P-E-01—Procedures for calibrating and certifying electricity meter calibration consoles pursuant to EL-ENG-12-01—Requirements for the certification of measuring apparatus —electricity meter calibration consoles
7.0 Procedures for the assessment of metrological requirements
(EL-ENG-12-01, s. 7.0) (part 1 of 4)
7.1 General procedures for the assessment of metrological requirements
7.2 General test setup
The purpose of this procedure is to provide setup and procedural information that is common to most of the tests and procedures related to the metrological requirements of section 7.0. The majority of the connections and test setups for the procedures related to metrological requirements have common elements. This section describes the various connections to be made depending on test conditions, console type and specified use.
7.2.2 Test socket connections
A test socket that provides terminals to take all applicable current and voltage measurements at the meter socket shall be used.
7.2.3 Isolation 1:1 current transformers in circuit
When 1:1 isolation transformers are used in the test circuit, it is important that both current elements be connected to the standard in the MUT position. The left current element must be measured on one tap of the standard and the right current element must be measured on another tap of the same standard. The middle current element is not used since 1:1 CTs are only used with single-phase, self-contained meters. When this setup is used, it is important to note that the Kh setting or expected number of pulses (calculated according to the Basic Procedure for Conducting Accuracy Tests set forth in section 7.3) must be doubled since the standard is measuring two times the test current. The test may also be performed using two standards, with the left current element measured on one standard, and the right current element measured on the other standard. The test voltage is applied to both standards. One standard output is connected to one of the standard inputs on the comparator, and the other standard output is connected to one of the other standard inputs on the comparator. In this case, the expected pulse count or Kh setting on the comparator remains as calculated and the comparator is set to "average" both the inputs.
7.2.4 Isolation 1:1 current transformers out of circuit
If a console operates in true series-parallel testing and no 1:1 isolation CTs are in the test circuit, only one current element connection to the standard is required. Since all the tests are performed with current elements in series, any one current element needs to be connected to a tap of the standard in the MUT position. The other two current elements are to be shorted at the test socket. Since 1:1 isolation CTs are not being used, the length of leads for the current connections is not restricted. However, they should not be any longer than is necessary to perform the test.
7.2.5 Burden connections
For all tests, the burden of the standard's current elements and associated connections are considered to approximate the burden exhibited by a meter current coil; therefore, no additional burden is required for the current elements of the standard in the MUT position.
22.214.171.124 Single-phase voltage burdens and connections
For all single-phase tests that require a voltage burden to be connected in parallel with the test voltage, the meter burden (which can be represented by a potential coil for electro-mechanical meters) should be connected in parallel across the terminals of the test socket that are also supplying the test voltage to the standard in the MUT position. Generally, for single-phase test points, this means that the voltage is supplied across the top left and top right current terminals at the test socket. In this case, the leads connecting the burden to the terminals should be as short as practicably possible.
126.96.36.199 Polyphase voltage and burden connections
For all polyphase tests that require a burden to be connected in parallel with the test voltage, the meter burden is to be connected in parallel across the terminals of the test socket. The test socket also supplies the test voltage to the standard in the MUT position (which can be represented by two or three potential coils for electro-mechanical meters). Generally for polyphase test points this will mean that the voltage is supplied across a set of potential pins in the socket. The length of the leads to the test burden is not restricted but should not be any longer than is necessary to perform the test.
7.2.6 Voltage connections
All voltage connections for calibration test points should be made exactly as they would for a meter that may be installed and verified on the console at that test point. Generally when a polyphase test point is being performed the parallel voltage transformer, if there is one, is used to supply voltage to the MUT positions. Connections are made to supply voltage to the appropriate voltage pins at the socket. Generally when a single-phase self-contained meter test point is being calibrated, the multiple voltage transformers, if there are any, are used to supply voltage to the MUT positions. Connections are made to supply voltage to the appropriate pins (or current lugs when 1:1 isolation transformers are used) at the socket. Voltage connections to the standard in the MUT position should be made from the applicable voltage terminal at the test socket.
