ACI A/DLP-D50-W-U-N-B-0-A-3P-S : Differential Low Pressure Transmitter, 0-0.5 in WC Unidirectional, 4-20 mA Output, +/-0.25% Accuracy, No LCD, 3-Point NIST Certificate, 5-Yr Warranty, Made in USA

What does the A/DLP-D50-W-U-N-B-0-A-3P-S measure and output?

It measures differential air pressure in the 0 to 0.5 inch WC range (unidirectional) and outputs a linear 4-20 mA analog signal proportional to the pressure. Accuracy is +/-0.25% FSO including linearity, hysteresis, and repeatability. The DLP is intended for HVAC and process applications using dry air or other non-corrosive, non-ionic gases - not liquids, refrigerants, or corrosive vapors.

Can I change the range or output mode in the field?

No - this is a custom-calibrated DLP. The range and output mode are set at the factory and the DIP switches are locked (per ACI's I0000977 installation manual: "This is a custom calibrated DLP and the output span switches CANNOT be adjusted"). If you need a field-selectable multi-range DLP, see the legacy catalog SKUs (A/DLP-001-W-U-N-A-0, A/DLP-010-W-U-N-A-0, A/DLP-040-W-U-N-A-0 and their LCD variants) - those ship with 8 selectable ranges per unit.

Should I use unidirectional or bidirectional mode?

This SKU is unidirectional (0 to +X) - correct for almost all HVAC applications where the HI port is always at higher pressure than the LO port: duct static measurements, filter loading, room-to-corridor pressurization. For applications where pressure can swing across zero (reversible-flow systems, makeup-air with mode switching, isolation rooms that flip between positive and negative pressure), order a bidirectional variant (direction code B) where 0 differential maps to mid-scale output.

When and how should I zero the device?

Zero on initial installation, after re-positioning, and any time the unit reads a non-zero offset with no pressure applied. Procedure: (1) Remove the tubing from the HI and/or LO pressure fittings (or short them together to neutralize external pressure). (2) Press and hold the ZERO button for more than 3 seconds, then release. For LCD variants, the AUTOZERO icon will appear on the screen during zero mode and flash twice on successful completion. The Span calibration is digital and factory-set; units requiring Span re-calibration must be returned to ACI.

What does the 3-Point NIST Certificate include?

The 3-Point NIST cert (10%, 50%, 90% FSO) documents the calibration measurements performed on this specific unit, with all measurements traceable to NIST standards. The 3-point cert documents readings at 10%, 50%, and 90% of full scale output - suitable for HVAC commissioning, spec-engineer documentation, and cleanroom certification baselines. The certificate ships with the unit; digital copies can be requested through ZOT Supply.

What accessories do I need for installation?

Required: pressure-sense tubing (0.25" OD x 0.17" ID medical-grade PVC - A/10' TUBE, A/20' TUBE, A/50' TUBE, A/100' TUBE), 16-24 AWG shielded cable, and a 24 VAC or 15-36 VDC power supply. Application-dependent: pitot tube for direct duct-static measurement - the DLP-specific A/PT-DLP (7") threads into the back of the enclosure, or use generic ACI pitots (PT 3", PT 5.2", PT 7.5", PT 9.7" with foam gaskets; SPT-3.5" / SPT-8.0" static; VPT / VPT-8" velocity). DIN rail clip for panel mounting: A/DRC-DLP (35 mm). Pickup ports for wall/room pressure taps: A/SP-PUP, A/R-PUP, A/R2-PUP, or outdoor weatherproof A/O-PUP-H / A/O-PUP-V. Keep tubing runs under 75 feet (23 meters).

Any tips for getting accurate readings on this ultra-low range?

Below 1 inch WC, several factors can swamp the signal: (1) Mount vertically with brass fittings pointing down - prevents condensation from affecting the sensor (horizontal mounting can cause a small zero shift). (2) Keep tubing runs short - long runs introduce lag. (3) Re-zero after installation and after temperature swings. (4) Avoid sharing the 24 VAC transformer with inductive loads (VFDs, relays, solenoids) - induced noise on the supply rail shows up as small offsets at these low ranges. (5) If 24 VDC or VAC power is shared with coils, add MOVs, Transorbs, or flyback diodes across each coil per ACI's installation guide.

How does the DLP compare to the MLP2?

Both are differential low-pressure transmitters using the same piezoresistive silicon sensing technology. DLP advantages: larger enclosure with hinged cover for easier zero/output access, optional 5-digit LCD display on the unit cover, watertight cordgrip for environmental sealing, factory-bundled Pitot/DIN rail accessory options, broader range coverage (up to 0-40" WC vs MLP2's 0-30" WC). MLP2 advantages: smaller compact form factor (designed for OEM/panel density), integrated DIN rail foot, lower price point. Choose DLP for applications needing the LCD, larger enclosure, or wider range options; choose MLP2 for OEM/panel-density installations.

What media can this sensor handle?

Dry air and inert non-conductive gases only: clean ambient air, nitrogen, argon, dry CO2. The DLP is NOT compatible with: liquids, refrigerants, corrosive gases (chlorine, ammonia, hydrogen sulfide, acid fumes), conductive gases, condensing moisture, or media containing particulates. Liquid contamination at the sensor diaphragm causes immediate damage and voids the warranty. For wet/wet differential pressure applications, see Senva PW30 or Belimo 22PDP series in the Liquid Pressure subcategory.

What's the warranty?

5-Year ACI Limited Warranty - covers manufacturing defects in materials and workmanship under normal use. Manufactured in Middleton, Wisconsin, USA. ZOT Supply is an authorized ACI distributor; warranty claims are processed directly with ACI. The full warranty terms are in the front of ACI's Sensors & Transmitters catalog.