Dwyer Series AT3A3000 Photohelic® Switch/Gages

 Flame-proof ATEX/IECEx approved Series AT3A3000 Photohelic® Switch/Gages, 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 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/IECEx 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.


  • 3-in-1 ATEX approved instrument allows the reduction of several instruments with one product, saving inventory, installation time and money
  • Flame-proof ATEX enclosure with optional glass window and aluminum housing protects the device in hazardous areas while giving local visibility to process pressure and set point status


  • Hazardous area pressure measurement and switching
  • Air conditioning systems
  • Clean rooms
  • Fume exhaust systems

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ServiceAir and non-combustible, compatible gases.
Wetted MaterialsConsult 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 Limits20 to 120°F (-6.67 to 48.9°C) LT low temperature option to -20°F available; (Note: Product temperature limits differ from case).
Dial Size4" (101.6 mm).
Mounting OrientationDiaphragm in vertical position
Set Point AdjustmentAdjustable knobs on Photohelic® gage face behind enclosure cover. Follow instructions and safety warnings to open cover.
Switch Specifications 
Switch TypeEach setpoint has 2 Form C relays (DPDT).
Repeatability±1% of FS.
Electrical Rating10 A @ 120 VAC, 6 A @ 240 VAC, 60 Hz res. 10 A @ 28 VDC.
Electrical WiringScrew terminals.
Power Requirements120 VAC, 50/60 Hz; 240 VAC & 24 VAC power optional.
Enclosure RatingIP66. IP65 with option OPV, overpressure relief valve.
Housing materialAluminum.
FinishingTexture epoxy coat RAL7038.
Pressure Connections1/8" NPT female brass (SS optional). In presence of acetylene it is necessary to use SS.
Electrical ConnectionsThree 1/2" FNPT. Cable gland not included.
Weight28.4 lb (12.9 kg).
ATEX CertificateBVI 14ATEX0072.
Agency ApprovalsTEX Compliant CE 1370 Ex II 2G Ex d IIC T6 Gb / II 2D Ex tb IIIC T85°C Db, -60°C=Tamb=+60°C IECEx Compliant: Ex d IIC T6 Gb / Ex tb IIIC T85°C Db

Download Data Sheet: Series AT3A3000 Photohelic® Switch Gages

Ref: dwyer-inst.com