Application Note

From the Fluke Digital Library @ www.fluke.com/library

Over the last few years the significance of accurate electricalenergy calibration has become increasingly important. Withderegulation, increased competition and more crossnetwork power supply transactions, the need to makemore measurements, more frequently, and at a higherdegree of accuracy, has neverbeen more important. As a consequence, both suppliersand consumers of electricalenergy now need to know thatwhat they have distributed orreceived is exactly what wasexpected. As a result energymeter calibrations have, inmost countries, now become compulsory.

However, energy meter calibration has, until recently,been a task of bringing togethera complex array of test instruments, including voltageand current supplies, energyreference meters and pulsecomparators. This in itself notonly has a detrimental effect onthe uncertainty of the wholeenergy meter calibrationprocess, but is also a costly oneto introduce and maintain.

With this in mind Flukerecently introduced the 6100AElectrical Power Standard,‘Energy’ option.

This application note sets outto explain how the 6100A canbe used to accurately calibrateenergy meters without theneed for a multitude of testequipment, thereby loweringboth testing and maintenancecosts while also optimizing themeasurement uncertainties andaccuracy.

Using the 6100A Electrical Power Standardto calibrate energy meters

The basic energy metercalibration applicationCalibration of instruments thatmeasure energy is no differentto any other calibration. Theinstrument under test is suppliedwith a known quantity of theparameter being calibrated,and the instrument is interro-gated in order to ascertain thevalue of the parameter that ithas measured. This value isthen compared with the quantity supplied, and themeasurement error is calculated.

Electricity meters, almostwithout exception, use a tech-nique of generating pulses toindicate the amount of energythey have measured. Eachpulse represents a specificnumber of watt-hours (or VAhours, VAR hours etc). Thesepulses are transmitted from themeter in a number of differentways.

1. On older meters, energy isrecorded by counting thenumber of passes of a blackmark on the surface of a spin-ning metal disc.2. By a flashing LED3. As a direct electrical output(Typically TTL)4. Some of today’s newermeters will even include highlyadvanced reporting mechanismssuch as Ethernet or Bluetoothinterfaces.

Because meters are used tomeasure a wide range ofenergy, from watt-hours toGigawatt-hours, the pulsesgenerated can represent differentamounts of energy. Thisamount of energy is specifiedby the meter manufacturer, andis known as the meter constant(sometimes referred to as ‘k’).

Firstly, it is used to provide areliable source of traceability,and secondly, to measure theamount of energy actuallydelivered. The 6100A’s abilityto measure or calculate time,means that it already knowshow much energy it has delivered with a high degree ofaccuracy. The function of thereference meter, therefore,becomes redundant. In thistype of setup, the comparator isstill used, but with the 6100Anow generating the pulses,instead of the reference meter.To mimic the ‘K’ value of themeter under test., it is possibleto program the 6100A to generatea specific number of pulses, perunit of energy delivered. Thiscalibration setup is shown infigure 2.

Replacing the comparatorwith a 6100A

The 6100A’s ability to receive,count, and compare pulsesmeans that it can also performall of the functions of the comparator, effectively makingit redundant as well. The set-up for this is shown in figure 3.

2 Fluke Corporation Using the 6100A Electrical Power Standard to calibrate energy meters

For example, a specific metermay generate 100 pulses forevery kilowatt-hour measured,another may generate the samenumber of pulses per megawatt-hour measured. Whatever thecriteria, the calibration systemmust have the ability to havethis number set within itssystem in order that it can calculate the correct quantity ofenergy from the pulse count.

Energy meter calibrationmethods

Calibrations are typically performed by using a referencemeasurement technique. Aknown amount of energy issimultaneously supplied to areference meter and to the unitunder test (UUT). A readingfrom the reference meter is thencompared to a reading from theUUT and the error is calculated.Three separate pieces of calibration equipment are typically required to completethis task.1. An energy supply (a powersupply)2. A reference energy meter3. A device for counting pulsesfrom both the reference meterand the UUT, which then compares the two counts andgenerates an error indication.

The block diagram of thecalibration set-up is shown infigure 1.

In this setup, the 6100A is usedsimply as the energy supply(current supply and voltagesupply), and without the use ofany other functions availablewith the 6100A’s energy option.

However, the 6100A energyoption does enable the user toperform the calibration withoutthe necessity of using the energy reference meter and/orthe pulse comparator, therebyeffectively replacing the functionality of both instruments.

Replacing the referencemeter with a 6100A

The energy reference meterserves two main purposes.

