Temperature compensated liquid level transmitter

Claim 1

In a transmitter for generating a signal proportional to the level of liquid in a tank or other vessel, the combination comprising: A. a meter having a pivoted force beam and producing an output signal that depends on the force applied to the beam, B. a sensor for detecting said liquid level and having a housing attachable to the wall of said tank, said housing having a well therein covered by a sensing diaphragm whose face is exposed to the liquid in the tank through an opening in said wall and whose periphery is bonded to the housing, and an insert seated in said well, the face of said insert being spaced from the diaphragm to define a fill chamber containing hydraulic fluid, the volume of hydraulic fluid in said fill chamber varying as a function of temperature, C. hydraulic means coupling said fill chamber to said beam whereby the force produced by the pressure of the liquid on said diaphragm is applied by the hydraulic fluid to said beam, said hydraulic means including a high-pressure chamber formed in the body of said meter and covered by a force-measuring diaphragm mechanically linked to the lower end of said force beam, and a capillary communicating between the fill chamber and said high-pressure chamber, said capillary being disposed within a support tube extending between the housing of the sensor and the meter body, said insert being formed of a metal having a coefficient of expansion that is low relative to the material of said housing, whereby variations in temperature produce changes in the dimensions of the housing relative to that of the insert and result in changes in the volume of said fill chamber to an extent compensating for concurrent changes in the volume of the hydraulic fluid, thereby rendering the force applied to said beam independent of said variations in temperature, D. a static pressure chamber formed in said meter body and covered by a second sensing diaphragm, said static pressure chamber and said high-pressure chamber being symmetrically arranged with respect to the force beam, and a second fill chamber extending between said force-measuring diaphram and said second sensing diaphragm, E. a second measuring diaphragm in parallel relation to said second sensing diaphragm to define a fill space, and F. a pin linking said second measuring diaphragm to said force beam.