175mm

Basic Design

Introduction

The 4920 ACV ranges extend from 300mV to 1000V, traceable between 30% and 110% of nominal range values. However, many modern calibrators in use have 10mV and 1mV ranges.

1-12

Operating Configuration

To permit traceable calibration of these ranges, an optional millivolt facility has been developed for the 4920 (Option 10), which produces the following ranges:

3mV: 0.9mV to 3.3mV 10mV: 3mV to 11mV 30mV: 9mV to 33mV 100mV: 30mV to 110mV

Option 10 provides for a x30 amplifier, with bypass switching, between the input terminals and the input attenuator/preamplifier system as represented in Fig. 1.3.

Page 25

Measurement Sequence

X30 Amplifier Gain Characterization

Before operating on the millivolt ranges, the gain of the x30 amplifier must first be characterized. To do this, the user inputs a stable signal of between 95mV and 105mV, within 2% of the frequency to be measured, and initiates the gain characterization. The process takes less than a minute.

The 4920 measures both the input to the amplifier (ACV 300mV range) and its output (ACV 3V range), and automatically computes a correction for the deviation of the gain from x30. This correction is applied to all subsequent readings until the next time the gain of the x30 amplifier is characterized.

Millivolt Measurements and Traceability

Once the gain value has been stored, the four millivolt ranges provide traceable measurements for signals within 2% of the characterization frequency. To measure at frequencies outside this narrow band, the gain must be re-characterized.

In use, readings will be traceable because: a. the x30 amplifier gain will have been measured

using traceably-calibrated ranges of the ACV function; and

b. all four millivolt ranges use the amplifier in

cascade with traceably-calibrated ACV ranges as follows:

3mV Range: ACV 300mV range; 10mV Range: ACV 300mV range; 30mV Range: ACV 1V range; 100mV Range: ACV 3V range.

Section 1 - Introduction and General Description

Implementation of Option 10

When Option 10 is fitted, the Terminal Switch Assembly is replaced by the AC mV Amplifier Assembly. This is connected between the front panel inputs and the AC Preamplifier Assembly, and also carries the input switching.

The x30 Amplifier, on the AC mV Amplifier Assembly, comprises a non-inverting x6 input stage followed by an inverting x5 driver. The whole amplifier is compensated for frequencies up to 1MHz. Input and feedback circuits of the input stage are each protected by a pair of transistors connected as back-to-back diodes.

The amplifier is inserted into the signal path only when a millivolt range is selected, or during its own digitally-controlled gain characterization sequence; at other times it is bypassed.

Final Width = 175mm

The amplifier has an input impedance close to 404kΩ//90pF. The accuracies of the four ranges are given in the millivolt specifications (Section 6,

pages 6-6 and 6-7).

1-13

Page 26

Final Width = 175mm

Section 1 - Introduction and General Description

Analog to Digital Converter

Introduction

The instrument’s analog-to-digital converter (AD) takes the form of a highly linear, low noise, fast and flexible multislope integrator. Timing, counting and control are executed by a custom ‘ApplicationSpecific Integrated Circuit’ (ASIC). A simplified schematic is given as Fig. 1.4. The A-D is involved in every measurement in ACV, mV and AC/DC operation.

Multislope Operation (Figs. 1.4 and 1.5) Multislope operation permits the integration capacitor value to be smaller than normally required for a more conventional circuit, greatly reducing problems due to dielectric absorption. Reference switching errors are reduced to a constant value, which are subtracted from the reading by the instrument’s microprocessor. A further benefit is that both the signal and the reference may be applied to the integrator simultaneously, greatly reducing the conversion time. A digital autozero system avoids the need for the more common sample-and-hold type of autozero circuit.

The timing and counting considerations with this design of A-D are quite complex. Programmable delay timers, a ramp timer and a counter for the number of completed ramps exercise great control flexibility over its performance. All of these timers and counters are integrated into a custom ASIC which includes a 32 bit control register, programmed by the instrument’s microprocessor via a special serial interface. The same serial loop is used to transmit the reading from the ASIC to the processor for calibration and display.

1-14

Page 27

Section 1 - Introduction and General Description

Features

The result is a compact A-D with the following features:

• Excellent rejection of normal-mode powerline interference (Integration time is fixed at

• Excellent linearity of 0.2ppm of full scale.

• Low noise of < 0.05ppm of full scale. 200ms, an exact multiple of 60Hz and 50Hz line supply periods).

Signal

Ref+

Ref-

Sub Ref+

Sub Ref-

Sig Switch

Ref Switch

Sub-Ref

Switch

Integrator

1st Null

Detector

Control Logic

2nd Null

Detector

FIG. 1.4 MULTISLOPE OPERATION - SIMPLIFIED A-D SCHEMATIC

time

Final Width = 175mm

FIG. 1.5 MULTISLOPE OPERATION - SIMPLIFIED A-D WAVEFORM

1-15

Page 28

Final Width = 175mm

Section 1 - Introduction and General Description

A-D Master Reference

Reference Module

The reference used in the analog to digital conversion is derived from a specially conditioned zener reference module. It contains the reference device and its associated support circuits. The module is stable to within ±4ppm per year, produces pk-pk noise less than 0.1ppm, and has a temperature coefficient better than 0.15ppm/°C. This temperature coefficient is held over a temperature span of 0°C to 70°C, and the reference exhibits negligible temperature shock hysteresis.

Module History

Extensive evaluation of successive reference modules has resulted in a burn-in process which equates to an ageing of 1 year, reducing infant mortalities and improving stability. Following this process, all reference modules are checked over a temperature span of 0°C to 70°C for temperature performance, and then monitored for long term drift over a period of three months minimum.

1-16

Page 29

Section 2 - Installation and Operating Controls

SECTION 2 Installation and Operating Controls

This section contains information and instructions for unpacking and installing the Datron 4920 Alternating Voltage Measurement Standard. It also introduces the layout of controls on the instrument.

Unpacking and Inspection

Every care is taken in the choice of packing material to ensure that your equipment will reach you in perfect condition.

If the equipment has been subject to excessive handling in transit, the fact will probably be visible as external damage to the shipping carton.

In the event of damage, the shipping container and cushioning material should be kept for the carrier’s inspection.

Unpack the equipment and check for external damage to the case, sockets, keys etc. If damage is found notify the carrier and your sales representative immediately.

Standard accessories supplied with the instrument should be as described in Section 1.

WARNING THIS INSTRUMENT CAN

DELIVER A LETHAL ELECTRIC SHOCK. NEVER TOUCH ANY LEAD OR TERMINAL UNLESS YOU ARE ABSOLUTELY CERTAIN THAT NO DANGEROUS

VOLTAGE IS PRESENT.

Calibration Enable Switch S2

NOTE

This two-position rear-panel switch protects the instrument calibration memory.

The instrument was initially calibrated at the factory, so the switch should always remain set to

DISABLE, until immediate recalibration is

intended.

For Recalibration:

If the external calibration menu is selected while the key is not in the enabling position, the menu is replaced by the warning message:

1002: calibration disabled

Final Width = 175mm

2-1

Page 30

Section 2 - Installation and Operating Controls

Introduction to the Front Panel

Cat I

290V

pk max

OPTION

1420V pk

10V pk

max

Store

CaltrigSRQLocalSampleExt'trigReset

Status Config

ACV

+/-4210

938765

mV AC/DC Input

Exp Enter Quit

Last rdg

Monitor Test Math

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Cal Power

Final Width = 175mm

The two displays on the front panel deal with different aspects of operation. We set up the instrument’s configuration using menus shown in the right-hand (dot-matrix 'menu') display, then readings appear in the left-hand ('main') display.

Menu Keys

There are two classes of front panel menu keys, those that lead to an immediate change of instrument state (i.e the major function keys ACV; mV; AC/DC), and those that do not (Status, Config, Cal, Monitor, Test, Math).

Numeric Keyboard

Seventeen of the menu and soft function keys also act as a keyboard for entry of parameters such as math constants, bus address, etc. The data entered is purely numeric, and can consist of either a keyboard-entered value or the value of the most recent reading.

Beneath the dot matrix display, all keys other than the Power key are associated with menus. The keys beneath the main display are direct action keys, associated with triggers, remote control, reading storage and instrument reset.

Major Function Keys: ACV, mV, AC/DC

Each of these keys defines a separate measurement state and activates its corresponding menu on the dot matrix display. Changing a selection alters the measurement state.

2-2

Page 31

Introduction to the Rear Panel

Section 2 - Installation and Operating Controls

SH1 AH1 T6 L4 SR1

RL1 PP0 DC1 DT1 CO E2

SK7

IEEE 488

230V-T500 mA H 5x20mm IEC127

F1 FUSE

POWER INPUT 115V - T1.0 A

115V

(100-130V)

POWER VOLTAGE

SELECTOR

1. DISCONNECT POWER AND SIGNAL LEADS

230V

BEFORE REMOVING COVERS.

2. FOR CONTINUED PROTECTION AGAINST

(200-260V)

ELECTRIC SHOCK THE POWER CORD PROTECTIVE CONDUCTOR MUST BE CONNECTED TO SAFETY EARTH (GROUND).

3. FOR CONTINUED PROTECTION AGAINST FIRE FIT A 250V FUSE OF THE CORRECT RATING.

4. READ THE OPERATORS HANDBOOK BEFORE USE. NOTE NO USER SERVICEABLE PARTS CONTAINED. DO NOT REMOVE THE COVERS. HAZARDOUS VOLTAGES PRESENT. REFER SERVICE TO QUALIFIED PERSONNEL.

SAFETY WARNING

PL10

POWER INPUT

37 VA max. 47 - 63Hz

Mechanical Access

The top or bottom cover is released for removal by undoing two screws visible at the rear. A single screw retains the corner block which covers the handle mechanism on each side panel.

Labels

The rear panel displays the identification label for the instrument, and a modification label.

External Connections

Apart from the front input sockets, connections to the internal circuitry enter via the rear panel.

SK7 is the standard IEEE 488 connector. A list of interface function subsets is printed next to the connector.

SK9 provides a coaxial BNC trigger input.

TRIG

SK9

EXT

ENABLE DISABLE

CALIBRATION

MADE IN

THE EC

Fuses

The fuse adjacent to the power input plug protects the power input line.

WARNING SEE SAFETY ISSUES AT THE

FRONT OF THIS MANUAL..

Voltage Selector

The recessed power line voltage selector adapts the instrument to either 115V or 230V line inputs.

CAUTION MAKE SURE THAT THE

CORRECT VOLTAGE IS SELECTED BEFORE YOU APPLY POWER TO THE INSTRUMENT (SEE NEXT

PAGE).

Calibration Switch

To calibrate the instrument, special menus are available from the front panel. But to enter these menus it is necessary to set the calibration Switch on the rear panel to ENABLE.

Final Width = 175mm

2-3

Page 32

Section 2 - Installation and Operating Controls

Preparation for Operation

Final Width = 175mm

WARNING THIS INSTRUMENT CAN DELIVER A LETHAL ELECTRIC SHOCK. NEVER

Power Cable

The detachable supply cable comprises two metres of 3-core PVC sheath cable permanently moulded to a fully-shrouded 3-pin cable socket. It fits into plug PL10 at the rear of the instrument and must be pushed firmly home.

The supply lead must be connected to a grounded outlet ensuring that the Protective Earth (Ground) lead is connected.

WARNING ANY INTERRUPTION OF THE

TOUCH ANY LEAD OR TERMINAL UNLESS YOU ARE ABSOLUTELY CERTAIN THAT NO DANGEROUS VOLTAGE IS PRESENT.

COVER INPUT A WITH ITS PROTECTIVE CAP WHEN NOT IN USE. READ THE SAFETY ISSUES SECTION AT THE FRONT OF THIS MANUAL

BEFORE ATTEMPTING TO INSTALL, USE OR SERVICE THIS INSTRUMENT.

Line Voltage Selection

When shipped, the instrument is packed ready for use. But before you connect the instrument to the line supply, check that the power input voltage selector and fuse ratings are correctly set for the local line supply voltage.

115V Line Supply

For 100V to 130V, 60Hz supplies, the legend ‘115’ must be visible in the window of the line voltage selector switch (S1) on the rear panel.

PROTECTIVE GROUND CONDUCTOR INSIDE OR OUTSIDE THE INSTRUMENT IS LIKELY TO MAKE THE

INSTRUMENT DANGEROUS.

230V Line Supply

For 200V to 260V supply, the legend ‘230’ must be visible in the window of the line voltage selector switch (S1) on the rear panel.

2-4

Automatic 50-60Hz Operation

The 4920 is capable of operation at any line frequency from 47Hz to 63Hz, so no means of line frequency selection is necessary, or provided.

Page 33

Power Fuse

Section 2 - Installation and Operating Controls

115V

(100-130V)

POWER VOLTAGE

SELECTOR

230V

(200-260V)

SAFETY WARNING

1. DISCONNECT POWER AND SIGNAL LEADS BEFORE REMOVING COVERS.

2. FOR CONTINUED PROTECTION AGAINST ELECTRIC SHOCK THE POWER CORD PROTECTIVE CONDUCTOR MUST BE CONNECTED TO SAFETY EARTH (GROUND).

