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Dwyer Series AT3A3000

ATEX Approved Photohelic Switch

Dwyer Series AT3A3000
Dwyer Series AT3A3000

Photohelic® Switch/Gages in Flame-Proof ATEX Enclosures

Flame-proof ATEX approved Dwyer Series AT3A3000 ATEX Approved Photohelic Switch, function 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. 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. Easy to adjust set point indicators are controlled by knobs located on the gage face (accessible opening case after de-energizing instrument). Set points can be interlocked to provide variable dead band – ideal for control of fans, dampers, etc. Gage reading is continuous and unaffected by switch operation, even during loss of electrical power. Flame-proof ATEX enclosures are available in aluminum with glass window which allows for viewing of set point needles and process pressure.

Important notes for installation:
• Cables must be fitted through 1/2″ NPT cable gland or ATEX conduit (not supplied with instrument).
• Make sure after cabling to close tight cover and cable gland, in order to keep IP66 rating (IP65 with option OPV, overpressure relief valve).
• Open cover only after de-energizing instrument.
• Attention: Check local safety rules and warnings on unit and manual for a correct use of the instrument in hazardous area.


  • Service:Air and non-combustible, compatible gases.
  • Wetted Materials:Consult factory.Accuracy:±2% of FS at 70°F (21.1°C); ±3% on -0 and ±4% on -00 models.
  • Pressure Limits:-20 in Hg to 25 psig (-0.677 to 1.72 bar). MP option; 35 psig (2.41 bar), HP option; 80 psig (5.52 bar).
  • Temperature Limits:20 to 120°F (-6.67 to 48.9°C) LT low temperature option to -20°F available; Case: -76 to 140°F (-60 to 60°C) (Note: Product temperature limits differ from case).Dial Size:4″ (101.6 mm).
  • Mounting Orientation:Diaphragm in vertical position.
  • Set Point Adjustment:Adjustable knobs on Photohelic® gage face behind enclosure cover. Follow instructions and safety warnings to open cover.


  • Switch Type:Each setpoint has 2 Form C relays (DPDT).
  • Repeatability:±1% of FS.Electrical Rating:10 A @ 28 VDC, 10 A @ 120, 240 VAC.
  • Electrical Wiring:Screw terminals.Power Requirements:120 VAC, 50/60 Hz; 240 VAC & 24 VAC power optional.
  • Enclosure Rating:IP66. IP65 with option OPV, overpressure relief valve.
  • Housing material:Aluminum.Finishing:Texture epoxy coat RAL7038.
  • Pressure Connections:1/8″ NPT female brass (SS optional). In presence of acetylene it is necessary to use SS.
  • Electrical Connections:Three 1/2″ FNPT. Cable gland not included.
  • Weight:28.4 lb (12.9 kg).
  • ATEX Approved Products from Comhas with ECN:BVI 14ATEX0072.
  • Agency Approvals:CE 1370 II2 GD Ex d IIC Gb T6; -60°C ≤ Ta ≤ +60°C Ex tb IIIC Db T 85°C.