E-Zine June 2005
Many of my recent articles focus on performance statements for flowmeters.
It is interesting how another twist can come along just when the subject seems
to be getting "old". Whereas reference flowmeter performance can generally be
expressed as one of four parameters, reference level gauge performance is
generally expressed as one of six parameters. This was not so bad. Even
more complicating is that the (often well-defined) published specifications
do not reflect what the suppliers intends.
Research for "The Consumer Guide to Non-Contact Level Gauges"
(http://www.spitzerandboyes.com/Product/noncontact.htm ) involved
extracting information from the level gauge specifications from
about 60 suppliers. These suppliers used a total of about 30
different terms to express performance. Let's think about this
for a minute --- on the average, there was one term used to express
performance for every two suppliers. This would seem to be far
In the early going, the well-defined published specifications
were tabulated and used for calculations. As research progressed,
conversations with suppliers made it apparent that the published
specifications could not be trusted --- even if they were
technically clear and well understood. As a result, I had to
contact the suppliers again to verify that their (supposedly)
well-defined published specifications reflected the supplier's
For example, after speaking with the suppliers, 0.25% of measuring
range, 0.25% of span, and 0.25% all meant 0.25% of maximum sensor range.
Think about this for a minute. Measuring range and span are well defined ---
or are they? The percentage is not well defined and begs the question,
"Percentage of what?"
On a positive note, despite the discrepancies noted in the published
specifications, suppliers were forthcoming in explaining their intentions.
Wouldn't it be nice if they would update/correct their specifications to
use standard terms that describe level gauge performance?