3. FOR CONTINUED PROTECTION AGAINST FIRE FIT A 250V FUSE OF THE CORRECT RATING.

4. READ THE OPERATORS HANDBOOK BEFORE USE. NOTE NO USER SERVICEABLE PARTS CONTAINED. DO NOT REMOVE THE COVERS. HAZARDOUS VOLTAGES PRESENT. REFER SERVICE TO QUALIFIED PERSONNEL.

Power Fuse:

The power fuse F1 is situated next to the power input plug on the rear panel.

CAUTION ENSURE THE CORRECT FUSE

IS FITTED BEFORE CONNECTING TO LINE POWER. SEE THE SAFETY ISSUES SECTION AT THE

FRONT OF THIS MANUA.L.

PL10

POWER INPUT

37 VA max. 47 - 63Hz

F1 FUSE

POWER INPUT

115V - T1.0 A

230V-T500 mA H

5x20mm IEC127

Final Width = 175mm

2-5

Page 34

Section 2 - Installation and Operating Controls

Mounting

Bench Use:

The instrument is fitted with rubber-soled plastic feet and tilt stand. It can be placed flat on a shelf or tilted upwards for ease of viewing.

Rack Mounting - Option 90:

Option 90 permits the instrument to be mounted in a standard 19 inch rack. The method of fitting this option is described below, the locations being shown in the diagram opposite.

N.B. The top or bottom cover should not be removed for this purpose.

Procedure

Final Width = 175mm

1. Remove each of the two rear corner blocks by

undoing its single crosspoint screw, and store safely for possible future use.

2. Invert the instrument, and remove each handle

as follows: a. Pull out the handle until the two 1.5mm

socket-headed screws are visible in the handle locking bar.

b. Loosen the two locking screws using the

1.5mm hex key provided. Leave the screws in the bar.

c. Slide the whole handle assembly to the

rear, out of the side extrusion.

3. Fit each front rack mounting ear as follows:

a. With its bracket to the front, slide the ear

into the side extrusion from the rear.

b. Loosely fasten the ear to the extrusion at the

front, using the four socket grubscrews provided.

c. Assemble the front plate and handle to the

front ear as shown in the diagram, and clamp them together using the two countersunk screws provided.

d. Tighten all six screws.

4. Remove the feet and tilt stand as follows:

a. Prize off the rubber pads from the four feet. b. Undo the two securing screws from each

foot. This releases the feet, washers and tilt stand so that they can be detached and stored safely for possible future use.

5. Fit the instrument to the rack as follows:

a. Attach the two rear ears to the back of the

rack, ready to receive the instrument.

b. With assistance, slide the instrument into

the rack, locating the rear ears in the side extrusions. Push the instrument home, and using screws, cage nuts etc. provided with the rack, secure the instrument by screwing the front ears to the front of the rack.

2-6

Page 35

1 Grubscrews in Handle

Section 2 - Installation and Operating Controls

Final Width = 175mm

2 Front Ear in

Extrusion

3 Final View from Top

RACK MOUNTING KIT - FITTING

2-7

Page 36

Section 2 - Installation and Operating Controls

Mounting (Contd.)

Rack Slide Kit - Option 95:

Option 95 permits the 4920 to be mounted on slides in a standard 19 inch rack. The instrument can be pulled forward into a position where its rear panel is clear of the rack, to give access to the rear connectors. Cables should not be connected to the instrument until it is mechanically secure in the slides. The method of fitting this option is described below, the locations being shown in the diagram on page 2-11.

N.B. Neither top nor bottom cover should be removed for this purpose.

Procedure

Final Width = 175mm

1. Remove each of the two rear corner blocks by

undoing its single crosspoint screw, and store safely for possible future use.

2. Invert the instrument, and remove each handle

as follows: a. Pull out the handle until the two 1.5mm

socket-headed screws are visible in the handle locking bar.

b. Loosen the two locking screws using the

1.5mm hex key provided. Leave the screws in the bar.

c. Slide the whole handle assembly to the

rear, out of the side extrusion.

3. Fit each slide mounting bracket (Pt. No. 450659)

as follows: a. With its ear to the front, slide the bracket

into the side extrusion from the rear.

b. Locate and loosely fasten the bracket to the

extrusion, using the six socket grubscrews provided.

4. Remove the inner section of each slide (Pt. No.

630353) from the other two sections as follows: a. Lay the slide flat with its inner section

uppermost. A rubber grip secured to the outer section at the rear holds the inner section fully home.

b. Slide the inner section forward to disengage

the rubber grip, then slide fully forward against the release latch.

c. When fully extended, invert the slide so

that the release latch is visible.

d. Press the bevelled side of the release latch,

while drawing the inner section out of the middle section.

5. Fit the inner section of each slide to its mounting

bracket (Pt. No. 450659) as follows: a. Assemble the slide to the bracket as shown

in the diagram (note the position of the release latch), and clamp them together using the three countersunk screws provided.

b. Tighten the six grubscrews and the three

countersunk screws.

c. Fit and secure the front plate and handle to

the slider ear, using the two M4 x 12 countersunk screws provided.

2-8

Page 37

Section 2 - Installation and Operating Controls

6. Remove the feet and tilt stand as follows:

a. Prize off the rubber pads from the four feet. b. Undo the two securing screws from each

foot. This releases the feet, washers and tilt stand so that they can be detached and stored safely for possible future use.

7. Fit each 10 inch mounting bracket to the correct

position on the rack as follows: a. Offer the bracket to the front of the rack as

shown in the diagram. Secure the bracket through the rack slots using two slotpan screws, two shakeproof washers, two plain washers and a 2.5 inch nut bar. Slacken the screws slightly to ease final positioning when the instrument is pushed home.

8. Fit each 2 inch mounting bracket to the correct

position on the rack as follows: a. Offer the bracket to the rear of the rack as

shown in the diagram. Secure the bracket using two slotpan screws, two shakeproof washers, two plain washers and a 2.5 inch nut bar. Slacken the screws slightly to ease final positioning when the instrument is pushed home.

9. The outer section of the slide has two securing

holes at the front and two slots at the rear, each within cut-out tongues. The slides are fixed to the adjustment slots in the 10 inch and 2 inch mounting brackets by two slotpan screws through the front holes, and one through one of the rear slots. (The rack depth determines which slide slot is to be used. If the rack is too shallow, the 2 inch bracket can be reversed so that it protrudes rearwards from the rack.)

a. Gain access to the rear slots by sliding the

middle section and bearing carriage to the front. The two front holes can be accessed by sliding the middle section and bearing carriage to expose each hole in turn through a rectangular cutout in the middle section.

10.Fit each slide to the correct position on the rack

as follows: a. Offer the slide outer and middle sections to

the 10 inch and 2 inch mounting brackets as shown in the diagram. Secure the slide to the brackets using the three slotpan screws, three shakeproof washers, three plain washers and three M4 nuts provided.

11.When sliding the instrument into the rack for

the first time, the slotpan screws securing the 10 inch and 2 inch mountings should have been slackened. This ensures that there is no lateral stress on the mounting system during the operation. These screws are finally tightened with the instrument sitting in the slides. a. Ensure that the screws securing the 10 inch

and 2 inch mountings have been slackened.

b. With assistance, locate the slide inner

section in the bearing carriage of the middle section, and carefully slide the instrument fully home into the rack. Slide it in and out of the rack several times until it is certain that there is no lateral stress.

c. Withdraw the instrument just sufficiently

to allow access to the slotpan screws securing the 10 inch and 2 inch mountings. Tighten the screws, and again slide the instrument in and out of the rack to be certain that there is no lateral stress.

12.Using screws, cage nuts etc. provided with the

rack, secure the instrument by screwing the mounting bracket ears to the front of the rack.

Final Width = 175mm

2-9

Page 38

Final Width = 175mm

Section 2 - Installation and Operating Controls

Mounting (Contd.)

Rack Slide Kit - Option 95 - List of Parts:

Rack mounting, especially using slides, is complicated by the diversity of rack fittings within the standard 19" concept. Although the Rack Slide Kit contains all the parts necessary to fit the instrument, on its slides, to a standard 19" rack; the assembly would normally be finally secured in position using attachments peculiar to the type and manufacturer of the rack. These final securing parts are not listed below.

The following list of parts is correct at the time of going to press, but our policy of product improvement means that alternative items could be employed for future issues. The current updated parts list is given in the Reference Handbook for the instrument.

Part No. Description UM Quantity

450655-1 Rack Ear, Handle................................................................ Ea 2

450659-1 Bracket, Slide Mounting...................................................... Ea 2

450680-3 Rack Mounting, Front Plate ................................................ Ea 2

611028 Screw, M4 x 8 POSIPAN SZP ............................................ Ea 6

611058 Screw, M4 x 8 POSICSK SZP ............................................ Ea 6

611059 Screw, M4 x 12 POSICSK SZP .......................................... Ea 4

611071 Screw, 10-32 x 1/2 SLOTPAN SZP ................................... Ea 8

611116 Screw, M3 x 12 SKT GRUB SZP ........................................ Ea 12

613013 Washer, M5 SZP................................................................. Ea 8

613020 Washer, M4 SZP................................................................. Ea 6

613021 Washer, M4 INT. SHAKP.................................................... Ea 6

613028 Washer, M5 INT. SHAKP.................................................... Ea 8

615011 Nut, Full, M4 SZP................................................................ Ea 6

630181 Bracket, 2", Mounting.......................................................... Ea 2

630182 Bracket, 10", Mounting........................................................ Ea 2

630183 Nut, 2.5" Bar........................................................................ Ea 4

630353-1 Slide, 24", 3-Section, Pair ................................................... Ea 1

2-10

Page 39

Section 2 - Installation and Operating Controls

Final

Width

= 277mm

RACK SLIDE KIT - FITTING

Fold at

175mm

from

other

(inside)

edge

2-11

Page 40

Final

Width

= 277mm

Fold at

175mm

from

other

(inside)

edge

Section 2 - Installation and Operating Controls

Connectors and Pin Designations

Inputs

Two input channels are provided:

Channel A Precision N-type Co-axial Socket. Channel B Two 4mm Binding Posts.

A third binding post is fitted to the terminal panel for the connection of a lead to Safety Ground.

SK9 - External Trigger Input

This co-axial BNC socket on the rear panel can be used to trigger a measurement when external triggers are enabled. The single pin is pulled up internally to +5V, and requires a negative-going TTL edge to initiate the reading.

SK7 - IEEE 488 Input/Output

Compatibility

The IEEE input/output is a 24-way Amphenol connector which is directly compatible with the IEEE 488 interface and the IEC 625 Bus.

Note that the Bus Address is set from the front panel (refer to Section 5).

Pin Layout

13 24

112

SK7 Pin Designations

Pin No. Name Description

1 DIO 1 Data Input/Output Line 1 2 DIO 2 Data Input/Output Line 2 3 DIO 3 Data Input/Output Line 3 4 DIO 4 Data Input/Output Line 4 5 EOI End or Identify 6 DAV Data Valid 7 NRFD Not Ready For Data 8 NDAC Not Data Accepted 9 IFC Interface Clear 10 SRQ Service Request 11 ATN Attention 12 SHIELD Screening on cable (connected

13 DIO 5 Data Input/Output Line 5 14 DIO 6 Data Input/Output Line 6 15 DIO 7 Data Input/Output Line 7 16 DIO 8 Data Input/Output Line 8 17 REN Remote Enable 18 GND 6 Gnd wire of DAV twisted pair 19 GND 7 Gnd wire of NRFD twisted pair 20 GND 8 Gnd wire of NDAC twisted pair 21 GND 9 Gnd wire of IFC twisted pair 22 GND 10 Gnd wire of SRQ twisted pair 23 GND 11 Gnd wire of ATN twisted pair 24 GND 4920 Logic Ground (internally

to 4920 safety ground)

connected to Safety Ground)

2-12

Page 41

Section 3 - Basic Measurements

SECTION 3 Basic Measurements

This section introduces the basic ‘User Interface’ of the 4920, describing how to make straightforward measurements without recourse to the more advanced features of the instrument. Descriptions of these other features can be found in Section 4.

The Measurement Task

With the external circuit properly connected, any measurement requires us to take two actions:

1. Configure the instrument;

2. Trigger the measurement and read the result.

The 4920 allows us to choose from many actions to control these processes. As an introduction, we shall concentrate on the selections for taking basic measurements. These are not complicated - all we need to do is to work through the instrument’s selection menus.

Introduction to the Front Panel

Final Width = 175mm

290V

max

OPTION

1420V pk

max

Cat I

10V pk

max

Store

CaltrigSRQLocalSampleExt'trigReset

Status Config

ACV

+/-4210

938765

mV AC/DC Input

Exp Enter Quit

Last rdg

Monitor Test Math

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Cal Power

The two displays on the front panel deal with different aspects of operation. Generally, we set up the instrument’s configuration using menus shown in the right-hand (dotmatrix) display, then readings appear in the left-hand (main) seven-segment display.

