Series A3000 Photohelic Pressure Switch/Gauge

Brand: Dwyer Instruments, LLC

The Series A3000 Photohelic® Switch/Gauges function as versatile, highly repeatable pressure switches combined with a precise pressure gauge employing the time-proven Magnehelic® gauge design.

The Photohelic® switch/gauge 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 gauge 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.

Gauge reading is continuous and unaffected by switch operation, even during loss of electrical power. Choose from full scale pressure ranges from a low 0-0.25 inches WC (0-6 mm) up to 30 psi (21 bar); single positive pressure to 6,000 psig (413 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.
  • Electronics are designed to operate on 50/60 Hz, 120 volt current with 10% over or under voltage. Special units for other voltages are available.
  • Switch set pointers show switch settings at all times.
  • Spring loaded friction clutch prevents operator damage of set point mechanism.
  • 3-in-1 instrument allows the reduction of several instruments with one product, saving inventory, installation time and money.
  • Patented design and 1% full scale dead band provides quick response to pressure changes means no delay in switching and chatter-free operation.
  • A wide range of models that can meet pressure measurement specifications from low to very high.



  • Flat Flush Mounting Bracket


  • ± 2 % of Full Scale at 21.1° C (70° F)
  • ± 3 %
  • ± 4 % of Full Scale

Adjustment Type

  • Adjustable Knobs on Face

Approvals & Certifications

  • CE
  • CSA
  • UL

Electrical Connectors

  • Screw Terminal 75° C (167° F) Copper Conductors Only

Electrical Rating

  • 10 A at 120/240 Vac
  • 10 A at 28 Vdc


  • Air & Non-Combustible, Compatible Gases

NPT Connection

  • 1/8” NPT Female

Power Requirement

  • 120 Vac, 50/60 Hz
  • 24 Vac
  • 240 Vac


  • ± 1 % of Full Scale

Sensor Orientation

  • Diaphragm in Vertical Position

Set Point - Decreasing

  • Inches WC: -10 to 100
  • kPa: 0 to 30
  • Millimeters WC: 0 to 100
  • Pa: -250 to 750

Set Point - Increasing

  • Inches WC: -10 to 100
  • kPa: 0 to 30
  • Millimeters WC: 0 to 100
  • Pa: -250 to 750


  • Dial: 4” (101.6 mm)
  • Dial: 5” (127 mm) O.D. x 8-1/4” (209.55 mm)

Switch Type

  • DPDT (Each Set Point Has 2 Form C Relays)

System Pressure

  • bar: 5.5
  • kPa: 550
  • psig: 80 (For hp Version. 35 for MP Version & 25 for Regular Version)

Temperature Range

  • -6.7° to 48.9° C (20° to 120° F)

  • Air Conditioning Systems
  • Clean Rooms
  • Fume Exhaust Systems
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