The 22DC-51 is a Belimo active 24V duct insertion air quality transmitter (2024 hardware revision: A-22D-A34 mounting flange, 1/2" NPT conduit adapter included) for measuring CO2. The CO2 measurement uses NDIR (non-dispersive infrared) dual-channel technology with self-calibration. Each measurement has its own analog output (1 total), jumper-selectable between 0–5V and 0–10V.
Demand-controlled ventilation (DCV) on commercial AHUs — modulating outdoor air based on CO2 levels in return air or zone supply. The single CO2 output drives a damper actuator or feeds the BAS for variable OA setpoint logic.
This is the newer 2024 hardware revision — ships with the A-22D-A34 mounting flange and includes a 1/2" NPT conduit adapter in the box for direct compliance with US/Canadian/Mexican NFPA conduit installations. Electronics, sensing technology, and accuracy specifications are identical to the earlier 2022 hardware revision (A-22D-A35 flange, no NPT adapter included).
Key Features
Each measured value (CO2) has its own dedicated analog output, jumper-selectable between 0-5V and 0-10V. Each output drives its own BAS input independently — no need to time-multiplex or read different addresses.
Non-dispersive infrared CO2 measurement with dual optical channels for self-calibration. The dual-channel design eliminates manual recalibration and resists drift from background gases. ±(50 ppm + 3% of measured value) accuracy.
UV-resistant orange polycarbonate enclosure with NBR70 seal. UL94 5VA flame class and UL 2043 plenum compliant for return-air ducts.
Default CO2 range is 0-2000 ppm, suitable for most occupied-space DCV applications. With the A-22G-A05 accessory, the range extends to 0-5000 ppm for industrial and high-occupancy applications.
Industry-leading factory warranty backed by Belimo's worldwide service network.
Technical Specifications
| Specification | Detail |
|---|---|
| Sensor Style | Active duct insertion air quality transmitter — CO2 |
| Measured Values | CO2 |
| Output Signals | 1× 0-5V or 0-10V (jumper-selectable, min 10 kΩ load) |
| Hardware Revision | A-22D-A34 with 1/2" NPT conduit adapter (2024 revision) |
| CO2 Sensing Technology | NDIR (non-dispersive infrared), dual-channel with self-calibration |
| CO2 Measuring Range | 0-2000 ppm default; 0-5000 ppm with A-22G-A05 accessory |
| CO2 Accuracy | ±(50 ppm + 3% of measured value) |
| CO2 Long-Term Stability | ±50 ppm per year |
| CO2 Time Constant τ (63%) | Typical 33 s @ 1 m/s air velocity |
| Application | Air — duct insertion |
| Operating Air Flow | min. 1 ft/s (0.3 m/s); max. 40 ft/s (12 m/s) |
| Mounting | Single-hole duct penetration; A-22D-A34 plastic mounting flange (up to 248°F / 120°C) included |
| Conduit | 1/2" NPT conduit adapter included + ø6-8 mm cable gland 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 |
| Cable Entry | Cable gland with strain relief, ø6...8 mm |
| Housing | UV-resistant polycarbonate, orange — UL94 5VA |
| Probe Material | PA6, black |
| Enclosure Rating | NEMA 4X / IP65 (UL Enclosure Type 4X), UL 2043 plenum compliant |
| Protection Class | IEC/EN III, SELV; UL Class 2 supply |
| Certification | IEC/EN 60730-1, CE Marking |
| Manufacturer | Belimo |
| Manufacturer Part Number | 22DC-51 |
| Warranty | 5-year factory warranty |
What's In the Box
- 22DC-51 active duct CO2 transmitter with insertion probe
- A-22D-A34 mounting flange (plastic, up to 248°F / 120°C)
- 1/2" NPT conduit adapter
For extended-range CO2 monitoring (up to 5000 ppm) for industrial or high-occupancy applications, see the A-22G-A05 accessory.
Documentation
Frequently Asked Questions
What does the 22DC-51 measure?
This SKU measures CO2. Each measurement has its own dedicated analog output (1 outputs total), so each value can be wired to a separate BAS analog input simultaneously.
What output signals can this provide?
All 1 analog outputs are voltage-only: jumper-selectable between 0-5V and 0-10V per channel, minimum 10 kΩ load resistance. For a 4-20 mA output option, see the universal-output 22DC-53 variant of this same product.
How does NDIR dual-channel CO2 sensing work?
NDIR (non-dispersive infrared) measures CO2 by detecting how much infrared light the gas absorbs at a specific wavelength. The 'dual-channel' design uses a second reference wavelength that CO2 does NOT absorb — by comparing the two signals, the sensor automatically corrects for lamp aging, dirt accumulation on the optics, and background gas interference. This is why the sensor is self-calibrating and rated for ±50 ppm/year long-term stability without manual recalibration.
Does it need 24V power?
Yes. The 22DC-51 requires 24 VAC or 24 VDC (19-29 VAC, 15-35 VDC). Power consumption is 4.3 VA AC / 2.3 W DC — higher than single-variable temperature sensors due to the active CO2 NDIR sensing element.
What air velocity does it need to operate?
Operating air flow range is 1-40 ft/s (0.3-12 m/s). The CO2 NDIR cell needs some air movement past the probe to refresh the gas sample for accurate readings. Below 1 ft/s the reading lags actual duct air composition; above 40 ft/s the response stays accurate but probe vibration becomes a long-term wear concern.
- Sensor Type:
- Air Quality / Duct
- Output Signal:
- CO2
- Output Style:
- Active Transmitter (0-10V)
- Power:
- 24 VAC/VDC
- Number of Outputs:
- 1 analog
- CO2 Element:
- NDIR Dual-Channel
- VOC Element:
- None
- Temperature Element:
- None
- Default Temperature Units:
- Fahrenheit (°F)
- Regional Configuration:
- North American (°F + NPT)
- CO2 Range:
- 0-2000 ppm (default); 0-5000 ppm with A-22G-A05
- Humidity Element:
- None
- Display:
- No Display
- Setpoint:
- No Setpoint
- Override:
- No Override
- Supported Protocols:
- None (analog)
- Enclosure:
- NEMA 4X Enclosure
