Environmental Influences on Pressure Transducer Performance

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The ideal pressure transducer responds to an input of pressure and pressure alone and has a unique, and preferably simple transfer function. The real transducer of course does not achieve this and its accuracy is characterised by the amount by which it deviates from ideal under the effect of pressure, the primary influence, or secondary influences such as temperature. Hysteresis and creep are two of the most serious errors, which occur even under constant environmental conditions, but usually as a result of changing pressure. Non-linearity is not necessarily to be regarded as an error. The errors that occur when the transducer is subjected to changes in a secondary influence such as acceleration, humidity and temperature are generally more severe. It is the purpose of this paper to demonstrate these effects, which fall into three categories: quasi-static changes, transient reversible and irreversible, in descending order of tolerability. As an example, the effect of acceleration may fall into any one of these categories. An inversion of a transducer may cause a steady and entirely reversible change in the output; shaking the device may give rise to a transient output which disappears when the excitation is removed, whereas a sudden and severe shock may irreversibly derange the transducer. In practice, the most important environmental influence is temperature, and the effects are examined in some detail. Thermal errors in the first and last category are well understood and are usually fully covered in manufacturers' specifications, but the most serious errors, and those for which it is most difficult to allow, occur in the second category under conditions of changing temperature. A good understanding of these effects is essential for the design of transducers and their installations.