sensortec AG - KACQTH-xxx - Duct air quality sensor CO2 and VOC

Installation

1. 1Wire the RS-485 A and B terminals of the sensortec AG KACQTH-xxx sensor to the corresponding Modbus RTU port on your ModbusCloud gateway (MCG or MLP series).
2. 2Supply the sensor with 24 Vac/dc and confirm the status LED indicates normal operation.
3. 3Set the Modbus slave address on the sensor according to the manufacturer instructions, ensuring it does not conflict with other devices on the bus.
4. 4Configure the gateway serial port to 19200 baud, even parity (parity 1) and one stop bit to match the sensor defaults.
5. 5Import the sensortec AG KACQTH-xxx template in the ModbusCloud portal and assign it to the correct gateway and slave address.
6. 6Verify that live readings for CO2, TVOC, temperature and humidity appear on your ModbusCloud dashboard.

Things to watch for

01

I only see values for some registers. Is the template broken?

No. The template covers all registers of the full KACQTH variant. If you use a KACTH or KAQTH model, some sensors are physically absent. Registers for missing sensors will return zero or stay empty. This is expected behavior.

02

Communication fails after wiring. What should I check?

Confirm the baud rate is set to 19200 and parity is set to even (parity 1) on the gateway. Also verify that the RS-485 A and B lines are not swapped and that the correct slave address is configured.

03

Do I need a bus termination resistor?

For short cable runs with only one or two devices, a termination resistor is usually not required. For longer runs or multiple devices on the same bus, add a 120 ohm termination resistor at each end of the RS-485 line.

04

Can I change the Modbus slave address of the sensor?

Yes. Refer to the sensortec AG product manual for the procedure to change the slave address. Make sure the new address matches the setting in the ModbusCloud template configuration.

Registers (5)

5 read / 0 write

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