7.2.7 Shorting bars
In all instances where shorting bars are used in the MUT positions, they must be connected so that the test current is applied to all the terminals of the MUT positions.
7.2.8 Consoles operating in simulated series-parallel mode
Consoles that operate in simulated series-parallel testing may not have exactly the same voltages, currents and phase angles on each phase. Therefore, if performing tests in "series" and using only one element for voltage and current (as described in section 7.2.4), an inaccurate error may be displayed. For single-phase test points on this type of console, use the test setup described in section 7.2.3. For polyphase test points on this type of console, the number of standards required is the same as the number of elements being tested in series. In some cases, the voltage may be common and in this case, one standard can be used with the current elements applied separately to each tap of the standard. When performing a test point associated with a three-element meter, three standards must be used. Each current element and its associated voltage element are connected in series-parallel with a standard. The outputs from the three standards in the MUT position should be connected to the three standard inputs on the comparator. Depending on the calculation used in the Basic Procedure for Conducting Accuracy Tests set forth in section 7.3, the comparator will be set to "average" or "sum" the three inputs.
7.3 Basic procedure for conducting accuracy tests
The procedures described in this section are to be used to conduct the accuracy tests set out in section 7.0 of EL-ENG-12-01. There are two basic procedures described in this section: one applies to calibration consoles used to verify energy meters and the other applies to consoles used to verify demand meters.
Note: This is an example of a procedure with specific equipment listed below to be used for guidance in calibrating a console.
7.3.1 Basic procedure for conducting energy accuracy tests
- The basic procedure for measuring the errors of a calibration console is to connect an appropriate energy standard to any necessary instrument transformers at a calibration console MUT position using an appropriate socket adaptor and to calibrate the standard (and transformer combination) as if it were a meter being verified.
- MC has developed a light pulser (infrared probe) that can be used to trigger the optical pick-up on the calibration console in the "direct mode". Radian Research has developed a light valve that can be used for the same purpose, can operate in the reflective mode and can be used with modulated light sources. Either device is controlled by a Radian comparator that can be configured to trigger the probe or valve after receiving a preset number of pulses from a Radian standard.
- This arrangement looks to the calibration console exactly like a MUT, as the triggering of the optical pick-up is analogous to the verification of a meter using the approved test provision. The calibration console control circuit is set up as it would be for normal verification work.
- In summary, this procedure assesses the accuracy of the electrical components and reference meter of the calibration console as well as the accuracy of the calibration console control circuit and any associated calculations performed by the console.
- These procedures are specific to the use of a Radian standard RM-109 comparator and the light infrared probe developed by MC. Other suitable devices can be used for calibration console assessment, where deemed acceptable by the Electricity Specialist.
- Radian watt hour standards.
- Radian comparator, model RM-109 or higher.
- Infrared probe OP-01 or Radian light valve RM-1P.
- Coaxial cables.
- Tripod, three-pronged clamp and clamp holder to provide free-standing support for the infrared probe or light valve.
- Test burdens as determined pursuant to section 7.2.3 of EL-ENG-12-01.
- Ensure the console is de-energized, install a socket adaptor in the MUT position on the calibration console and install burdens as determined in section 7.2.3 of EL-ENG-12- 01.
- Connect the potential and current cables from the socket adaptor to the potential and current circuits of the Radian standard.
Notes: For a single-phase calibration console, only one Radian standard is required. To improve stability and repeatability, three Radian standards connected in series/parallel can be used. For such an application, the outputs of the standards are connected to standard inputs A, B and C of the comparator and its output set to avg mode. If one Radian standard is used, as will normally be the case, the sum mode of the comparator is to be used. For a true polyphase calibration console, one Radian standard would be required per phase and would be connected to standard inputs A, B and C of the comparator. The sum mode would be used for this application.
- Connect auxiliary power of the Radian standard to an appropriate power source.
- Connect input of the Radian standard to RM on the comparator with a short coaxial cable.
- Connect the Radian standard output to the standard input on the comparator.
- Connect the infrared probe or the Radian light valve to the led output of the comparator.
- Verify that all connections are made correctly.
