*Failures and Abnormalities: -Over-Pressure: All of the pressure sensors are designed to operate over a rated pressure range. -Plant operating systems rely on these pressure sensors to maintain high accuracy over that given range. -If a pressure sensor is over ranged, pressure is applied to the point where it can no longer return to its original shape, thus the indication would return to some value greater than the original. -Diaphragms and bellows are usually the most sensitive and fast-acting of all pressure sensors. -Even a small fracture will cause them to read low and be less responsive to pressure changes. -Also, the linkages and internal movements of the sensors often become distorted and can leave a permanent offset in the measurement. *Bourdon tubes are very robust and can handle extremely high pressures although, when exposed to over- pressure, they become slightly distended (puffy) and will read high. - Very high over-pressuring will of course rupture (split) the tube. *Faulty Sensing Lines -Faulty sensing lines create inaccurate readings and totally misrepresent the actual pressure. -When the pressure lines become partially blocked, the dynamic response of the sensor is naturally reduced and it will have a slow response to change in pressure. -Depending on the severity of the blockage, the sensor could even retain an incorrect zero or low reading. *Loss of Loop Electrical Power -As with any instrument that relies on AC/DC power, the output of the D/P transmitters will drop to zero or become irrational (illogical) with a loss of power supply or the transmitter internal wiring.
Posted on: Mon, 05 Jan 2015 13:39:11 +0000
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