Adjustable overload mechanism for a differential pressure transmitter

Abstract

An adjustable overload mechanism for a differential fluid pressure transmitter includes a first and a second overload control diaphragm and an adjustable spring pressure means for applying an adjustable preload pressure to the control diaphragms. The spring pressure means for each diaphragm includes a spring such as a Belleville washer spring located between a diaphragm back-up plate in contact with a side of the control diaphragm and a wedge shaped support for the Belleville washer spring. A wedge shaped drive means is arranged to be selectively movable with respect to the wedge shaped spring support while maintaining the sloping wedge surfaces in contact. An adjustable drive screw is connected to the drive wedge to provide a means for changing the relative position of the support wedge and drive wedge. The relative motion between the two wedge shaped elements displaces the support wedge transversely to the Belleville washer to change the height of the Belleville washer which affects the preload or spring pressure against the control diaphragm. Each control diaphragm is used to control the valving of a fill fluid in contact with a respective barrier diaphragm subjected to an input fluid pressure. The fill fluid is pressurized by the movement of the barrier diaphragm and transmits the input pressure to a pressure sensor. An excessive or overload input pressure overcomes the preload or spring pressure biasing the control diaphragm to divert the fill fluid displaced by the barrier diaphragm to protect the sensor from the overload pressure.