ABSTRACT
Three methods exist for testing the response times of pressure transmitters in situ: the power interrupt test, the noise analysis technique, and the pink noise technique. The noise (or random signal) analysis technique is a passive in situ technique that does not interfere with plant operation, uses already existing plant sensors and instrumentation, accounts for the effects of process conditions on plant equipment performance, and includes any response-time delays caused by transmitter sensing lines. The power interrupt test is a simpler and less-time-consuming test than noise analysis for measuring the response time of force-balance pressure transmitters. The pink noise test is useful for pressure transmitters where process fluctuations do not normally exist or they are inadequate for using the noise analysis technique to test response time.
Subject(s)
Nuclear Power Plants/instrumentation , Pressure , Algorithms , Data Collection , Data Interpretation, Statistical , Electric Power Supplies , Electronics , Equipment Design , Reproducibility of Results , Transducers, PressureABSTRACT
This paper discusses the key causes of calibration drift in pressure transmitters and procedures for calibrating pressure transmitters to ensure their accuracy. Calibrating pressure transmitters involves adjusting the potentiometers in the sensor that controls the zero (lowest pressure at which a transmitter is calibrated) and span (the range of pressure the transmitter is to indicate) of the transmitter. The initial or bench calibration of pressure transmitters involves using a constant pressure source such as a deadweight tester. Once the transmitters are installed, temperature, pressure, humidity, vibration, maintenance activities, and normal aging can degrade their accuracy. Transmitter accuracy can also be degraded by transmitter sensing lines, when the water in a sensing line reference leg boils off, when non-condensable gases in the reference leg dissolve, and when voids, blockages, freezing, or leakage occur in sensing lines. On-line calibration techniques enable plants to avoid these accuracy problems by monitoring the output of an individual transmitter.
