Dwyer A3000 Photohelic Pressure Switch / Gages

Dwyer A3000 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 (2.4) or 80 (5.5 bar) psig. 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. Choose from full scale pressure ranges from a low 0-.25 in (0-6 mm) w.c. up to 30 psi (21 bar).

Dwyer A3000 Photohelic Features

  • Bezel 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.


  • Air Conditioning Systems
  • Clean Rooms
  • Fume Exhaust Systems

Another Article:

Dwyer A3000 Photohelic Specification

Gage Specifications
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″ 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). -20 to 120°F (-28 to 48.9°C) with low temperature option.
Process Connections 1/8″ female NPT.
Size 4″ (101.6 mm) dial face, 5″ (127 mm) O.D. x 8-1/4″ (209.55 mm).
Weight 4 lb (1.81 kg).
Switch Specifications
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 Connections Screw terminals. Use 167°F (75°C) copper conductors only.
Power Requirements 120 VAC, 50/60 Hz; 240 VAC & 24 VAC power optional.
Mounting Orientation Diaphragm in vertical position. Consult factory for other position orientations.
Set Point Adjustment Adjustable knobs on face.
Agency Approvals CE, CSA, UL.

Download Data Sheet: Series A3000 Photohelic® Pressure Switch/Gage

Ref: dwyer-inst.com

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