- Turn on the calibration console, the calibration console accessory instruments, the Radian standard and the comparator.
- Turn on the applicable standard input on the comparator by pressing the appropriate on/off button. Ensure that the appropriate on annunciator is illuminated.
- Set the toggle switch avg/sum on the comparator as explained in the notes contained in step (2) above, and ensure that the sum annunciator is illuminated. Set the gate/pulse switch to pulse and ensure that the pulse annunciator is illuminated.
- Set the thumb wheel switches on the comparator and the number of revolutions of the calibration console control circuit to the values determined from the following relationship:
- TWSc = thumb wheel switch setting on comparator
- R = number of revolutions set on the calibration console control unit
- Vs = voltage applied to the Radian standard
- Is = current applied to the Radian standard
- Vr = voltage applied to the calibration console energy reference meter
- Ir = current applied to the calibration console energy reference meter
- kr = pulse constant of the calibration console energy reference meter in watt-hours per pulse.
This formula allows R and TWSc to be chosen so that TWSc is within its maximum range of 999.99999 watt hours. The factor of 10 000 in the formula is to ensure that 10 000 pulses are emitted by the calibration console reference meter. If the control circuit on the console has a setting for expected pulses from the energy reference meter, it should be set to 10 000.
A calibration console reference meter at a test load of 120 volts, 5 amperes has a pulse constant of kr = 0.0015 watt hours per pulse. The Radian standard at the MUT position experiences a test load of 120 volts and 5 amperes.
TWSc × R = 15
Set R to 1 and TWS to 15.000
For the same calibration console reference meter, but with the Radian standard now experiencing a test load of 240 volts and 10 amperes, the relationship becomes:
TWSc × R = 60
Set R to 1 and TWS to 60.000
- Set the calibration console to any load. The input annunciator on the comparator illuminates, indicating a valid input is being fed to the comparator. If this annunciator does not illuminate, re-verify for proper connections of the Radian standard.
- Press the RM-10 reset button on the comparator to stop and reset the LCD display of the Radian standard. Press the reset button on the comparator to reset the comparator to a new value of TWS.
- Press the start button on the comparator. The test annunciator should illuminate, indicating that the comparator is receiving pulses from the Radian standard. The LCD display of the Radian standard should be recording watt hours. Each time pulses corresponding to the value set on the thumb wheel switches of the comparator are received, an output pulse is sent to both the LED and the RM outputs of the comparator. The output pulses to LED drive either the infrared probe or the light valve to mimic the passage of a hole or a dark spot on the rotating disc of an induction-type meter. The light source excites the calibration console's optical sensor and increments (or decrements) by one the disc revolution count on the calibration console control circuit. See sections 188.8.131.52 and 184.108.40.206 of this procedure for aligning the light source. The output pulses to RM provide a series of control signals to the Radian standard: stop, reset and start. The first pulse from RM freezes the Radian standard display, the next pulse resets the display to zero and the following pulse restarts the display. The sequence continuously repeats while the test is running. With this mode of operation, the Radian standard delivers pulses continuously, although its display only runs every third interval.
- The procedure given above can also be modified to apply to:
- calibration consoles that automatically determine and display MUT errors; and
- consoles that emit a pulse train from a reference meter (the test length is set in the test parameters rather than being determined by an operator setting the number of expected reference meter pulses).
In these types of consoles, the test parameters are set in the computer for a specific meter type. Set up the console as if testing a three-element meter (if the console is used for testing polyphase and single-phase meters), or a single-phase three-wire meter, (if the console is used for testing single-phase meters only). The voltage, current and Kh are preset in the setup selection chosen. Ensure that the values set are correct for the test point being performed. The thumb wheel setting (TWS) on the Comparator should be chosen as follows:
- Khc = the Kh set in the console setup
- EIs = the number of test socket elements that the Radian standard is connected to (generally one)
- EIc = the number of elements that the console is set to test (three for polyphase if the test is performed in series, one for single-phase or if the polyphase test is performed with a single element)
- Vs = the voltage applied to the Radian standard
- Vc = the voltage that the console sets
- Is = the current applied to the Radian standard
- Ic = the current that the console sets
Ensure that you adhere to the minimum time limits specified in section 7.1.3 of EL-ENG-12-01.
