Pressure sensor application

Typically the maximum overpressure specified for a sensor is the highest value of pressure that can be applied without affecting sensor performance once the pressure returns to its usual operating range. Beyond the overpressure limit, permanent offset or damage may occur that affects the performance of the device but the pressure media will be contained up to the burst pressure rating. “Burst Pressure” is the value where pressure can no longer be safely contained within the device and the diaphragm may rupture.

These electronic sensors can be supplied for use in a relatively wide media temperature range, typically from -40 to +125 degC or even 180 / 200 degC. The higher temperature ratings can be accommodated directly at the sensor inlet by means of an integral cooling fin design or remote electronics package, avoiding the need for precooling of the pressure media using a separate component such as a temperature reducing coil or pigtail syphon.

Consideration must also be made regarding the ambient temperature environment where the sensor will be installed / operating, as the rating is often lower, for example typically in the region 85 -105 degC maximum.

Solutions can also be supplied that offer a span “turndown” ratio, enabling for example a 10 bar (g) device to be reset by the user to a lower value such as 4 bar (g). The zero signal point can also be elevated or suppressed to a value above or below atmospheric e.g 1 to 4 bar(g) or -1 to 4 bar(g).

Alternatively, for “differential” pressure (dP) transducers or transmitters, full range output represents the maximum working difference in two input pressures. The zero point occurs when both input pressures are equal value (zero differential). Maximum system pressure is important, otherwise known as line pressure. This is the maximum pressure that can be applied to both of the differential pressure ports simultaneously without degradation in performance. Consideration also needs to be given if the pressure differential occurs in the positive, negative or both directions as a custom calibrated / bilateral output may be required. E.g to measure P1 - P2, P2 - P1 or both.

Commercially available pressure transducers and transmitters are often priced according to accuracy, from low cost OEM to premium performance units for test / R&D applications. For the user it is therefore very important to determine exactly what performance is required and the prevailing operating conditions in order to secure the most cost effective solution for each particular application. For example measurement accuracy at room temperature conditions can vary from 1% to 0.1% with uncertainty factors such as non-linearity, hysteresis, repeatability and zero/span offset. If the temperature varies considerably then these values can be much greater. However manufacturers do not always use consistent and inclusive terms for measurement uncertainty so it is important to carefully compare the product performances offered by each prospective supplier.

Published 25/04/2016
Author: Tony Cuttill

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