The 22DTC-51 is a Belimo active 24V duct insertion sensor measuring CO2, and Temperature (North American variant, configured with Fahrenheit (°F) default temperature output). CO2 sensing uses NDIR (non-dispersive infrared) dual-channel technology with self-calibration; temperature uses an active Pt 1000 RTD. Each measured value has its own dedicated analog output (2 outputs total), 0-5V or 0-10V (jumper-selectable per channel).
Combined duct CO2 and temperature monitoring where both signals are needed from the same duct location — for example, demand-controlled ventilation (DCV) on commercial AHUs that also need supply air temperature feedback. Single sensor consolidates two BAS inputs.
This is the North American variant — temperature output configured in Fahrenheit (°F), includes the A-22D-A34 mounting flange and a 1/2" NPT conduit adapter. For US, Canadian, and Mexican installations following NFPA / NEC electrical codes.
Key Features
Each measured value (CO2, Temperature) has its own dedicated analog output, jumper-selectable between 0-5V and 0-10V. Each output drives its own BAS input independently.
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.
Active Pt 1000 platinum RTD on the same probe body, with its own analog output. ±0.5°F accuracy at 77°F. Eliminates the need for a separate 22DT sensor at the same duct location.
Tap a phone with NFC to the housing to read live values, change output mode, adjust CO2 scaling, set Modbus/BACnet addresses (where applicable), and view diagnostics. The Belimo Duct Sensor Assistant App is free for iOS and Android.
UV-resistant orange polycarbonate enclosure with NBR70 seal. UL94 5VA flame class and UL 2043 plenum compliant for return-air ducts.
Industry-leading factory warranty backed by Belimo's worldwide service network.
Technical Specifications
| Specification | Detail |
|---|---|
| Sensor Style | Active duct insertion sensor — CO2 + Temperature |
| Measured Values | CO2, Temperature |
| Output Signals | 2× 0-5V or 0-10V (jumper-selectable per channel, min 10 kΩ load) |
| 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 |
| Temperature Sensing Element | Active Pt 1000 platinum RTD |
| Temperature Measuring Range | 40–140°F (4–60°C) |
| Temperature Accuracy | ±0.5°F (±0.3°C) at 77°F |
| Temperature Time Constant τ (63%) | Typical 125 s @ 3 m/s |
| Default Temperature Units | Fahrenheit (°F) |
| Regional Variant | North American |
| NFC Configuration | Yes — Belimo Duct Sensor Assistant App (iOS / Android) |
| 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 |
| 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 | 22DTC-51 |
| Warranty | 5-year factory warranty |
What's In the Box
- 22DTC-51 active duct CO2 + Temperature transmitter with insertion probe
- A-22D-A34 mounting flange (plastic, up to 248°F / 120°C)
- 1/2" NPT conduit adapter
Documentation
Frequently Asked Questions
What does the 22DTC-51 measure and output?
It measures CO2, Temperature. Each value has its own dedicated analog output (2 outputs total), 0–5V or 0–10V (jumper-selectable).
How do I choose between 22DTC and 22DTM?
The 22DTC family measures CO2 + Temperature (2 outputs). The 22DTM family adds humidity to the mix: CO2 + Humidity + Temperature (3 outputs). Choose 22DTC when your BAS doesn't need duct humidity at this location — for example, a CO2-only DCV scheme where humidity is monitored separately at outdoor air or return air. Choose 22DTM when you need all three values at one duct location and want to consolidate sensors. Pricing reflects this — 22DTC at $994 vs 22DTM starting at $1,329.
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 22DTC-51 requires 24 VAC or 24 VDC (19-29 VAC, 15-35 VDC). Power consumption is 4.3 VA AC / 2.3 W DC.
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 + Temperature
- Output Style:
- Active Transmitter (0-10V)
- Power:
- 24 VAC/VDC
- Number of Outputs:
- 2 analog
- CO2 Element:
- NDIR Dual-Channel
- CO2 Range:
- 0-2000 ppm (default); 0-5000 ppm with A-22G-A05
- Temperature Element:
- Active Pt 1000
- Default Temperature Units:
- Fahrenheit (°F)
- Regional Configuration:
- North American (°F + NPT)
- Display:
- No Display
- NFC Configuration:
- Yes (Belimo Duct Sensor Assistant App)
- Setpoint:
- No Setpoint
- Override:
- No Override
- Supported Protocols:
- None (analog)
- Enclosure:
- NEMA 4X Enclosure
