The 22ADP-55QB is a Belimo active 24V differential pressure transducer for air, with a low / sensitive pressure range of -0.6 to 1 inch WC (-150 to 250 Pa) and eight DIP-switch-selectable measuring sub-ranges. One SKU adapts to multiple applications without re-specifying a range variant. The sensor uses a piezo measuring element with ±0.02 inch WC accuracy below 2 inch WC and ±0.04 inch WC above. Two active analog outputs deliver pressure and volumetric flow (0-5V or 0-10V switch-selectable), while Modbus RTU on RS-485 exposes all values to the BAS as a native bus device. The auto-zero feature automatically compensates for sensor drift at configurable intervals — critical for low-range applications. An integrated LCD display with backlight shows live values with programmable units. The orange polycarbonate housing is rated NEMA 4X / IP65 with UL 2043 plenum compliance. A 1/2" NPT conduit adapter, mounting plate, and duct connector kit ship in the box.
HVAC differential pressure monitoring in the -0.6 to 1 inch WC range: cleanroom and laboratory differential pressure monitoring, isolation room positive/negative pressure verification, biosafety cabinet face velocity, low-velocity duct measurement, and any application where measurements below 1 inch WC require high analog resolution. Same range, different configurations: 22ADP-55Q ($596), 22ADP-55QA ($777). For medium pressure (-0.4 to 10 inch WC, filter and damper applications), see the 22ADP-554 family.
This sensor communicates with the BAS via Modbus RTU on RS-485, exposing all measured values (differential pressure, volumetric flow), selected sub-range, calibration status, and configuration parameters as Modbus registers. Modbus address, baud rate, and parity are configurable. Analog 0-5V/0-10V backup outputs remain available alongside.
An internal solenoid valve periodically isolates the sensor from the pressure ports and re-zeros the reading automatically at a configurable interval. This eliminates the typical drift that affects piezo sensors at low pressure ranges, removing the need for frequent manual zero-point calibration. Especially valuable at the most sensitive sub-ranges (S5–S7) where a small offset translates to a large percentage error.
After initial commissioning, perform manual zero-point calibration to set the sensor's reference offset. Recommended interval depends on the active sub-range: ‚â§1 inch WC: every 3 months; ‚â§2 inch WC: every 6 months; >2 inch WC: every 12 months. Procedure: power the sensor for at least 15 minutes, release both tube connectors from the + and - pressure ports (calibration is required even if display reads 0), press and hold the calibration button until the LED illuminates steadily, then wait for the LED to flash and reinstall the tubes (observing + and - polarity). Note: this SKU also has the auto-zero feature that handles routine zero-point correction automatically — manual calibration is needed less frequently as a result.
Key Features
Combines automatic zero-point correction (eliminates routine manual calibration drift) with an on-housing LCD display for live pressure and flow readout. Top-of-the-line variant for low-range and critical applications where both maintenance reduction and on-wall visibility matter.
One SKU covers eight pressure ranges within the -0.6 to 1 inch WC envelope, selectable via on-board DIP switch. Narrower sub-ranges give higher analog resolution — particularly valuable for low-velocity filter monitoring and cleanroom applications. Settings can also be changed remotely via the bus.
Belimo's proven piezo measuring element with ±0.02 inch WC accuracy below 2 inch WC and ±0.04 inch WC above. Long-term stability ±2.5% FSO over 4 years. Covers low-velocity duct measurements where a thermal-mass element would be too noisy.
Burst pressure tolerance of 160 inch WC (40 kPa) — survives transient overpressure events from damper closures, fan starts, and pressure tests without damage.
Channel 2 outputs volumetric flow calculated from differential pressure and a configured K-factor. Selectable units: m³/h, m³/s, or cfm. Default range 0-750,000 cfm. Eliminates the need for a separate flow meter when the application has a known venturi or orifice K-factor.
UV-resistant orange polycarbonate housing rated NEMA 4X / IP65 (UL Enclosure Type 4X). UL 2043 plenum compliant for return-air ducts. UL94 5VA flame class. NBR70 seal for chemical resistance against typical HVAC environment exposures.
Industry-leading factory warranty backed by Belimo's worldwide service network.
Selectable Measuring Sub-Ranges (DIP Switch S0–S7)
The active measuring sub-range is set via on-board DIP switch (settings S0 through S7) or remotely via the bus. The factory default is S0 (full range); narrow the range to higher S-numbers for low-velocity applications where higher analog resolution matters.
| Setting | inch WC | Pa | Note |
|---|---|---|---|
| S0 | 0–1 inch WC | 0–250 Pa | ‚òÖ Factory setting |
| S1 | 0–0.8 inch WC | 0–200 Pa | |
| S2 | 0–0.6 inch WC | 0–150 Pa | |
| S3 | 0–0.4 inch WC | 0–100 Pa | |
| S4 | 0–0.2 inch WC | 0–50 Pa | |
| S5 | 0–0.1 inch WC | 0–25 Pa | |
| S6 | 0–0.04 inch WC | 0–10 Pa | |
| S7 | -0.6–1 inch WC | -150–250 Pa | Full bidirectional, factory commissioning |
Technical Specifications
| Specification | Detail |
|---|---|
| Sensor Style | Active differential pressure transducer for air |
| Measured Values | Differential pressure, Volumetric flow |
| Measuring Fluid | Air and other non-aggressive, non-flammable gases |
| Sensing Element | Piezo measuring element |
| Output Signals | 2× active analog: Output 1 = Pressure, Output 2 = Volumetric Flow; 0-5V or 0-10V switch-selectable |
| Output Load | min. 10 kΩ load resistance |
| Communication | Modbus RTU (RS-485) |
| Modbus Configuration | Address, baud rate, parity configurable via Modbus |
| Pressure Measuring Range (Default) | -0.6 to 1 inch WC (-150 to 250 Pa) — DIP setting S0 |
| Pressure Measuring Range (Selectable) | 8 sub-ranges via DIP switch S0–S7 within the low / sensitive pressure envelope |
| Pressure Direction | Bidirectional |
| Pressure Accuracy | ‚â§2 inch WC: ±0.02 inch WC; >2 inch WC: ±0.04 inch WC |
| Long-Term Stability | ±2.5% FSO (Full Scale Output) per 4 years |
| Burst Pressure | 160 inch WC (40 kPa) |
| Volumetric Flow Range | Default 0-750,000 cfm; configurable via Modbus |
| Volumetric Flow Units | m³/h, m³/s, or cfm (parameterizable) |
| Typical Response Time | Adjustable: 0.8 s or 4.0 s |
| Manual Zero-Point Calibration | Single-button with LED feedback; recommended every 3-12 months depending on range |
| Auto-Zero Feature | Yes — internal solenoid valve periodically re-zeros at configurable interval |
| Application | Air monitoring — duct-mounted |
| Mounting | Wall/duct mount with included A-22D-A10 mounting plate |
| Pressure Connection | Two ports (+/-) with included A-22AP-A08 duct connector kit (PVC tube + connectors) |
| Conduit | 1/2" NPT conduit adapter included; cable gland 2x ø6 mm with strain relief |
| Power Supply | 24 VAC/VDC (19-29 VAC, 15-35 VDC) |
| Power Consumption | 4.3 VA AC / 2.3 W DC |
| Electrical Connection | Pluggable spring-loaded terminal block, max 2.5 mm² |
| Display | LCD 1.14×1.38" (29×35 mm) with backlight; programmable units (Pa, inch WC; m¬≥/h, m¬≥/s, cfm) |
| Housing Material | Polycarbonate, orange — UL94 5VA, UV-resistant; NBR70 seal |
| Enclosure Rating | NEMA 4X / IP65, UL Enclosure Type 4X |
| UL 2043 Plenum Compliance | Suitable for use in air plenums per NEC 300.22(C) and IMC Section 602 |
| Protection Class | IEC/EN III, SELV (Safety Extra-Low Voltage) |
| Power Source UL | Class 2 Supply |
| Pollution Degree | 3 |
| Ambient Humidity | Max. 95% RH, non-condensing |
| Ambient Temperature | 14-122°F (-10 to 50°C) |
| Fluid Temperature | 15-120°F (-10 to 50°C) |
| Storage Temperature | -4 to 176°F (-20 to 80°C) |
| EU Conformity | CE Marking |
| Certification | IEC/EN 60730-1 and IEC/EN 60730-2-6 |
| Quality Standard | ISO 9001 |
| Manufacturer | Belimo |
| Manufacturer Part Number | 22ADP-55QB |
| Warranty | 5-year factory warranty |
What's In the Box
- 22ADP-55QB differential pressure transducer with LCD display with auto-zero feature in orange polycarbonate housing
- A-22D-A10 mounting plate (L housing)
- A-22AP-A08 duct connector kit — 2 m PVC tube, 2× plastic duct connectors
- Cable gland with strain relief, ø6...8 mm
- 1/2" NPT conduit adapter, 2× ø6 mm
- Mounting dowels and screws
Compatible accessories sold separately: A-22AP-A01 metal duct connector (1.5" L, 0.2" tube connection) for steel ducts where the included plastic connectors are not preferred.
