Newtons4th PSM3750 NumetriQ User Manual

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PSM3750 - NumetriQ

Version 1.10 06th April 2017

USER MANUAL

“ Do not be hasty when making measurements.”

NumetriQ is a precision instrument that provides you with the

tools to make a wide variety of measurements accurately, reliably, and efficiently - but good metrology practice must be observed. Take time to read this manual and familiarise yourself with the features of the instrument in order to use it most effectively.

DANGER OF ELECTRIC SHOCK

Only qualified personnel should install this equipment, after reading and understanding this user manual. If in doubt, consult your supplier.

RISQUE D'ELECTROCUTION

L'installation de cet équipement ne doit être confiée qu'à un personnel qualifié ayant lu et compris le présent manuel d'utilisation. Dans le doute, s'adresser au fournisseur.

GEFAHR VON ELEKTRISCHEM SCHOCK

Nur entsprechend ausgebildetes Personal ist berechtigt, diese Ausrüstung nach dem Lesen und Verständnis dieses Anwendungshandbuches zu installieren. Falls Sie Zweifel haben sollten, wenden Sie sich bitte an Ihren Lieferanten.

RISCHIO DI SCARICHE ELETTRICHE

Solo personale qualificato può installare questo strumento, dopo la lettura e la comprensione di questo manuale. Se esistono dubbiconsultate il vostro rivenditore.

PELIGRO DE DESCARGA ELÉCTRICA

Solo personal cualificado debe instalar este instrumento, después de la lectura y comprensión de este manual de usuario. En caso de duda, consultar con su suministrador.

IMPORTANT SAFETY INSTRUCTIONS

This equipment is designed to comply with BSEN 61010-1 (Safety requirements for electrical equipment for measurement, control, and laboratory use) – observe the following precautions:

 Ensure that the supply voltage agrees with the rating of

the instrument printed on the back panel before connecting the mains cord to the supply.

 This appliance must be earthed. Ensure that the

instrument is powered from a properly grounded supply.

 The inputs and outputs must not be connected to

common mode signals greater than 500V peak.

 The inputs must not be connected to signals greater

than 500V peak.

 Keep the ventilation holes on the underneath and sides

free from obstruction.

 Do not operate or store under conditions where

condensation may occur or where conducting debris may enter the case.

 There are no user serviceable parts inside the

instrument – do not attempt to open the instrument, refer service to the manufacturer or his appointed agent.

Note: Newtons4th Ltd. shall not be liable for any consequential damages, losses, costs or expenses arising from the use or misuse of this product however caused.

PSM3750 user manual

DECLARATION OF CONFORMITY

Manufacturer: Newtons4th Ltd. Address: 1 Bede Island Road Leicester

LE2 7EA

We declare that the product:

Description: Phase Sensitive Multimeter Product name: NumetriQ Model: PSM3750

Conforms to the EEC Directives:

2014/30/EU relating to electromagnetic compatibility:

EN 61326-1:2013

2014/35/EU relating to Low Voltage Directive:

EN 61010-2-030:2010:

January 2017

Eur Ing Allan Winsor BSc CEng MIEE (Director Newtons4th Ltd.)

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III

WARRANTY

This product is guaranteed to be free from defects in materials and workmanship for a period of 36 months from the date of purchase.

In the unlikely event of any problem within this guarantee period, first contact Newtons4th Ltd. or your local representative, to give a description of the problem. Please have as much relevant information to hand as possible – particularly the serial number and release numbers (press SYSTEM then LEFT).

If the problem cannot be resolved directly then you will be given an RMA number and asked to return the unit. The unit will be repaired or replaced at the sole discretion of Newtons4th Ltd.

This guarantee is limited to the cost of the NumetriQ itself and does not extend to any consequential damage or losses whatsoever including, but not limited to, any loss of earnings arising from a failure of the product or software.

In the event of any problem with the instrument outside of the guarantee period, Newtons4th Ltd. offers a full repair and re-calibration service – contact your local representative. It is recommended that NumetriQ be recalibrated annually.

PSM3750 user manual

ABOUT THIS MANUAL

PSM3750 has of number of separate measurement functions that share common resources such as the keyboard and display.

Accordingly, this manual first describes the general features and specification of the instrument as a whole; and then describes the individual functions in detail.

Each function is described in turn, in its own chapter, with details of the principles on which it is based, how to use it, the options available, display options, specifications etc.

Detailed descriptions of the RS232 command set is given

in the separate manual “PSM3750 communications manual”.

Revision 1.10

06th April 2017

PSM3750 user manual

CONTENTS

1 Introduction – general principles of operation ........ 1-1

1.1 Generator output .................................................... 1-4

1.2 Voltage inputs ........................................................ 1-5

2 Getting started ................................................. 2-1

2.1 Unpacking .............................................................. 2-1

2.2 Keyboard and controls ............................................. 2-3

2.3 Basic operation ....................................................... 2-4

2.4 Measurement Selectivity .......................................... 2-5

3 Using the menus ............................................... 3-1

3.1 Selection from a list ................................................ 3-3

3.2 Numeric data entry ................................................. 3-4

3.3 Text entry .............................................................. 3-5

4 Special functions ............................................... 4-1

4.1 Display zoom .......................................................... 4-1

4.2 Program store and recall .......................................... 4-2

4.3 Zero compensation.................................................. 4-3

4.4 Alarm function ........................................................ 4-4

4.5 Analogue output ..................................................... 4-6

4.6 Data hold ............................................................... 4-7

4.7 Results store and recall ............................................ 4-8

5 Using remote control ......................................... 5-1

5.1 Standard event status register .................................. 5-4

5.2 Serial Poll status byte .............................................. 5-5

5.3 RS232 connections .................................................. 5-6

6 System options ................................................. 6-1

6.1 User data ............................................................... 6-3

7 Measurement options ......................................... 7-1

7.1 ACQU - Acquisition options ....................................... 7-1

7.2 Datalog .................................................................. 7-4

7.3 SWEEP - Frequency sweep options ............................ 7-6

7.4 TRIM - Trim function ............................................... 7-8

8 Output control .................................................. 8-1

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8.1 Generator specifications ........................................... 8-3

9 Input channels .................................................. 9-1

9.1 Trimming x10 oscilloscope probes ............................. 9-5

10 True RMS Voltmeter ........................................ 10-1

10.1 RMS voltmeter specification.................................... 10-5

11 Frequency response analyser ............................ 11-1

11.2 Quick start guide to Feedback Loop Analysis ............. 11-5

12 Phase angle voltmeter (vector voltmeter) ........... 12-1

12.1 Phase angle voltmeter specification ......................... 12-4

13 Power meter ................................................... 13-1

13.1 Power meter specification ...................................... 13-5

14 LCR meter ...................................................... 14-1

14.1 Nyquist Diagram ................................................... 14-7

14.2 LCR meter specification ......................................... 14-9

15 Harmonic analyser .......................................... 15-1

15.1 Harmonic analyser specification .............................. 15-4

16 Transformer analyser ....................................... 16-1

16.1 Turns ratio ........................................................... 16-3

16.2 Inductance & leakage inductance ............................ 16-4

16.3 AC resistance and Q factor ..................................... 16-5

16.4 DC resistance ....................................................... 16-5

16.5 Interwinding capacitance ....................................... 16-6

16.6 Magnetising current ............................................... 16-7

16.7 Return loss ........................................................... 16-8

16.8 Insertion loss ....................................................... 16-9

16.9 Harmonics and distortion ......................................16-11

16.10 Longitudinal balance .............................................16-12

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VII

APPENDICES

Appendix A Accessories

Appendix B Serial command summary

Appendix C Available character set

Appendix D Configurable parameters

Appendix E Contact details

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1-1

1 Introduction – general principles of operation

NumetriQ is a self-contained test instrument, with one output and two or three inputs, which incorporates a suite of test functions.

NumetriQ has a wide bandwidth, isolated, generator output that can be used as signal generator for sine, square, triangle, or sawtooth waveforms, or true white noise. A dc offset may be added to the signal generator output. The output is fully isolated from earth to 600Vpk cat II.

NumetriQ has two or three isolated, high bandwidth, voltage inputs, which use direct digital analysis at low frequencies and a heterodyning technique to give high accuracy at high frequencies. The inputs are fully isolated from each other and from earth to 600Vpk cat II.

NumetriQ has two processors:

a DSP (digital signal processor) for data analysis a CPU (central processing unit) for control and display

At the heart of the system is an FPGA (field programmable gate array) that interfaces the various elements, see diagram below:

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FPGA

CPU

DSP

This general purpose structure provides a versatile hardware platform that can be configured by firmware to provide a variety of test functions, including:

Signal generator Two channel true rms voltmeter Phase angle voltmeter (vector voltmeter) Frequency response analyser (gain/phase analyser) Harmonic analyser

With additional external interfaces, such as current shunts, other functions are possible:

True rms current meter LCR meter Power meter

NumetriQ is configured to perform the required test function by simple user menus, or can be controlled remotely via a serial interface (RS232), or optionally LAN interface or GPIB interface.

OUT

CH1

CH2

CH3

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The programmable nature of the instrument means that new functions can be added as they become available, or existing functions can be enhanced, by simple firmware download.

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1.1 Generator output

The output sinewave is generated by direct digital synthesis (DDS). Amplitude is set in 2 stages - a fine control and a coarse control to give good resolution over the whole range. The output, has a variable offset added, is filtered and is buffered by a high speed, high current buffer. There is also an earth referenced TTL Sync output for oscilloscope synchronization etc, constantly running at the selected generator frequency.

The DDS is clocked at 210 MHz. The DAC resolution is 14 bit. The fine amplitude control is 10 bit (0.1% fsd). The coarse amplitude control is 4 bit. The maximum output level is 10V peak. The maximum output current is 200mA peak. The 0V of the output is isolated from earth. The output impedance is 50. The output frequency range is 10uHz to 50MHz. The Sync output is TTL level at generator frequency.

attenuate

offset

filter

50

DDS

output

buffer

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1.2 Voltage inputs

Each input consists of a pair of ac, or ac+dc, coupled high impedance buffers, one for the high voltages and one for lower voltages. The BNC safety connector and 4mm safety connectors are in parallel – either connector may be used.

