Dwyer Series A3000 Photohelic® Pressure Switch/Gage

 Known for quality, reliability and accuracy, Dwyer designs and manufactures a full-line of Controllers, Data Loggers, Gages, Manometers, Monitors, Remote Displays, Switches, Transmitters, and Accessories to measure, monitor and control pressure, air velocity, flow, fan pressure, duct, and more.

Dwyer’s wide selection extends to Gages, Transmitters, Switches, Data Loggers, and Monitors for Differential Pressure. Dwyer manufactures a range of dial and digital gages to reliably measure and display pressure difference, between two pressure sources using gas or liquid in a process flow.

Dial Gages and Switches are compatible with air and other non-combustible and non-corrosive gases. Dial Gages and Dial Switches are indicators for the difference between two pressures that also have switch outputs. They can also be used for single pressure.

The Series A3000 Photohelic® Pressure 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 dead-band is one pointer width - less than 1% of full scale. 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. Choose from full scale pressure ranges from a low 0-.25 in (0-6 mm) w.c. up to 30 psi (21 bar).


  • 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:


Gage Specifications 
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" 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). -20 to 120°F (-28 to 48.9°C) with low temperature option.
Process Connections1/8" female NPT.
Size4" (101.6 mm) dial face, 5" (127 mm) O.D. x 8-1/4" (209.55 mm).
Weight4 lb (1.81 kg).
Switch Specifications 
Switch TypeEach setpoint has 2 Form C relays (DPDT).
Repeatability±1% of FS.
Electrical Rating10 A @ 28 VDC, 10 A @ 120, 240 VAC.
Electrical ConnectionsScrew terminals. Use 167°F (75°C) copper conductors only.
Power Requirements120 VAC, 50/60 Hz; 240 VAC & 24 VAC power optional.
Mounting OrientationDiaphragm in vertical position. Consult factory for other position orientations.
Set Point AdjustmentAdjustable knobs on face.
Agency ApprovalsCE, CSA, UL.

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

Ref: dwyer-inst.com