Documentation
Frequently Asked Questions
What does the 22ADP-55QB measure and output?
It measures differential air pressure (between the + and - ports) and outputs volumetric flow calculated from that pressure plus a configured K-factor. Two analog outputs: AO1 = pressure, AO2 = flow, both switch-selectable between 0-5V and 0-10V. All values are also exposed via Modbus RTU on RS-485.
Why 8 measuring ranges? Which to use?
The 8 sub-ranges (S0–S7) let one sensor body cover applications across the -0.6 to 1 inch WC envelope. Choose the narrowest range that covers your expected reading — narrower ranges give higher analog resolution. Set via DIP switch or remotely via Modbus RTU.
How does the Auto-Zero feature work?
An internal solenoid valve briefly isolates the sensor from the pressure ports at a configurable interval, reads its own zero reference, and updates the offset correction. Eliminates the drift that affects piezo sensors at low ranges — especially important for cleanroom/lab applications where a 0.05 inch WC offset would be a 5-50% reading error. Belimo still recommends annual manual zero-point verification.
What does the LCD display show?
The 1.14×1.38" backlit LCD cycles through differential pressure (Pa or inch WC) and volumetric flow (m¬≥/h, m¬≥/s, or cfm). Status icons show fault state, service due, and current sub-range. Useful for commissioning and service-call diagnostics without a laptop.
How is volumetric flow calculated?
Volumetric flow Q = K × ‚àö(ŒîP), where K is a K-factor specific to your venturi, orifice plate, or pitot tube. K-factor is set via Modbus RTU. Default 0-750,000 cfm full scale. Without a known K-factor, use only AO1 (pressure).
What is the burst pressure rating?
160 inch WC (40 kPa). Survives transient overpressure events (fan starts, damper closures, pressure tests) without calibration drift or seal damage.
How often is manual calibration needed?
Interval depends on active sub-range: 3 months at S5-S7 (≤1 inch WC), 6 months at S3/S4 (≤2 inch WC), 12 months at S0-S2 (>2 inch WC). Lower ranges drift more noticeably. Auto-Zero on this variant handles routine correction automatically.
How is this different from other 22ADP variants?
All 22ADP variants share the same chassis and piezo element. This SKU is the low / sensitive-range variant (-0.6 to 1 inch WC). Other ranges: 22ADP-554 (medium, -0.4 to 10 inch WC); 22ADP-556 (high, 0 to 28 inch WC). Output styles: -58x = V+mA analog only, -55x = V + Modbus RTU, -56x = V + BACnet MS/TP. Choose by BAS protocol and range.
Where can I install this sensor?
Wall or duct mount indoors, NEMA 4X / IP65. UL 2043 plenum compliant for return-air ducts (NEC 300.22(C)). Operating: 14-122°F ambient, 15-120°F fluid. Mounting plate and duct connector kit (2 m PVC tubing) included.
Power requirements?
24 VAC or 24 VDC (19-29 VAC, 15-35 VDC). Power consumption 4.3 VA AC / 2.3 W DC — compatible with standard 24V control transformers shared with actuators.
- Sensor Type:
- Differential Pressure / Air
- Sensing Element:
- Piezo
- Output Signal:
- Pressure + Volumetric Flow
- Output Style:
- Active Transmitter (V) + Modbus RTU
- Output Voltage Options:
- 0-5V / 0-10V
- Power:
- 24 VAC/VDC
- Number of Outputs:
- 2 analog
- Pressure Range (Default):
- -0.6 to 1 inch WC (-150 to 250 Pa)
- Pressure Range Variant:
- Low / Sensitive
- Multi-Range:
- 8 DIP-selectable sub-ranges
- Pressure Direction:
- Bidirectional
- Pressure Accuracy:
- ±0.02 inch WC (‚â§2 in WC range), ±0.04 inch WC (>2 in WC)
- Burst Pressure:
- 160 inch WC (40 kPa)
- Volumetric Flow Output:
- Yes (default 0-750,000 cfm)
- Auto-Zero:
- Yes
- Display:
- LCD with Backlight
- Supported Protocols:
- Modbus RTU + Analog
- Mounting:
- Duct/Wall (Indoor)
- Conduit:
- 1/2 NPT (included)"
- Enclosure:
- NEMA 4X / IP65 / UL 2043 Plenum
