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Measurement Tutorial

3

Keysight U2741A User’s Guide

49

Noise Rejection

Rejecting power-line noise voltages

An important property of integrating analog-to-digital (A/D) converters is their 

ability to reject power-line related noise that is present on the DC input signals. 

This is called normal mode noise rejection, or NMR. The digital multimeter 

achieves NMR by measuring the average DC input by “integrating” it over an 

integral number of power line cycles.

Common mode rejection (CMR)

Ideally, a digital multimeter is completely isolated from earth-referenced circuits. 

However, there is a finite resistance between the digital multimeter's input LO 

terminal and earth ground, as shown below. This can cause errors when 

measuring low voltages that are floating in relative to earth ground.

Figure 3-1

Common mode source error

V

f

 = Float Voltage

R

s

 = DUT Source Resistance Imbalance

R

i

 = digital multimeter Isolation Resistance 

C

i

 = digital multimeter Input Capacitance 

Error (v) = 

R

s

 + R

i

V

f

R

i

R

s

 

C

i

LO

HI

Ideal

Meter

V

test

V

f

 x R

s

(LO-Earth)

Содержание U2741A

Страница 1: ...Keysight U2741A USB Modular 5 5 Digits Digital Multimeter User s Guide Test Equipment Depot 800 517 8431 99 Washington Street Melrose MA 02176 TestEquipmentDepot com ...

Страница 2: ... commercial computer software or commercial computer software documentation No additional government requirements beyond those set forth in the EULA shall apply except to the extent that those terms rights or licenses are explicitly required from all providers of commercial computer software pursuant to the FAR and the DFARS and are set forth specifically in writing elsewhere in the EULA Keysight ...

Страница 3: ...ng current Caution risk of electric shock Three phase alternating current Caution risk of danger refer to this manual for specific Warning or Caution information Earth ground terminal Caution hot surface Protective earth ground terminal Out position of a bi stable push control Frame or chassis ground terminal In position of a bi stable push control Equipotentiality Category II 300 V overvoltage pr...

Страница 4: ...ce and application system power before connecting to the I O terminals When servicing the device use only the specified replacement parts Do not operate the device with the cover removed or loosened Use only the power adapter provided by the manufacturer to avoid any unexpected hazards CAUTION If the device is used in a manner not specified by the manufacturer the device protection may be impaired...

Страница 5: ...perature 0 C to 50 C Operating humidity 20 to 85 RH non condensing Storage temperature 20 C to 70 C Storage humidity 5 to 90 RH non condensing CAUTION The U2741A USB modular digital multimeter complies with the following safety and EMC requirements IEC 61010 1 2001 EN61010 1 2001 2nd Edition Canada CAN CSA C22 2 No 61010 1 04 USA ANSI UL 61010 1 2004 IEC 61326 2002 EN 61326 1997 A1 1998 A2 2001 A3...

Страница 6: ...ith the Australia EMC Framework regulations under the terms of the Radio Communication Act of 1992 ICES NMB 001 indicates that this ISM device complies with the Canadian ICES 001 Cet appareil ISM est conforme a la norme NMB 001 du Canada This instrument complies with the WEEE Directive 2002 96 EC marking requirement This affixed product label indicates that you must not discard this electrical or ...

Страница 7: ...t This affixed product label indicates that you must not discard this electrical or electronic product in domestic household waste Product category With reference to the equipment types in the WEEE directive Annex 1 this instrument is classified as a Monitoring and Control Instrument product The affixed product label is as shown below Do not dispose in domestic household waste ...

Страница 8: ...8 Keysight U2741A User s Guide THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK ...

Страница 9: ...d Introduction 16 Product at a Glance 17 Product outlook 17 Product Dimensions 19 Dimensions without bumpers 19 Dimensions with bumpers 20 Standard Shipped Items 21 Inspection and Maintenance 22 Initial inspection 22 Electrical check 22 General maintenance 23 Installation and Configuration 24 Instrument Configuration 25 55 Pin backplane connector pin configuration 25 Chassis installation 26 2 Oper...