Fig. 1 A typical energy meter calibration setup

Fig. 2 An energy meter calibration setup using a 6100A Electrical Power Standard

Replacing the referencemeter and the comparatorwith a 6100A

Having established that it caneffectively replace both thecomparator and the referencemeter, the 6100A can alsocombine both of these functionstogether, and so replace all ofthe other instruments required,thereby allowing it to performthe complete calibration processon its own. This more consoli-dated setup is shown in figure 4.

One such standard is IEC 61036.Standards around the worldvary considerably, as does theirimplementation and legalstatus. The waveshapes givenin figures 5, 6, 7 and 8 are allexamples specifically requiredby IEC 61036, and were allgenerated by a 6100A ElectricalPower Standard. The half waverectified signal, phase firedsignal and burst fire signal canall be generated on either thevoltage or current channels, butunder normal circumstanceswould usually be performedusing the latter. These wave-shapes are easily replicated onthe 6100A’s voltage or currentchannels.

The 6100A’s four testingmodes

When used to test, calibrate orverify energy meters, the6100A can be used in any oneof four testing modes. These are:

• Free running mode

• Counted/Timed mode

• Gated mode

• Energy packet mode (also known as Dose mode)

Each offer benefits specific tothe type of test being performed.

Fluke Corporation Using the 6100A Electrical Power Standard to calibrate energy meters 3

Fig. 3 The 6100A Electrical Power Standard eliminates the need for comparators in the calibration setup

Complex waveshapes - aunique 6100A attribute

In the applications alreadydescribed, there is a growingrequirement to verify or calibrate measurements undernon-sinusoidal conditions. Infact, various standards havebeen in place for a number ofyears which define testingtechniques for energy meters,and, in some cases, actuallyspecify detailed waveshapesthat are used for ‘type testing’(design qualification againststandards).

Fig. 4 Using a 6100A Electrical Power Standard to eliminate the comparator and reference meter, as well as a supply for both voltage and current

Free running mode

In free running mode, the6100A will not begin countingmeter pulses until the output(OPER)ate switch is turned on.Once the output switch isenabled, counting will continueindefinitely until the switch isonce again turned off.

In this mode no time constantsor energy criteria are specified.This is particularly useful formeter verification testing, as itquickly establishes the conditionof the energy meter.

Free running mode is alsouseful for carrying out creeptests or even simply to makeadjustments to a meter.

Fig. 5 Half-wave rectified signal Fig. 6 Phase fired signal

Fig. 7 Burst fire signal Fig. 8 Voltage dips and short interruptions

4 Fluke Corporation Using the 6100A Electrical Power Standard to calibrate energy meters

Fig. 9 Energy Counter/Timer mode configuration screen

Creep testing is when thevoltage coils of the energymeter are energized with therated voltage, but with nocurrent in any current coil. Thetest is performed over a specificperiod of time and, fundamen-tally, establishes how much themeter dial advances withoutany usage by the consumer.

This is easily done using the6100A’s basic setup user inter-face screens described on page6 of this application note.

Counted/Timed mode

When the 6100A is setup inCounted/Timed mode the usermust first enter or select datawithin three panels on the‘energy counter/time mode’screen before counting is initiated(see figure 9).

Firstly, a warm-up time canbe specified. This allows theuser to run the meter for auser-definable period of time,so that the energy meter canreach a suitable operating temperature, prior to testing.

Then, the test period criteriamust be selected. This panelincorporates three selection criteria:

1. Derivation

2. Duration

3. Pulse source

The selection made withinthe ‘Derivation’ drop downmenu determines the way the6100A delivers the energyrequired. This can be specifiedin either time, pulse counts, oras a measure of energy.

The ‘duration’ entry ismerely a length or period oftime, dependent upon theselection made within the‘Derivation’ drop down menu.This will be specified as eithera time in seconds, minutes orhours, a number of counts, orWatt hours (stated in eitherWatt hours, kilo Watt hours orMega Watt hours).

Having chosen the methodin which energy is delivered, apulse source must then bechosen. This will identify whichchannel, or channels, on the6100A are used to input thecounting pulses from theenergy meter. It is worth notingat this point that with six channels, the 6100A is alsocapable of testing multi-phaseenergy meters with multiplepulse outputs, as well as thosewith a single pulse output.

Finally, an ‘Energy GateIn/Out’ socket on the rear ofthe 6100A can be enabled andthen configured according tothe user’s requirements. Having enabled the ‘EnergyGate Out’ function, the operatorcan select the signal types aseither a signal consisting of alevel to the required durationor as a start and end pulse.This can also be either activehigh or low. Lastly, the sourceimpedance of the internal pull-up resistor can be specified aseither 150 Ω or 1 kΩ, to matchthe meter or monitoring system’sown source impedance. Thisshould be determined from theequipments own user manualprior to connecting to the 6100A.

Gated mode

In Gated mode the user has theopportunity to remotely activatethe 6100A’s output and countingcycle. This is achieved byapplying an ‘active’ signal tothe 6100A’s ‘Energy Gate In/OutConnector’ on the rear panel.This connector automaticallybecomes an input socket whenthe gated mode is selected.However, before testing canbegin, the parameters of the‘active’ signal being used mustfirst be configured within the6100A’s ‘Energy Gated ModeConfiguration’ screen (see figure10). Here, the signal type,active signal level and internalpull-up parameters must initiallybe set-up. Details on how to dothis can be found in the 6100Auser manual.

Having completed this process,the 6100A now requires theuser to enter the length of thetest period, in readiness toswitch either the output orcounting function on and offfrom an alternative piece of testequipment or system with‘active’ signal capability. Thiscould be a PC set up with theusers own dedicated softwareprogram, designed specificallyto give arbitrary time, energy orcount control of the 6100A.

Fluke Corporation Using the 6100A Electrical Power Standard to calibrate energy meters 5

Fig. 10 Energy Gated mode configuration screen

Energy packet mode

In energy packet mode, alsoknown as dose mode, thepower from the output terminalsis timed to deliver the requestedamount of energy to the meterunder test. This can be definedas either energy, counts or time.

However, unlike Counted/Timed mode, there is no warm-up period. This is advantageousto those wishing to eliminateinitial dial advance on themeter under test. Dial advanceis when both the referencemeter and meter under testadvances more than the meas-ured amount on the 6100A.This is perfectly normal andrepresents settling and warm-uptimes included in the test.Furthermore, please note thatwhen using the 6100A’s othermodes, the actual test durationand count to achieve the displayed result is perfectlyaccurate. In energy packetmode dial advance does notbecome an issue as there is nowarm-up period.

As with other modes, themode’s own configurationscreen must be setup prior totesting. See Figure 11.

The 6100A’s user interface and basic setup

The 6100A’s energy user inter-face can be accessed via thewaveform menu. Note: Ifaccessed directly from power-up,then the ‘Esc’ key on the key-board must be pressed first.Here, a softkey labeled ‘EnergyCounting’ can be found. Uponselecting this key, the usermust then configure the 6100Aaccording to his test setup. Thiscan be done by selecting thesoftkey ‘Configure Meter Constants’,which in turn accesses the‘Channel Configuration andMeter Constants’ screen (seefigure 12).

The first panel, ‘MUT Source’,determines which sockets onthe front panel of the 6100Aare being used as energy pulseinputs.

A number of different configu-rations can be setup in thispanel, from one to six singlephase meters, or even a singlepulse three phase meter (The‘Sum of Channel 1,2 and 3’check box).

Having identified the pulsesource channel(s), the usermust then select the referencesource. This will depend uponwhich circuit (as shown infigures 2, 3 and 4) the user haschosen to perform the tests. Ifthe 6100A’s internal referenceis being used, as shown infigure 4, the check box ‘MainOutput’ must be selected.Alternatively, if either an externalsingle phase or three phase,meter are utilized as a reference,then one of other five checkboxes must be selected, accordingto the test setup being used. Twosuch examples are shown infigures 1 and 3.

The ‘Meter Constant Base’drop-down menu allows usersto select any one of threemeter base units, dependingupon the meter being tested —Wh (Real power), VAh(Apparent power or VARh(Reactive power). Havingselected this, the meter constantsmust then be specified. Thismust be done for both the meterunder test, the external energyreference meter (if used) andfinally, the reference pulse outputof the 6100A. For both the ‘MeterConstant (MUT)’ and ‘MeterConstant (Reference)’ panels, thiswill be entered according to theoutput specifications of the meterunder test and external energyreference meter (if used).

In the case of the ‘MeterConstant (Output)’ panel, a valuecan be set which specifies theeffective meter constant of the‘Pulse Out’ connector. Wheneveran energy test is active, thisoutput is a pulse stream representing the total powerand energy of the active V/Ioutputs of all 6100A/ 6101A’s inthe system.

There are also internal userselectable pull-up resistors forpulse inputs. This is particularlyuseful for meters with open-collector outputs. A separate pull-up resistor is associated witheach meter constant. For the meter under test and reference meter, these can beselected as either 150 Ω or 1 kΩ. Similarly, a user selectableinternal pull-up is provided forthe main output’s energy pulseoutput. This can be selected ordeselected using the ‘UseInternal pull-up’ check box.