After the selectable heterodyning and filtering, there is a series of gain stages leading to an A/D converter. The data from the A/D is transmitted across an isolation barrier to the DSP. Selection of the input gain, the heterodyning and the sampling of the A/D converter are under the control of the DSP. There is an autozero switch at the front end for dc accuracy.

The maximum input is 500V peak. The full scale of the lowest range is 3mV peak. The input frequency range is dc to 50 MHz. The A/D converter resolution is 14 bit. The A/D sample rate is variable to 1M samples/s.

input

selection,

heterodyning,

& filtering

A/D

isolation

barrier

variable

gain

high Z

input buffers

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2 Getting started

The NumetriQ is supplied ready to use – it comes complete with an appropriate power lead and a set of test leads. It is supplied calibrated and does not require anything to be done by the user before it can be put into service.

2.1 Unpacking

Inside the carton there should be the following items:

one NumetriQ unit one appropriate mains lead two or three voltage probes one set of output leads with croc clips one null modem cable to connect to a computer one USB to connect to a computer this manual one communications manual

Having verified that the entire above list of contents is present, it would be wise to verify that your NumetriQ operates correctly and has not been damaged in transit.

First verify that the voltage rating on the rear of the NumetriQ is appropriate for the supply, then connect the mains cord to the inlet on the rear panel of the NumetriQ and the supply outlet.

Switch on the NumetriQ. The display should illuminate with the model name and the firmware version for a few seconds while it performs some initial tests. It should then default to the FRA display. Note that the switch on message can be personalised – see the User Data section under System Options.

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The generator is off by default so the display may read some random values due to noise pick up. Connect the Red and Black output leads to the 4mm output sockets on the rear of the NumetriQ and input probes to the BNC on each of the input channels. Connect the output to all the inputs by connecting the black clip on the output lead to the 0V clip on each of the input probes, and the red clip of the output lead to the input probes. Note that this is easiest to do by connecting across a resistor (any value above 1k).

Press the OUT key to invoke the output menu, then press the UP key to select the output on/off control then the RIGHT key to turn on the output by selecting “on”.

Exit the menu by pressing the ENTER button or the HOME button twice.

The display should now indicate a magnitude value of about 1.4V on all channels, each of which should indicate the 3V range; check that the gain reads 0.000dB 0.010dB, and that the phase reads 0.000 0.010.

In the event of any problem with this procedure, please contact customer services at Newtons4th Ltd. or your local authorised representative: contact addresses and telephone numbers are given in the appendix at the back of this manual.

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2.2 Keyboard and controls

The keyboard is divided into 5 blocks of keys:

display control (5 keys top left) function keys (6 keys top right) setup keys (12 keys lower left) menu control keys (7 centre keys) action keys (4 keys lower right)

In normal operation, the cursor keys give one-touch adjustment of various parameters, such as generator amplitude and frequency, without having to access the menu system.

The setup keys provide access to the menus and are used for numeric data entry.

The function keys (FRA, PAV, LCR, RMS, POWER and SCOPE) are also used for entering the multipliers (G, M, k, m, u, n) for date entry and letters for text entry.

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2.3 Basic operation

The required function can be selected by pressing the function key, FRA, PAV, LCR, RMS, POWER, or SCOPE. Pressing the same function key again brings up the menu options specific to that function. For example, press PAV to select phase angle voltmeter mode; press PAV again to gain access to the PAV specific menu options.

Alternatively, press MODE to bring up the function specific menus.

There are a number of menus available to configure the instrument. All of these menus are directly accessible with one press of the appropriate menu key. The cursor keys allow navigation around the menus and also control the generator when not accessing a menu.

For example, to turn on the output, press OUT to bring up the generator control menu, press UP to select the output on/off option, press RIGHT to select the output from the available options. Press ENTER, or HOME twice, to exit the menu. Press FRA to select frequency response analyser mode and the instrument will now display the gain and phase of the transfer function of the circuit under test at the spot frequency specified by the output control menu.

Press LEFT or RIGHT to adjust the frequency, Press UP or DOWN to adjust the amplitude (use the OUT menu to change the size of the steps).

Press START and NumetriQ will start a frequency sweep over the specified range (set in the SWEEP menu); press TABLE to see the table of results, GRAPH to see a graph of the results and REAL TIME to return to the real time data.

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2.4 Measurement Selectivity

In many applications that require frequency response analysis, it is common for the frequency of interest (sometimes referred to as the injected frequency) to be immersed in noise. It is therefore important that the FRA instrument being used is able to reject frequencies other than that of the signal of interest. This feature is usually described as the measurement selectivity of the instrument and in most cases; selectivity is increased as the measurement speed is slowed down.

N4L frequency response analysers incorporate analogue

circuits with high common mode rejection and unique ‘real time’ DFT (discrete fourier transform) analysis to provide

exceptional wideband frequency response measurements even when the signal of interest is immersed in noise. As a result of this design technique, users are not required to concern themselves with the careful choice of selectivity criteria to achieve stable measurements.

In most applications, the signal of interest is generated by the FRA itself. When using this normal mode of operation, PSM units from N4L will automatically analyse the measurement signal with a DFT algorithm running at exactly the same frequency as the injected signal. This process eliminates the problem of signal frequency detection.

Where an external signal source is used for signal injection, the PSM units will detect the injected frequency with a greater level of selectivity as the measurement speed is slowed down. The user need only select the measurement speed to achieve the optimum balance of speed and measurement stability.

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While it is not required for the user to define the selectivity, nominal values used by the PSM units are defined in the following table:

NOTE:

Some FRA instrument manufacturers use the term ‘IF Bandwidth’. While this term is usually used in general

electronics to refer to the intermediate frequency of analogue RF circuits, in FRA applications the term actually relates to measurement selectivity.

speed

update rate

normal time constant

slow time constant

Measurement Selectivity

fast

1/20s

0.2s

0.8s

24Hz

medium

1/3s

1.5s

3Hz

slow

2.5s

12s

48s

0.4Hz

very slow

10s

48s

192s

0.1Hz

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3-1

3 Using the menus

NumetriQ is a very versatile instrument with many configurable parameters. These parameters are accessed from the front panel via a number of menus.

Each of the main menus may be accessed directly from a specific key.

ACQU

data acquisition parameters such as speed and filtering

SWEEP

frequency sweep control

TRIM

generator trim control (amplitude compression)

COMMS

communications options (RS232 etc)

ALARM

control of audible alarm and analogue output

OUT

signal generator control

CH1

channel 1 input control

CH2

channel 2 input control (and channel 3)

SYS

general system options such as phase convention, keyboard beep etc.

MODE

function control

PROG

recall/store/ delete of non-volatile programs

Each menu starts with the currently set parameters visible but no cursor. In this condition, pressing the menu key again or the HOME key aborts the menu operation and reverts back to normal operation.

To select any parameter, press the UP or DOWN key and a flashing box will move around the menu selecting each parameter. In this condition the keys take on their secondary function such as numbers 0-9, multipliers n-G etc.

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Pressing the HOME key first time reverts to the opening state where the parameters are displayed but the cursor is hidden. Pressing the HOME key at this point exits the menu sequence and reverts back to normal operation.

To abort the menu sequence, press the HOME key twice.

There are three types of data entry:

selection from a list numeric text

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3-3

3.1 Selection from a list

This data type is used where there are only specific options

available such as the output may be ‘on’ or ‘off’, the graph drawing algorithm may use ‘dots’ or ‘lines’.

When the flashing cursor is highlighting the parameter, the RIGHT key steps forward through the list, and the LEFT key steps backwards through the list. The number keys 09 step directly to that point in the list, which provides a quick way to jump through long lists. There is no need to press the ENTER key with this data type

For example, if the speed selection list comprises the options:

very slow (item 0) slow (item 1) medium (item 2) fast (item 3)

window (item 4) and the presently selected option is “medium”, there are 3 ways to select “window”:

press RIGHT twice

press LEFT three times

press number 4

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3.2 Numeric data entry

Parameters such as frequency and offset are entered as real numbers; frequency is an example of an unsigned parameter, offset is an example of a signed parameter.

Real numbers are entered using the number keys, multiplier keys, decimal point key, or +/- key (if signed value is permitted). When the character string has been entered, pressing the ENTER key sets the parameter to the new value. Until the ENTER key is pressed, pressing the HOME key aborts the data entry and restores the original number.

If a data value is entered that is beyond the valid limits for that parameter then a warning is issued and the parameter set as close to the requested value as possible. For example, the maximum amplitude of the NumetriQ generator is 10V peak; if a value of 15V is entered, a warning will be given and the amplitude set to the maximum of 10V.

When the parameter is first selected there is no character cursor visible – in this condition, a new number may be entered directly and will overwrite the existing number.

To edit a data value rather than overwrite it, press the RIGHT key and a cursor will appear. New characters are inserted at the cursor position as the keys are pressed, or the character before the cursor position can be deleted with the DELETE key.

Data values are always shown in engineering notation to at least 5 digits (1.0000-999.99 and a multiplier).

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3.3 Text entry

There are occasions where it is useful to enter a text string; for example, a non-volatile program may have some text as a title.

Text is entered by selecting one of 6 starting characters using the main function keys on the top right hand side of the keyboard (FRA etc), then stepping forwards or backwards through the alphabet with the UP and DOWN keys.

The starting letters are A (FRA), E (PAV), I (LCR), O (RMS), U (POWER), or space (SCOPE).

Numbers can also be inserted using the number keys.

The UP and DOWN keys step forward and backward using the ASCII character definitions – other printable characters such as # or ! can be obtained by stepping on from the space. The available character set is given in the Appendix.