Страница 10: ...nt State 40 Autozero 40 Ranging 41 Default Settings 42 Triggering the U2741A 43 System Related Operation 45 Error conditions 45 3 Measurement Tutorial DC Measurement Considerations 48 Noise Rejection 49 Resistance Measurement Considerations 52 AC Measurements 55 Other Primary Measurement Functions 57 Frequency measurement errors 57 DC current measurements 57 Other Sources of Measurement Error 59 4...

Страница 11: ...er s Guide 11 List of Figures Figure 1 1 55 pin backplane connector pin configuration 25 Figure 3 1 Common mode source error 49 Figure 3 2 Ground loop induced error 51 Figure 3 3 Burden voltage in current measurement 58 ...

Страница 12: ...12 Keysight U2741A User s Guide THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK ...

Страница 13: ...1 1 SSI connector pin description 25 Table 2 1 Default settings summary 42 Table 3 1 Thermoelectric voltage for dissimilar metals connections 48 Table 3 2 Power dissipation for various resistance ranges 54 Table 3 3 Waveform shapes and their parameters 55 ...

Страница 14: ...14 Keysight U2741A User s Guide THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK ...

Страница 15: ...gits Digital Multimeter User s Guide 15 1 Getting Started Introduction 16 Product at a Glance 17 Product Dimensions 19 Standard Shipped Items 21 Inspection and Maintenance 22 Installation and Configuration 24 Instrument Configuration 25 ...

Страница 16: ...USB modular instrument chassis U2741A can perform the following measurements DC Voltage AC Voltage DC Current AC Current Resistance Diode Test Continuity Test Temperature Frequency The U2741A is controlled remotely over a USB interface via the Keysight Measurement Manager KMM software The U2741A can also be programmed using the provided drivers or via SCPI commands in your customized application ...

Страница 17: ...Getting Started 1 Keysight U2741A User s Guide 17 Product at a Glance Product outlook Top view Bumpers ...

Страница 18: ...741A User s Guide Front view Rear view USB Indicator Power Indicator Fuse holder 4 wire Ω Lo Sense 4 wire Ω Hi Sense VOLT HI VOLT LO 55 pin backplane connector USB inlet Power inlet Fastening hole for USB cable with locking mechanism ...

Страница 19: ...Getting Started 1 Keysight U2741A User s Guide 19 Product Dimensions Dimensions without bumpers Top view Front view 105 00 mm 175 00 mm 11 50 mm 25 00 mm ...

Страница 20: ...1 Getting Started 20 Keysight U2741A User s Guide Dimensions with bumpers Top view Front view 180 00 mm 8 60 mm 117 00 mm 41 00 mm ...

Страница 21: ...2 V 2 A AC DC adapter Power cord Standard Test Lead USB Standard A to Mini B interface cable L Mount kit used with the modular instrument chassis Keysight Automation Ready CD ROM contains the Keysight IO Libraries Suite Keysight USB Modular Products and Systems Quick Start Guide Keysight USB Modular Products and Systems Product Reference DVD ROM Keysight Measurement Manager Quick Reference Card Ce...

Страница 22: ...ely The front of this manual contains the warranty information Keep the original packaging in case the U2741A has to be returned to Keysight in the future If you return the U2741A for service attach a tag identifying the owner and model number Also include a brief description of the problem Electrical check For verification procedures refer to Keysight U2741A USB Modular 5 5 Digits Digital Multime...

Страница 23: ...wer cord and I O cable from your device 2 Remove your module from the bumper casing 3 Shake out any dirt that may have accumulated on the module 4 Wipe your module with a dry cloth and install the bumper back in place NOTE Any repair that is not covered in your modular product manuals should only be performed by qualified personnel ...

Страница 24: ...by step instructions shown in the Keysight USB Modular Products and Systems Quick Start Guide to get started with the preparations and installations of your U2741A NOTE You need to install the IVI COM driver if you are going to use the U2741A with Keysight VEE Pro LabVIEW or Microsoft Visual Studio ...

Страница 25: ...tion GND NC GND TRIG4 nBPUB NC 11 GND NC TRIG3 GND CLK10M NC 10 GND NC GND TRIG5 GND NC 9 GND NC STAR_TRIG NC 8 TRIG2 GND GND NC ND TRIG6 GA2 NC 7 GND NC TRIG1 GND GA1 NC 6 GND NC GND TRIG7 GA0 NC 5 GND NC TRIG0 GND NC NC 4 GND VBUS GND 12 V 12 V 12 V 3 GND GND GND 12 V 12 V 12 V 2 GND USB_D USB_D GND 12 V 12 V 1 F E D C B A Table 1 1 SSI connector pin description SSI timing signal Functionality G...

Страница 26: ...741A module from the bumper casing 3 Use a Phillips screwdriver to fasten the L Mount kit to your U2741A module 4 Insert your U2741A module into the U2781A chassis with the 55 pin backplane connector positioned at the bottom of the module 5 Once you have slotted in the module tighten the screws of the L Mount kit to secure the connection CLK10M 10 MHz clock source STAR_TRIG Star trigger GA0 GA1 GA...

Страница 27: ...storing Instrument State 40 Default Settings 42 Triggering the U2741A 43 System Related Operation 45 This chapter contains the details on how to configure your U2741A USB modular digital multimeter to perform the various measurement functions either through the software front panel or by sending SCPI commands remotely via the USB interface ...

Страница 28: ...two LED indicators Refer to Chapter 1 Product outlook on page 17 Power indicator lights up once the U2741A is powered up It will blink if there is a system error USB indicator will only blink when there is data exchange activity between the U2741A and the PC You can control your U2741A via the KMM for U2741A or via SCPI commands sent through the USB interface from your own application programs The...

Страница 29: ...nctions from the front panel for each of the measurement functions Measuring DC voltage The DC voltage measurement function has the following features Five ranges to select 100 mV 1 V 10 V 100 V and 300 V or auto range Input impedance is 10 MΩ for all ranges typical Input protection is 300 V on all ranges HI terminal Make the connection as shown below DC Voltage Source ...

Страница 30: ...ation Select the DCV function and desired range A suitable range should be selected to give the best measurement resolution The reading is displayed and updated continuously SCPI commands The following example shows how to make a DC voltage measurement using SCPI commands MEASure VOLTage DC ...

Страница 31: ...est factor of a maximum of 5 1 full scale Input impedance is 1 MΩ 2 in parallel with less than 120 pF capacitance on all ranges Make the connection as shown below Keysight Measurement Manager operation Select the ACV function and desired range A suitable range should be selected to give the best measurement resolution The reading is displayed and updated continuously SCPI commands The following ex...

Страница 32: ...use is 2 A voltage rating 250 V on all ranges Make the connection as shown below Keysight Measurement Manager operation Select the DCI function and desired range A suitable range should be selected to give the best measurement resolution The reading is displayed and updated continuously SCPI commands The following example shows how to make a DC current measurement using SCPI commands MEASure CURRe...

Страница 33: ... Measures true rms value Make the connection as shown below Keysight Measurement Manager operation Select the ACI function and desired range A suitable range should be selected to give the best measurement resolution The reading is displayed and updated continuously SCPI commands The following example shows how to make an AC current measurement using SCPI commands MEASure CURRent AC AC Current Sou...

Страница 34: ... the following features Seven ranges to select 100 Ω 1 kΩ 10 kΩ 100 kΩ 1 MΩ 10 MΩ and 100 MΩ or auto range Supports two wire and four wire resistance measurement Open circuit voltage is limited to less than 4 5 V on all ranges The figure below shows a two wire resistance measurement connection Resistance Test Current ...

Страница 35: ... for two wire resistance measurement Select the 4 Wired Ω function and desired range for four wire resistance measurement A suitable range should be selected to give the best measurement resolution The reading is displayed and updated continuously SCPI commands The following example shows how to make a resistance measurement using SCPI commands Two wire MEASure RESistance Four wire MEASure FRESist...

Страница 36: ...unting technique as the measurement method Gate time can be set at 0 1 second or 1 second of the input signal Make the connection as shown below Keysight Measurement Manager operation Select the Freq function and desired range The reading is displayed and updated continuously SCPI commands The following example shows how to make a frequency measurement using SCPI commands MEASure FREQuency Frequen...

Страница 37: ...less than 4 5 V for all ranges Continuity threshold is fixed at 10 Ω Response time is 60 samples second Make the connection as shown below Keysight Measurement Manager operation Select the Cont function The reading is displayed and updated continuously SCPI commands The following example shows how to make a Continuity Test measurement using SCPI commands MEASure CONTinuity Open or closed circuit C...

Страница 38: ... circuit voltage is limited to less than 4 5 V for all ranges Response time is 60 samples second Make the connection as shown below Keysight Measurement Manager operation Select the Diode function The reading is displayed and updated continuously SCPI commands The following example shows how to make a Diode Test measurement using SCPI commands MEASure DIODe Forward bias ...

Страница 39: ...refer to Chapter 4 Characteristics and Specifications Measurements are in auto range for 5 kΩ thermistor probe Supports the thermistor Make the connection as shown below Keysight Measurement Manager operation Select the Temp function and the type of thermistor used The reading is displayed and updated continuously SCPI commands The following example shows how to make a temperature measurement usin...

Страница 40: ...onnects the input signal following each measurement and takes a zero reading It then subtracts the zero reading from the preceding reading This prevents offset voltages present on the digital multimeter s input circuitry from affecting measurement accuracy This is applicable to DC voltage DC current two wire ohms and temperature measurements only SCPI Commands The following commands are used to se...

Страница 41: ...the input signal is greater than the present range can measure the digital multimeter gives an overload indication 9 9E 37 from the remote interface For auto range the digital multimeter will give an overload indication 9 9E 37 if the input signal is greater than the highest measurement range The range is fixed for continuity tests 1 kΩ range and diode tests 1 VDC range with 1 mA current source ou...

Страница 42: ...Range AUTO AUTO Resolution 5 5 digits 5 5 digits Temperature Unit C User setting Trigger Operation Trigger Source Auto Trigger Auto Trigger System Related Operation Power Down Recall Disabled User Setting Stored States 0 10 Cleared No Change Reading Output Buffer Cleared Cleared Error Queue Cleared Cleared Power on Status Clear Enabled User Setting Status Registers Masks Transition Filter Cleared ...

Страница 43: ...e the trigger signal is always present When you place the U2741A in the wait for trigger state the trigger is issued immediately This is the default trigger source SCPI command The following command sets the trigger source to immediate TRIGger SOURce IMMediate Software bus triggering The bus trigger mode is initiated by sending a bus trigger command after selecting BUS as the trigger source SCPI c...

Страница 44: ...tiple modular units in the chassis SCPI command TRIGger SOURce STRG Synchronization Status This is to configure the synchronization of multiple units of U2741A slave only when used in the U2781A modular instrument chassis Only one master can be assigned at a time SCPI command CONFigure SSI NONE SLAVe Refer to the Keysight U2741A Programmer s Reference for complete description and syntax for these ...

Страница 45: ...rforming a self calibration routine and reading error conditions Error conditions A record of up to 20 errors can be stored in the U2741A s error queue Refer to the programming guide for more information on the error messages Keysight Measurement Manager Operation A message box will appear once an error occurs while operating the U2741A using the KMM ...

Страница 46: ...2 Operation and Features 46 Keysight U2741A User s Guide THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK ...

Страница 47: ...easurements 55 Other Primary Measurement Functions 57 Other Sources of Measurement Error 59 The Keysight U2741A is capable of making accurate measurements but in order to achieve the best accuracy you must take the necessary steps to eliminate potential measurement errors This chapter describes common errors found in measurements and gives suggestions to help you avoid or minimize these errors ...

Страница 48: ...ture You should take the necessary precautions to minimize thermocouple voltages and temperature variations in low level voltage measurements The best connections are formed using copper to copper crimped connections as the digital multimeter s input terminals are copper alloy The table below shows common thermoelectric voltages for connections between dissimilar metals Table 3 1 Thermoelectric vo...

Страница 49: ... over an integral number of power line cycles Common mode rejection CMR Ideally a digital multimeter is completely isolated from earth referenced circuits However there is a finite resistance between the digital multimeter s input LO terminal and earth ground as shown below This can cause errors when measuring low voltages that are floating in relative to earth ground Figure 3 1 Common mode source...