3-1

Page 42

Section 3 - Basic Measurements

Menu Keys

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Final Width = 175mm

Status Config

ACV

3 8765

AC/DC

Exp Enter Quit

+/-4210

Input

Monitor

Last rdg

Test Math

Cal Power

There are two classes of front panel menu keys; those that lead to an immediate change of instrument state (i.e the major function keys ACV and mV), and those that do not (Status, Config, Cal, Input, Monitor, Test, Math).

The AC/DC key activates the AC/DC Transfer mode, which is associated with the ACV function.

As well as the menu selection keys, there are seven soft function selection keys which have different actions depending on the selected menu. An arrowhead printed on each soft key lines up with a label on the display which defines the action of the key.

Also, system messages (all in capitals) may appear, these assist to clarify operation. The labelled soft keys have actions which fall into the following classes:

• Select another menu.

• Enable or disable a facility (e.g. Range selection). When enabled, the soft key label is underlined by a cursor.

• Trigger a direct action (e.g. ‘Oper’ in the TEST menu activates an operational selftest).

An error message appears if a selection cannot be executed.

3-2

Page 43

Numeric Keyboard

Status Config

Section 3 - Basic Measurements

ACV

3 8765

AC/DC Input

Exp Enter Quit+/-4210

Monitor

Last rdg

Test Math

Some menu and soft function keys, shown above, also act as a keyboard for entry of parameters such as math constants, bus address, etc. The data entered is purely numeric, such as a keyboard-entered value or the value of the most recent reading.

Exit from Menus

We can generally exit from any menu by selecting another menu key. For those menus where the numeric keyboard is active, we can exit by pressing either Enter or Quit. For some menus, a special soft key permits exit by a single keystroke.

Final Width = 175mm

3-3

Page 44

Section 3 - Basic Measurements

Major Function Keys:

98765

Final Width = 175mm

ACV

AC/DC

ACV (AC Voltage) - specified between 90mV and 1100V RMS in eight ranges;1Hz to 1MHz at high impedance (subject to V-Hz limit of 7.5 x 107). Spot-Frequency accuracy enhancement and alternative Digital Filter settings available.

mV (AC milliVolts) - specified between 0.9mV and110mV RMS in four ranges;10Hz to 1MHz at high impedance. Alternative Digital Filter settings are available.

AC/DC (Transfer Measurement mode) - In this mode, the RMS value of an AC voltage is compared with the combined RMS value of two DC reference voltages of equal value and opposite polarity. The voltage ranges and analog processes, used for each individual RMS measurement, are the same as for the ACV function.

The DC reference signals are applied in sequence and their individual RMS values are measured and stored. The system digitally computes the RMS of these two stored values to form the 'DCRMS equivalent', which is also stored.

The system then measures the RMS value of the applied AC signal, and digitally computes its deviation from the 'DCRMS equivalent'. The deviation is displayed in ppm on the dot-matrix display.

Each of these function keys defines separate measurement states and activates its corresponding menu on the display. Changing a function therefore commands changes of measurement state. In general, the instrument remembers the pattern of parameter conditions in each function, so that when it is subsequently reselected, it remains set up as before until we change it or turn off the instrument power.

The three functions have access to an RMS LOW FREQ menu, using the Config key, which can be used to alter the integration parameters of the analog RMS computation.

3-4

Page 45

Section 3 - Basic Measurements

Initial State at Power On

To see this condition, ensure that the instrument has been correctly installed in accordance with Section 2.

Operate the Power switch on the front panel. The 4920 forces the following state:

Function ACV Range 1kV Input Channel Ch B (Terminal Posts) Spot Off Digital Filter Off ACV Low Frequency 100Hz Monitor Off Millivolt (Option 10) Off AC/DC Transfer Off Math Off

Observe the ACV Menu: 1kV is underlined, showing the active selection. It can be cancelled by any other range selection. Ranges themselves cross-cancel.

Final Width = 175mm

ACV: Spot Filt 30V 100V 300V 1kV Down

Leave the power switched on. We have next to distinguish between three main types of action built into the operation

of the soft keys. These are defined overleaf, together with the shorthand conventions we use in the quick tour to refer to them.

3-5

Page 46

Final Width = 175mm

Section 3 - Basic Measurements

Soft Key Conventions

Now look at the soft keys (the ones with the arrowheads) to make some distinctions in a little more detail. Each soft key’s action is defined by the legend presented above it on the display. The legends usually define three different types of soft key:

Choice key Chooses one of several possible states. Deselection is by cross-

cancelling, i.e. by selecting another state.

cursor underline indicates ‘active’, no cursor indicates ‘not active’.

Toggle key Activates a particular facility - a second press when its state is

active will cancel it.

cursor underline indicates ‘active’, no cursor indicates ‘not active’.

Menu key Activates another menu - cursor not used. The whole aim of

branching via a menu is to gain access to further grouped state keys at an end of the branch.

N.B. When introducing soft keys in this text we shall differentiate between the three

types (to avoid lengthy paragraphs) as follows:

Choice key Underlined e.g. 300mV Toggle key Underlined italic e.g.

Filt

Menu key Not underlined e.g. Filt

Note that this is purely a short method of identifying the type, and bears no relation to its physical appearance on the instrument. Some displays do not relate to soft keys.

3-6

Page 47

Section 3 - Basic Measurements

Quick Tour of the Major Function Menus

The following introduction takes the form of a quick tour of the main functions, starting from Power On. To relate the descriptions to the physical appearance, process through the sequence as indicated by the bullet (•).

ACV Menu

(See the figures on pages 3-2 and 3-5)

This menu defines the following choice and menu keys. Spot This calls up the SPOT menu for selection of one of up to 100 spot

frequencies. A number of these can have been pre-calibrated to provide extra 'spot-corrections' for enhanced accuracy. The Hz annunciator on the main display is lit.

(Refer to Section 4, page 4-15)

Filt Filt opens the DIGITAL FILTER menu to select one of three 'rolling-

average' modes of 4, 8 or 16 readings or OFF (1 reading) Any selection other than OFF lights the Filt annunciator on the main display, and underlines the Filt label on the ACV Menu.

(Refer to Section 4, page 4-13)

Low Voltage Ranges: 0.3V 1V 3V 10V Up High Voltage Ranges: 30V 100V 300V 1kV Down

Up on the low voltage menu. When pressed selects the high voltage menu.

Final Width = 175mm

Down on the high voltage menu. When pressed selects the low voltage menu.

3-7

Page 48

Section 3 - Basic Measurements

ACV Configuration

(RMS Converter Low Frequency Extension)

• Press the Config key to see the RMS LOW FREQ menu:

RMS LOW FREQ: 100Hz 40Hz 10Hz 1Hz

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Final Width = 175mm

Status Config

+/-42103

Exp Enter Quit

Cal Power

100Hz: RMS converter normal low frequency limit of 100Hz. 40Hz: RMS converter low frequency limit extended to 40Hz. 10Hz: RMS converter low frequency limit extended to 10Hz. 1Hz: RMS converter low frequency limit extended to 1Hz. At Power On, 100Hz is active.

Note: Necessary Settling Times

In order to yield a valid signal sample in any form of RMS conversion, a lower input frequency will always require a longer settling time. In the 4920, for each low frequency limit selected in this menu, the internal measurement program will impose the appropriate settling time before initiating an A-D conversion.

For further details refer to Section 4 page 4-14.

3-8

Page 49

ACV (AC Voltage) - Movement between Menus

Power

Section 3 - Basic Measurements

ACV

∗

ACV:

Spot

Filt

30V 100V 300V

1000V

†

SPOT:

∗

†

(Spot Frequency)

NONE

Down

∗

ACV:

Spot

Filt

0.3V 1V 3V

10V

†

DIGITAL

FILTER:

∗

†

OFF

4 8

∗ Press the Config key to see the ACV Low Frequency selection. † Escape by pressing any front panel Menu key.

Config

RMS

LOW FREQ:

100Hz

40Hz 10Hz

1Hz

For details of

Spot Frequency

operation, refer to

Section 4

page 4.15

†

Final Width = 175mm

3-9

Page 50

Section 3 - Basic Measurements

mV Menu (Option 10) - Millivolt Ranges

Operation is described in Section 4 page 4-6

• Press the mV key to see the MV menu:

MV: Gain 3mV 10mV 30mV 100mV Filt

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Final Width = 175mm

Status Config

+/-42103

Exp Enter Quit

Cal Power

Gain: Characterize the gain of the X30 Amplifier. 3mV: Display reading in the range 0.9mV to 3.3mV. 10mV: Display reading in the range 2.7mV to 11mV. 30mV: Display reading in the range 9mV to 33mV. 100mV: Display reading in the range 27mV to 110mV. Filt Filt opens the DIGITAL FILTER menu to select one of three averaging

modes or OFF (1 reading). Any selection other than OFF lights the Filt annunciator, and underlines the Filt label on the mV Menu.

(Refer to Section 4, page 4-13)

Readings can be taken only after the gain of the internal X30 amplifier has been determined, and if the frequency of the applied signal is valid (for more details refer to Section 4; page 4-6).

At Power On: 100mV is selected, but the MV menu is inactive.

3-10

Page 51

mV - Movement between Menus

MV:

Gain

3mV 10mV 30mV

100mV

Filt

∗

†

‡ ‡ ‡ ‡

Digital Filter operation,

refer to

For details of

Section 4

page 4-13

DIGITAL

FILTER:

OFF

4 8

Section 3 - Basic Measurements

Config

RMS

LOW FREQ:

100Hz

40Hz 10Hz

∗

1Hz

†

Final Width = 175mm

∗ Press the Config key to see the RMS Low Frequency selection. † Escape by pressing any front panel Menu key. ‡ Selection available only after x30 amplifier gain has been characterized,

and within 2% of characterization frequency.

3-11

Page 52

Section 3 - Basic Measurements

AC/DC Menu (Transfer Measurement)

Operation is described in Section 4 page 4-9

• Press the AC/DC key to see the TFER menu:

TFER: dc+ dc- dcrms Tfer Filt Spot

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Final Width = 175mm

Status Config

+/-42103

Exp Enter Quit

Cal Power

The following four choice keys are used in sequence to perform an AC/DC transfer (each choice key can also be toggled off):

dc+: Reads and displays positive DC signals. Reading must be stored. dc-: Reads and displays negative DC signals. Reading must be stored. dcrms: Checks stored dc+ and dc- values for consistency.

Computes and displays the RMS equivalent. Reading must be stored.

Tfer: Reads AC signals, computes RMS value and compares with the stored

dcrms value. Deviation is displayed as ppm of the stored dcrms value.

The following two menu keys are also present: Filt Filt opens the DIGITAL FILTER menu to select one of three averaging

modes or OFF (1 reading). Any selection other than OFF lights the Filt annunciator, and underlines the Filt label on the TFER Menu (refer to

Section 4, page 4-13).

Spot This calls up the SPOT menu for selection of spot frequencies. The Hz

annunciator on the main display is lit (refer to Section 4, page 4-15).

At Power On, the TFER menu is inactive. For further details of the transfer, refer to

Section 4, page 4-9.

3-12

Page 53

Section 3 - Basic Measurements

AC/DC (AC/DC Transfer) - Movement between Menus

AC/DC

Config

TFER:

dc+

dc-

dcrms

Tfer

∗

†

DIGITAL

FILTER:

OFF

‡

◊

4 8

∗

†

LOW FREQ:

Filt

Spot

SPOT:

∗

†

(Spot Frequency)

NONE

operation, refer to

Down

∗ Press the Config key to see the RMS Low Frequency selection. † Escape by pressing any front panel Menu key. ‡ dcrms selection available only after valid dc positive and negative references

have been entered.

◊ Tfer selection available only after dcrms value has been calculated.

RMS

100Hz

40Hz 10Hz

1Hz

For details of

Spot Frequency

Section 4

page 4.15

†

Final Width = 175mm

3-13

Page 54

Section 3 - Basic Measurements

'Input' and 'Status' Keys

So far in this section, we have concentrated on the menus of the keys which select the type of physical quantity to be measured - we call them the Main Function keys. With these, we can configure the functions so that basic measurements conform to our requirements. Obviously the instrument is capable of more sophisticated operation than just taking straightforward measurements.

These are discussed in subsequent sections, but there are two keys which are relevant to basic measurements.

Input Key

The Input key and its menu permit us to select any one of the two external connections on the front panel. Channel A is a precision N-type connector, and Channel B is a set of three 4mm banana terminal posts.

Final Width = 175mm

Status Key

Using the Status key, we can review the instrument parameters which are currently set up, over and above those indicated by the annunciators on the main display.

In addition, the IEEE 488 bus address can be displayed and changed if required.

3-14

Page 55

Input Switching

Input Menu

Operation is described in Section 4 page 4-12

• Press the Input key to see the INPUT menu:

INPUT: ChA ChB

Section 3 - Basic Measurements

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Status Config

+/-42103

Exp Enter Quit

Cal Power

The INPUT menu defines two choice keys. The Config key is inactive.

ChA Activates Precision N-type Input Channel A only. ChB Activates Terminal Input Channel B only.

It is not possible to select both channels together. At power on, Channel B is active. When Channel A is not in use, cover Input A with its protective cap.

Final Width = 175mm

3-15

Page 56

Section 3 - Basic Measurements

Instrument Status Reporting

• Press the Status key to see the STATUS report:

STATUS: FNC RNG RMS FIL INPUT TFER

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Status Config

+/-42103

Exp Enter Quit

Cal Power

Status is a complete report of the most recent selections made using any of the various menus. It can be used at any time as a fast means of checking that the 4920 selections are suitable for the measurement being made.

The legends shown in the above diagram do not actually appear, they only mark the approximate positions for legends which can appear. Each is an abbreviation which merely acts as a key to the list below. The meaning and possible parameters which appear in each position are given in the list:

Abbr. Meaning Possible Parameters

FNC: Function ACV, mV. RNG: Range (ACV) 0.3V, 1V, 3V, 10V, 30V, 100V, 300V, 1kV.

Range (mV) 3mV, 10mV, 30mV, 100mV.

RMS: Low Frequency Limit 1Hz, 10Hz, 40Hz, 100Hz. FIL: Digital Filter Off, AV4, AV8, AV16. INPUT: Input Channel ChA, ChB. DCPOS; DCNEG; DCRMS; TFER:

AC/DC Transfer If present, AC/DC Transfer mode is active.

3-16

Page 57

Section 3 - Basic Measurements

Status Configuration

• Press the Config key to see the STATUS CONFIG menu:

STATUS CONFIG: Addr Date Cal? Due? Ser#

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Status Config

+/-42103

Exp Enter Quit

Cal Power

Unlike the STATUS display, this is a menu, defining the following menu keys.

Addr: displays the ADDRESS menu, to review and change the IEEE-488

bus address of the instrument.

Date: activates the DATE display, showing the present date and time. Cal?: presents the LAST CAL display, showing the date of the most recent

calibration of the instrument and the cal-store code.

Due?: presents the CAL DUE display, showing the due date of the next

calibration.

Ser#

presents the SER# and S/W ISS displays, showing the serial number and software issue of the instrument.

3-17

Page 58

Section 3 - Basic Measurements

IEEE 488 ADDRESS

• In the STATUS CONFIG menu: press the Addr key to see the IEEE 488 ADDRESS:

ADDRESS = XX Enter Quit

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Status Config

+/-42103

Exp Enter Quit

Cal Power

This menu permits entry of a value to be used as an IEEE-488 bus address.

Initially, the menu displays the present address value, and the numeric-keyboard keys are activated. Any valid numeric value (0-30) may be entered.

Pressing Enter stores the new value (or restores the old value if unchanged), but pressing Quit leaves the old value intact.

Either Enter or Quit causes exit back to the STATUS CONFIG menu.

• Transfer from the ADDRESS menu back to the STATUS CONFIG menu by pressing the Config key.

3-18

Page 59

Section 3 - Basic Measurements

Current Date

• In the STATUS CONFIG menu: press the Date key to see the DATE display:

DATE: m m . d d . y y . h h . M M

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Status Config

+/-42103

Exp Enter Quit

Cal Power

The meaning of this display is self-evident. Leading zeros are used, and the date/time is presented numerically as follows:

m m = month; d d = day; y y = year; h h = hour; M M. = minute.

The display shows the time when the display was called up. The current time cannot be altered except in one of the calibration menus. Time information is not lost when the instrument power is turned off.

• Transfer to the STATUS CONFIG menu by pressing the Config key.

3-19

Page 60

Section 3 - Basic Measurements

Calibration Dates

• In the STATUS CONFIG menu: press the Cal? key to see the LAST CAL and cal-store code displays:

LAST CAL: m m . d d . y y CODE: X X . X X . X X

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Status Config

+/-42103

Exp Enter Quit

Cal Power

The LAST CAL date is the most-recent date on which the instrument was last exited from Calibration mode. Leading zeros are used, and the date is presented numerically as follows: m m = month; d d = day; y y = year.

The date cannot be altered except in one of the calibration menus. The information is not lost when the instrument power is turned off.

The CODE: display registers the 'Cal-store Code'. This is a 6-ASCII character decode (upper-case alpha and numeric) of a count of the total number of individual times that the cal-store has been written to.

This code is intended to be used to detect whether an unauthorized calibration has been carried out. If the code has changed since the last authorized calibration, this indicates that the calibration store has been written to at on least one occasion. The code is made secure by obscuring the method of incrementation; it will repeat on a cycle of about 200,000 complete calibrations of the instrument.

• Transfer to the STATUS CONFIG menu by pressing the Config key.

3-20

Page 61

Section 3 - Basic Measurements

Calibration Due Date

• In the STATUS CONFIG menu: press the Due? key to see the CAL DUE display:

CAL DUE: m m . d d . y y

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Status Config

+/-42103

Exp Enter Quit

Cal Power

The meaning of this display is self-evident. Leading zeros are used, and the date is presented numerically as follows: m m = month; d d = day; y y = year.

The date cannot be altered except by calculation as a result of entries in calibration menus. The information is not lost when the instrument power is turned off.

• Transfer to the STATUS CONFIG menu by pressing the Config key.

3-21

Page 62

Section 3 - Basic Measurements

Serial Number and Software Issue

• In the STATUS CONFIG menu: press the SER# key to see the SER# and S/W ISS displays:

SER# = XXXXXX - XX . XX S/W ISS: XX.YY

ALTERNATING VOLTAGE MEASUREMENT STANDARD

4920

Status Config

+/-42103

Exp Enter Quit

Cal Power

Inspect the instrument serial number and software issue number. This display is for information only. The serial number cannot be altered except in one

of the calibration menus, and this facility is only provided for use during manufacture or when the Digital Assembly is replaced or repaired. Once changed, the new number is not lost when the instrument power is turned off.

The software issue number is embedded in the software itself, and is not user-alterable.

3-22

Page 63

Status Reporting - Movement between Menus

Status

Config

STATUS

Active Status

Function

Range

RMS LF Limit

Digital Filter

Input Channel

Transfer

STATUS CONFIG

Addr Date Cal?

Due?

Ser#

ADDRESS

IEEE 488

Address

Enter (New

Address) Quit (Old

Address)

Section 3 - Basic Measurements

Keyboard

DATE

Today's Date &

Present Time

mm.dd.yy.hh.MM

SER#

Serial Number

XXXXX

S/W ISS

Software Issue

XX.XX

LAST CAL

Last Cal Date

mm.dd.yy

CAL DUE

Next Due Date

mm.dd.yy

3-23

Page 64

Section 3 - Basic Measurements

Conclusion

We have now come to the end of our introductory tour of the main menu keys. This is, however, not the end of the instrument’s facilities. Now that you are more conversant with the operation of the front panel, it is not necessary to continue in the same sort of programmed way.

You will find that the information in Section 4 is presented in a more concise and accessible form than here in Section 3. Your familiarity with the instrument will allow you to progress rapidly to the facilities you wish to investigate.

Section 4 details the manual selection of instrument functions and facilities; Section 5 is devoted to the operation of the instrument via the IEEE 488 Interface.

3-24

Page 65

SECTION 4 Using the 4920

Section 4 - Using the 4920

Preliminaries

This section details the methods of using the 4920, divided so as to provide an easy reference for particular functions and facilities. The divisions are as follows:

Functions

AC Volts; AC Millivolts; AC/DC Transfer.

Facilities

Input channel selection; Digital filter - rolling-average window size; RMS low frequency limit selection; Spot frequency selection and calibration; Status reporting; Monitoring; Math; Test; Calibration.

The descriptions include: methods of connection, input limits, types of configurations, methods of access to facilities, and calculations available.

Where appropriate, examples of procedures are given in a format similar to that used in Section 3. Although the menus for calibration are shown, all routine calibration should be referred to Section 8.

Safety

See the Saftey Issues section at the front of this manual before you attempt to install, operate or service this instrument:

WARNING THIS INSTRUMENT CAN

DELIVER A LETHAL ELECTRIC SHOCK. NEVER TOUCH ANY LEAD OR TERMINAL UNLESS YOU ARE ABSOLUTELY CERTAIN THAT NO DANGEROUS

VOLTAGE IS PRESENT.

Final Width = 175mm

Installation

Before using the instrument, it is important that it has been correctly installed as detailed in Section 2.

Limiting Characteristics

Maximum inputs are detailed in Section 6.

4-1

Page 66

Section 4 - Using the 4920

Interconnections - General Guidelines

Importance of Correct Connections

When calibrated, the 4920 is capable of giving highly accurate traceable measurements. To attain this, it is necessary to use the correct connections to any external circuitry or load. A few general guidelines for correct external connection are given in the following paragraphs.

Final Width = 175mm

Sources of Error

E-M Interference

Noisy or intense electric, magnetic and electromagnetic effects in the vicinity can disturb the measurement circuit. Some typical interfering sources are:

• Fluorescent lighting.

• Inadequate screening, filtering or grounding of power lines.

• Transients from local switching.

• Induction and radiation fields of local E-M transmitters.

• Excessive common mode voltages between source and load.

Separation of leads and creation of loops in the circuit can intensify the disturbances.

Lead Impedance

The resistance of the connecting leads can drop significant voltages between the source and load, especially at higher frequenciess.

Avoidance Tactics

E-M Interference:

• Choose as “quiet” a site as possible (a screened cage may be necessary if interference is heavy). Suppress as many sources as possible.

• Always keep interconnecting leads as short as possible, especially unscreened lengths.

• Run leads together as twisted pairs in a common screen (or use coax) to reduce loop pick-up area, but beware of leakage problems and excessive capacitance.

• Where both source and load are floating, connect Lo to ground at the source to reduce common mode voltages.

Lead Impedance:

• Keep all leads as short as possible.

• Use conductors with a good margin of currentcarrying capacity.

• Use Remote Guard or 4-wire connections where necessary.

4-2

Page 67

Current Shunt Adaptor Model 4921

Use of 4921

The 4920 Alternating Voltage Measurement Standard is designed for AC Voltage calibration applications where Thermal Transfer Standards (TTSs) are presently used.

For AC Current calibration with TTSs, the user requires sets of current shunts (often the Fluke Models A40 and A40A).

The Model 4921 Current Shunt Adaptor permits the user to retain the use of these shunt sets in conjunction with the 4920 to provide AC Current calibration capability.

Full instructions for use of the adaptor are provided with the 4921 itself; The following paragraphs describe the concepts and connections.

Current Shunt Adaptor

4921

OUTPUT

4920

(0.5V NOM)

Section 4 - Using the 4920

Final Width = 175mm

SHUNT

Connecting Shunts to the 4921

The 4921 Adaptor simulates the 90Ω input impedance across which the shunts are designed to be connected; and matches to the high input impedance of the 4920.

The Current to be measured by the 4920 is passed through the requisite shunt, whose ends are connected to the SHUNT terminals of the 4921. The output voltage from the 4921 is passed out to the 4920 through the precision N-type coaxial connector on the side of the 4921. (The black 4921 terminal is connected directly to the outer of the Ntype connector.)

When used with the A40 and A40A Current shunts, the 4920 is operated in AC/DC Transfer mode to make normal transfer comparisons between the output from a DC Current Calibrator (such as the Datron Model 4808 or 4708) and the AC Current source to be calibrated.

The nominal output voltage from the shunt/4921 combination is 0.5V RMS. The 4920 should therefore be set to its 1V Range with AC/DC Transfer selected.

4-3

Page 68

Section 4 - Using the 4920

Functions

Measurement of AC Voltage

Generalized Procedure

ACV Key and Menus

A description of the User Interface is given in Section 3 for the main functions. If you are unfamiliar with the front panel controls, you should complete the quick tour which is the subject of Section 3. Specific reference to AC Voltage measurement appears on Pages 3-7 to 3-9.

ACV Menus

Final Width = 175mm

Range Switching

In order to achieve the high specification of the 4920, the full span of ACV voltage from 90mV to 1100V is divided into eight ranges. As the additional selections of Spot Operation and Digital Filter need to be accessed for each of these ranges, a total of ten selections are required. With seven soft keys available on each menu, four ranges have been assigned to each of two menus, plus a soft key which switches between the two, occupying five of the seven menu choices.

Down/Up Soft Key

The 'Down' soft key is used to switch from the high ranges menu (30V, 100V, 300V and 1kV) to the low ranges menu (0.3V, 1V, 3V and 10V), where the same key is reassigned as the 'Up' key for switching back again.

Spot and Filt Keys

The remaining two menu choices are assigned to spot frequency operation (Spot key) and digital filtering (Filt key). Their use is described under 'Facilities' on pages 4-15 and 4-13 respectively.

Setup Sequence

Input Channel (Refer to page 4-12)

The Power On and Reset default on the INPUT menu is Channel B selected (4mm Terminal Posts). If Channel A is to be used, ensure that the it has been selected by first pressing the front-panel Input key, then pressing the soft ChA key.

Power On

• The power-on default function is ACV, and the default range (1kV) is selected (underlined) on the ACV menu.