When entering alphabetic characters, the ZOOM+ and ZOOM- keys select upper and lower case respectively for the character preceding the cursor and the next characters to be entered.

The editing keys, RIGHT, LEFT, DELETE and ENTER operate in the same way as for numeric entry.

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4 Special functions

4.1 Display zoom

NumetriQ normally displays many results on the screen in a combination of small font size (no zoom) and up to 4 values in a larger font size (first zoom level). There is also an even larger font for up to 4 selected values (second zoom level).

To set the data values for the larger font size, first return to no zoom by pressing ZOOM-, up to three times if necessary. Press ZOOM+ key to view the presently selected data, and press DELETE to clear the selection.

A flashing box surrounds the first available result. The flashing box is moved around the available results using the cursor keys, UP, DOWN, LEFT and RIGHT. Pressing the ENTER key selects the result for zoom and the box ceases to flash. Further results (up to four in total) can then be selected using the cursor keys in the same way – a solid box remains around the already selected item, and a new flashing box appears.

Having selected the desired results, pressing the ZOOM+ key invokes the first zoom level, pressing it again selects the higher level. Pressing ZOOM-, steps back down one level each time.

Note that any of the parameters selected for the zoom function can be used as the input for the alarm monitoring and analogue output.

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4.2 Program store and recall

There are 999 non-volatile program locations where the settings for the entire instrument can be saved for recall at a later date. Each of the 999 locations has an associated name of up to 20 characters that can be entered by the user to aid identification.

Program number 1 (if not empty) is loaded when the instrument is powered on, so that NumetriQ can be set to a user defined state whenever it is switched on. This is particularly useful to set system options such as phase convention etc. If no settings have been stored in program 1 then the factory default settings are loaded (program number 0).

Program numbers 1-6 may be recalled with a single press of the function keys if the direct load option is selected in the system menu (see system options).

The instrument can be restored to the factory default settings at any time by recalling program number 0.

The program menu is accessed using the PROG key. The program location can be selected either by stepping through the program locations in turn to see the name, or by entering the program number directly.

When storing a configuration in a program, there will be a slight pause (of about 1 second) if the program has previously been written or deleted. The process will be very quick if the location has not been used.

When supervisor mode is disabled (see system options), programs can only be recalled, not stored nor deleted, to avoid accidental modification.

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4.3 Zero compensation

There are 3 levels of zero compensation:

Trim out the dc offset in the input amplifier chain.

Measure any remaining offset and compensate.

Measure parasitic external values and compensate.

The trim of the dc offset in the input amplifier chain can be manually invoked at any time with the ZERO key, or over the RS232 with the REZERO command.

The measurement of the remaining offset also happens when the offset is trimmed but is also repeated at regular intervals when using a measurement function that requires dc accuracy (such as the rms voltmeter). This is to compensate for any thermal drift in the amplifier chain. This repeated autozero function can be disabled via the SYSTEM OPTIONS menu.

The compensation for parasitic external values (for example to compensate for the capacitance of the test leads when measuring capacitance) is invoked manually by the ZERO key. Refer to each function section for the function specific operations.

Any compensation values are stored along with the instrument configuration when a program is stored.

To restore operation without function specific compensation press ZERO then select the clear option.

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4.4 Alarm function

NumetriQ has two independent alarms that can be read remotely or can generate an audible sound each of the alarms can be triggered by comparison to one or two thresholds:

Sound the alarm if the value exceeds a threshold Sound the alarm if the value is below a threshold Sound the alarm if the value is outside a window Sound the alarm if the value is inside a window

Additionally, one of the alarms can be used to generate a sound which varies linearly between thresholds

The value to which each alarm is applied can be any of the measurements selected for zoom. The alarm status is also available as a logic output on the parallel port.

To program an alarm, first select the functions for the zoom; up to four measurements can be selected for the display, the alarm is applied to any of them; then press ALARM to invoke the alarm menu:

Select which of the zoom functions is to be used Select the type of alarm Set the upper limit (if appropriate) Set the lower limit (if appropriate) Select whether the alarm is to be latched Select whether the alarm sounder is enabled

If the alarm latch is selected then the alarm will continue to sound even if the value returns to within the normal boundaries. To clear the alarm, press HOME.

The linear alarm option allows tests to be carried out even if it is not possible to see the display. Pressing ZERO in the alarm menu sets the upper and lower threshold to 4/3 and

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1/3 of the measured value respectively. The repetition rate of the sounder then varies linearly as the value changes between these thresholds.

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4.5 Analogue output

The analogue output is a 0 to 10V dc level that represents the selected measurement.

To program the analogue output, first select the functions for the zoom; up to four measurements can be selected for the display, the alarm is applied to any one of them; then press ALARM to invoke the alarm and analogue output menu:

Select which of the zoom functions is to be used Set the value for zero volts output Set the analog scaling factor

The analog output level is computed as:

10 x (measured - zero) / (full scale - zero)

The output is updated whenever new data is available. For

maximum update speed, select “fast analogue output”

mode in the ACQU menu and enter a window value for 10ms or higher. When START is pressed, the instrument enters a special mode where all non-essential functions are suppressed (including the display). Press STOP to return to the normal display.

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4.6 Data hold

When in real time display mode, the data on the display can be held at any time by pressing the REAL TIME key. When HOLD is activated a warning message is briefly displayed and the word HOLD appears in the top right hand corner of the display instead of the time.

Press the REAL TIME key again or the HOME key or START key to release HOLD; in this case, HOME and START do not have their normal functions.

When HOLD has been activated, the DSP continues to sample, compute and filter the results but the data is ignored by the CPU. When HOLD is released the display is updated with the next available value from the DSP.

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4.7 Results store and recall

There are 999 non-volatile storage locations that can store either real-time results or frequency sweeps. Each location can store the sweep results for up to 50 points.

When storing a result, a text string may be entered to help identify the data.

Each stored result also saves the instrument configuration along with the data (same as program store/recall), so that the instrument is restored to the same settings when the result is recalled.

The results data may be restored manually or via communications for download to a PC. To manually access the results data store, press PROG and select memory type “results”.

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5 Using remote control

NumetriQ is fitted with an RS232, USB serial and LAN communications port as standard, and may have an IEEE488 (GPIB) interface fitted as an option. All the interfaces use the same ASCII protocol with the exception of the end of line terminators:

Rx expects

Tx sends

RS232 USB

carriage return (line feed ignored)

carriage return and line feed

LAN

carriage return (line feed ignored)

carriage return and line feed

IEEE488

carriage return or line feed or EOI

carriage return with EOI

All the functions of the NumetriQ can be programmed via either interface, and results read back.

The commands are not case sensitive and white space characters are ignored (e.g. tabs and spaces). Replies from NumetriQ are always upper case, delimited by commas, without spaces.

Only the first six characters of any command are important – any further characters will be ignored. For example, the command to set the generator frequency is FREQUE but the full word FREQUENCY may be sent as the redundant NCY at the end will be ignored.

Fields within a command are delimited by comma, multiple commands can be sent on one line delimited with a semicolon eg.

AMPLIT, 1.5; OUTPUT, ON

Mandatory commands specified in the IEEE488.2 protocol have been implemented, (e.g. *IDN? *RST) and all

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commands that expect a reply are terminated with a question mark.

NumetriQ maintains an error status byte consistent with the requirements of the IEEE488.2 protocol (called the standard event status register) that can be read by the mandatory command *ESR? (See section 5.1).

NumetriQ also maintains a status byte consistent with the requirements of the IEEE488.2 protocol, that can be read either with the IEEE488 serial poll function or by the mandatory command *STB? Over RS232 or IEEE or LAN (see section 5.2).

The IEEE address defaults to 23 and can be changed via the COMMS menu. Setting the LAN IP address to 0.0.0.0 will enable the DHCP and the unit will obtain its IP-Address from the DHCP server. DHCP server must be present on the network for this to work. The LAN will not start normal operation until it receives an IP address from the server.

Setting the LAN IP manually will disable the DHCP and the unit will use a fixed IP address, defined by the IP Address setting in the REMOTE menu.

The keyboard is disabled when the instrument is set to “remote” using the IEEE. Press HOME to return to “local”.

RS232 data format is: start bit, 8 data bits (no parity), 1 stop bit. Flow control is RTS/CTS (see section 5.2), baud rate is selectable via the COMMS menu. When connecting to a PC use the supplied null modem cable.

A summary of the available commands is given in the Appendix. Details of each command are given in the communication command manual.

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Commands are executed in sequence except for two special characters that are immediately obeyed:

Control T (20) – reset interface (device clear)

Control U (21) – warm restart

To maintain compatibility with some communication systems, there is an optional “protocol 2” which requires a space between the command and any arguments.

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5.1 Standard event status register

PON

CME

EXE

DDE

QYE

OPC

bit 0 OPC (operation complete)

cleared by most commands set when data available or sweep complete

bit 2 QYE (unterminated query error)

set if no message ready when data read

bit 3 DDE (device dependent error)

set when the instrument has an error

bit 4 EXE (execution error)

set when the command cannot be executed

bit 5 CME (command interpretation error)

set when a command has not been recognised

bit 7 PON (power on event)

set when power first applied or unit has reset

The bits in the standard event status register except for OPC are set by the relevant event and cleared by specific command (*ESR? *CLS, *RST). OPC is also cleared by most commands that change any part of the configuration of the instrument (such as MODE or START).

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5.2 Serial Poll status byte

ESB

MAV

FDV

SDV

RDV

bit 0 RDV (result data available)

set when results are available to be read as enabled by DAVER

bit 1 SDV (sweep data available)

set when sweep results are available to be read as enabled by DAVER

bit 2 FDV (fast data available (streaming))

set when data streaming results are available to be read as enabled by DAVER

bit 4 MAV (message available)

set when a message reply is waiting to be read

bit 5 ESB (standard event summary bit)

set if any bit in the standard event status register is set as well as the corresponding bit in the standard event status enable register (set by *ESE).

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5.3 RS232 connections

The RS232 port on NumetriQ uses the same pinout as a standard 9 pin serial port on a PC or laptop (9-pin male ‘D’ type).

Function

Direction

DCD

in (+ weak pull up)

RX data

in 3 TX data

out

DTR

out

GND

DSR

not used

RTS

out

CTS

not used

NumetriQ will only transmit when CTS (pin 8) is asserted, and can only receive if DCD (pin 1) is asserted. NumetriQ constantly asserts (+12V) DTR (pin 4) so this pin can be connected to any unwanted modem control inputs to force operation without handshaking. NumetriQ has a weak pull up on pin 1 as many null modem cables leave it open circuit. In electrically noisy environments, this pin should be driven or connected to pin 4.

To connect NumetriQ to a PC, use a 9 pin female to 9 pin female null modem cable:

1 & 6

2 4 -

1 & 6

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6 System options

Press SYSTEM to access the system options.

The time and date are maintained by a battery backed real time clock. Time is expressed in 24 hour format.

The display is normally in colour but it can be set to black on white or white on black.

There is a choice of screen brightness – “high” suits most

typical environments but “low” may cause less eye strain

in low light conditions.

Measurements of phase can be expressed in one of three conventional formats:

-180 to +180 (commonly used in circuit analysis) 0 to -360 (commonly used in power applications) 0 to +360

The measurement is exactly the same it is only the way that it is expressed that changes.

Blanking can be applied to a number of measurements so that zero is shown when the measurement is below a certain level. This blanking can be disabled if desired.

Each key press is normally accompanied by an audible

‘beep’ as well as the tactile ‘click’. The ‘beep’ can be

disabled for quiet environments if the feel of the key is sufficient feedback

Regular autozero measurements can be suppressed.

The 6 main function keys, FRA, PAV, LCR, RMS, POWER, HARM, can be used to load stored configurations as a “one-touch” way of configuring the instrument for specific applications. This is particularly useful in a production

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environment where an operator has a small number of specific tests to perform.

Most data is displayed to 5 digits but for extra resolution 6 digits can be displayed when in ZOOM level 2 or 3.

When using external shunts or attenuators, the range can be shown either as the normal peak voltage or scaled by the shunt or attenuator factor.

Levels are usually expressed in volts but can be set and displayed in dBm, which is a logarithmic scale referred to

1mW in 600Ω, often used when testing communications

components.

To save these system settings as default, store the setup in program 1 so that they are reloaded on power on.

Pressing RIGHT from the SYSTEM OPTIONS menu selects the USER DATA screen (see next section).

Pressing LEFT from first SYSTEM OPTIONS menu displays the serial number, release versions, and calibration date.

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6.1 User data

NumetriQ can be personalised by entering up to 3 lines of user data as text (see section on text entry).

User data is displayed every time that the instrument is switched on to identify the instrument. The entered text may also be read over the communications to identify the instrument (see USER?).

Typical arrangement of the user data might be:

line 1 company name line 2 department or individual name line 3 unique identifying number (eg. asset number)

Any user data may be entered as required, as the lines are treated purely as text and are not interpreted by NumetriQ at all.

For use in a production environment, NumetriQ supports two modes of operation, supervisor and user. When supervisor mode is disabled, the stored programs can only be recalled, not changed. In user mode NumetriQ will also not accept any commands which could change the calibration data.

After changing the user data or supervisor status, execute ‘store’ to save the data in non-volatile memory.

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7 Measurement options

7.1 ACQU - Acquisition options

NumetriQ comes in 2 channel or 3 channel version. The 3 channel version can be set to display just 2 channels if the third channel is not in use.

In normal acquisition mode the window over which the measurements are computed is adjusted to give an integral number of cycles of the input waveform. The results from each window are passed through a digital filter equivalent to a first order RC low pass filter.

There are six pre-set speed options – very fast, fast, medium, slow, very slow and window – that adjust the nominal size of the window, and therefore the update rate and the time constant of the filter. Greater stability is obtained at the slower speed at the expense of a slower update rate.

Note that the measurements have to be made over an integral number of cycles of the waveform so the window is extended to cover one or more complete cycles even if this is a longer period than the nominal update rate. The minimum number of cycles to be measured in each window can be set from 1 to 100.

There are two time constants for the filter, normal or slow, or the filter can be deselected. The filter applies an auto reset function to give a fast dynamic response to a change of measurement – this function can be deselected and the filter forced to operate with a fixed time constant for use with noisy signals.

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The nominal values are:

speed

update rate

normal time constant

slow time constant very fast

1/50s

0.1s

0.4s

fast

1/12s

0.4s

1.5s

medium

1/3s

1.5s

slow

2.5s

12s

48s

very slow

10s

48s

192s

There is also an option to set a specific size of the window to a value other than the preset options. In order to synchronise to an integral number of cycles, the window size is either reduced by up to 25% or increased as necessary.

The filter dynamics are usually set to “auto reset” where

the filtering is reset in response to a significant change in data. This speeds up the response of the instrument to changing conditions. This function can be disabled so that the filtering has a fixed time constant, which would have an exponential response to a step change. The filter can also be reset by pressing TRIGGER.

When the generator is not used and so the measurement is synchronised to the input frequency measured on CH1, there is a low frequency option that extends the frequency measurement down to 20mHz. This low frequency option also applies a digital filter, which can be useful when measuring in a low frequency, noisy environment.

In the case where there is very little signal on CH1, the reference for the phase can be set to another channel to give a more accurate measurement. This does not change the phase result it only helps to reduce the uncertainty due to noise.

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The bandwidth of the instrument, usually set to “auto”,

can be forced to “wide” or “low”. When not in auto selection, heterodyning is disabled and the bandwidth is either 5MHz (wide) or 100 KHz (low) to minimise noise when making measurements at low frequencies.

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7.2 Datalog

NumetriQ can store and display measurements recorded at regular intervals over a time period. Each data record consists of the elapsed time and up to four data values selected by ZOOM.

The actual interval between data points is governed by the measurement speed and the datalog interval. NumetriQ stores the next available measurement after the datalog interval has elapsed: the actual elapsed time is attached to each datalog record, is displayed with the data on the table or each graph, and returned with each record over the communications (RS232, USB, LAN or GPIB).

The data values may be stored to RAM or directly into either internal non-volatile memory or USB memory stick as each value becomes available. The non-volatile option is useful for acquiring data over long periods, to prevent the loss of data in the event of a power failure.

The RAM datalog can hold up to 32000 records if one value is selected; more than 12000 records if four values are selected. Data that has been stored into RAM may be subsequently transferred to non-volatile memory using the PROG menu.

For high speed data acquisition, the datalog interval may be set to zero so that each measurement is stored. The measurement interval is controlled with the “speed” option in the ACQU menu. Using the “window” option for speed, allows greater control of the measurement interval. In this mode, the display flashes “DATALOG RUNNING” and only shows the acquisition time. The minimum datalog interval depends on the function but is typically 10ms.

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Note that in all cases the measurement interval is necessarily adjusted to be an integral number of cycles of the measured waveform.

The datalog options are set up with the ACQU menu. The datalog is started with the START key, and stopped with the STOP key unless the store becomes full first. The zero reference for the elapsed time is taken as the first data measurement after START.

The data can be viewed as a table or as individual graphs. Pressing GRAPH steps the graph through the stored parameters. If more than 250 records have been stored, the graph can show the data for the whole period or pressing ZOOM redraws the graph to show 250 records about the cursor. The cursor can be moved in single steps (LEFT or RIGHT) or large steps (UP or DOWN). Pressing UNZOOM shows the whole data gain. Movements of the cursor are synchronised in both the TABLE and GRAPH views.

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7.3 SWEEP - Frequency sweep options

All ac measurements using the NumetriQ generator can be swept across a frequency range. The start frequency, stop frequency and number of steps up to 2000 can be specified. The measurements are subjected to the same speed constraints set in the ACQU menu, but the filtering does not apply on each measurement point. If continuous sweep is selected, then the filtering is applied to each successive sweep.

At the end of a sweep the generator may be set to be on, off, or dc only. The settings used are those in the normal generator menu.

The graph normally sets the y axis automatically to the extremes of the measurements (or in FRA mode to 20dB/decade of frequency) but the axis can be fixed if required. The graph of the second parameter (usually phase) can also be independently manually set.

A vertical marker can be placed on the graph to reference a specific frequency.

Each frequency point is an entirely new measurement and autoranging is restarted (if enabled). For the fastest possible sweeps, select manual ranging. As each frequency point is a new measurement, filtering has no effect on a single sweep, but fixed time filtering can be applied independently on each frequency point if repeat sweep in selected.

For maximum sweep speed, particularly when using a

large number of points, there is a “fast sweep” mode

which disables all non-essential functions, including the display, during the sweep. In this mode the display is

blank except for a flashing message “ACQUIRING SWEEP DATA” until the full sweep has been completed when

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normal display functions are restored. This mode is automatically selected when a user defined window of less than 100ms has been set.

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7.4 TRIM - Trim function

The trim function on NumetriQ is a powerful and versatile feature that allows closed loop control of the generator amplitude. It allows a specific measurement from CH1, CH2 or CH3, if fitted, and the generator output will be adjusted to maintain the measured voltage or current. This allows the excitation level to be controlled over changing conditions such as a frequency sweep.

At each measurement point, the measured level is checked against the specified level and tolerance; if an adjustment is needed the data is discarded and a new measurement made at the new output level. The user is alerted to the adjustment by an audible beep.

Particularly important in control loop analysis, where it is sometimes referred to as amplitude compression, it prevents the control loop being overdriven as the frequency changes.

It is also useful in a more general case where test levels are specified.

Note that when dBm mode level control is selected, the trim level is entered as dBm but the tolerance remains a linear percentage of the actual voltage not the logarithmic dBm measure.

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8 Output control

The output for the signal generator is digitally synthesised at an update rate of 150Msamples/s. With the output filtering, this gives a good sinewave waveform, even at 35MHz, while preserving very accurate frequency control.

