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 ABCTM logic. The ABCTM logic 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 series devices include:
• Separate field configurable Modbus output 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
• Optional relay output

Technical details

Communication: RS-485 Modbus (RTU)
Accuracy: CO2: ±40 ppm + 2 % 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
Measurement elements: Pt1000 temperature sensor, 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 1: 0/2…10 V (linear to CO2), L min 1 kΩ or 4…20 mA (linear to CO2), L max 500 Ω
Output signal 2: 0/2…10 V (linear to rH), L min 1 kΩ or 4…20 mA (linear to rH), L max 500 Ω
Output signal 3: 0/2…10 V (linear to Temp), L min 1k Ω or 4…20 mA (linear to Temp), L max 500 Ω
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

Relay (only for wall mount model)

With relay
Without relay

Relative humidity sensor (only for wall mount model)

With relative humidity sensor
Without relative humidity sensor


With display
Without display