IEC 62765-1-2015 pdf free download.Nuclear powers plants – Instrumentation and control important to safety – Management of ageing of sensors and transmitters – Part 1: Pressure transmitters.
A sealed pressure sensing part has a fluid medium isolated from process fluid. This type of sensor provides a degree of damping of the pressure variation and may eliminate rapid fluctuations
5.2.2 Interface between sensing part and process
5.2.2.1 SensIng line for pressure transmitters
Sensing lines (instrumentation line or impulse line) are tubes that connect the process to be
measured to the sensing part of pressure transmitters. Sensing line may contain liquid or gas.
5.2.2.2 Primary elements for flow measurement
Where pressure transmitters are used for measurement of flow, a primary element
(mechanical 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 element is defined as flow transmitters
(FT).
5.2.2.3 Reference leg for level measurement
Where pressure transmitters are used for measurement of level, a reference leg with condensation pot that creates the head pressure as a reference level of full tank is needed. The differential pressure between reference leg tap (high-pressure side) and tank tap (lowpressure side) is inversely proportional to the level of tank. The differential pressure transmitter with a reference leg is defined as level transmitters (LT).
5.3 Reasons for transmitter ageing management
Ageing of pressure transmitters can cause measurement errors, erratic signals, spikes, noise, degradation of response time, and other anomalies that may affect plant operation or safety. Ageing can also invalidate the environmental qualification 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 performance degradation. In transmitters, transfer agent such as oil 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 oil is not as detrimental 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. Examples of ageing effects that can cause calibration failure, slow response time or total failure of PTs are summarised in Table 1 (this information is also provided in Table B.1 of IEC 62342:2007 and the related research report Sensor Performance and Reliability listed in the bibliograhy).IEC 62765-1 pdf download.