Страница 50: ...t leads will also induce error voltages Tie test leads securely when operating near magnetic fields Whenever possible use magnetic shielding materials or increase the distance from magnetic sources to minimize this error Noise caused by ground loops When measuring voltages in circuits where the digital multimeter and the device under test are both referenced to a common earth ground a ground loop ...

Страница 51: ...ing the input terminals If the digital multimeter must be earth referenced connect it and the device under test to the same common ground point Also connect the digital multimeter and device under test to the same electrical outlet whenever possible RL Lead Resistance Ri digital multimeter Isolation Vground Voltage Drop or Ground Bus RL Ri 10 GΩ Vground RL Vtest LO HI Meter Ideal Resistance ...

Страница 52: ...wire ohms the voltage drop across the resistor being measured is sensed internal to the digital multimeter Therefore test lead resistance is also measured For 4 wire ohms separate sense connections are required Since no current flows in the sense leads the resistance in these leads does not give a measurement error The errors mentioned earlier in this chapter for DC voltage measurements also apply...

Страница 53: ... wire resistance null value and the digital multimeter will subtract this value from the value of subsequent measurements Minimizing power dissipation effects When measuring resistors designed for temperature measurements or other resistive devices with large temperature coefficients be aware that the digital multimeter will dissipate some power in the device under test If power dissipation is a p...

Страница 54: ...ue to moisture absorption in insulating materials and dirty surface films Nylon and PVC are relatively poor insulators 109 Ω when compared to Polytetrafluoroethylene PTFE insulators 1013 Ω Leakage from nylon or PVC insulators can easily contribute a 0 1 error when measuring a 1 MΩ resistance in humid conditions Table 3 2 Power dissipation for various resistance ranges Range Test current DUT power ...

Страница 55: ...ional to the square of the voltage waveform This digital multimeter accurately measures true RMS voltage or current as long as the wave shape contains negligible energy above the instrument s effective bandwidth NOTE The U2741A uses the same techniques to measure true RMS voltage and true RMS current Table 3 3 Waveform shapes and their parameters Waveform shape Crest factor CF AC RMS AC DC RMS 2 V...

Страница 56: ... RMS measurement is desirable when you are measuring small AC signals in the presence of large DC offsets A good example is measuring AC ripples that are present in DC power supplies There are situations however where you might want to know the AC DC true RMS value You can determine this value by combining results from DC and AC measurements as shown below Equation 1 1 For the best AC noise reject...

Страница 57: ...en measuring slow signals The error is inversely proportional to frequency Measurement errors also occur if you attempt to measure the frequency of an input following a DC offset voltage change and therefore you must allow the digital multimeter s input to fully settle before making frequency measurements DC current measurements When you connect the digital multimeter in series with a test circuit...

Страница 58: ...ght U2741A User s Guide Figure 3 3 Burden voltage in current measurement Vb Rs LO HI R Ideal Meter Vs Error 100 Vb Vs Vs Source Voltage Rs DUT Source Resistance Vb digital multimeter Burden R digital multimeter Current Shunt Voltage ...

Страница 59: ...cted range Autoranging occurs at 10 down range and 120 up range of full scale This enables you to measure some inputs at full scale on one range and 10 of full scale on the next higher range In general the accuracy is better on the lower range for the highest accuracy select the lowest manual range possible for the measurement High voltage self heating errors If you apply more than 300 Vrms self h...

Страница 60: ...p create error voltages across any impedance in series with the digital multimeter s input For this reason you should apply low level AC voltages to the digital multimeter through shielded cables You should connect the shield to the input LO terminal Make sure the digital multimeter and the AC source are connected to the same electrical outlet whenever possible You should also minimize the area of...

Страница 61: ...Multimeter User s Guide 61 4 Characteristics and Specifications For the characteristics and specifications of the U2741A USB Modular 5 5 Digits Digital Multimeter refer to the datasheet at http literature cdn keysight com litweb pdf 5991 0042EN pdf ...

Страница 62: ...4 Characteristics and Specifications 62 Keysight U2741A User s Guide THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK ...

Страница 63: ...This information is subject to change without notice Always refer to the Keysight website for the latest revision Keysight Technologies 2008 2017 Edition 10 March 17 2017 Printed in Malaysia U2741 90001 ...

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