| Minimum flow rate |
Meters are to be considered capable of measuring accurately down to the minimum flow rate for accurate measurement specified by the manufacturer, i.e. Qmin. While a meter will generally continue to register flow at flow rates less than Qmin, no corrections to volumes measured may be based on the performance of the meter at flows below Qmin if the meter was known to have been operating below Qmin. Any such corrections may only be applied if other suitable data is available. |
| Meter equipment failure |
Where metering equipment has failed completely, the methods of calculating delivered volume, in order of preference, are:
To use data from check metering;
- To aggregate data from downstream metering equipment (with due allowance for UFG if applicable);
- To estimate based on historical consumption data;
- To estimate based on downstream consumer production figures.
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| Meter found to be in error |
- If during as-found testing any test result is outside the allowable error limits, the meter is to be tagged to show that a correction may be required. The meter must not have its seals broken until such tests, as may be required, are completed.
- If the in-service operating range of the meter is known (for example, from TOU data or otherwise), correction is to be based on the error or errors applicable to that range. Generally, a volume-weighted error, or the error-versus-flow relationship established from testing across the range is to be used to determine the correction.
- If the in-service operating range of the meter is not known, the correction is to be based on the arithmetic average of the errors found from tests performed as specified above, i.e. at Qmin, 20%, 50% and Qmax.
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| Corrector failure |
Where a corrector has failed completely, the corrected volume will be calculated from the uncorrected volume measured by the meter, using:
- An appropriate correction factor from a period when the corrector was functioning properly; or
- Independent corrections for pressure and temperature and other factors (as applicable).
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| Corrector found to be in error |
Correctors generally operate within a narrow range in terms of correction factor, reading or output signal (as the case may be). If during as-found testing such instruments are found to be in error, corrections are to be based on adjustments for the difference between the as-found factor, reading or output and the normal or expected value of such factor, reading or output. |
| TOU device or data logger failure |
Where a datalogger associated with a TOU meter fails, and daily quantity data is not available, the methods of determining a correction, in order of preference, are:
- To distribute the total volume for the period over the days in the period by applying a typical profile from a corresponding prior period; and
- To use data from check metering where available.
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