TRANSMITTER WITH MAGNETIC ZERO/SPAN ACTUATOR

摘要

A transmitter (10) for use in a process control system has externally accessible actuators for permitting adjustment of the zero and span (or full scale) settings of the transmitter (10). The transmitter (10) has an explosion-proof housing (12) which includes an interior chamber (14, 16) in which transmitter circuitry is located. Each of the actuators includes a movable magnet (52A, 52B) which operates a magnetic reed switch (62A, 62B) located within the interior chamber (14) of the housing (12) through a wall (17) of the housing (12). By moving the magnet (52A, 52B) the corresponding reed switch (62A, 62B) can be changed from a non-actuated to an actuated state. When the zero reed switch (62A) is actuated, the transmitter circuitry adjusts its output so that the present value of the parameter represents a process zero. When the span reed switch (62B) is actuated, the transmitter circuitry adjusts its output so that the present value of the sensed parameter represents a process maximum.