ACV

Spot Filt 30V 100V 300V 1kV Down

• Choose a range as required, or press the Down key for a lower range.

ACV

Spot Filt 0.3V 1V 3V 10V Up

• Choose a range as required, or press the Up key for a higher range.

4-4

Page 69

Broadband Frequency Operation

Section 4 - Using the 4920

Frequency Bands

The instrument operates over a frequency spectrum from 1Hz to 1.25MHz, (with appropriate choice of RMS Converter integration times - ACV Config). The Specifications for broadband operation are given in Section 6. These show the performance of the analog circuitry in up to seven frequency bands per range between 1Hz and 1MHz. The bands merely provide suitable specification break points; they are not used to allocate correction factors.

Flatness Corrections

During calibration processes, at internally-measured input frequencies, the 4920 stores correction constants which are unique to each voltage range.

During normal measurement, the 4920 measures the signal frequency. The stored constants are recovered and processed by a proprietory algorithm which describes the flatness profile. The algorithm calculates the correction to be applied at that particular input frequency on the selected range.

RMS Low Frequency Limits - ACV Config

An essential part of the RMS measurement process is to calculate a mean value using an integrator.

To allow low frequencies enough time for measurement, and for higher frequencies to be measured more quickly, a switched range of integration time constants is often provided, each described by the lowest acceptable frequency.

In the 4920, four switched time constants are available:

100Hz, 40Hz, 10Hz and 1Hz.

They are available in ACV, mV and AC/DC functions, and are described under 'Facilities'. In ACV function they are switched by pressing Config when in the

ACV menu. To meet the instrument specification,

the selected ACV Low Frequency must be equal to or lower than the lowest frequency to be measured.

Refer to Page 4-14

Final Width = 175mm

4-5

Page 70

Section 4 - Using the 4920

Functions (Contd.)

mV Function - AC Millivolt Ranges (Option 10)

General

Final Width = 175mm

Ranges

In addition to the 0.3V range used for the standard ACV function, Option 10 introduces four further ranges with the following voltage spans:

3mV: 0.9mV to 3.3mV 10mV: 3mV to 11mV 30mV: 9mV to 33mV 100mV: 30mV to 110mV

X30 Amplifier

A bypassable x30 amplifier is used to perform ratiometric transfers from traceably-calibrated ranges to millivolt levels; at constant frequency.

Gain Determination

The first part of the transfer is to determine the gain of the x30 amplifier. Once this has been done, normal readings can be taken (using the millivolt ranges) for signals whose frequencies lie within ±2% of that at which the gain was determined.

The gain is evaluated by applying a signal of approx. 100mV to the input of the amplifier, and comparing the amplifier output (x30) with the same signal applied with the amplifier bypassed (x1).

A value close to 100mV is chosen because this is:

(a) within the traceable span of the 300mV

range (> 90mV); and

(b) when amplified by 30, within the traceable

span of the 3V range (< 3.3V).

These are the ranges used for the two measurements.

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Section 4 - Using the 4920

mV Key and 'MV' Menu

A description of the User Interface is given in Section 3 for the main functions. If you are unfamiliar with the front panel controls, you should complete the quick tour which starts on Page 3-1.

An introduction to Millivolt measurement appears on Pages 3-10 and 3-11.

Filt Key

Digital filtering is available in millivolt ranges using the Filt key in the MV menu. Its use is described under 'Facilities' on page 4.13. The rolling average window size which is active when mV is selected will remain in force.

mV Config

Pressing the Config key when in a millivolt range will open the RMS LOW FREQ menu (refer to page 4-14). The low frequency limit which is active when mV is selected will remain in force.

Execution Errors

'NO MV GAIN VALUE' will be generated if the gain was not determined successfully.

CAL mode cannot be entered; an execution error

CAL/MV INCOMPATIBLE is generated instead.

Notes on the Millivolt Function:

1. Effect of Input Impedance: The input impedance of the 4920 on Millivolt Function is close to 404kΩ//90pF. Most calibrators have relatively high non-active outputs for their millivolt ranges. Typical values are between 30Ω (including Datron calibrators) and 50Ω.

Equivalent open-circuit millivolts can be estimated by multiplying the reading by (1 + A/B); where:

A = Output impedance of the source;

B = Input impedance of 404kΩ//90pF;

at the frequency of the measurement.

2. Spot calibrations are ignored in mV function.

3. AC/DC transfer cannot be used when the

millivolt function is active. The action of selecting AC/DC will deselect the millivolt range and destroy the stored (x30 amplifier) gain value.

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Final Width = 175mm

Section 4 - Using the 4920

mV Function (Contd.)

Millivolt Measurement Procedure

N.B. Input Channel The Power On and Reset default on the INPUT menu is Channel B selected (4mm Terminal Posts). If Channel A is to be used, ensure that the it has been selected by first pressing the frontpanel Input key, then pressing the soft ChA key.

X30 Amplifier Gain Measurement

• Enter the MV menu by pressing the mV key.

MV:

Gain 3mV 10mV 30mV 100mV Filt

Apply a stable voltage of between 95mV and 105mV, at within 2% of the frequency to be measured, to the input terminals.

• Press the Gain soft key. The Gain label above the key is underlined.

MV:

Gain 3mV 10mV 30mV 100mV Filt

The 4920 checks the signal level, measures it on the 300mV ACV range and applies it to the x30 amplifier input. Then it measures the amplifier output on the 3V AC range, and calculates the amplifier gain. During the whole of this gain measurement the

Busy annunciator lights and remains lit, and the Math annunciator is lit for two shorter periods of

time. The Busy light then goes out, and the value of the gain is presented on the main display. The

Gain label above the key remains underlined.

Check that the gain presented on the Main display is between 26 and 32. The gain level at 1MHz should lie within ±5% of that at 1kHz.

• Press the Store key to register this gain value for use in subsequent calculations. The Gain label

Store

remains underlined until a millivolt range is selected.

Gain Corrections

Having determined the gain of the millivolt amplifier, the necessary correction to account for its deviation from nominal x30 will automatically be applied to all readings taken on the millivolt ranges, provided that they are within 2% of the frequency at which the gain was characterized. The stored values are destroyed when the instrument is Reset or Powered-down, or any ACV calibration is carried out.

Millivolt Measurements

The four ranges are now available for use.

• Select the required millivolt range by pressing the appropriate soft key. The underline moves from the Gain label to the selected range.

MV:

Gain 3mV 10mV 30mV 100mV Filt

Millivolt Measurement Traceability

The gain value is traceable because it was derived using traceable ranges of the normal ACV function.

In use, readings are traceable because all four millivolt ranges use the amplifier in cascade with ACV traceable ranges as follows:

3mV Range: ACV 300mV range; 10mV Range: ACV 300mV range; 30mV Range: ACV 1V range; 100mV Range: ACV 3V range.

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Section 4 - Using the 4920

Functions (Contd.)

AC/DC Function - AC to DC Transfer

N.B. Input Channel The Power On and Reset default on the INPUT menu is Channel B selected (4mm Terminal Posts). If Channel A is to be used, ensure that it has been selected by first pressing the frontpanel Input key, then pressing the soft ChA key.

General

Transfer Mode

The 4920 is capable of making AC/DC (or AC/AC) transfer measurements to very high accuracy, particularly at or near full range. Use of these modes is easier and much faster than conventional thermal transfer devices. It is also very linear and so is capable of indicating AC/DC differences directly, with the sources considerably off null or off balance.

Benefits

The AC/DC Transfer mode removes two sources of error - drift with time and temperature in:

• the internal DC reference

• input preamplifiers;

• input attenuators.

Use of the AC/DC transfer mode gives added confidence where a known DC source is available. A prime application is the calibration of the AC voltage ranges of a multi-function calibrator when its DC voltage ranges have already been calibrated.

Measurement of +ve and -ve DC Values

The quality of a thermal transfer element is often interpreted from its DC turnover error: that is its difference in response to identical magnitude positive and negative DC signals.

In electronic devices which employ a high impedance preamplifier, offsets in the input amplifers and attenuators can cause large turnover errors. The 4920 eliminates the effect of these turnover errors by computing the equivalent RMS value from the DC positive and negative values of the DC reference source.

Before the DCRMS value is displayed, it is corrected for the factory-calibrated AC/DC difference of the 4920's RMS converter. Note that this difference can be derived by measuring a 1kHz AC signal on DC+ and DC-, then comparing the mean with the DCRMS value.

Positive/Negative DC Reference Inputs Order of Application

In the Transfer procedure given on page 4-11, the positive reference voltage is applied and stored before the negative. This is the natural order because of the positions of the soft keys, but the reverse order works as well, and is just as valid.

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Section 4 - Using the 4920

Using AC/DC Transfer Mode

Transfer Process

Programming AC/DC transfer measurements from the front panel is straightforward, but requires a knowledge of what results are desired.

Once the required range and any digital filtering is programmed (without this the transfer process will be three times as vulnerable to noise as the ACV measurement function), the positive DC input is applied. When the display has settled, this reading is stored in the DC+ memory. The same process is repeated with the DC- input and the DC- memory. After the two DC values are stored, the DC RMS value is computed and stored as a reference.

When the AC input is applied and transfer mode selected, the data display indicates the difference in ppm between the stored DC RMS reference value and the unknown AC input.

Transfer Mode and Spot Calibration

Spot Frequencies can be selected and deselected in AC/DC Transfer, as in ACV (refer to page 4-15). If a Spot Frequency or Spot Frequency Calibration is already selected when the transfer is invoked, it will remain in force. Note that the DC measurements and RMS calculation are not corrected for spot or flatness, and hence do not change.

AC/DC Config

Pressing the Config key when in AC/DC Transfer mode will open the RMS LOW FREQ menu (refer to page 4-14). Whatever low frequency limit is active when the transfer is invoked will remain in force.

Input Channel Selection

Two input channels: 'A' and 'B' are provided on the front panel of the 4920.

The most convenient way of connecting AC and DC inputs is for the AC to go to the precision Ntype socket of Channel A, and the DC to the terminal posts of Channel B, using the Input facility to select between them. Differences between the input characteristics of the two channels are negligible.

When connected this way, the DC and AC sources are isolated from each other. Using programmable AC and DC sources, this method of connection permits full remote programming of the transfer via the IEEE 488 interface.

Transfer Mode with other Facilities

The mode selected in the TFER menu remains in force until a primary function key is pressed, when the normal read mode appropriate to that function is forced. This means that the numeric values derived in dc+, dc- and Tfer modes can be digitally filtered, input to math blocks, or monitored.

Stored mV values are destroyed when in AC/DC transfer function. AC/DC transfer cannot be used in mV function; transfer selection or values are destroyed.

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Section 4 - Using the 4920

AC/DC Transfer Procedure

1. Press the ACV key and select the desired

range.

2. Press the Filt soft key and select the desired

averaging mode or 'Off'.

3. Press the AC/DC key to open the TFER menu.

TFER:

AC/DC

dc+ dc- dcrms Tfer Filt Spot

4. Apply the reference source of positive DC

Voltage.

5. Press the dc+ soft key.

TFER:

dc+ dc- dcrms Tfer Filt Spot

Wait for the main display reading to settle.

6. Press the Store key.

Store

7. Apply the reference source of negative DC

Voltage.

8. Press the dc- soft key.

TFER:

dc+ dc- dcrms Tfer Filt Spot

Wait for the main display reading to settle.

9. Press the Store key.

Store

10. Press the dcrms soft key.

TFER:

dc+ dc- dcrms Tfer Filt Spot

The 4920 checks the stored DC positive and negative values for consistency, then calculates the RMS equivalent.

(If dcrms is selected without both dc+ and dcvalues having been stored, the 4920 will generate an execution error, displayed on the menu screen as either NO DC+ VALUE or NO DC- VALUE).

The result is displayed with the symbol ±.

(When calculating the RMS value, if the stored dc+ and dc- values differ by more than 1%, the 4920 will generate a device error, displayed on the menu screen as DCRMS MISMATCH).

11. Press the Store key.

Store

12. Apply the AC Voltage to be measured.

13. Press the Tfer soft key.

TFER:

dc+ dc- dcrms tfer Filt Spot

The 4920 reads the AC signal and calculates the deviation of its RMS value from the stored DCRMS equivalent value. The deviation is displayed on the main display as ppm.

(If Tfer is selected without a dcrms value having been stored, the 4920 generates an execution error on the menu screen as NO DCRMS VALUE)

Filt Key

The Filt key is used to access the DIGITAL FILTER menu, in order to select a rolling average for noise reduction during the transfer (refer to page 4-13).

Use of AC/DC dc+ Mode for Readings <1Hz

In AC/DC: dc+ and dc-, the signal frequency is not computed. The dc+ mode can therefore be used to measure signals at frequencies below the normal limit of 1Hz without generating an error message. It is, of course, necessary to select 1Hz integration from the RMS LOW FREQ menu, and use digital filtering or block mean. Accuracy will be degraded, but stability will be good.

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Section 4 - Using the 4920

Facilities

Input Channels A and B

Final Width = 175mm

Front Panel Terminals

Two separate inputs are fitted on the left of the front panel. Channel A is a precision 'N' type coaxial socket, and Channel B consists of three 4mm binding posts. Their functions are as follows:

Channel A

Inner AC Voltage Input - Hi Max Input 290V peak to meet the EN61010

safety specifications.

Outer Safety Ground

Channel B

Hi AC Voltage Input - Hi Max Input 1420V peak, 1000V RMS

AC Current Input - Hi

Lo AC Voltage Input - Lo

AC Current Input - Lo Safety Ground

Input Switching

Either channel can be selected as input to the measurement circuits. Input switching is carried out under front panel or IEEE-488.2 control, with negligible difference errors due to the high input impedance of the measurement channel. Since these switches are programmable, it is possible to perform very efficient AC/DC transfer measurements in an automated system by connecting AC input to channel A and DC to channel B.

Under these conditions, fully automated, multirange and very high accuracy AC/DC transfer measurements are possible.

Channel Selection

Before any measurement can be performed, the correct input channel must be connected to the measurement circuits.

Input Key

Press the front panel Input key to open the INPUT menu.

INPUT:

Input

ChA Precision N-Type ChB Hi and Lo terminals

ChA ChB

If the channel has not been changed since Power On or Reset, then Channel B will be already selected.

Either: leave Channel B connected or select ChA as required.

Channel A outer is connected to Safety Ground, even when Channel B is connected.

WARNING THIS INSTRUMENT CAN

DELIVER A LETHAL ELECTRIC SHOCK. NEVER TOUCH ANY LEAD OR TERMINAL UNLESS YOU ARE ABSOLUTELY CERTAIN THAT NO DANGEROUS

VOLTAGE IS PRESENT.

WHEN NOT IN USE, COVER INPUT A USING ITS PROTECTIVE CAP.

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Digital Filter

Section 4 - Using the 4920

Rolling Average

The 4920 has an averaging mode which combines the results from a series of readings to obtain an average value, thus reducing the effects of random noise. The effect is that of a 'Digital Filter'.

The mode uses a rolling average technique in which the results of the most-recent 4, 8 or 16 readings are combined and displayed as a simple arithmetic mean. A 'window' memory of the requisite size is updated with every trigger by removing the earliest reading and adding the latest as soon as it becomes available. The readings contained in the window are then processed and the new result is displayed. This result remains on the display until the next reading becomes available.

Digital Filtering in All Functions

ACV, MV and TFER menus each have a Filt soft key,

which is used to open the DIGITAL FILTER menu. Any rolling average window selection made in one function is applied when operating subsequently in any other, until the selection is cancelled.

Selecting the Digital Filter

• Press the Filt key in any of the function menus:

ACV

Spot Filt 300mV 1V 3V 10V Up

• This opens the DIGITAL FILTER menu. If the facility has not already been selected, the Poweron default Off is underlined, and no window size is underlined:

DIGITAL FILTER:

OFF 4 8 16

• To select digital filtering, press either the 4, 8 or

16 key. This also lights the Filt annunciator on

the main display and selects the reading window size for the results to be averaged, e.g:

DIGITAL FILTER:

OFF 4 8 16

• Exit from the menu by pressing the required function key. When any of the three filters is selected, the selection Filt is underlined.

• To change from one window size to another, merely enter the DIGITAL FILTER menu and press the appropriate key, then exit.

• To deselect digital filtering, enter the DIGITAL

FILTER

menu and press the Off key, then exit. This also extinguishes the Filt annunciator on the main display.

Final Width = 175mm

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Section 4 - Using the 4920

Facilities (Contd.)

RMS Computation - Low Frequency Limits

Need for Switched Integration Times

An essential element in the analog RMS measurement process is to calculate a mean value using an integrator circuit. For periodic signals, practical analog methods require the measurement to continue over a number of cycles to avoid runaround due to signal-following. The lower the frequency of the signal , the longer the required measurement time, and the longer the required time constant of the integrating circuit.

In the 4920, four switched time constants are available:

100Hz, 40Hz, 10Hz and 1Hz.

To meet the instrument specification, the selected RMS Low Frequency must be equal to or lower than the lowest frequency to be measured.

Config Key

To Alter the RMS Low-Frequency Limit when in

ACV, MV or AC/DC menu:

• Press the Config key.

Config

RMS LOW FREQ

If the frequency has not already been changed since power on, then the default of 100Hz will be active.

• If required, select from 40Hz, 10Hz, 1Hz by pressing the appropriate choice key.

A change from the100Hz setting will cause the read-rate to slow perceptibly.

Exit back to the ACV, MV or TFER menu by pressing the ACV, mV or AC/DC key respectively.

100Hz 40Hz 10Hz 1Hz

Access from Main Function Menus

The integration time constants are switched via the

RMS LOW FREQ menu. This menu can be accessed

when in ACV, mV or AC/DC Transfer; by pressing the front panel Config key.

Reasonable readings for signals below 1Hz can be achieved using the DC-coupled 'dc+' mode in the

AC/DC function. Refer to page 4-11. The RMS

low-frequency limit of 1Hz must also be selected using the Config key.

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Spot Frequency Operation

Section 4 - Using the 4920

Using Spot Frequencies

To pay for the convenience of obtaining a broad frequency range, any measuring instrument must incur errors due to 'flatness' uncertainties.

For applications that require lower measurement uncertainties than those available from 'broadband' operation, the 4920 incorporates a facility for eliminating flatness errors using 'spot' frequency calibration.

A Spot Frequency can be created only by being calibrated. The method is detailed, with other calibration procedures, in Section 8.

Each spot is really a band of frequencies of ±2% about the calibrated spot frequency. It specifies a span of voltage between 50% and 110% of nominal range and frequency, for which an extra correction is obtained during 'spot calibration', and reapplied when using Spot Frequency mode.

A grand total of up to 100 spots can be allocated, during calibration, to particular ranges and frequencies.

Calibrated Spot Frequencies

Once in normal operation after a spot has been created, the instrument can be placed into Spot Frequency mode by selecting Spot either from an ACV menu, or from the AC/DC TFER menu; then selecting the required spot. An extra correction will be applied for signal frequencies within ±2% of that spot frequency. An input signal whose frequency does not fall within ±2% of the spot will elicit an 'Error HF' or 'Error LF' message instead of a reading.

Applying Spot Frequency Corrections

Any spot frequency is valid only for the ACV voltage range in which it was calibrated, and so can be selected only on that range. If a different range is selected when the ACV function is operating at a spot frequency, then Spot mode will be deselected.

The Spot Calibration data itself is a gain correction with respect to readings already corrected for normal AC linearity, gain and flatness. Spot-corrections are therefore applied to a reading after these normal corrections and any digital filter corrections have been implemented. Re-calibration of either linearity, gain or flatness will destroy the spot data. The spot will then cease to exist.

Spot frequency mode is not available for use with millivolt ranges, and is cancelled as soon as the mV key is pressed.

Use of Spot Frequency in Transfer Mode

If the AC/DC key is pressed when the ACV function is operating at a spot frequency, then that particular spot is carried over into the AC/DC Transfer function. It does not become active until the AC signal is selected by pressing the Tfer soft key in the

TFER menu. Spot is similarly available as a normal

AC reading in Monitor and Math processes. On return to the ACV range where the spot was selected, the same spot frequency will still be active.

Spot Calibration

When in an ACV range, new spots can be created (and old ones recalibrated) using a calibration menu. This can also be done when AC/DC has been selected, but with dc+, dc-, dcrms and Tfer all deselected.

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Section 4 - Using the 4920

Facilities (Contd.)

Spot Frequency Operation (Contd.)

Final Width = 175mm

Selecting a Spot Frequency

• Press the Spot key in either of the ACV menus or in the TFER menu. For example:

ACV

Spot Filt 300mV 1V 3V 10V Up

• The SPOT menu is opened. If no spot frequency is currently selected on the active range, then the word NONE appears in the menu. The Hz annunciator on the main display remains unlit.

SPOT:

NONE Up Down

• If a spot has been selected on the range, its frequency will replace the word 'NONE' on the menu display, and the Hz annunciator on the main display remains lit.

For example:

SPOT:

1.234567 kHz Up Down

• To select the next-higher frequency spot on the range, press the Up key. If more than one spot has been calibrated, successively pressing the

Up key will select them in ascending order of

frequency. As each spot is selected, its frequency is displayed. The Hz annunciator remains lit.

The Down key cycles through the spots in the same way, but in descending order of frequency.

Up and Down keys can be used in succession to

search for a known, required spot. Whenever

NONE is displayed, Spot mode is deselected and

the Hz annunciator goes out. Once Spot mode has been set up or deselected as

required, revert to the ACV menu by pressing the

ACV hard key. If a Spot remains selected, then 'Spot' on the ACV menu will be underlined and the Hz annunciator is lit.

Using Spot Frequencies

Once a spot has been selected, a signal at the connected input will be assessed for correct frequency, and if within ±2% of the spot will be accepted. The measurement will be made with enhanced accuracy as shown in the 'Spot' columns of the ACV or AC/DC specifications in Section 6, pages 6-5 or 6-9 respectively.

For any input signal with frequency higher than 2% above the spot frequency, the message 'Error HF' will appear instead of a reading on the main display. 'Error LF' appears for signals with frequency lower than 2% below the spot frequency. The usual meanings of the messages 'Error Ur' and 'Error OL' also apply to these measurements.

Spot Frequency Cycling

Once the highest-frequency spot on the range has been reached, the next press on the Up key reverts to NONE again, deselecting Spot mode and putting out the Hz annunciator. The next press on the Up key starts another 'up' cycle.

4-16

To Deselect Spot Mode

• Use the Up or Down key in the SPOT menu as above to select NONE, then select the required

function Spot on the ACV or AC/DC function menu loses

. Spot mode is deselected, the label

its underline and the Hz annunciator goes out.

Page 81

Facilities (Contd.)

Section 4 - Using the 4920

Status Reporting

This subject is fully described in Section 3, pages 3-14 to 3-23.

Monitoring

Introduction

The measurements taken by the 4920 can be analysed to indicate the signal frequency and deviation from a voltage reference value, using the

Monitor facility.

Frequency

The instrument continuously measures the input signal frequency. When the LOW FREQ limit of

1Hz is active , the signal is counted during a two-

second gate. For all other measurements, the gate length is 400ms.

The count for each measurement is made available for viewing via the monitor facility.

Signal Deviation

When in an ACV or mV range, with the Monitor facility active, a measurement voltage value appearing on the main display can be stored as reference.

When in an AC/DC Transfer mode, a ppm value appearing on the main display can be stored as reference.

Subsequent monitored measurements will be compared against the reference. Each measurement's deviation from the reference value is shown in ppm on the dot-matrix display.

Monitor Key (ACV and mV Functions)

• Select the required ACV/mV function and range.

• Select the appropriate input channel and input the required reference ACV signal.

• Press the Monitor key.

The FREQ/DEV presentation is displayed:

Monitor

FREQ = n.nnnnn kHz DEV = NOT VALID

The DEV display shows 'NOT VALID' when a reference value has not been entered.

• Press the Store key to register this reference value for use in

Store

subsequent calculations.

After the next A-D conversion, the deviation of the signal voltage from the reference value, in ppm, will replace the NOT VALID display.

Monitor

FREQ = n.nnnnn kHz DEV = xxxxxx.x ppm

Each subsequent measurement conversion will cause a comparison to be made against the registered reference, updating the displayed deviation.

Deviation is calculated by:

[(Reading - Reference) / (Reference)] in ppm.

At any time, by pressing the Store key, a reading on the main display can be registered as a new reference.

The stored reference is destroyed whenever the range or function is changed.

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Section 4 - Using the 4920

Facilities

Monitoring (Contd.)

Final Width = 175mm

Monitor Key (AC/DC Transfer Function)

• Select ACV function and the required range.

• Press the AC/DC key and perform an AC/DC transfer (refer to pages 4-9 to 4-11). When the transfer is complete, the main display will show a deviation in ppm.

• Press the Monitor key. The FREQ/DEV presentation is displayed:

Monitor

FREQ = n.nnnnn kHz DEV = NOT VALID

The DEV display shows 'NOT VALID' when a reference value has not been entered.

• Press the Store key to register this reference value for use in

Store

subsequent calculations.

After the next A-D conversion, the deviation of the signal voltage from the reference value, in ppm, will replace the NOT VALID display.

Monitor

FREQ: n.nnnnn kHz DEV: xxxxxx.x ppm

Validity Messages

The following combinations have the indicated meanings:

FREQ: n.nnnnn kHz DEV: NOT VALID

1. No reference value has been registered.

FREQ: NOT VALID DEV: xxxxxx.x ppm

2. The frequency display is inapplicable.

Each subsequent measurement conversion will cause a comparison to be made against the registered reference, updating the displayed deviation.

Deviation is calculated by:

(Reading - Reference) in ppm.

At any time, by pressing the Store key, a reading on the main display can be registered as a new reference.

The stored reference is destroyed whenever the range or function is changed.

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Facilities (Contd)

Math

Section 4 - Using the 4920

Introduction

This facility is used to record a block of measurements from those being taken by the instrument in ACV, mV or AC/DC functions; then derive their arithmetic mean and standard deviation. The two results are presented on the dot-matrix display.

The Math facility does not initiate measurements; those recorded within a block are triggered by normal means.

The number of measurements to be recorded for processing are set in a BLOCK SIZE menu. The action of pressing the Enter key in this menu starts the block, which ends when the number of measurements specified as block size have been recorded.

'Block Average' Process

A portion of memory is assigned to store block readings. As each subsequent reading becomes available, it is added to the others in the store. When a block of the registered size is complete, the mean and standard deviation of the stored readings is calculated and displayed, and the memory is cleared ready for the next block.

Math Menus

A description of the User Interface is given in Section 3 for the main functions.

If you are unfamiliar with the front panel controls, you should complete the quick tour which starts on Page 3-5.

To give an overall view, movement among the MATH group of menus is described by the following diagram:

Math

Config

MEAN:

+ n.nnnnnnn

SIGMA:

+ nnnn.n ppm

BLOCK

SIZE =

XXX

Enter

Quit

MEAN:

blank

SIGMA:

blank

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Section 4 - Using the 4920

Enter the Math Menus Start a Block of Readings

Final Width = 175mm

Math Key

• Press the Math key to show the MEAN/SIGMA display.

MEAN/SIGMA Display

This is a display, not a menu, and so no soft keys are defined. Initially:

Math

MEAN= (blank) SIGMA= (blank)

MEAN The mean of the block of readings is

calculated and displayed. Units are not shown; they are the same as on the main display.

SIGMA The Standard Deviation of the block of

readings is calculated and displayed. When the main display units are volts, then SIGMA is calculated in ppm of mean. When the main display units are ppm (as in Transfer mode), then SIGMA is calculated in ppm.

Until a block of readings has been started (via 'Math Config') and completed; neither the mean nor the standard deviation are available, and so no values are displayed in either of the two areas on the dotmatrix display.

CONFIG Key

• Press the Config key in MATH to cause the

BLOCK SIZE menu to be displayed.

BLOCK SIZE Menu

This menu allows the number of readings in the block to be set. Each time the Config key is pressed to enter the menu, the block size always reverts to zero. The numeric keyboard is activated and two menu keys (Enter and Quit) are defined:

Config

BLOCK SIZE = 0 Enter Quit

• Use the numeric keyboard to register the number of readings in the block; for example:

BLOCK SIZE = 10 Enter Quit

Either:

• Press the Enter key to start recording the registered block. The dot-matrix display reverts to the MEAN/SIGMA presentation.

or:

• Press the Quit key to revert to the MEAN/SIGMA display, which is presented with both areas blank. Reselect either a main function or press the Config key to reset the block size.

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Page 85

Results

Section 4 - Using the 4920

MEAN/SIGMA Display

The MEAN and SIGMA areas remain blank until the instrument has completed the number of A-D conversions registered as block size; then the calculated mean and standard deviation values appear against MEAN and SIGMA respectively:

MEAN = + n.nnnnnnnE+XX SIGMA = + nnnn.n ppm

One-Shot Operation

Because of the possible need for a user to redefine the block size, alter the input, reconfigure the 4920 and decide the timing of the next block, there is no automatic repetition of block recording.

Once the block results are presented, they remain on the display until further user-action takes place.

To record another block, press the Config key and set the required number of readings in the BLOCK

SIZE

menu, then press ENTER to start recording.

Validation

Messages are displayed to give information when it is not possible to perform the full analysis:

Invalid Reading:

MEAN = NOT VALID SIGMA = NOT VALID

Reading Too Noisy, or for a calculated Sigma of 20,000 or more:

MEAN = + n.nnnnnnnE+XX SIGMA = NOT VALID

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Section 4 - Using the 4920

Direct Action Keys

These seven keys are located beneath the main display. They allow the operator to act as follows:

Final Width = 175mm

Reset

Provides a quick means of resetting the instrument to the power-up state, when in local operation.

The instrument default states for Power On are given in Appendix B to Section 5. Pressing Reset provides the same result, except that any settings directly concerned with remote operation are not altered.

Ext’trig

Disables internal triggers, and enables the external trigger sources: 'Sample' and SK9. The 'Ext' annunciator on the main display is lit.

Ext’trig can be self-cancelled by a second press, to enable internal triggers. The Ext annunciator is turned off when internal triggers are enabled.

External Trigger Socket SK9 (Rear Panel)

External

Trigger

Case

Ground

Sample Key

Triggers a single-shot measurement if the 4920 is in Ext’trig mode. All 'Sample' measurements are subject to the standard acquisition times given in the specifications (Section 6).

During the measurement the 'Busy' annunciator on the main display is lit.

Local

Returns the 4920 to front panel control when operating on the IEEE-488 bus, provided that it is not disabled by remote command. It will cause the

Rem annunciator on the main display to turn off. Local can be disabled by a controller using the

LLO (Local Lockout) function.

SRQ

If set to remote in IEEE 488 system operation, with 'URQ' and 'ESB' bits enabled; this key generates a Service Request (SRQ) on the IEEE 488 bus. It causes the SRQ annunciator on the main display to light, and remain lit until the request is serviced.

SRQ can be disabled via the IEEE 488 bus using the 'Event Status Enable' or 'Service Request Enable' register commands.

For further information refer to Section 5.

Caltrig

This key is only active when the Cal annunciator is lit in the main display. It is used to trigger all operations selected in the calibration menus, except those concerned with entry of numeric data (in which case the menu contains an 'enter' command).

Store

In mV and AC/DC functions, also when using the Monitor facility to calculate 'Deviation'; it is necessary to store relevant data, by pressing the

Store key, as part of the measurement procedure.

For details, refer to the appropriate procedure.

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‘Numeric Keyboard’ keys

Keyboard Facility

Section 4 - Using the 4920

Numeric Function

Seventeen of the menu keys double as numeric keyboard keys when certain menus appear on the dot-matix display, and in most cases all other keys are locked out. As well as the numbers 0 to 9, the decimal point and the polarity changeover (+/-) keys, five other functions are represented.

Exp

The number appearing on the numeric display to the right of ‘E’ is a power of ten, by which the number to the left of the E is multiplied. The Exp key is used to enter E into the expression.

Exp can be preceded by a minus sign to indicate fractional powers of ten: to do this press the +/- key before pressing Exp.

Enter

After assembling the number within a menu, the Enter key is pressed to confirm that it is to be used. Usually the word Enter also appears in the menu. In some cases the Enter command enables another key, or presents another menu.

Quit

For a few menus (associated with ‘Math’ and ‘Cal’) the Quit key is provided for convenient exit, without activating any process.

← (‘Monitor’ key)

Deletes the previous numerical character.

Last rdg

When a reading from the main display is required to be incorporated into a process, the Last rdg key can be used to enter the value of the most-recent measurement on to the dot-matrix menu.

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Section 4 - Using the 4920

Test Facilities

Test Menus

A description of the User Interface is given in Section 3 for the main functions.

If you are unfamiliar with the front panel controls, you should complete the quick tour in Section 3.

Test

To give an overall view, movement among the TEST group of menus is described by the following diagram:

ANY KEY : CONTINUE TEST KEY : EXIT

Main Display

Walking Segments &

Walking Blocks

Final Width = 175mm

TEST

Oper Diag

Disp

Keys

Spcl

OPER TEST:

(While running):

'TEST NAME'

If failure

(When finished):

COMPLETED

OPER FAIL:

(What failed):

'TEST NAME'

Cont

Dot-matrix Display

KEYBOARDTEST

KEY # XX : SXX Key Name

To exit from Display Test or Keyboard Test,

Press the Test key.

DIAG TEST:

(While running):

'TEST NAME'

If failure

(When finished):

COMPLETED

DIAG FAIL:

(What failed):

'TEST NAME'

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Test Key

The front panel Test key causes the TEST menu to be displayed. Different types of selftest can be chosen from this menu.

Section 4 - Using the 4920

OPER FAIL Menu

When an operational test has failed, the test sequence is stopped, and the OPER FAIL menu is opened.

TEST

Test

Oper Diag Disp Keys Spcl

Caution

Disconnect any signal inputs. The success of the Operational and Diagnostic

Tests can be inhibited by:

• temperature not in the range: 13°C to 33°C;

• more than 1 year since the most-recent external calibration; or

• presence of excessive RFI or power-line noise.

Oper Key

Oper transfers to the OPER TEST menu, starts an operational test, disabling all menu and direct action keys, signal inputs and normal trigger sources. This test includes a calibration memory check.

OPER TEST Menu

OPER TEST

'TEST NAME'

OPER FAIL

'TEST NAME'

Cont

The name of the failed test appears, and a soft key (Cont) is allocated to allow a user to continue the test after noting the failure.

Disp Key

A reminder menu appears first, noting the actions of the keys.

ANY KEY : CONTINUE TEST KEY : EXIT

Repeatedly pressing any key other than Test increments both displays through a sequence of 'walking strobes', which allow a user to inspect individual segments and complete blocks.

Keys Key

The Keys soft key presents the KEYBOARD TEST menu.

KEYBOARD TEST

Key # XX : SXX XXX

Final Width = 175mm

While operational test is running, the display shows the name of the test currently being performed. Once a failure is noted, the test is halted and transfers to the OPER FAIL menu, showing the test which failed and a key to permit a user to continue the operational test.

All keys other than the Test key can be tested by pressing. For each key pressed, the 'Key #' is followed by the key's hexadecimal matrix positon, then after a colon an 'S' is followed by the key's switch ident number. The name of the key is given on the right of the display.

Exit

During 'Disp' or 'Keys' checks, pressing the Test key terminates the sequence.

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Section 4 - Using the 4920

Diag Key

Diag transfers to the DIAG TEST menu, starts a diagnostic test, disabling all menu and direct action keys, signal inputs and normal trigger sources. This test includes a calibration memory check.

DIAG TEST Menu

DIAG TEST

'TEST NAME'

While diagnostic test is running, the display shows the name of the test currently being performed. Once a failure is noted, the test is halted and transfers to the DIAG FAIL menu, showing the test which failed.

Final Width = 175mm

DIAG FAIL Menu

When an diagnostic test has failed, the test sequence is stopped, and the DIAG FAIL menu is opened.

DIAG FAIL

'TEST NAME'

The name of the failed test appears. No means of continuing the test is provided, as the failure could affect subsequent tests.

Exit

To exit from Diagnostic Test after a test failure, press any major function key. Pressing the Test key then choosing Diag again will lead to the same failure condition and report.

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Section 4 - Using the 4920

Calibration Operations

Note

The descriptions in the following pages are intended only as a guide to the operations available to calibrate the instrument. They contain neither examples nor calibration routines, and should NOT be used directly as a basis for calibrating any part of the instrument. Some of the commands, if used unwisely, will obliterate an expensive calibration or recalibration.

For a guide to calibration routines refer to Section 8.

General Outline of Calibration Operations

The calibration process generally conforms to a set sequence of operation:

1. The rear-panel switch must be set to ENABLE, then calibration is enabled by pressing the Cal key (this may need further parameters to be specified). Optional parameters are available for Spot calibration, and for use when the calibration is to be performed at a non-nominal value.

2. With the appropriate analog input applied, the calibration operation is triggered. The relevant corrections are calculated and stored in nonvolatile memory. Subsequently, in normal use; gain and flatness calibrations are applied to correct the pre-selected function and range. Filter and linearity calibrations are carried out on one range and applied to correct all ranges of the pre-selected function.

3. Other operations can be carried out, such as

setting the calendar/clock or the calibration interval.

4. When calibration is complete, calibration is

finally disabled by setting the rear panel switch to DISABLE.

Note: Spot Frequency calibration puts corrections

into memory which are relative to the broadband calibration constants. Because of this, any recalibration of GAIN or FLATNESS on an ACV range will invalidate the spot frequencies on that range, so they are cancelled by the 4920.

Re-establish a set of spot frequencies by recalibrating each spot. To avoid newlycalibrated spot frequencies being cancelled by broadband calibration: ensure that any spot frequency calibrations are not performed until all scheduled broadband calibrations have been completed.

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Page 92

Final Width = 175mm

Section 4 - Using the 4920

CAL Group of Menus - Overall View

ENABLE DISABLE

CALIBRATION

Rear Panel

CALIBRATION switch

to 'ENABLE'

Refer to

Servicing

Handbook Section 1.

DATE

mm.dd.yy.hh.MM

Enter

Quit

∗

Numeric

Keyboard

SER#

XXXXXX

Enter

Quit

∗ ∗

Numeric

Keyboard

∗ = Reverts to CAL menu. † = Escape via any front

panel menu key.

Cal

CAL

Cal Legend Lit

Date Ser# Spcl Freq Spot

Set

Due

'Due Date'

Information

Triggers routine calibration of the currently-selected function and range: at the nominal calibration point suggested by the input value and frequency.

Caltrig

Triggers Routine or Spot Calibration of the currently-selected function and range: at the voltage calibration point defined by the SET value.

Caltrig

Triggers calibration of the Frequency Counter, assuming that the input frequency is 1MHz

Caltrig

Triggers Spot Calibration at Full Range voltage value, creating or recalibrating a Spot at the input frequency.

SET VALUE

±XXX......E±XX

Enter

Quit

∗

Numeric

Keyboard

CAL DUE

mm.dd.yy

New

Intvl Quit

CAL INTERVAL (DAYS)

XXX

Enter

Quit

Numeric

Keyboard

†

Caltrig

SET VALUE

†

±XXX......E±XX

Cal Legend Off

Returns to the menu which was active when the Cal key was pressed.

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Calibration Menus

Section 4 - Using the 4920

Front Panel Cal Key

The Cal key on the front panel causes the CAL menu to be displayed in the dot matrix display, so long as the instrument is not already in Cal mode. This menu provides access to the calibration menus, also permitting some other non-volatile memory data to be accessed and changed.

CAL Group of Menus

A description of the User Interface is given in Section 3 for the main functions.

If you are unfamiliar with the front panel controls, you should complete the quick tour which starts on Page 3-5.

To give an overall view, movement among the CAL group of menus is described by the diagram on the opposite page.

Access Conditions

Rear panel switch S2 provides access to the CAL menu, and to the non-volatile calibration memory. S2 must be set to 'ENABLE' for calibration.

ENABLE DISABLE

CALIBRATION

S2 is recessed to avoid inadvertent operation. A paper seal can be placed over the switch to protect calibration.

CAL Menu

Pressing the Cal key opens the CAL menu. The main group of calibration menus is available.

CAL

Cal

Date Ser# Spcl Freq Spot Set Due

NOTE:

In this and other calibration menus the Caltrig key is enabled, and when pressed alters the calibration memory. To reduce the possibility of inadvertently obliterating the previous calibration, the menu should only be used during a genuine recalibration. Refer to Section 8.

Cal Trigger

Once the 'Cal' legend is lit, the major function hard keys can be selected and the various ranges calibrated at lower and upper cardinal points, using the Caltrig direct action key.

Spot Cal Trigger

If Spot calibration is required, and the input value is the Full Range voltage, then the Caltrig key can be used directly to create or recalibrate a Spot at the input frequency. Note: Any GAIN or FLATNESS calibration will clear all spot frequencies on the range being calibrated.

SET Cal Trigger

If the values are not exactly at the cardinal points, then Set in the CAL menu can be used to inform the instrument of the exact value. This facility can also be used with Spot calibration.

Menu Description

This menu defines five menu keys, and one Toggle key (Spot), all of which are not selected at Power On. They are described overleaf.

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Section 4 - Using the 4920

Calibration Menus (Contd.)

Final Width = 175mm

Spcl This key displays the SPCL menu,

which accesses five 'special' calibration operations. They can be regarded as 'presets'; being intended for use at manufacture and at times when certain assemblies are repaired. They are not

to be used for routine calibration purposes.

Quit transfers back to the CAL menu.

Selects Frequency Calibration. With an

Freq

accurate 1MHz signal applied on the 0.3V, 1V, 3V or 10V range, the action of pressing the Caltrig key performs calibration of the internal Frequency Counter.

Spot Selects Spot Calibration. With a full range

signal applied at the required spot frequency, the action of pressing the Caltrig key creates or recalibrates a spot frequency.

By pressing Spot followed by Set on the same menu, a particular cal source value can be entered as target value for non-nominal spot calibration. Refer to 'Set' on the next page.

Date Opens the DATE menu. This shows the

present date in the format:

mm.dd.yy.HH.MM

where the pairs of digits have the meanings:

mm = month dd = day yy = year hh = hour MM = minute

DATE

mm.dd.yy.hh.MM Enter Quit

The date and time can be changed in this menu, by operating the numeric keyboard keys. Pressing any numeric key will cancel the whole date, permitting the present date to be written, in the same format.

Enter causes the internal calendar/clock to

be reset to the date/time just written.

Quit aborts the attempt to reset the

calendar/clock, which continues uninterrupted running.

Both Enter and Quit transfer back to the CAL menu.

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Section 4 - Using the 4920

Ser# Opens the SER# = menu. This shows the

assigned instrument serial number, and the numeric keyboard is activated. A numeric value can be entered.

SER # =

XXXXXX Enter Quit

Enter writes the new serial number into

non-volatile RAM, overwriting the old number.

Quit aborts the attempt to reset the serial

number. The existing serial number remains stored in non-volatile memory.

Both Enter and Quit transfer back to the CAL menu.

Set Opens the SET VALUE = menu. This shows

a value of zero, and the numeric keyboard is activated.

SET VALUE =

+0.0000000E±00 Enter Quit

A particular cal source value can be entered as target value for non-nominal wideband or spot calibration.

Enter writes the new target value into non-

volatile RAM, and generates a new

SET VALUE = display. Pressing the Caltrig key performs the 'SET'

calibration.

Quit aborts the attempt to reset the target

value and transfers back to the CAL menu. The newly-written value is destroyed.

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Section 4 - Using the 4920

Final Width = 175mm

Due This is intended to be used following a

calibration, in order to note the date when the next calibration is due. The new date is calculated from the current date registered by the internal calendar/clock, and calibration-interval information entered via the CAL DUE and CAL INTERVAL menus.

The Due key opens the CAL DUE menu.

CAL DUE

mm.dd.yy New Intvl Quit

This shows the old due date for the next calibration, calculated at the previous calibration.

New causes the instrument to calculate the

date when the next calibration is due, from the date currently registered by the internal calendar/clock, and calibrationinterval information entered via the CAL

INTERVAL

menu.

The new 'Cal Due' date is presented on the DUE DATE menu instead of the old due date.

Intvl Opens the CAL INTERVAL (DAYS) =

menu. this displays the currentlyregistered calibration interval, and the numeric keyboard is activated. A new interval can be written using the numeric keyboard.

CAL INTERVAL (DAYS)

XXX Enter Quit

Enter causes the new interval to be written

into non-volatile memory, in place of the old interval.

Enter transfers back to the CAL DUE

menu, where the Cal Due date changes to show the effect of the new interval.

Quit aborts the attempt to reset the

calibration interval. The old interval remains stored in non-volatile memory.

Quit transfers back to the CAL DUE

menu. The Cal Due date does not change.

CAL DUE Menu - Exit from Calibration mode.

Quit from the CAL DUE menu. The Cal legend on

the main display is extinguished.

Quit returns either to the menu which was

open when the Cal key was pressed; or to a 'neutral' menu, whereupon a main menu key can be pressed to select the next required menu.

Calibration Store Code

After performing a calibration and having exited from Calibration mode, it is advisable to enter the STATUS CONFIG menu and select Cal? to observe the Calibration Store Code: 'CODE'.

The code should be recorded, so that on a subsequent occasion, a check can be made to determine whether the calibration store integrity is intact. Refer to Section 3, Page 3-20.

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Section 4 - Using the 4920

Appendix A to Section 4 of the User’s Handbook for Model 4920

Note to users:

generated either on the instrument front panel, or via the IEEE 488 system bus.

For the sake of completeness, this appendix collects together the error codes which might be

Error Detection

All errors which cannot be recovered without the user's knowledge, result in some system action to inform the user via a message, and where possible restore the system to an operational condition. Errors are classified by the method with which they are handled. Recoverable errors report the error

and then continue. System errors which cannot be recovered cause the system to halt with a message displayed. Restarting the instrument from Power On may clear the error, but generally such messages are caused by hardware or software faults, which require user action.

Error Messages

Fatal System Errors

For all fatal system errors, the error condition is reported only via the front panel. The processor stops after displaying the message. A user must respond by retrying operation from power on, and

9000 - System Kernel Fault 9001 - Run Time System Error 9002 - Unexpected Exception 9005 - Serial Interface Fault 9099 - Undefined Fatal Error

initiate repair if the fault persists. The following is a list of error numbers displayed, with their associated fault descriptions:

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Section 4 - Using the 4920

Recoverable Errors

Final Width = 175mm

These consist of Command Errors, Execution Errors and Device-Dependent Errors. Command Errors can only be generated due to incorrect remote programming. Some Execution Errors and all Device-Dependent Errors can all be generated by manual operation as well. Each of the reportable Execution and Device-Dependent Errors are identified by a code number.

Error Reporting

Whether in response to a bus or a keyboard error, the instrument reports an Execution Error or a Device-Dependent Error to both local and remote operators. It displays the error on the front panel; it also sets the ESR bit, and adds the error to the queue.

A Command Error is related to bus command syntax, and so is not reported via the front panel.

Command Error (CME) (Remote operation only)

A Command Error is generated when the remote command does not conform, either to the device command syntax, or to the IEEE 488.2 generic syntax. The CME bit (5) is set true in the Standarddefined Event Status Byte, but there is no associated queue.

The error is reported by the mechanisms described in the sub-section of Section 5 which deals with status reporting.

Execution Errors (EXE)

An Execution Error is generated if a received command cannot be executed due to it being incompatible with the current device state, or because it attempts to command parameters which are out-of-limits.

In remote operation, the EXE bit (4) is set true in the Standard-defined Event Status Byte, and the error code number is appended to the Execution Error queue.

The error is reported by the mechanisms described in the sub-section of Section 5 which deals with status reporting, and the queue entries can be read destructively as LIFO by the Common query command ∗EXQ?.

The Execution Error numbers are given below, with their associated descriptions.

List of Execution Errors

1000 - No Execution Error 1001 - No Test in Cal Mode 1002 - Resume test not allowed 1003 - Cal Switch disabled 1004 - Cal Mode not enabled 1005 - Set nominal not allowed 1006 - Invalid range/function 1007 - Invalid numeric data 1008 - No DCPOS Ref value 1009 - No DCNEG Ref value 1010 - No DCRMS Ref value 1011 - No Cal in Millivolt Mode 1012 - No Millivolt in Cal Mode 1013 - No Millivolt Gain value 1014 - mV Option not fitted 1015 - WB Option not fitted 1016 - WB serial number invalid 1017 - No Spot selected

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Page 99

Recoverable Errors (contd)

Section 4 - Using the 4920

Device-Dependent Errors (DDE)

A Device-Dependent Error is generated if the device detects an internal operating fault (eg. during self-test). The DDE bit (3) is set true in the Standard-defined Event Status Byte, and the error code number is appended to the Device-Dependent Error queue. The code number and description appear on the right-hand display, remaining visible until the next key-press or remote command.

In Remote, the error is reported by the mechanisms described in the sub-section of Section 5 which deals with status reporting, and the queue entries can be read destructively as LIFO by the Common query command ∗DDQ?.

Note that error codes beginning 2... can be caused by incorrect operation or instrument failure; error codes beginning 3... are almost certainly due to instrument failure.

Device-Dependent Error Lists

Device-dependent errors are associated mainly with test and calibration operations. The error numbers in the following pages are therefore listed in these categories. There is some overlap.

The error list for calibration operations, with their associated descriptions, commences overleaf, followed by the selftest error list.

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Final Width = 175mm

Section 4 - Using the 4920

Device-Dependent Messages: Normal and Calibration Operations

Normal Operation

2000 - No Device Error in List 2006 - Invalid Calstore Read 2009 - Invalid Serial Data 2010 - Corrupt Datarec Value 2011 - DCPOS Invalid 2012 - DCNEG Invalid 2013 - DCPOS/DCNEG Mismatch 2015 - Spot Frequency Invalid 2016 - mV Gain Error

Calibration Illegalities

3001 - Illegal Cal Exercise 3002 - Illegal Special Cal Step 3003 - Illegal Cal Update 3004 - Illegal Calstore Access 3005 - Illegal Calstore Clear 3006 - Illegal Calstore Func 3007 - Illegal Calstore Range 3008 - Illegal Calstore Length 3009 - Illegal Clock Destinatn 3010 - Illegal Clock Reading

Calibration Invalidities

2001 - Invalid Gain Cal 2002 - Invalid HF Trim Cal 2003 - Invalid Flatness Cal 2004 - Invalid Linearity Cal 2005 - Invalid Frequency Cal 2007 - Invalid Calstore Write 2008 - Invalid Cal Arithmetic 2014 - Spot Cal Table Full

Serial Loop Initialization

3028 - Chip Test AC Pre-amp 3029 - Chip Test AC RMS Control 3030 - Chip Test A-to-D DAC 3031 - Chip Test A-to-D Switch

3011 - Illegal Clock Setting 3012 - Illegal Clock Access 3013 - Illegal Measure Phase 3014 - Illegal Scale Index 3015 - Illegal Flatness Value 3016 - Illegal Linearity Value 3017 - Illegal HF Correction 3018 - Illegal Gain Correction 3024 - Illegal Test Stage 3025 - Illegal Test Store 3026 - Illegal Test Polarity 3027 - Illegal Engine Op-Code 3034 - Illegal Operation 3035 - Illegal Parameter

3032 - Chip Test A-to-D Tester 3033 - Serial Loop Failure

4-A4

Wavetek 4920 User manual

Specifications and Main Features

Frequently Asked Questions

User Manual