1. Differential
Pressure
Switch/Gages
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2. Differential Pressure
Switch/Gages
•Photohelic
•3000MR/MRS
•Capsu-Photohelic
•Mini-Photohelic

3. Magnehelic Principle
The Photohelic and Capsu-Photohelic
models combine our most precise
pressure switch with our time-
proven Magnehelic design. The
knob controls adjust the set points.
Two phototransistor actuated, DPDT
relays are included for low/high
limit control.

4. Typical Applications
To measure liquid level
Use a Photohelic®, Magnehelic®, or Minihelic® gage in conjunction with a
Dwyer flowmeter with constant differential pressure regulator as show.
Flowmeter provides constant rate of purge air to dip tube. Changes in liquid
level affect head, causing static pressure changes inside tube. These
changes are sensed by the gage. This same kind of setup will also detect
specific gravity changes in the liquid if level is kept constant. Using a Dwyer
Photohelic® pressure switch/gage instead of the Magnehelic® permits both
measuring and controlling liquid level plus easily changing the level control
settings.
To control pressure in air-inflated buildings
Photohelic® switch/gage senses over-pressure that may extend building, or
loss of pressure that may cause collapse, and controls the blower to
maintain correct pressure. Gage is easily reset to conserve power - or
provide extra pressure to resist strong winds.
To control material weight
On paper making or textile machinery, a Photohelic® switch/gage
controls weight of material gathered by sensing pressure changes
caused by changes in permeability and thickness of the material.

5. Typical Applications
Monitor air conditioning systems
Adjustments in air flow due to seasonal changes may require resetting the
control points on a regular basis. The Photohelic® unit's ability to monitor
pressures through the gage portion also permits accumulation of operating
data. This is useful in adjusting operation of variable pressure and volume
systems and in making system changes when necessary.
For life support or kidney machines
Photohelic® switch/gage controls pressure on circulating system of
machine and alarms in event of too high or low pressure.

6. Specifications
Series A3000/3000
Photohelic Differential Pressure Switch/Gages
• Media: Air and non-combustible, compatible
gases
• Pressure Limits: -20” Hg to 25 psig
• Temperature Limits: 20o to 120o F
• Connections: 1/8” female NPT
• Accuracy: +/- 2% full scale (3% on -0, 4% on -00 ranges)
• Wetted Parts: Aluminum housing with silicone
diaphragm
• Power Supply: 120 VAC
• Special Note: For non UL/CSA listed Photohelic
models delete the “A” prefix from the model
number.

7. Design & Construction
Features
1. Bezel and front cover (with set point knobs and zero
adjustment screw) removed to expose Photohelic set point
1 mechanism. Cover is clear polycarbonate plastic.
2 2. Gage pointer and light shutter are mounted on helix and
balancing counterweight. Shutter passes through slot in optical
3
limit switch to expose phototransistors to integral infrared light
source or mask them depending on applied pressure
3. Light shield effectively protects phototransistors from strong
4 outside light sources yet allows free pointer movement. It also
gives interior a clean "finished" look.
4. Semi-Flexible drive shaft connects to set point knobs.
5 5. 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.
6
6. Zero adjustment screw connects to screw in cover to adjust
zero pressure reading.

8. Design & Construction
Features
7. Plastic enclosure protects electronic components and
7 electrical connections.
8 8. Polycarbonate connection or terminal board is self-
9 extinguishing(A3000 only).
9. Glass epoxy printed circuit boards for durability and
permanence.
10 10. Load relays are DPDT with latching feature for maximum
application versatility.
11. Electronics are designed to operate on 50/60 Hz, 120 volt
current with 10% over or under voltage. Special units for other
11 voltages are available.
12. Switch set pointers show switch settings at all times.
12 13. Spring loaded friction clutch prevents operator damage of
set point mechanism.
13

