TABLE OF CONTENTS Nuclear plant pressure transmitters are electromechanical systems that are designed to measure pressure and differential pressure (including level and flow). In this book, the term pressure transmitter is used to mean pressure, level, or flow transmitter.
A pressure transmitter may be viewed as a combination of two systems: a mechanical system and an electronic system.[18] The pressure transmitter's mechanical system contains an elastic sensing element (diaphragm, bellows, Bourdon tube, etc.) that flexes in response to pressure. The movement of this sensing element is detected using a displacement sensor and converted into an electrical signal that is proportional to pressure.
Typically, two types of pressure transmitters are used in most nuclear power plants' safety-related pressure measurements. These are referred to as motion-balance and force-balance, depending on how the movement of the sensing element is converted into an electrical signal. In motion-balance transmitters, the displacement of the sensing element is measured with a displacement sensor (e.g., a strain gauge or a capacitive detector) and converted into an electrical signal (e.g., 4-20 mA DC current) that is proportional to pressure. In force-balance transmitters, the applied pressure forces a sensing rod in the transmitter to deflect. This deflection is opposed by an electromechanical feedback system in the transmitter. The feedback system consists of a force motor that works to keep the sensing rod at an equilibrium position. The amount of electrical current supplied to the force motor is proportional to the applied pressure.
The transmitter's electronics consist of...
