On Sat, 08 Jan 2005 18:34:24 +0000, Capitol
wrote:



Andy Hall wrote:

If the manufacturers intended their meters to run as a design goal at
50% over stated capacity, they would rate them that way.
Alternatively, they would manufacture them down to the stated spec.
with much less headroom and more cheaply.

If there is overdesign on the part of the manufacturers it is for
reasons of a safety or accuracy purpose.

This doesn't sound right. In the 1970s the specification was set by the
gas boards engineers. All good engineers overspecify if they want a long
lifetime product.

If one overspecifies, it is on the basis that the product will be used
within the specification, not at 1.5 or 2x the specification.

The manufacturers tested the product to a supervised
gas board standard, knowing that if it failed, they would lose the
business. These were the days when products were properly tested for
reliability and products were rated on their lifetime cost as much as on
the ex works price. So IMM is probably right in saying that a gas meter
of his era would perform adequately with a 100% overload.

This is a bogus argument. Assuming that the meter manufacturers did
overspecify to apparently improve reliability, and the bodgers abused
it by using it beyond spec. then that reliability margin would be
lost. This then takes the manufacturer back to where he started.

Now that
IEC9000 defines the quality standard, the product is extremely likely to
be crap when it leaves the production line having been built for the
lowest possible cost and may not withstand the 100% overload which IMM
wishes to use.

This is a common misconception. ISO9000 defines quality standards in
the technical and not the colloquial meaning of the word. In other
words, it is documentation of and adherence to a set of processes and
procedures. This bears absolutely no relationship to whether the
resulting product is any good or not. Moreover, processes can be
treated as uncontrolled and then anything can be happening.



I wouldn't even bet that the modern meter would stay
working correctly when used at 100% load for a couple of years!
Certainly some modern semiconductor electricity meters have a very short
lifespan (12 months AIUI)

None of which has anything to do with ISO9000 and specification of
products.



--

..andy

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