220.127.116.11 Procedure for aligning the infrared probe OP-01
- Mount the infrared probe on a free-standing tripod with a three-pronged clamp such that its LED end points upward or horizontally. This position facilitates the alignment of the probe with the photocell of the optical pick-up on the calibration console.
- Swing the calibration console photocell in front of the infrared probe and align the photocell with the probe.
- The distance between the lenses should be ½ to 1 cm, unless the photocell is an Infrascan L31, in which case, the distance should be 1 to 2 cm.
- If required, use another three-pronged clamp to hold an odd-shaped photocell in alignment with the infrared probe.
- If the infrared probe or the light valve fails to operate and the optical pick-up has adjustable sensitivity, reduce the optical pick-up sensitivity. Otherwise, move the probe away from the optical pick-up by a few centimetres.
- Set the calibration console control circuit to direct or holes mode. Align the probe with the optical pick-up photocell by using the sensitivity indicator on the control circuit or equivalent instrument. The sensitivity meter should read high when the probe and the photocell are aligned.
18.104.22.168 Procedure for aligning the Radian light valve RM-1P
Same steps as in 22.214.171.124 above, except:
- For direct mode, select direct or holes on the calibration console control circuit and align the large transparent LED source with the photocell in the calibration console optical pick-up.
- For reflective mode, select reflective or edge mode on the calibration console control circuit and align the round dark flat window (on the opposite side of the valve from the large transparent LED) with the light source and photocell assembly of the calibration console. The two small dark LEDs at the sides of the window generate light pulses.
- For a calibration console with a modulated light source, all four small dark LEDs generate light pulses. The two at the sides of the large transparent LED are used as light sources for direct mode and the other two are used for reflective mode.
126.96.36.199 Procedure for aligning the infrared probe OP-01 and the Radian light valve RM-1P
- Set the calibration console to the desired test load and adjust the settings of TWS and R (step (11) of section 188.8.131.52) if necessary.
- Press the reset button on the Radian standard and the reset and start buttons on the comparator.
- Press the start button on the calibration console control circuit to start a test. The control circuit starts to count pulses from the calibration console reference meter when the first pulse from the infrared probe or the light valve strikes the photocell.
- Each subsequent pulse from the probe or valve increments (or decrements) the preset number of revolutions on the calibration console control circuit.
- When the preset number of revolutions is reached, the control circuit stops accepting pulses from the calibration console reference meter and displays the number of pulses received or calculates an error.
184.108.40.206 Calibration console error calculation (EL-ENG-12-01, s. 7.1.2)
220.127.116.11.1 Guideline for section 18.104.22.168 of EL-ENG-12-01
- The error of a calibration console (Econs) at any test point is the difference between the results obtained for the standard (and transformer combination) when its apparent error is measured on the calibration console (Esm), and the overall known (certified) error for the standards used (Ec), or:
- Econs = calibration console error in percent
- Esm = measured error of the standard (and transformer combination) in percent that is either read directly off the calibration console or calculated by the operator according to the operating principle of the console
- Ec = certified error of the standard
If instrument transformers are used, the following formula is applied to determine the combined error:
- Es = certified error of the standard in percent at a given test load from the calibration certificate for the standard
- RCFe = certified ratio correction factor for the voltage transformer at the ratio and burden used
- RCFi = certified ratio correction factor for the current transformer at the ratio and burden used
- β = certified phase angle error of current transformer at the ratio and burden used in degrees
- τ = certified phase angle error of voltage transformer at the ratio and burden used in degrees
- Φ = phase angle between voltage and current in degrees
The test load applied to the Radian standard is 120 volts, 5 amperes at 0.5 power factor with Ec = 0.01 percent. Suppose the apparent error measured by the calibration console is Esm = −0.07%.
The calibration console error is determined as:
- Conduct the tests and calculations at the various test loads and at the various MUT positions pursuant to the requirements of EL-ENG-12-01.
- Date modified: