What is Barton 288A?

The Barton* weatherproof Model 288A is a differential pressure indicating switch. The Model 288A has 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. The large cover lens allows maximum readability of the indicating pointer. Switches and all adjustments are readily accessible when the cover is removed. The built-in switches energize either single or dual alarm circuits when the measured differential pressures exceed predetermined limits. These limits may be either maximum, minimum, or both.

Theory of Operation

The Die-cast Aluminum indicating switch housing is attached directly to the actuating unit (224 DPU). The indicating switch assembly consists of a drive arm with an integral switch actuator cam, linkage, and a jeweled movement assembly to which the indicating pointer is attached. Also included are the Micro switches and associated linkages, switch set point indexes, and set point locks. Changes in differential pressure is sensed by the differential pressure units bellows and transmitted as rotary motion through the torque tube, to the drive arm assembly of the indicating switch. The linkage and movement assembly respond to the action of the drive arm assembly to position the pointer on the scale to the indication relative to the differential pressure sensed by the DPU and simultaneously actuate the switch when the desired setpoint is reached. It does this because the drive arm has an integral switch actuating cam and is attached to the torque tube shaft which rotates between 8-10 degrees with the motion of the torque tube shaft. Two cam follower roller/actuator arm assemblies, one for each switch, respond to drive arm movement by opening and closing the switches as they ride on and off the cam. The levels of differential pressure at which the switches actuate are adjustable with high and low alarm switch adjustment indexes below the scale plate.

Minor adjustments to the switch set point can be made without removing the scale plate. Barton Models 288A/288C can have up to 4 alarm switches, but one or two alarm switches are standard. Each switch can be connected to operate normally opened or normally closed. The switch set points are adjustable between 5-95% of the scale range. SPDT and DPDT switch configurations are available.

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.

The rotation of the 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 the 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.

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.

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