6 Fluke Corporation Using the 6100A Electrical Power Standard to calibrate energy meters

Fig. 11 Energy packet mode configuration screen

The basic setup is now complete. The user can nowenter the required combinationsfor L1 (L2 and L3 if using a two,three or four phase system) viathe 6100A’s output menu. Now the meter testing is ready tobegin. To start the test the usersimply presses the 6100A’sgreen ‘OPER’ button — unless in‘Gated mode’, whereupon the6100A’s ‘OPER’ button must firstbe pressed, before the 6100Acan identify the appropriate gatesignal to begin the test. A typicaloutput menu screen whenrunning a full test can be seen infigure 13.

At this point it is worth notingthat the 6100A can only be usedwith devices that have a provisionfor independent (auxiliary) powerfor their internal circuits. The taskof the 6100A is to accuratelymaintain its voltage output at theshape and level demanded bythe user for a wide range ofloads. The 6100A cannot maintainits precision output if loaded bythe short-term cycle by cyclevariations in current demandedby the meter under test’s powersupply units.

Typical 6100A energyapplications

Energy meter testing typicallyfalls into one of three categories:

• In service testing/calibration

• Manufacturing testing

• Type testing/approval

In service testing/calibrationIn service testing/calibration iswhere energy meters alreadyin the field are brought in atregular intervals for verificationand/or calibration. This regimevaries from country to country,however in most cases energymeters will be batch tested in ameter shop, several meters at atime. This is particularly prominent in some countrieswhere state law dictates thatconsumer energy meters mustbe tested each year. With thisin mind, these countries havemeter testing shops in abundance.Clearly, to get through suchnumbers in one year requiresbatch testing on a large scale.To overcome this, severalenergy meters are wired intovast meter testing arrays withmultiple sensors. Smaller arrayscan test ten meters simultane-ously.

In some countries, thisnumber can rise to one hundredand beyond. There may bemany advantages to testingmeters in this way — not leastthe high numbers that can betested at one time. However,there are several disadvantagestoo. The greatest one being theamount of power required tocarry out such tests. Plainly,this type of application, onpower alone, is outside the6100A’s, or any of its config-ured systems, intended work-load. However, that said, it isalso becoming common forsuch meter shops to employ a ‘specials’ test rig. This type ofversatile test rig is designed toaccommodate other such energymeters that for one reason oranother cannot be tested in thelarger arrays. This may be dueto physical size, unique environ-ment requirements or even fornon compatibility reasons. Forsuch lower denomination testrigs the 6100A is ideal. Powerrequirements are a lot lowerand the number of input channels required to performthe tests is easily within even asingle 6100A’s capability.

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Fig. 12 Channel Configuration and Meter Constants screen

Fig. 13 The 6100A’s Output Status screen

With several different ‘typetesting’ applications around theworld, most users see it as ameans to verify, calibrate ordesign their energy meters fortype approval. In many countries,conforming to the necessarystandards has become a legalrequirement

Fluke Corporation Using the 6100A Electrical Power Standard to calibrate energy meters

The most accurate, comprehensive and flexiblesource of electrical power signals

Fluke 6100A Electrical Power Standard

Fluke. Keeping your worldup and running.

Fluke CorporationPO Box 9090, Everett, WA USA 98206

Fluke Europe B.V.PO Box 1186, 5602 BD Eindhoven, The Netherlands

For more information call:In the U.S.A. (800) 443-5853 or Fax (425) 446-5116In Europe/M-East/Africa (31 40) 2 675 200 or Fax (31 40) 2 675 222Canada (800)-36-FLUKE or Fax (905) 890-6866From other countries +1 (425) 446-5500 or Fax +1 (425) 446-5116Web access: http://www.fluke.com/

©2004 Fluke Corporation. All rights reserved. Trademarks are the property of their respective owners.Printed in UK 02/2004 2130388 A-ENG-N Rev A, DS272

In Europe meter manufacturers,utility companies and externalregulatory agencies all adhereto the requirements of IEC61036. In other parts of theworld, similar standards existand consequently dictate theway energy meters are bothmanufactured and applied.

Manufacturing testing andType testing/approval

Meter manufacturers are using6100A’s and 6100A systemsfor meter type testing andapproval work, within theirown design centers and engineering development groups.With a multitude of new anddiffering standards, all withseveral derivations fromcountry to country, regularlybeing introduced around theworld, the 6100A is being recognized as the only singlebox solution that can replicateand test them all. Furthermore, itcan do so with the highestaccuracy and traceability.

For the energy meter manufacturers this whole newphilosophy of type testing andapproval was driven primarilyby their customers — utilitycompanies (and other similaroperators) and the regulatoryagencies associated with them.Now, all of these organizationsuse the 6100A to test theirenergy meters prior to deploy-ment, to verify them before useinto a new installation. However,these very same companiesand organizations are now alsousing the 6100A to verify existingmeters in the field, particularlyin circumstances of dispute.