Uncertainty Determination – Electricity Meter Verification Tests

Uncertainty Determination — Electricity Meter Verification Tests (PDF, 56 KB, 6 pages)

Category: ELECTRICITY
Procedure: EL-ENG-09-03
Document(s) : S-E-01, S-E-02
Distribution Date: 2011-12-05
Effective Date: 2011-12-05
Supersedes :

Table of Contents

1.0 Scope

This document provides guidelines for establishing uncertainties when verifying single phase and polyphase electronic energy and demand meters as well as electromechanical energy meters.

2.0 References

  • GUM — Guide to the Expression of Uncertainties
  • S-E-01 — Specifications for the Calibration, Certification and Use of Electricity Calibration Consoles
  • S-E-02 — Specifications for the Verification and Reverification of Electricity Meters
  • S-S-02 — Measurement Uncertainty and Meter Conformity Evaluation Specifications

3.0 Introduction

The uncertainty calculations established in this document are based on recommendations and principles provided by International Standards Organization (ISO) document Guide to the Expression of Uncertainties (GUM). The need to establish uncertainties for meter verification is driven by Measurement Canada policies provided in the document 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 are achieved by counting pulses from each device.

The typical electricity meter verification setup can be illustration by the block diagram in figure 1.

Figure 1: Block diagram Meter Verification Setup
Figure 1: Block diagram Meter Verification Setup [Description of Figure 1]

In the diagram above, the phantom load and console reference meter are shown integrated as one device. This device is referred to as the calibration console. In this setup the electricity calibration console is used to determine the error for the meter under test (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 an 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 meter under test. 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:

  1. the calibration console and
  2. the meter under test.

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 S-E-01: Specifications for the Calibration, Certification and Use of Electricity Calibration Consoles. A procedures document (P-E-01: Procedures For Calibrating And Certifying Electricity Calibration Consoles) along with associated worksheets for S-E-01, provides the procedure for establishing the data used to determine the standard uncertainty for the calibration console.

The uncertainty for the meter under test is determined using procedure (EL-ENG-09-02) Uncertainty Determination of Electricity Meter Types.

4.2 Uncertainty in Meter Verification Tests

The following formula shall be used to determine the combined standard uncertainty for meter verification tests.

Equation 1 [Description of Equation 1]

Where:

  • 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 meter under test.

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 Electricity and Gas Inspection Regulations Section 21(h).

5.0 Example

For the case of the following data:

  • Meter error = ei = 0.36%
  • uc(con) = ±0.01
  • us(dev) = ±0.03
  • k=3

The standard uncertainty is:

Equation 2 [Description of Equation 2]
  • The expanded uncertainty would be Uce = (±0.03 x 3) = ±0.09%

With this value the error of the meter (ei) can be reported on the meter record as:

  • 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.