Dwyer 3000MR-500PA : Series 3000MR Photohelic Differential Pressure Switch/Gage, 0-500 Pa, Dual Setpoint Switches (Electromechanical SPDT), 24 VDC, 4 in Dial Face, Compact 3-1/8 in Depth, +/-2% FS Accuracy, CE

The 3000MR-500PA is a Series 3000MR Photohelic® Differential Pressure Switch/Gage — a compact, solid-state-controlled combination of a differential pressure gage and a dual-setpoint switch in one 4 in dial-face housing. This model is calibrated for 0-500 Pa. Compared to the standard Dwyer A3000 Photohelic, the 3000MR is much more compact (3-1/8 in deep vs. 8-1/4 in), much lighter (1.8 lb vs. 4 lb), and runs on 24 VDC instead of 120 VAC. Pressure ports are duplicated on both side and back. Switch is single-pole (Form C SPDT) rather than the A3000's DPDT — sufficient for most alarming applications.

Pick the 3000MR (electromechanical) when (1) you're switching low-voltage, low-current signal-level loads like PLC digital inputs, BMS contact closures, DCS inputs, or annunciator panels - the gold over clad silver contacts are specifically designed for these dry-circuit conditions; (2) you need both N.O. and N.C. contacts available per setpoint - the Form C SPDT relay gives you both; (3) you're switching DC loads - the MR handles up to 1.0 A @ 30 VDC, the MRS is AC-switching only. Pick the 3000MRS (solid-state) if the application involves high cycle rates (rapid alarm sequencing, OEM cycling equipment, automated test stands) where electromechanical contact wear would limit life - solid-state relays have effectively unlimited switching life with no contact bounce or wear, but are AC-only (20-280 VAC) and N.O. only.

The 3000MR requires 24 VDC regulated power, +/-10% tolerance — it is not designed for AC line voltage (do NOT apply 120 VAC to the power input or you will damage the unit). Wiring is via an included 18 in (45 cm) cable assembly with a multi-pin female connector on one end (plugs into the rear of the gage) and bare lead wires on the other end (terminate to your control panel terminal strip). The harness has 8 conductors: Red (24 V+), Black (24 V-), Brown (Low Setpoint COM), Violet (Low Setpoint NC), Blue (Low Setpoint NO), Green (High Setpoint COM), White (High Setpoint NC), Orange (High Setpoint NO). Optional cable lengths to 100 ft (30.5 m) available from Dwyer.

Yes, recommended for switching inductive loads (solenoid valves, contactor coils, relay coils, motor starter coils, etc.). The R/C snubber suppresses the inductive kickback that would otherwise pit and erode the gold-over-silver contacts. Order Dwyer P/N A-600. For DC inductive circuits, additionally include a 1N4005 flyback diode across the inductor in reverse-bias configuration. For pure resistive loads (e.g. driving a PLC input), no snubber is required.

Two mounting methods are supported: (1) Panel mounting - cut a 4-3/4 in (120 mm) diameter hole in the panel, insert the gage from the front, slip on the supplied mounting ring and snap ring from behind, and tighten the four supplied 6-32 x 1-1/4 in screws. (2) Surface mounting - drill three 3/16 in diameter mounting holes (4-1/8 in bolt circle) and one 7/8 in wire-pass hole on the mounting surface, then screw the gage into place with the three supplied 6-32 x 5/16 in screws. If using rear pressure ports, also drill two 1/2 in clearance holes for the tubing. For -SS stainless bezel option: panel hole is 4-9/16 in (matches the Magnehelic® gage cutout for drop-in field upgrade).

The gage has two complete sets of 1/8 in female NPT pressure ports — one set on the side, one set on the back. Use only one set, and plug the unused set with the supplied 1/8 in NPT pipe plugs. Choose whichever orientation suits your tubing routing — the side ports work well for surface-mounted gages, the back ports for through-panel installations where tubing runs straight back out of the panel. Connect the higher-pressure source to the HI port, the lower-pressure source (or atmosphere reference for gauge readings) to the LOW port. Zero the gage before plumbing the pressure source — with both ports open to atmosphere, turn the small slotted screw at center-bottom of the gage face until the needle reads exactly zero.

Yes — that's the purpose of the -SS stainless bezel option. The -SS bezel has the same installation diameter as a standard Magnehelic® gage. Field upgrading from a Magnehelic to this Photohelic switch/gage requires no new hole cutting in the panel: simply unscrew the Magnehelic, swap in this Photohelic with the -SS bezel, secure with the supplied mounting hardware, and wire up the 24 VDC harness. Order code: 3000MR-500PA-SS. Note: this only applies when ordered with the -SS option; the standard bezel uses a 4-3/4 in / 120 mm panel cut.

Standard rating: 25 psig (1.72 bar) with -20 in Hg (-0.677 bar) negative pressure handling. For higher-pressure systems, two factory-installed options upgrade the rating: -MP option (Medium Pressure): 35 psig (2.41 bar) max, and -HP option (High Pressure): 80 psig (5.52 bar) max. Specify the option suffix at order time. Temperature range is 20-120 deg F (-6.67 to 48.9 deg C); for use below 20 deg F, specify the -LT low-temperature option. For weatherproof outdoor installations, the -WP option adds a weatherproof housing.