BS IEC 62765-1 :2015 pdf download-Nuclear powers plants一 Instrumentation and control important to safety一 Management of ageing of sensors and transmitters Part 1: Pressure transmitters
5.2.2.2 Pr im ary el e ment s for flow mea sur ement Where pressure transmitters are used for measurement of fl ow , a primary element (mechanica l devices) that creates the differential pressure that is related to flow is needed . The primary element may be an orifice plate , a venturi tube , a pipe elbow , or a flow nozzle. The differential pressure transmitter with a primary el ement is defined as flow transmitters (FT). 5.2.2.3 Ref e rence leg for le ve l m eas urem e nt Where pressure transmitters are used for measurement of level , a reference leg with condensation pot that creates the head pressure as a reference l eve l of full tank is needed . The differential pressure between reference leg tap (high- pressure side) and tank tap (Iow- pressure side) is inversely proportional to the l eve l of tank. The differential pressure transmitter with a reference leg is defined as l eve l transmitters (L T). 5.3 Reasons fo r t ran s mitt er ag ei ng managem e nt Ageing of pressure transmitters can cause measurement errors , erratic signals , spikes , noise , degradation of response time , and other anomalies that may affect pl ant operation or safety . Ageing can also invalidate the environmenta l qua lification of pressure transmitters that are required to operate in harsh environments during accident conditions . Such effects may affect individual transmitters or result in common cause failure of transmitters . There are also problems such as loss of fill fluid due to ageing , which can occur in pressure transmitters leading to degradation . In transmitters , transfer agent such as oi l may be used. Any leakage of oil can lead to calibration change , response time increases , and loss of linearity. In other transmitters where oil is used for lubrication and other purposes , leakage of oi l is not as detrimenta l to transmitter performance . Both calibration changes and response time degradation due to oil loss can be identified using the online-monitoring techniques mentioned in this standard .