Dwyer Digihelic Series DH Differential Pressure Controller

Fits HVAC and clean-process panels that need a 1/8 DIN 3-in-1 Digihelic — gage + dual switches + transmitter — with ±0.5% accuracy, scalable 4–20 mA, two SPDT relays, and Modbus RTU, not a Magnehelic-only gage.

Key advantages

• 3-in-1 Digihelic — Differential pressure gage, dual set-point switches, and transmitter in one 1/8 DIN controller.
• Ranges — Unidirectional 0.25–100 in w.c. and bi-directional ±0.25…±10 in w.c. (DH-002…017 model chart); pressure / velocity / flow engineering units.
• Accuracy — ±0.5% at 77 °F (25 °C) including hysteresis and repeatability (after 1 hour warm-up).
• I/O — Scalable 4–20 mA DC into 900 Ω max; 2× SPDT relays 8 A @ 240 VAC; Modbus RTU RS-485 9600 baud.
• Panel / power — Face designed to meet NEMA 4X (IP66); 100–240 VAC / 132–240 VDC or 24 VDC ±20%; cutout 1.772 × 3.620 in (45 × 92 mm).

Typical applications

• HVAC filter and room differential pressure control with dual relay setpoints.
• Cleanroom or isolator DP indication plus 4–20 mA to a BMS.
• Fan/duct velocity or flow indication when using Digihelic velocity/flow engineering units.
• Panel upgrades that replace separate gage + switch + transmitter with one DH controller.

Selection guide

• Range code — Pick DH-002…017 from the OEM chart (0.25–100 in w.c. uni or ±0.25…±10 in w.c. bi-dir) before RFQ.
• Engineering units — Pressure, velocity, or flow — state which display units the loop uses.
• Supply — High-voltage 100–240 VAC (50–400 Hz) / 132–240 VDC vs low-voltage 24 VDC ±20%.
• Outputs — Confirm need for 4–20 mA scaling, both SPDT relays, and/or Modbus RTU RS-485.
• Fittings — Compression for 1/8 in ID × 1/4 in OD tubing; optional −B barb for 3/16 in ID; horizontal 1/8 DIN mount.

Common mistakes

• Ordering without a DH range code — accuracy and span are model-chart specific.
• Expecting vertical mounting — OEM mounting is horizontal-plane 1/8 DIN panel mount.
• Skipping the 1-hour warm-up when verifying the ±0.5% accuracy claim.
• Confusing Series DH Digihelic with Digihelic II (DHII) — confirm series before RFQ.

When to RFQ / what to tell us

1. Differential range (in w.c.), uni vs bi-directional, and pressure/velocity/flow units.
2. Supply (100–240 VAC / 132–240 VDC vs 24 VDC), relay + 4–20 mA + Modbus needs.
3. Fitting preference (compression vs −B barb), quantity, ship-to, and any factory/NIST certificate need.

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Specs

Documents

• Dwyer Digihelic Series DH instruction manual (PDF)
• Dwyer Digihelic Series DH catalog sheet (PDF)

FAQ

Q: What does “3-in-1” mean on Digihelic DH? A: One instrument combines differential pressure indication, two SPDT set-point relays, and a scalable 4–20 mA transmitter (plus Modbus RTU).

Q: Which range do I order? A: Use the OEM DH-002…017 chart for 0.25–100 in w.c. unidirectional or ±0.25…±10 in w.c. bi-directional — state the code or span on the RFQ.

Q: What should I send for a quote? A: Range, supply, outputs, fittings, quantity, ship-to. Compatible with systems using Dwyer Digihelic Series DH — we do not claim authorized-dealer status.

Links

• Pressure instruments · Pressure transmitter buying guide
• Request a Quote · Get selection help