Dwyer, A3203, Series A3000 Photohelic Pressure Switch/Gage, 0-3 psid3-in-1 Indicating Gage, Lo-limit and Hi-limit ControlPhotohelic® Switch/Gagesfunction as versatile, highly repeatable pressure switches combined with a precise pressure gage employing the time-proven Magnehelic® gage design. The Photohelic® switch/gage measures and controls positive, negative or differential pressures of air and compatible gases. Two phototransistor actuated, DPDT relays are included for low/high limit control. Easy to adjust set point indicators are controlled by knobs located on the gage face. Individual set point deadband is one pointer width - less than 1% of full scale. Set points can be interlocked to provide variable deadband - ideal for control of fans, dampers, etc. Gage reading is continuous and unaffected by switch operation, even during loss of electrical power. Photohelic Sensing - How It WorksIn typical applications, these Dwyer switch/gages control between high and low pressure set points. When pressure changes, reaching either set point pressure, the infrared light to the limiting phototransistor is cut off by the helix-driven light shutter. The resulting phototransistor signal is electronically amplified to actuate its DPDT slave relay and switching occurs. Dead band between make and break is 1% of full scale or less - just enough to assure positive, chatter-free operation.Relay-Transformer Features A plastic housing protects all electronic components. Solid-state and integrated circuit electronics are on glass-epoxy printed circuit boards and self-extinguishing terminal boards.Product ApplicationsAir Conditioner SystemsClean RoomsFume Exhaust SystemsFeaturesBezel and front cover (with set point knobs and zero adjustment screw) removed to expose Photohelic® switch/gage set point mechanism.Cover is clear polycarbonate plastic.Gage pointer and light shutter are mounted on helix and balancing counterweight. Shutter passes through slot in optical limit switch to expose phototransistors to integral infrared light source or mask them depending on applied pressure.Light shield effectively protects phototransistors from strong outside light sources yet allows free pointer movement. It also gives interior a clean"finished" look.Optical limit switches are used for reliability and long service life. Attached directly to set pointers, they are individually aligned to assure precise switching accuracy.Semi-Flexible drive shaft connects to set point knobs.Zero adjustment screw connects to screw in cover to adjust zero pressure reading.Plastic enclosure protects electronic components and electrical connections.Polycarbonate connection or terminal board is self-extinguishing.Glass epoxy printed circuit boards for durability and permanence.Load relays are DPDT with latching feature for maximum application versatility.Electronics are designed to operate on 50/60 Hz, 120 volt current with 10% over or under voltage. Special units for other voltages are available.Switch set pointers show switch settings at all times.Spring loaded friction clutch prevents operator damage of set point mechanism.ApprovalsCSA Certified - Industrial Control EquipmentCSA Certified - SwitchesUL Approval - USCEGOST-R Certificate.