EL-ENG-09-03 — Uncertainty determination–electricity meter verification tests
Revision number: Rev. 1
Table of contents
- 1.0 Scope
- 2.0 References
- 3.0 Introduction
- 4.0 Measurement process
- 5.0 Example
This document provides guidelines for establishing uncertainties when verifying single phase and polyphase electronic energy and demand meters.
- Guide to the Expression of Uncertainty in Measurement (GUM):1993 (corrected and reprinted 1995), BIPM/IEC/IFCC/ISO/IUPAC/IUPAP/OIML
- EL-ENG-12-01—Requirements for the Certification and Use of Measuring Apparatus—Electricity Meter Calibration Consoles
- 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
- S-E-02—Specifications for the Verification and the Reverification of Electricity Meters
- S-S-02—Measurement Uncertainty and Meter Conformity Evaluation Specifications
The uncertainty calculations established in this document are based on recommendations and principles provided in the Guide to the Expression of Uncertainty in Measurement (GUM). The need to establish uncertainties for meter verification is driven by Measurement Canada policies provided in S-S-02—Measurement Uncertainty and Meter Conformity Evaluation Specifications.
4.0 Measurement process
Electricity meter verification is traditionally performed by comparing outputs from a reference meter with those of a meter under test (MUT). Both the reference meter and the MUT are energized by applying a phantom load. Comparison of outputs from the reference meter and the MUT is achieved by counting pulses from each device.
The typical electricity meter verification set-up can be illustrated by the block diagram in figure 1.
Figure 1: Block diagram meter verification set-up
In the diagram above, the phantom load and console reference meter are shown integrated as one device. This device is referred to as the electricity calibration console. In this set-up, the calibration console is used to determine the error for the MUT. Electricity meters approved for use in Canada are required to provide a pulse output as a means for facilitating testing. The pulse output is typically provided using a light pulsing device such as a light-emitting diode (LED). The calibration console provides a voltage source and a current source in order to energize the meter at a nominal test load. The console counts pulses representing the energy being metered by the energized MUT. The pulses from the MUT are compared with pulses from the console reference meter and the difference in pulse counts is used to establish an error for the MUT. The uncertainty in the error established by this process can be determined using the principles of the GUM.
4.1 Sources of uncertainty
In the measurement process described above, the sources of uncertainty are the following:
- calibration console; and
The uncertainty in measurement which is introduced by the calibration console is determined from data obtained during the certification of the console. The console is certified to the requirements of EL-ENG-12-01—Requirements for the Certification and Use of Measuring Apparatus—Electricity Meter Calibration Consoles. Procedures document P-E-01—Procedures for Calibrating and Certifying Electricity Calibration Consoles, along with associated worksheets, provide the procedure for establishing data used to determine standard uncertainty for the calibration console.
The uncertainty for the MUT is determined using procedure EL-ENG-09-02—Uncertainty Determination of Electricity Meter Types.
4.2 Uncertainty in meter verification tests
The following formula must be used to determine the combined standard uncertainty for meter verification tests.
- uci is the combined standard uncertainty for the verification test
- uc(con) is the combined standard uncertainty for the calibration console
- us(dev) is the standard uncertainty for the MUT.
The standard uncertainty determined above should be stated as an expanded uncertainty. The k-factor which is applied to the standard uncertainty is determined on the basis of requirements found in S-E-02—Specifications for the Verification and Reverification of Electricity Meters. The expanded uncertainty should be included with any documented meter errors from verification test results as required by paragraph 21(1)(h) of the Electricity and Gas Inspection Regulations.
- Meter error = ei = 0.36%
- uc(con) = ±0.01
- us(dev) = ±0.03
- k = 3
The standard uncertainty for the above data is the following.
The expanded uncertainty would be Uce = (±0.03 x 3) = ±0.09%.
With this value, the error of the meter (ei) can be reported in the meter record as follows.
- ei= 0.36% Uce= ±0.09%, k=3
Where the same expanded uncertainty applies to several measurement errors, a note can be included with the documented errors indicating that the same expanded uncertainty applies to all meter test results.
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