The output amplitude is controlled in 2 stages – a fine control with 10 bit resolution, with coarse control with 5 steps. This gives 10mV resolution at high output levels and 1mV resolution at low output levels.

The maximum output available from the generator is a function of frequency:

max frequency

output level into 50Ω

MHz

peak V

rms V

7.5

5 5 5

3.5

3 2 15

1.4

1.5

1.2

0.8

0.7

0.75

0.5

0.6

0.5

0.4

0.25

An offset may be added to any output to bias the signal or to null out any dc present with a resolution of +/-10mV.

The LEFT and RIGHT keys adjust the frequency of the generator by a fixed increment stored via the STEP menu; the UP and DOWN keys adjust the amplitude (except for

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the harmonic analyser and power analyser where UP and DOWN step the selected harmonic).

The generator output may be set to be on, off, or dc only.

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8.1 Generator specifications

General

accuracy

accuracy (with trim)

frequency 0.05% amplitude 5% (10% > 50MHz) amplitude 1% < 10MHz

output impedance

50 2%

output voltage

15V peak

Offset

10V peak maximum

waveforms

sine, square, triangle, sawtooth, pulse and white noise

frequency

10uHz to 50MHz

output control

10mV to 2mV steps

Type

direct digital synthesis

update rate

210MHz

DAC resolution

14 bit

phase accumulator

48 bit

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9 Input channels

The two or three input channels are fully isolated from each other and earth. The two channels are controlled independently but sampled synchronously.

Each input channel may be selected to be:

direct

external shunt

external attenuator

If the external shunt option is selected, the data is scaled by the shunt value (entered under the relevant channel menu) and the units are displayed in Amps. Any resistor can be used as a shunt, or precision low inductance current shunts are available as accessories. Current transformers can be used if fitted with an appropriate burden resistor.

Note that the external shunt input polarity is reversed compared to that of the voltage input: ie the - input becomes non-inverting and the + input becomes inverting. This is so that the capacitance to

ground of the probe cable screen is driven with the lower source impedance in order to minimise errors at high frequency.

Note that some modes force the input channels to be voltage or current automatically, eg. the power meter defaults to channel 1 as voltage and channel 2 as current. This automatic selection can be overridden if required.

The input ranges have nominal full scale values set with a ratio of 1:10 from 3mV to 300V and a top range of 500V. This gives the following ranges:

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range

reference

nominal full scale

3mV

3.16mV

10mV

30mV

31.6mV

100mV

300mV

316mV

3.16V

10V

30V

31.6V

100V

300V

316V

500V

1000V

Because of slew rate limitations of the input amplifiers, the maximum input signal that can be accurately measured varies with frequency:

frequency

max input level

MHz

peak V

rms V

500

353.5

400

282.8

200

141.4

100

70.7

56.5

35.3

28.3

The input ranges may be selected manually, or by autoranging (default). The start range for autoranging may be selected if it is known that the signal will not be below a certain level.

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There is also an option to autorange ‘up only’ so that a test

may be carried out to find the highest range. Once the highest range has been determined, the range can be set to manual and the measurement made without losing any data due to range changing. Pressing the HOME key (or sending *TRG) restarts the autoranging from the selected minimum range.

When in an input channel menu, the ZERO key provides a quick way to lock and unlock the range. When no flashing box is visible in the input channel menu and autoranging is selected, pressing the ZERO key selects the range that the instrument is currently using and sets the autoranging to manual, thus locking the range and preventing further autoranging. Pressing the ZERO key again returns to full autoranging from the bottom range.

For most measurement functions full autoranging is the most suitable option but some applications, such as where transient events are occurring, are more reliable with manual ranging. Manual ranging (or up-only autoranging) is essential for low frequency measurements.

For measuring signals that are biased on a dc level (such as an amplifier operating on a single supply or the output of a dc PSU), ac coupling can be used. AC+DC coupling is the normal option and should be used where possible.

A scaling factor can be entered for each channel for use with attenuators such as x10 oscilloscope probes. A nominal value can be entered or the attenuation factor of the probe can be measured and the precise value entered. The measured voltage will be displayed after multiplication by the scale factor. The scale factor can be set automatically by pressing TRIG when in an input channel menu. For example, with a x10 oscilloscope probe on channel 1 input, a x1 probe on channel 2 input and both probes connected to the same voltage; press CH1 to

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invoke the input menu for channel 1 then press TRIG and the scale factor for channel 1 is computed so that channel 1 reads the same as channel 2. Note that when using external divider probes to increase the maximum input voltage it is important to use active probes if accurately measuring dc. This because the dc input impedance is different from the ac input impedance. When using passive probes the dc would read about 10% high.

If the channel has been set for use with an external shunt then the value of the shunt can be entered.

The secondary channel has a control to adjust the gain so that common mode rejection may be maximised when using oscilloscope probes.

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9.1 Trimming x10 oscilloscope probes

To minimise the loading effects at high frequencies, x10 oscilloscope probes can be used with NumetriQ. For optimum performance, the probes need to be trimmed to match the input capacitance of the instrument and the probes need to be corrected for gain errors. A small plastic screwdriver is provided with each probe for this purpose. In all, there are three processes that must be carried out to optimise the performance:

probe trim

probe scaling

Connect the instrument output across a convenient resistor (anything above 1k) using the supplied BNC to crocodile clip output lead. Connect the probes from the input channels across the resistor. Observe the colour of which probe connects to each of the four input terminals for future use.

Press OUT and set the generator to 1kHz squarewave with 2V amplitude. Press HARM to invoke harmonic analyser mode and select third harmonic. Set all probes to x1.

To trim the probes connected to the main inputs.

The measured third harmonic should read 33.33% +/-

0.05%. Select x10 on one of the probes and adjust the trimmer in the body of the probe until the third harmonic again reads the same value. Switch the probe back to x1 and verify that the third harmonic reads the same. Repeat the adjustment if necessary. Select x10 on the other probe and adjust in the same way. To verify the adjustment at higher frequency, select the 25th harmonic for measurement. The reading should be 4.00% +/-0.5% in both x1 and x10 settings.

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To adjust for the tolerance within the probes (typically 1%), the main inputs can be scaled and the secondary inputs can be adjusted. Press OUT and set 1kHz sinewave, 2V amplitude; and press FRA to invoke frequency response analyser.

To adjust for tolerance within the probes connected to the main inputs:

With both probes set to x1 check that the measured magnitudes are about the same. Set the probe connected to CH1 to x10 and set the probe connected to CH2 to x1. Press CH1 then TRIG – the scaling factor for channel 1 will be automatically adjusted to a number about 10. Press HOME to exit the menu and observe that the readings for CH1 and CH2 are again about the same.

Set the probe connected to CH1 to x1 and set the probe connected to CH2 to x10. Press CH2 then TRIG – the scaling factor for channel 2 will be automatically adjusted to a number about 10. Press HOME to exit the menu and observe that the readings for CH1 and CH2 are again about the same.

If you have a three channel instrument set the probe connected to CH1 to x1 and set the probe connected to CH2 to x10. Press CH2 then RIGHT to access the CH3 menu. Press TRIG and the scaling factor for channel 3 will be automatically adjusted to a number about 10. Press HOME to exit the menu and observe that the readings for CH1 and CH3 are again about the same.

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10 True RMS Voltmeter

The RMS voltmeter measures the total rms of the signal present at the input terminals to the bandwidth of the instrument (>1MHz). Care must be taken when measuring low signal levels to minimise noise pick on the input leads.

The RMS voltmeter measures the elementary values:

rms

peak

surge

mean And derives the values: ac, dBm, crest factor and form factor.

The rms value of a periodic waveform, v(), is given by:

2

rms =  [ 1/2



() d ]

For a sampled signal, the formula becomes:

i = n-1

rms =  [ 1/n



[i] ]

i = 0

Where n is the number of samples for an integral number of complete cycles of the input waveform.

These are fundamental definitions that are valid for all waveshapes. For a pure sinewave, the formulae equate to peak/2, but this cannot be applied to other waveshapes. NumetriQ computes the true rms value from the fundamental definition for sampled data.

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The dc present is given by:

2

dc = 1/2  v() d

For a sampled signal, the formula becomes:

i = n-1

dc = 1/n



v[i]

i = 0

Where n is the number of samples for an integral number of complete cycles of the input waveform.

Having computed the true rms and the dc component, the ac component can be derived from:

rms2 = ac2 + dc2 => ac2 = rms2 – dc2

The ac component is also expressed in dB referred to 1mW into 600 (dBm):

dBm = 20 log (Vac/Vref)

where Vref =  (1mW x 600)

or 20 log (Iac/Iref)

where Iref =  (1mW / 600)

The peak measurement is simply the value with the largest magnitude. Positive and negative peaks are independently filtered then the result with the largest magnitude is taken as the peak value.

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In order to measure surge conditions, the maximum instantaneous peak value (unfiltered) is also recorded. It is important that NumetriQ does not autorange while measuring surge – either set the range to manual or repeat the test with ranging set to up only. To reset the maximum, press START.

Crest factor is derived from the peak and rms:

cf = peak / rms

The rectified mean measurement is given by:

2

mean = 1/2  |v()| d

For a sampled signal, the formula becomes:

i = n-1

mean = 1/n

 |

v[i]|

i = 0

The mean is then normalised to give the same value as rms for a pure sinewave:

Normalised mean = mean x /22

Form factor is derived from the normalised mean and rms:

ff = mean / rms

The measurements are computed over rectangular windows with no gaps. The processing power of the DSP allows the measurements to be made in real time without missing any samples. In this way, the measured rms is a true value even if the signal is fluctuating. The only occasion when data is missed is when an autozero

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measurement is requested – this can be disabled in the SYSTEM OPTIONS menu if required.

The ZOOM function can be used to select any combination of up to four parameters from the display.

Note that the wideband nature of true rms measurements prevents the use of heterodyning so the frequency range of the measurement is limited to 5MHz. To minimise noise, there is a 100kHz filter applied by default. To obtain the full bandwidth press ACQU, highlight bandwidth and select “wide”.

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10.1 RMS voltmeter specification

DVM

Channels

2 or 3 fully isolated

Display

5 digits

measurement

true rms, ac, dc, dBm, peak, cf, surge.

Coupling

ac or ac+dc

frequency

DC to 5MHz (heterodyning not available)

ac coupling cut off

~1.5Hz (–3dB)

max input

500V peak

input ranges

*300mV, *1V, *3V, *10V, *= High Voltage Attenuator. 500V, 300V, 100V, 30V, 10V, 3V, 1V, 300mV, 100mV, 30mV, 10mV, 3mV

Ranging

full auto, up only, or manual

input impedance

1M // 30pF (exc. leads)

accuracy (ac)

0.075% range + 0.075% reading +

0.1mV <1kHz

above + 0.003%/kHz < 5MHz

accuracy (dc)

0.1% range + 0.1% reading + 0.5mV

CMRR (typical)

160dB @ 230V 50Hz 140dB @ 100V 1kHz 70dB @ 10V 1MHz

time constant

0.2s, 1.5s or 12s

Conditions:

23ºC +/- 5ºC ambient temperature

instrument allowed to warm up for 30 minutes

Sinewave

slow speed, normal filtering

ac+dc coupling

autoranging or manual ranging  1/3 range

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11 Frequency response analyser

NumetriQ measures the gain and phase of channel 2 relative to channel 1 using a discrete Fourier transform (DFT) algorithm at the fundamental frequency.

The DFT technique can measure phase as well as magnitude and is inherently good at rejecting noise – it is much more reliable than measuring the rms at one point relative to another point.

The circuit can be characterised by computing the gain and phase at a number of points over a frequency range. This gives results that show the transfer function of the circuit as a graph on the display.

The DFT analysis yields two components – in-phase and quadrature, or ‘a’ and ‘b’ values – from which the magnitude and phase can be derived.

Considering the components at the fundamental frequency:

The fundamental in-phase and quadrature values of a periodic waveform, v(), are given by:

2

a1 = 1/  v().cos() d

2

b1 = 1/  v().sin() d

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For a sampled signal, the formulae become:

i = n-1

a1 = 1/n



v[i].cos(2ci/n)

i = 0

i = n-1

b1 = 1/n



v[i].sin(2ci/n)

i = 0

Where n is the number of samples for an integral number of complete cycles of the input waveform, and c are the number of cycles.

Having computed the real and quadrature components, the magnitude and phase of each channel can be derived:

mag =  (a

+ b

)

 = tan-1(b1/a1)

The relative gain and phase of the circuitry under test at that particular frequency is derived from the real and quadrature components by vector division:

vector gain = (a + jb) {ch2} / (a + jb) {ch1}

gain = magnitude (vector gain)

phase = tan-1(b/a (vector gain))

The gain is usually quoted in dB:

dB = 20 log10(gain)

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To look at differences in gain from a nominal value, an offset gain can be applied either manually or by pressing ZERO.

Offset gain = measured dB – offset dB

The filtering is applied to the real and quadrature components individually, rather than the derived magnitude and phase values. This gives superior results as any noise contribution to the components would have random phase and therefore would be reduced by filtering.

NumetriQ can operate either in real time mode at a single frequency where the gain and phase are filtered and updated on the display; or it can sweep a range of frequencies and present the results as a table or graphs of gain and phase.

The frequency points to be measured are specified with three parameters:

number of steps

start frequency

end frequency NumetriQ computes a multiplying factor that it applies to the start frequency for the specified number of steps. Note that due to compound multiplication it is unlikely that the end frequency will be exactly that programmed. The frequency sweep is initiated by the START key, and when completed the data can be viewed as a table or graphs.

Following a sweep on a control loop, the gain and phase margins can be computed and displayed on the graph.

The window over which the measurements are computed is adjusted to give an integral number of cycles of the input waveform. In real time mode the results from each window are passed through a digital filter equivalent to a first order RC low pass filter; in sweep mode each result

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comprises a single window without any filtering unless repeat sweep is selected.

The top of the vertical axis for the graph is normally set to be the highest measured value during the sweep. The bottom of the vertical axis is normally either set to the lowest measured value or the result of the highest value less 20dB/decade of frequency. The vertical axis can be fixed to a manual scale using the menus.

The ZOOM function can be used to select up to four parameters from the display when in real time mode. It has no function following a sweep.

Following a sweep the GRAPH key selects between:

Graph of gain v frequency

Graph of phase v frequency

Graph of gain and phase v frequency If three channels are being used then the three graphs above are repeated for computation 2 (as selected in the main FRA menu).

Pressing HOME or TRIG restarts the real time measurement at the selected frequency.

Although it is most usual to use the NumetriQ generator when performing gain/phase analysis, there may be circumstances where this is impractical, for example measuring across a transformer under load. In this case, turn off the NumetriQ generator (OUT menu) and the frequency reference for the analysis is measured from channel 1. Provided that the signal is clean enough for an accurate frequency measurement (and for DFT analysis the frequency does need to be accurately known), then the gain and phase can be measured reliably.

When using an external frequency reference there can be no sweep function.

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11.2 Quick start guide to Feedback Loop Analysis

This section is aimed as a helpful guide to enable you to set up your PSM3750 with the aid of screenshots and instructions with respect to Feedback Loop Analysis.

Setting Input Channels to be used.

Action Result

Press ‘ACQU’ Acquisition Control Menu appears

Press ‘↓’ Flashing Red Box appears around the Input Channels

selection

Press ‘→’ Flashing Red Box appears around 2 channels / 3 channels

Press ‘↓’ Select 2 Channel Option

Press ‘ENTER’ 2 Channels have been selected as the Input

Press ‘HOME’ Flashing Red Box now disappears

Press ‘HOME’ Display returns to measurement window

*Depending on the actual measurements to be made it may also be necessary to Use the ‘↓’ key to step down the screen until the Flashing Red Box appears around the Speed Setting. Then select the desired speed from the drop down list. Press ‘ENTER’ then ‘HOME’ twice to return to the measurement window.

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Setting the Amplitude and Output to On.

Action Result

Press ‘OUT’ Output Control Menu appears

Press ‘↓’ 3 TIMES Flashing Red Box appears around the Amplitude Setting

Press ‘300m’ 300mv now appears in the Amplitude Option

Press ‘ENTER’ 300mv is selected as the Amplitude

Press ‘↓’ 7 TIMES Flashing Red Box appears around the Output Mode

Press ‘→’ Off, On, DC Only, options appear on screen

Press ‘↓’ Select ‘On’ option

Press ‘ENTER’ Output On is now selected

Press ‘HOME’ Flashing Red Box will now disappear

Press ‘HOME’ Display returns to measurement window

*Depending on the actual measurements to be made it may also be necessary to Use the ‘↓’ key to step down the screen until the Flashing Red Box appears around the Frequency Setting. Then type in the desired frequency. Press ‘ENTER’ then ‘HOME’ twice to return to the measurement window.

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Gain and Phase Margins: Enable / Disable

Action Result

Press ‘MODE’ Measurement Settings Control Menu appears

Press ‘↓’ 7 TIMES Flashing Red Box appears around the Gain / Phase

selection

Press ‘→’ Flashing Red Box appears around disabled / enabled options

Press ‘↓’ Select Enabled Option

Press ‘ENTER’ Enabled Option has now been selected for the Gain /

Phase margins

Press ‘HOME’ Flashing Red Box now disappears

Press ‘HOME’ Display returns to measurement window

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Setting Channels 1&2 Input Ranges & Coupling

Action Result

Press ‘CH 1’ Channel 1 Control Menu appears

Press ‘↓’ 5 TIMES Flashing Red Box appears around the Coupling selection

Press ‘→’ Flashing Red Box appears around ac+dc, ac options

Press ‘↓’ Select ac only

Press ‘ENTER’ Flashing Red Box appears around ac selection

Press ‘HOME’ Flashing Red Box now disappears and ac is selected

Press ‘HOME’ Display returns to measurement window

To change any of the other Input settings follow steps as above to enable the parameters to be amended

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Action Result

Press ‘CH 2’ Channel 2 Control Menu appears

Press ‘↓’ 5 TIMES Flashing Red Box appears around the Coupling selection

Press ‘→’ Flashing Red Box appears around ac+dc, ac options

Press ‘↓’ Select ac only

Press ‘ENTER’ Flashing Red Box appears around ac selection

Press ‘HOME’ Flashing Red Box now disappears and ac is selected

Press ‘HOME’ Display returns to measurement window

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Frequency Sweep Data Settings

Action Result

Press ‘SWEEP’ Frequency Sweep Control Menu appears

Press ‘↓’ Flashing Red Box appears around the Sweep Start selection

Sweep Start now requires setting

Press ‘100’ 100 now appears in the Sweep Start Option

Press ‘ENTER’ 100Hz has now been selected for the Frequency Sweep start

Point

Press ‘↓’ Flashing Red Box appears around Sweep End selection

Sweep End now requires setting

Press ‘250k’ 250k now appears in the Sweep End Option

Press ‘ENTER’ 250 KHz has now been selected for the Frequency Sweep end

Point

Press ‘↓’ Steps Option now selected

Steps for plotting Frequency now requires setting

Press ‘100’ 100 now appears in the Steps Option

Press ‘ENTER’ 100 Steps has now been selected for Frequency Plotting

Press ‘HOME’ Display returns to measurement window

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Perform Sweep and Review.

Action Result

Press ‘SWEEP’ Frequency Sweep Control Menu appears

Check Sweep data parameters (as Frequency Sweep screen )

Press ‘SWEEP’ Display returns to measurement screen

Press ‘START’ Frequency Sweep will begin

Press ‘GRAPH’ View all data from sweep, keep pressing Graph to view more

results

Press ‘TABLE’ View data from all plotting points

Press ‘REAL TIME’ Display returns to measurement window

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Screen Print Options.

Action Result

Press ‘COMMS’ Remote Settings Control Menu appears

Press ‘↓’ 5 TIMES Flashing Red Box appears around the Screen Print

selection

Press ‘→’ Flashing Red Box appears around disabled, RS232, USB memory stick

Press ‘↓’ Select ‘USB memory stick’ only

Press ‘HOME’ USB memory stick mode has now been selected for

screen prints

Press ‘HOME’ Display returns to measurement window

* The above description applies when the interface used is RS232. It may first be necessary to use the ‘↓’ & ‘→’ keys to select the required interface before following the above steps. The actual number of ‘↓’ key presses required depends on the interface selected.

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Frequency response analyser specification

Frequency response (gain/phase) analyser

frequency

10uHz to 50MHz (own generator) 20mHz to 5MHz (external source)

max input

500V peak

input ranges

*300mV, *1V, *3V, *10V, *= High Voltage Attenuator. 500V, 300V, 100V, 30V, 10V, 3V, 1V, 300mV, 100mV, 30mV, 10mV, 3mV

ranging

full auto, up only, or manual

input impedance

1M Ohm // 30pF (exc. leads)

magnitude accuracy

0.075% range + 0.075% reading + 50uV <10kHz

(auto)

as above + 0.0003%/kHz < 50MHz

(wide)

as above + 0.003%/kHz < 5MHz

gain accuracy

0.01 dB < 10kHz

(auto)

0.01 dB + 0.0001 dB/kHz < 5MHz

0.31 dB + 0.00004 dB/kHz < 50MHz

(wide)

0.01 dB + 0.001 dB/kHz < 5MHz

phase accuracy

0.025 < 10kHz

(auto)

0.05 + 0.00025/kHz < 50MHz

(wide)

0.025 + 0.002/kHz < 5MHz

CMRR (typical)

160dB @ 230V 50Hz 140dB @ 100V 1kHz 70dB @ 10V 1MHz

sweep step rate

1/20s, 1/3s or 2.5s (approx.)

Conditions:

23ºC +/- 5ºC ambient temperature

instrument allowed to warm up for 30 minutes

ac+dc coupling

autoranging or manual ranging  1/3 range

signals > 10mV

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12 Phase angle voltmeter (vector voltmeter)

A phase angle voltmeter (or vector voltmeter, or phase sensitive voltmeter) measures the signal at one input compared to the phase of the signal at a reference input. The results may be expressed as magnitude and phase, or as separate in-phase and quadrature components.

NumetriQ measures the in-phase and quadrature components at the fundamental frequency using DFT analysis as described in the section on frequency response analysis. CH2, the measurement input, is phase referred to CH1, the reference input. The individual components are filtered separately to minimise the effects of noise, which would have random phase and would therefore be filtered out. The true rms of the input signals is also computed.

CH1 and CH2 may be voltage inputs or may use external shunts.

From the phase referred fundamental components, (a + jb), the following results can be derived:

magnitude =  (a2 + b2)

phase = tan-1(b/a)

tan  = b/a

in-phase ratio = a2 / a1

LVDT (diff) = scale * a2 / a1

LVDT (ratio) = scale * (m1-m2) / (m1+m2)

Where a1 and a2 are the in-phase components, and m1 and m2 are the magnitudes, of the signals present at ch1 and ch2 respectively.

The parameter of interest is selected via the PAV or MODE menu. The frequency and phase are always displayed.

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A null meter display may be selected via the PAV menu to allow adjustment of a circuit for minimum phase or component. The parameter on the display depends on the selected component:

parameter

display

null meter

in-phase

quadrature

tan

magnitude

phase

rms

rms2

rms2/1

rms2/rms1

in-phase ratio

LVDT diff

LVDT

LVDT ratio

LVDT

The null meter may be manually ranged or will automatically range as the signal varies. When manually ranging, ZOOM+ and ZOOM- adjust the range by a decade.

There is a phase offset option that applies a vector rotation of a user selectable phase shift to the CH2 input data.

NumetriQ can operate either in real time mode at a single frequency where the measurements are filtered and updated on the display; or it can sweep a range of frequencies and present the results as a table or graphs. Before performing a sweep, the desired parameter must be selected.

The frequency points to be measured are specified with three parameters:

number of steps

start frequency

end frequency

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NumetriQ computes a multiplying factor that it applies to the start frequency for the specified number of steps. Note that due to compound multiplication it is unlikely that the end frequency will be exactly that programmed. The frequency sweep is initiated by the START key, and when completed the data can be viewed as a table or graphs or printed out.

The ZOOM function can be used to select up to four parameters from the display when in real time mode. It has no function following a sweep.

Although it is most usual to use the NumetriQ generator when making Phase Angle Voltmeter measurements, there may be circumstances where this is impractical, for example measuring LVDT displacement under actual circuit conditions. In this case, turn off the NumetriQ generator (OUT menu) and the frequency reference for the analysis is measured from channel 1. Provided that the signal is clean enough for an accurate frequency measurement (and for DFT analysis the frequency does need to be accurately known), then the measurements can be made reliably.

When using an external frequency reference there can be no sweep function.

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12.1 Phase angle voltmeter specification

Phase angle voltmeter (vector voltmeter)

frequency

10uHz to 50MHz (own generator) 20mHz to 5MHz (external source)

measurement type

DFT analysis, and true rms

measurements

Magnitude, Phase, In-Phase & Quadrature components, TanΦ, InPhase Ratio, LVDT (diff), LVDT (ratio), Rms, Rms Ratio

phase resolution

0.001

tanΦ resolution

0.0001

other

as FRA

Conditions:

23ºC +/- 5ºC ambient temperature

instrument allowed to warm up for 30 minutes

ac+dc coupling

autoranging or manual ranging  1/3 range

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13 Power meter

The power meter measures the total power and fundamental power of the signal present at the input terminals to the bandwidth of the instrument (>1MHz). Above 5MHz, only the fundamentals are measured.

One of the inputs must be configured as an external shunt input. The external shunt may be a simple resistor or dedicated high frequency precision shunts are available as accessories. Current transformers and clamps may be used if fitted with a suitable burden resistor. For use at mains voltages, a mains power adaptor incorporating voltage and current transformers is available.

The power meter will operate either from its own generator or, more normally, will use the frequency measured on channel 1 (usually voltage).

The power meter measures the elementary values:

V rms

A rms

V fundamental (in-phase and quadrature)

A fundamental (in-phase and quadrature)

V dc

A dc

V harmonic (in-phase and quadrature)

A harmonic (in-phase and quadrature)

frequency

and derives the following values: V & A fundamental magnitude

VA (true and fundamental)

power factor (true and fundamental)

fundamental W

harmonic W

phase shift

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When the integrator function is activated, the following values are available:

Elapsed time (in hours, minutes and seconds)

Watt-hours (true and fundamental)

VA hours (true and fundamental)

average power factor (true and fundamental)

Ampere hours (true and fundamental)

The power dissipated in a load subjected to a periodic voltage, v(), with a current flowing a(), is given by:

2

w = 1/2  v().a() d

For a sampled signal, the formula becomes:

i = n-1

w = 1/n



v[i].a[i]

i = 0

Where n is the number of samples for an integral number of complete cycles of the input waveform.

These are elementary definitions that are valid for all waveshapes. NumetriQ computes the true watts value from the elementary definition for sampled data. Formulae for the components at the fundamental frequency are given in the section on frequency response analysis; formulae for the harmonic components are given in the section on harmonic analysis.

The formulae for the derived results are:

VA = V

rms

x A

rms

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power factor = Watts/VA

fundamental Watts = V

real

x A

real

+ V

quad

x A

quad

harmonic Watts = VH

real

x AH

real

+ VH

quad

x AH

quad

fundamental VA = V

fund

x A

fund

fund power factor = W

fund

/ VA

fund

In power meter mode, the UP and DOWN key do not adjust the amplitude but step the harmonic number.

The measurements are computed over rectangular windows with no gaps. The processing power of the DSP allows the measurements to be made in real time without missing any samples. In this way, the measured power is a true value even if the signal is fluctuating. The only occasion when data is missed is when an autozero measurement is requested – this can be disabled in the SYSTEM OPTIONS menu.

The high linearity of NumetriQ allows real-time measurements be made on waveforms with periodic bursts

such as low standby power PSUs. Use “autorange up” to

find the range.

NumetriQ blanks the results when either of the measured rms signals are low compared to the full scale range. This function can be disabled if desired in the SYSTEM menu.

The ZOOM function can be used to select any combination of up to four parameters from the display.

The integrator is started, or reset, by pressing the START key. The Watt hour integration and the Ampere hour integration can be selected to be signed or magnitude. To integrate the total power in terms of heating effect, choose magnitude. If signed integration is selected then the rms current is given the sign of the power before integration. The Ampere hours and Watt hours then reflect the power

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taken by the load, less any power generated by the load, such as during regenerative braking in battery systems.

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13.1 Power meter specification

Power meter

current input

External shunt or Voltage CT

display

5 digits

measurement

W, VA, PF,V,A, - Total, Fundamental and Integrated, Power Harmonics

coupling

AC+DC, AC(<10VDC), AC(<500VDC)

frequency

DC & 10mHZ to 5MHz 5MHz to 50MHz (fundamentals only)

ac coupling cut off

~1.5Hz (–3dB)

max input

500V peak

input ranges

300mv* 1v* 3v* 10v* *=High Voltage Attenuator: 500V, 300V, 100V, 30V, 10V, 3V, 1V, 300mV, 100mV, 30mV, 10mV, 3mV

ranging

Full Auto, Up Only, or Manual

input impedance

1M Ohm

accuracy (ac)

0.1% range + 0.1% reading +external shunt tolerance

accuracy (dc)

0.2% range + 0.2% reading

CMRR (typical)

160dB @ 230V 50Hz 140dB @ 100V 1kHz 70dB @ 10V 1MHz

time constant

0.2s, 1.5s or 12s

Conditions:

23ºC +/- 5ºC ambient temperature

instrument allowed to warm up for 30 minutes

sinewave, power factor > 0.7

slow speed, normal filtering

ac+dc coupling

autoranging or manual ranging  1/3 range

tolerance of current shunt to be added

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14 LCR meter

In LCR meter mode, channel 1 measures the voltage across the component under test, and channel 2 measures the current through it. To measure the current, channel 2 must be connected across an appropriate external shunt.

The easiest way to use the LCR meter is with the ‘IAI – impedance analyser interface’ (see accessories) that sits under the NumetriQ and provides 4 wire Kelvin clip connections to the component under test. The IAI provides a choice of four shunts, selectable from the front panel, and buffers the signals to minimise the effects of stray capacitance and inductance.

Measurements can be made without the IAI by simply connecting a series shunt. The shunt chosen must be appropriate for the voltage, the current and the frequency of operation.

There are three manual connection options, “shunt”, “divider Zx low”, “divider Zx high”.

CH2 Zs +

GEN

+ CH1 Zx

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For “shunt” connection, shown above, the current is measured directly across the shunt using CH2 while the voltage across the Zx is measured by CH1. Notice that the positive inputs to both CH1 and CH2 are connected to the midpoint to minimise common mode loading effects.

Then : Zx = Zs x CH1 / CH2

+ + GEN CH1

- + CH2 Zx

For “divider Zx low” connection, shown above, the total voltage is measured by CH1 and the voltage arising from the potential divider effect of Zs and Zx is measured by CH2. Notice that all the negative terminals are connected together.

Then: Zx = Zs / ((CH1 / CH2) – 1)

The connections for “divider Zx high” are the same as

above but with Zx in the high arm of the potential divider and the shunt in the low arm.

Then: Zx = Zs x ((CH1 / CH2) – 1)

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NumetriQ measures the real and imaginary components at the fundamental frequency using DFT analysis as described in the section on gain/phase analysis. The frequency may be taken from its own generator or from the circuitry under test.

From the fundamental components of voltage, (a + jb), and those of the current, (c + jd), NumetriQ computes the complex impedance given by:

z = v / i

= (a + jb) / (c + jd)

The components of the complex impedance are filtered independently to minimise the effects of noise, which would have random phase and would therefore be filtered out.

The magnitude of the voltage and current are also computed.

From the complex impedance the following parameters can be derived:

ac resistance

inductance,

capacitance

impedance

phase

tan (= real/imaginary)

Q factor (= imaginary/real)

Values are displayed for both series and parallel configurations.

Optionally, the values can be expressed as admittance, conductance, and susceptance instead of impedance, resistance and reactance.

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If the parameter option in LCR menu is set to ‘auto’, NumetriQ will display capacitance or inductance according to the phase of the measurement. Alternatively, the display can be forced to capacitance, inductance or impedance.

Capacitance is displayed with tan, inductance is displayed with Q factor, and impedance is displayed in its resistive + reactive form and as magnitude. The phase of the impedance is displayed with all options.

The operating conditions for the component under test may be selected manually or NumetriQ will automatically try to find appropriate conditions.

When measuring large electrolytic capacitors, it may be necessary to add an appropriate bias voltage to polarise the electrodes. In this case it may be necessary to select ac coupling in the CH1 menu in order to reliably measure the small ac voltage present.

When measuring small inductance or capacitance, it may be necessary to zero out the stray effects from the test connections. Press ZERO to access the compensation menu. For inductance connect together the test leads to a good short and select “short circuit” – the message ‘SHORT CIRCUIT ZERO SET’ will be displayed; for capacitance disconnect the test leads and press ZERO – the message ‘OPEN CIRCUIT ZERO SET’ will be displayed. To remove the zero, press ZERO then press DELETE within

1.5s – the message ‘ZERO CLEARED’ will be displayed.

For repeated measurements under the same test conditions (eg. production testing of a batch of capacitors) it is possible to compensate for the inherent phase shift of the connection jig. Connect a known reference component to the system, enter the known phase shift of the component as the “phase reference” in the ZERO menu

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and select “phase adjust”. NumetriQ then applies a compensating vector rotation to all subsequent measurements.

The frequency points to be measured are specified with three parameters:

number of steps

start frequency

end frequency

Very good results can be obtained in a reasonable time using the medium speed setting (e.g. 50 points x ~1/3s  17s); for the very best results, use the slow setting (50 points x ~2.5s  125s or 2 minutes, 5 seconds).

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The ZOOM function can be used to select up to four parameters from the display when in real time mode. It has no function following a sweep.

Although it is most usual to use the NumetriQ generator when performing LCR measurements, there may be circumstances where this is impractical, for example measuring the inductance of a transformer primary winding under load. In this case, turn off the NumetriQ generator (OUT menu) and the frequency reference for the analysis is measured from channel 1. Provided that the signal is clean enough for an accurate frequency measurement (and for DFT analysis the frequency does need to be accurately known), then the measurements can be made reliably.

When using an external frequency reference there can be no sweep function.

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14.1 Nyquist Diagram

The PSM3750 can display impedance on either Bode or Nyquist plots. The Nyquist plot separates the Real and Imaginary components of impedance on an X-Y plot.

To display a Nyquist plot, the PSM must be in LCR meter mode with the measurement parameter set to impedance as shown below:

There two plotting parameters specific to the Nyquist plot:

 Invert Nyquist

o When enabled, this option inverts the Y (Im)

axis on the Nyquist plot.

 Nyquist Origins

o When enabled, vertical and horizontal dashed

lines will indicate the zero point on both the X and the Y-axis (when zero falls within the autoscale range).

Note: Invert Nyquist is enabled by default.

While in LCR mode, begin a sweep by pressing the START key and then repeatedly press the GRAPH key to toggle through the graphing options until Nyquist is displayed.

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The axes are scaled to fit the sweep and a cursor is automatically displayed. The directional keys on the PSM’s front panel can be used to navigate the cursor.

The following parameters are shown for the sweep step and are all updated by movement of the cursor:

1. Sweep step number

2. Frequency

3. Imaginary component of impedance

4. Real component of impedance

2 1 3

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14.2 LCR meter specification

LCR meter

frequency

10uHz to 50MHz (own generator) 20mHz to 50MHz (external source)

measurement type

DFT analysis

measurements

L, C, R (ac), Q, tan, impedance, phase, admittance series or parallel circuit

conditions

auto, or manual

display

numeric values table of sweep results graph of any measurement Nyquist (Impedance only)

ranges (with external shunt)

100pF to 100uf 1H to 100H 1 to 1M

ranges (with IAI2)

1pF to 1000uF 10nH to 10kH 1m to 500M

basic accuracy

0.1% + tolerance of Shunt

sweep step rate

1/20s, 1/3s or 2.5s (approx.)

Conditions:

23ºC +/- 5ºC ambient temperature

instrument allowed to warm up for 30 minutes

ac+dc coupling

autoranging or manual ranging  1/3 range

using impedance interface adaptor

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15 Harmonic analyser

The NumetriQ harmonic analyser computes multiple DFTs on the input waveforms in real time (refer to the chapter on frequency response analysis for the formulae for DFT analysis).

There are three modes of operation: single harmonic, difference thd, and series thd. In single harmonic mode, the specified harmonic is displayed both in Volts and as a ratio to the fundamental; in either thd mode, the computed thd and a specified harmonic are displayed as a ratio to the fundamental.

In difference thd mode, the thd is computed from the rms and fundamental:

thd = 1/h1 √ ( rms

² - h1²)

In series thd mode, the thd is computed from a series of up to 64 harmonics.

i = n

thd = 1/h1 √

 h

² where hi is the ith harmonic

i = 2

In series mode the magnitude and phase of all the harmonics can be seen as a table or the magnitudes can be displayed as a bargraph which changes in real time with the measurements. When viewing the bargraph, ZOOM+ and ZOOM- change the vertical axis by a factor of 10.

In all cases the harmonics are phase referred to CH1 fundamental so that their in-phase and quadrature components may be separately filtered to minimise noise.

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The single harmonic and the thd are expressed relative to the fundamental either as a percentage or in dB, as selected via the HARM menu.

The frequency points to be measured are specified with three parameters:

number of steps

start frequency

The ZOOM function can be used to select up to four parameters from the display when in real time mode. It has no function following a sweep.

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Although it is most usual to use the NumetriQ generator when making harmonic measurements, there may be circumstances where this is impractical, for example measuring harmonic currents drawn from the mains. In this case, turn off the NumetriQ generator (OUT menu) and the frequency reference for the analysis is measured from channel 1. Provided that the signal is clean enough for an accurate frequency measurement (and for DFT analysis the frequency does need to be accurately known), then the measurements can be made reliably.

When using an external frequency reference there can be no sweep function.

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15.1 Harmonic analyser specification

Harmonic analyser

fundamental frequency

20mHz to 50MHz (own generator) 20mHz to 5MHz (external source)

harmonic frequency

10uHz to 1MHz

measurement type

multiple DFT analysis

measurements

single harmonic, differential thd, thd by series of harmonics

max harmonic

100

max input

10V peak

input ranges

10V*, 3V*, 1V*, 300mV* *= High Voltage Attenuator. 500V, 300V, 100V, 30V, 10V, 3V, 1V, 300mv, 100mV, 30mV, 10mV, 3mV.

ranging

full auto, up only, or manual

input impedance

1M // 30pF (exc. leads)

magnitude accuracy

0.1% of fundamental + 0.01mV + accuracy of fundamental

sweep step rate

1/20s, 1/3s or 2.5s (approx.)

Conditions:

23ºC +/- 5ºC ambient temperature

instrument allowed to warm up for 30 minutes

ac+dc coupling

autoranging or manual ranging  1/3 range

Newtons4th PSM3750 NumetriQ User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual