Dwyer A3000 Photohelic Switch / Gauges function as versatile, highly repeatable pressure switches combined with a precise pressure gauge employing time-proven Magnehelic gauge design. The A3000 measures and controls positive, negative or differential pressures of air and compatible gases. The A3000 can be ordered in ranges up to 150 inH2O, 30 psi, 8 kPa, 80 mmH2O, or 80 cmH2O and are accurate up to ±2% of FS at 70°F. Some bidirectional ranges are also available.

The Dwyer A3000 includes two phototransistor actuated, DPDT relays for low/high limit control. Easy to adjust set point indicators are controlled by knobs located on the gauge face. In typical applications, these Dwyer switch/gauges 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.