Dwyer Instruments’ flame-proof, ATEX-approved Photohelic switch/gauge, Series AT3A3000, combines a highly repeatable pressure switch with a precise pressure gauge employing Dwyer’s Magnehelic gauge design. The Photohelic switch/gauge measures and controls positive, negative or differential pressures of air and compatible gases. Standard models are rated to 25 PSIG (1.7 bar) with options to 35 PSIG (2.4 bar) or 80 PSIG (5.5 bar). Two phototransistor-actuated DPDT relays are included for low/high limit control. Adjustable set-point indicators are controlled by knobs located on the gauge face (accessible opening case after de-energizing instrument). Set points can be interlocked to provide variable dead band, suitable for control of fans, dampers, etc. Gauge reading is continuous and unaffected by switch operation, even during loss of electrical power. Series AT3A3000 flame-proof ATEX enclosures are available with glass window, which allows for viewing of set-point needles and process pressure.