| 摘要 |
A differential-pressure transmitter adapted to produce a signal proportional to a process variable such as flow rate in a line conducting fluid or the level of liquid in a tank, the process fluid being at a temperature markedly at variance with ambient temperature. The transmitter is constituted by high and low pressure sensors which are coupled to the force beam of a force balance transducer so that the beam is responsive to the difference between sensed high and low pressures derived from the process variable, the transducer being exposed to ambient temperature. Each sensor is constituted by a housing having a well therein covered by a sensing diaphragm and an insert seated in the well, the face of the insert being spaced from the diaphragm to define a fill chamber containing hydraulic fluid, the sensor diaphragm being exposed to the process liquid, whereby heat transfer takes place between the liquid and the hydraulic fluid. The insert is formed of a metal having a low coefficient of expansion relative to the material of the housing whereby variations in temperature produce changes in the dimensions of the housing relative to that of the insert and give rise to changes in the volume of the fill chamber to an extent compensating for the concurrent changes in the volume of hydraulic fluid as a result of said heat transfer, thereby rendering the sensor insensitive to temperature changes.
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