105/ 106 sensor unit, styled by Switzer Instrument Limited, consists of an assembly of sensitive multiple diaphragm [capsule] or bellows which reacts to differential pressure across it. The output motion of the diaphragm/ bellows assembly is channelised by a free spring torque tube through the wall of the pressure housing. The output motion of the torque tube forces an external pointer movement. A test gauge quality bourdon tube assembly powers Switzer style 109. It is enclosed in a high-pressure chamber fitted with a pressure connection to the inside of the bourdon tube and a second connection to the pressure chamber. Switzer style 180 DP gauges are Diaphragm operated with ranges from0-125 mmWC to 0-1.0 bar. The gauge is isolated from the pressure changes through a unique magnetically coupled movement. These DP gauges can be installed in level monitoring [or] DP measurement. Switzer style 120 gauges consist of a piston opposed by a calibrated spring. A barium ferrite magnet implanted in the piston actuates a rotary magnet, which in turn drives the indicating pointer. It is an excellent choice for monitoring filters and pressure differences. Switzer Mid-West Locked Logic Control [LLC] system is an all-solid state switching facility available in 105, 106 & 109 differential pressure indicating instruments for one or two set points. This LLC system applies miniaturized solid-state components that have proved their reliability and austerity in a variety of industrial process applications.