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1. 2004 Voltech Instruments All rights reserved VOLTECHNOTES Low POWER MEASUREMENTS SET UP Ss Voltech PM3000ACE aint Ams Auto saco INT eEXT MEAN OT sc aa On the Voltech PM100 i d lanni E a n the Voltec a special long averaging mode is a eo A i i e Samples at 200kHz to ensure no loss of data Ai a E e Continuously averages all results together to constantly M and display the averaged measurements aca e Allows the user to select an appropriate averaging time Displays all results including volts amps watts and harmonics PM100 Example An ac power supply is equipped with a low power standby mode In this mode current is drawn from the supply in bursts that occur every 300ms or so The wave form is shown below A measurement of the average input power is required to check the rating of the Current mA 800 Time 4 seconds power supply With default settings the PM100 makes measurements at high speed and updates the display approximately every 2 second With the waveform above the measurements are not stable and the analyzer pauses while it auto ranges inbe 2004 Voltech Instruments All rights reserved Low Power MEASUREMENTS VOLTECHNOTES 2000 200 1000 100 50 i eadings 100 10 50 5 0 20 stable R measurements follow this procedure 10 1 0 5 0 5 2 asure the peak current 0 4 EN al power on mode press the A key and then the PEAK key Amps2. VOLTECHNOTES Voltech Instruments Ltd 148 Sixth Street Harwell International Business Centre Didcot Oxon OX11 ORA UK Telephone 44 0 1235 834555 Facsimile 44 0 1235 835016 E mail sales voltech co uk Voltech Instruments Inc 11637 Kelly Road Suite 306 Fort Myers FL 33908 USA Telephone 1 239 437 0494 Facsimile 1 239 437 3841 E mail sales voltech com www voltech com Note While every care has been taken in compiling the information for this publication Voltech Instruments cannot accept legal liabil ity for any inaccuracies Voltech Instruments reserves the right to alter product specifications without notice and whenever necessary to ensure optimum performance from its product range VPN 104 054 1
3. mode where less than 1W of 50 consumed What value of external shunt should be used to make accu 1 0 surements with a standard Voltech power analyzer an external shunt V ac the current will be aur 1W 110V 9 09mA at a power factor of 1 Let us say that the minimum current to be measured is 5mA which allows some margin for other products and voltages b The minimum recommended external shunt voltage input of the PM3000ACE is 6 25mV Minimum resistive shunt value is 6 25mV 5mA 1 25Q Choose a readily available 0 1 tolerance resistor 10Q c Connect the analyzer to the equipment under test EUT as shown below eee Consult the product Scaling user manual for safety 10 Volts Amp information Voltech Power Analyzer 2004 Voltech Instruments All rights reserved Vo ia d 045 INLONE Low Power MEASUREMENTS mas SETUP AUTO e AC0C INT A Voltech breakout box may be used to simplify the power connections if required EXT d Next and on the front panel of the PM100 or PM3000ACE select External a Shunt as the current input and enter the scale factor A Sahm Bho cbc at e 10 Volts Amp for the PM100 and 800 for the PM3000ACE ss O G user manual for details e The power analyzer is now ready to make accurate low current measurements A convenient way of connecting an external shunt resistor is to purchase a ready made assembly such as that shown below Fo
4. VOLTECHNOTES Standby and Low Power Measurements VPN 104 054 1 Low PowER MEASUREMENTS Introduction Voltech power analyzers provide a comprehensive range of accurate measuring instru ments for voltage current and all power parameters Each instrument features fully isolated floating inputs for the easy and safe connection of the ac power to be measured Accuracy of the measurements is guaranteed over the following broad ranges Model Current Range Voltage Range ms peak firms 20mA to 20A 200A 2V to 700V 1000V PM3000ACE 90mA to 30A 200A 0 5V to 1000V 150V The measuring ranges of the analyzers may be extended both higher and lower using readily available transformers and other transducers For high power measurements current transformers such as the Voltech CL100 CT1000 and CL3000 100 1000 and 3000A are ideal for many applications Voltech high current transducers 2004 Voltech Instruments All rights reserved Low POWER MEASUREMENTS Vfo Ha i 107 INON 2000 JU 1000 100 500 50 20 200 schnical note discusses how Voltech power analyzers may be used to 100 50 his a measure the relatively small current and power quantities found when ac line 2 20 10 owe equipment is Operating in a standby mode s 0 5 Tech 1 0 5 al Challenges a is increasing legislative and consumer pressure to minimize the standby as power consumption of common domestic a
5. nd office electrical equipment For example USA Presidential Executive Order 13221 requests that government agencies shall purchase products that use no more than one watt in their standby power consuming mode It is thus important to product design and test engineers to have the ability to accurately measure ac power below one watt This can be more difficult than it would first appear for two main reasons 1 Dynamic Range If the range and accuracy of the measuring instrument and its current transduc ers are not carefully considered the measurement may be inaccurate or obscured by noise For example a clamp on power meter rated to 100A is used to measure 10mA In this case the reading is 1 10000 full scale of the meter The current clamp designed for 100A will introduce very significant measurement errors and may not register a current at all To make accurate low power measurements the current transducer should be appropriate to the level of current being measured and matched to the abilities of the power meter 2 Burst Mode Standby The switching power supplies found inside most domestic office and industrial equipment will often draw greater than 1 Watt just to supply their own control circuits To minimize consumption at no load various techniques are applied that shut down the power supply controller for intermittent periods Terms used are 2004 Voltech Instruments All rights reserved VOLTECHNOTES Lo