9. Options
• -24VAC: 24 VAC Relay Pack • -M: Mirror Overlay
• -240VAC: 220/240 Relay Pack • -MP: Medium Pressure (35 psi)
• -EXPL: Explosion Proof Housing • -NIST: NIST Certificate
• -G: Green Overlay • -RMR: Remote Mounted Relay (5ft)
• -HC: Horizontal Calibration • -SRH: Single Right Hi Latching
• -HJ: Helix Jump Preventer • -SRL: Single Right Lo Latching
• -HP: High Pressure (80 psi) • -R: Red Overlay
• -OLS: Less Relay • -TAMP: Tamperproof Knobs
• -LT: Low Temperature • -WP: Weather Proof Housing
Accessories: A-601, manual reset switch

10. Special Scales
Like the Magnehelic, Dwyer also
offers special scales on the
Photohelic. Any equivalent range
within the gage’s capabilities can be
made. These scales include ranges
in Pa, KPa, mm WC, and inches Hg
or flow ranges in FPM, CFM, GPM,
CFH, M3H, and PPH.

11. Specifications
Series 43000
Capsu-Photohelic Differential Pressure Switch/Gages
• Media: Compatible gases and liquids
• Pressure Limits: -20” Hg to 500 psig
• Temperature Limits: 20o to 120o F
• Connections: 1/4” female NPT
• Accuracy: +/- 3% full scale (2% on 43000S models, 4% on
43215, 43220, 43500)
• Wetted Parts: Aluminum housing with silicone
diaphragm, optional brass housing
• Power Supply: 120 VAC

12. Options
• -24VAC: 24 VAC Relay Pack • -M: Mirror Overlay
• -240VAC: 220/240 Relay Pack • -NIST: NIST Certificate
• -EXPL: Explosion Proof Housing • -RMR: Remote Mounted Relay (5ft)
• -G: Green Overlay • -SRH: Single Right Hi Latching
• -HC: Horizontal Calibration • -SRL: Single Right Lo Latching
• -OLS: Less Relay • -R: Red Overlay
• -LT: Low Temperature • -TAMP: Tamperproof Knobs
• -WP: Weather Proof Housing

13. Special Scales
Dwyer also offers special scales on
the Capsu-Photohelic. Any
equivalent range within the gage’s
capabilities can be made. These
scales include ranges in Pa, KPa,
mm WC, and inches Hg or flow
ranges in FPM, CFM, GPM, CFH,
M3H, and PPH.

14. Specifications
Series 3000MR/MRS
Photohelic Differential Pressure Switch/Gages
• Media: Air and non-combustible, compatible
gases
• Pressure Limits: -20” Hg to 25 psig
• Temperature Limits: 20o to 120o F
• Connections: 1/8” female NPT
• Accuracy: +/- 2% full scale (3% on -0, 4% on -00 ranges)
• Wetted Parts: Aluminum housing with silicone
diaphragm
• Power Supply: 24 VDC

15. Differences from
standard model
Only 2 SPDT contacts on MR model.
The MRS has SPST solid state outputs.
3000MR/MRS has cable for wiring
instead of screw terminal relay pack.

16. Options
• -24VAC: 24 VAC Relay Pack • -LT: Low Temperature
• -EXPL: Explosion Proof Housing • -MP: Medium Pressure (35 psi)
• -G: Green Overlay • -M: Mirror Overlay
• -HC: Horizontal Calibration • -NIST: NIST Certificate
• -HJ: Helix Jump Preventer • --R: Red Overlay
• -HP: High Pressure (80 psi) • -TAMP: Tamperproof Knobs
• -WP: Weather Proof Housing

17. Specifications
Series MP
Mini-Photohelic Differential Pressure Switch/Gages
• Media: Air and non-combustible, compatible
gases
• Pressure Limits: 30 psig
• Temperature Limits: 20o to 120o F
• Connections: Barbed for 3/16” tubing
• Accuracy: +/- 5% full scale
• Wetted Parts: Nylon housing with silicone
diaphragm
• Power Supply: 24 VDC or 24 VAC

18. Questions
To order a free catalog or for more information contact;
Dwyer Instruments, Inc., P.O. Box 373,
Michigan City, IN., 46361
Telephone: (800) 872-9141 or (219) 879-8000
Fax: (219) 872-9057
Internet address: www.dwyer-inst.com
E-mail: info@dwyer-inst.com