Multifunctional CO2 transmitters for building automation systems that use Modbus serial communication protocol

CDT series air quality transmitters are engineered for building automation systems in the HVAC/R industry. The CDT series measures carbon dioxide (CO2) utilizing the industry standard NDIR measurement principle, and temperature (T). Optional relative humidity (rH) measurement is also available in the same device. CDT series devices are available with large touchscreen display making configuration of the device quick and easy. Configuration is also possible via Modbus network.


The CDT-MOD-2000 series transmitters calibrate themselves automatically using ABC logicTM. The ABC logicTM requires that the space in which the transmitter is used needs to to be unoccupied for four hours per day so that the indoor CO2 concentration drops to the outside level. CDT-MOD-2000-DC is a dual channel model with a measuring channel and a reference channel that makes a continuous comparison and the necessary adjustment accordingly. CDT-MOD-2000-DC is also suitable for buildings that are continuously occupied.


CDT-MOD-2000 series devices include:

• Separate field configurable Modbus output for each measurement parameter (CO2, rH, T)

• Offset feature enabling field calibration for each measurement parameter (CO2, rH, T)

• One analog output for selected measurement: voltage (0/2–10 V) or current (4–20 mA)

•  2″ x 3″ touchscreen display

• Time extension button that enables boosting ventilation manually using the touchscreen display 

• Optional relay output


See how easy it is to use the time extension mode:

Technical details

Communication: RS-485 Modbus (RTU)
Accuracy: CO2: ±40 ppm + 3 % of reading, DC model: 75 ppm or 10 % of reading (whichever is greater)
Temperature: <0.5 °C
Relative humidity: ±2…3 % rH at 0…50 °C and 10…90 % rH
Total error band includes accuracy, hysteresis and temperature effect over 5...50 °C and 10–90 % rH
Measuring elements: Temperature sensor: Pt1000 / Integrated (models with rH-measurement), Non Dispersive Infrared (NDIR) CO2 sensor, thermoset polymer capacitive sensing element for humidity
Measuring units: ppm, °C, % rH
Calibration: Automatic self-calibration, ABC LogicTM or continuous comparison (DC)
Supply voltage: 24 VDC/VAC ±10 %
Current consumption: max 90 mA (at 24 V) + 10 mA for each voltage output or 20 mA for each current output
Output signal for selected measurement: 0/2…10 V (linear to CO2, rH or T) (2–10 VDC display models only) or 4…20 mA (linear to CO2, rH or T)
Optional relay output: Potential free SPDT 250 VAC, 6 A / 30 VDC, 6 A with adjustable switching point and hysteresis
Operating temperature: 0...50°C
Protection standard: IP20




Product series

Carbon dioxide transmitter, analog outputs
Carbon dioxide transmitter, Modbus communication


ABC logic™, Automatic Background Calibration
Dual channel, for continuosly occupied space


Wall mount


With relay
Without relay

Relative humidity sensor

With relative humidity sensor
Without relative humidity sensor


With display
Without display

Other Modbus products: