Rotation of DPU torque tube shaft of the Barton MODELS 288A/288C/290D is coupled through connecting linkage within the switch case to move the pointer across the scale plate. An actuating cam, directly connected to torque tube shaft, rotates with the motion of the shaft. Two cam follower roller/actuator arm assemblies, one for each switch, respond to torque tube rotation by opening and closing the switches as they ride on and off the cam. The levels of DP at which the switches actuate are adjustable with high and low alarm switch adjustments on the scale plate.
The weatherproof Models 288A, 288C, and the explosion-proof Model 290D of Barton are DP Indicating Switches. The 288A and 288C have a NEMA-4 watertight die-cast aluminum case (finished with a weather-resistant black epoxy resin paint). The cover lens is secured in the bezel with an elastomer ring to reduce the possibility of accidental breakage. This ring also acts as a seal between the bezel and the case to ensure a moisture, fume and dust-free atmosphere for the indicator and switch mechanism. Barton Model 290D has an explosion-proof case that is certified for Class I, Division 1, Groups B, C & D service. The large cover lens allows maximum readability of the indicating pointer.
Barton MODELS 288A/288C/290D can have one or two alarm switches. Each switch can be connected to operate normally-opened or normally-closed. The direct-set switch contacts are adjustable over a scale range of 5-95% nominal.