Dear Mr. Watson. You can take ...
Published by Igor Dundovic
1 Comment
I think we are talking about two different things here.
Accuracy is often considered as the accuracy of the measurement within the meters operating range. In most transaction metering applications this is important, in some such as fuelling your car, critically important. However, in utility metering the unique circumstances are such that it doesn't matter much if the meter is (+/-)0.1% accurate of reading or (+/-)2.0% or reading accurate.
However, that accuracy may be a perceived quality factor. On the other hand what is important is the accuracy with which the meter registration reports the true consumption and because no meter in use today can do this, the meter reading is a proxy for the true consumption but is required to be "equable". That is, no one consumer should be significantly advantaged or disadvantaged by the reading.
My problem explaining this or getting a response is that terminology changes. "Equability" was the term used by my mentor at Tylors when explaining the necessity for this when the end came for PD meters (due, he said, to the 1945 Rural water supplies act in the UK).
This is today referred to as bias e.g. in this:
"2006 No. 1268WEIGHTS AND MEASURES
The Measuring Instruments (Cold-water Meters) Regulations2006
"(4)The errors of a cold-water meter at flows outside the controlled range shall not be unduly biased. ""
In other words, the unregistered flow should not be significantly different fro different users. It is of little value to have a meter capable of (+/-)0.25% accuracy of reading when the error due to unregistered flow can be 5% and vary from 0% to 10% across different users.
Published by Jon Watson, Technical manager at Razaghi Meyer International