Abstract: A process control instruments includes a sensor for sensing a process variable in a processing environment, and a switch, a gauge, and a transmitter. The sensor, switch, gauge, and transmitter, a controller to which each of the stated and related components are connected, are powered via a two-wire power loop. In particular, the two-wired power loop also comprises the transmitter, such that the controller, upon receiving information indicative of the level of a variable being sensed by the sensor, modulates the amplitude of the current on the two-wire loop to a level corresponding to the level of the processed variables sensed. Each of the switch, gauge, and transmitter are independently scalable. In the preferred embodiment of the invention, a pair of switches in the form of relays are provided, and a logic circuit operates to power the components of the invention, with the exception of the relays, when the process variable being sensed with within a selected range.

Abstract: A movable piston is supported by a flexible angular membrane around the perimeter of the piston in a piston chamber, having opposed walls which confront the opposite faces of the piston. The chamber has low and high pressure sides at said opposite sides of the piston. The potential movement of the piston is limited by contact of the piston face with the chamber wall, with the entire resistance to piston movement beyond the limit point being born by the chamber. The piston controls activation of an electric switch in response to movement of the piston.

Abstract: A pressure switch device having a fire resistant welded assembly of corrosion resistant steel components exposed to the fluid medium which is being monitored. A flexible diaphragm constructed of corrosion resistant steel film is overlaid by a backing disc and backing ring both formed of corrosion resistant steel. Inside the backing ring is an elastomer disc which receives a stainless steel piston that moves up and down in response to changes in the fluid pressure applied to the diaphragm through a pressure port. The piston has a shaft which actuates an electrical switch in response to changes in the pressure of the fluid medium. The periphery of the diaphragm is secured by a pressure tight weld to the housing, the upper corrosion resistant steel disc and the backing ring to provide a fire resistant assembly which confines the pressure medium in the event of a fire.

Abstract: A switch which is actuated when a preselected fluid pressure differential is exceeded. A piston exposed to the pressure differential carries a plunger which contacts a lever arm mounted on a shaft. A spring normally prevents the shaft from turning but is overcome when an excessive pressure differential is applied across the piston. A switch arm mounted on the shaft actuates the switch in response to turning of the shaft.