Measurement Systems Engineering: Sampler

The Transient Case: A Sampler
Part 1 of 2
Caution: Data may not be what they seem! So, what questions must you ask about data validity?

SUPPOSE THAT this typical record shows the output from a resistance-based, flush-diaphragm pressure transducer. How should we interpret this trace---is it simply the record of a pressure pulse?

Before we can answer our question, we must first ask---and answer---questions such as the following:

Was the transducer responding not only to pressure but also to other factors---such as temperature or magnetic field?

Does this output show only the resistance change in the transducer---or are we also seeing how the pressure pulse acted on the cable capacitance?

Did a self-generated voltage, perhaps caused by the same pressure pulse (correlated with the resistance change---and to the same frequency and time scale), contribute significantly to the output?

Did the dynamic volume change of the transducer's diaphragm significantly affect the dynamic pressure being measured?

Conclusion: . .In order to prove that our data are "valid"---that is, to prove that we are really measuring what we think we are measuring---certain predictable questions must be raised and addressed.

(Questions like those raised above are discussed in. "The Engineering of Measurement Systems"---my first of two videotaped short courses consisting of lectures with integrated demonstrations.)

Continue to Part 2 of 2