6. peak will be displayed In this example the maximum reading was approximately mA _750mA 2 Set up a fixed current range Press MENU 1 and then 4 until you see MANUAL A RANGE X xk and then enter the nominal peak current ignoring the sign PEAK CURRENT gt 0 750 lt 3 Now set up long averaging in MENU 2 LONG AVERAGING X xk The averaging time should include several cycles of operation of the equipment Equipment Cycle Time Long Averaging Time lt 1 sec Power supply in low power 10 sec standby mode Signs message boards 100 sec oscillating fan 10 60 sec Soldering iron Washing machine 300 sec Integrator 2004 Voltech Instruments All rights reserved VOLTECHNOTES Low POWER MEASUREMENTS o E D TA CA In this case the power supply current seems to vary over a two second period RT i i eEXT MEAN en AC EXT Choose 20 seconds for the averaging time This can be increased later if the m MENUS ee measurements are not stable AVERAGING TIME WIRING gt 20 0 lt Ty a a Ser Press MENU again and the analyzer will now begin to make measur enmep s ia red PROG LED will flash to indicate that the PM100 is in long averaging mode All measurements are stable reliable accurate and continuously updated Conclusion 1 Accurate stable and reliable measurements of electrical equipment that is operating in a standby mode differ
7. r improved accuracy and frequency response non inductive and four terminal Kelvin connection shunts may be used Precision Resistor Co Inc www precisionresistor com PRC shunt shown fitted to a PM100 Special channels are not required 2004 Voltech Instruments All rights reserved Low PoweR MEASUREMENTS VOLTECHNOTES APK 200 E np on prob S designed specifically for low current measurements are also 20 Chauvin Arnoux E6N e 5mA to 1 5A e DC to 2kHz e Scale factor 1V A www chauvin arnoux com Note Consider also the maximum current that will be passed through the shunt or transducer When a resistive shunt is used consider its current and power rating I7R and fitting a fuse in series with the shunt This will protect the shunt from damage should an accidental over current occur Voltech power analyzers are fitted with over current devices which will protect them from damage in the majority of circumstances 2 Burst mode standby To overcome the problems encountered in measuring the time varying current and power in a stable fashion the power analyzer must make continuous measurements at a high sample rate over an extended period of time and display the averaged results Watt hour integration features may be used to do this but they are often processed at a lower sample rate and data especially that related to the dead period in between bursts may be lost This is not the case with the
8. s from normal power measurements in two ways a The low current of typically less than 10mA may be below the specified operating range of the analyzer As a result measurements will be inaccurate or even totally obscured by noise b The current may be drawn in bursts and that requires specific measurement techniques to provide reliable measurements 2 The low current range of Voltech power analyzers may be extended by using an appropriate current transducer It is not necessary to purchase special power analyzer models to measure low current and power 3 The long averaging and integration techniques of Voltech power analyzers may be used to provide burst power measurements that are accurate stable and repeatable 2004 Voltech Instruments All rights reserved Low Power MEASUREMENTS VOLTECHNOTES ir E g E 2000 200 1000 100 500 50 oo References 100 10 50 sch Technical Note Single Shunt Technology item number 104 114 20 ane 10 1 0 5 2 Ve ch Technical Note Kelvin Connections item number 104 104 1 0 1 0 0 0 5 3 Voltech Technical Note Back to Basics AC Theory item number 104 109 4 PM100 300 User Manual item number 98 052 5 EU Energy Efficiency Initiative http energyefficiency jrc cec eu int All Voltech items are available free of charge from your Voltech supplier or from our website at www voltech com 2004 Voltech Instruments All rights reserved
9. w Power MEASUREMENTS SET UP AUTO AC OL INT AMS iC gees e EXI eNEAN N PAL burst mode and skip cycle amongst others The effect on the input is that intermittent bursts of current and power are drawn from the line Significant current may still be drawn in the dead period he are regular and repetitive but may vary with line voltage load etc and are not WIRING crystal controlled ae g Current mA 800 Time 4 seconds When current and power is drawn in bursts like this from the ac supply power meters will attempt to track the variations and will often only provide a varying and inconsistent power measurement that is not definitive Voltech Solution 1 Dynamic Range Voltech power analyzers are equipped with an external shunt input that may be connected to any suitable external shunt or current transducer By entering a scale factor into the analyzer the correct current and power quantities can then be displayed and transferred over the communication interfaces Notice that it is not necessary to purchase an expensive special model power analyzer the standard models are capable of measurements from micro amps to mega amps as long as an appropriate transducer is used 2004 Voltech Instruments All rights reserved Low PoweR MEASUREMENTS VOLTECHNOTES VPK 2000 200 1000 100 500 50 200 100 10 laser eater is designed to have a standby
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