Sewi Modbus

Indoor Sensors

The indoor sensors Sewi AQS/TH Modbus and Sewi TH Modbus measure the indoor temperature and humidity and also calculate the dew point temperature. The Sewi AQS/TH also records the CO2 concentration.
The devices are Modbus slaves with a RS485 interface and a RTU protocol. The Modbus master, such as PC, SPS or MC can read the Sewi Modbus Indoor Sensors measurement values with "Function 04h (Read Input Register)".


N° 30174 Sewi AQS/TH Modbus, CO2, temperature and humidity sensor
N° 30175 Sewi TH Modbus, temperature and humidity sensor

  • Sewi AQS/TH Modbus (30174) Sewi AQS/TH Modbus (30174)
  • Sewi TH Modbus (30175) Sewi TH Modbus (30175)

Sewi TH Modbus Indoor Sensor Functions:

  • Temperature measurements
  • Humidity measurements
  • Calculating the dew point temperature

Sewi AQS/TH Modbus Indoor Sensor Functions:

  • • Measuring the CO2concentration in the air
  • Temperature measurements
  • Humidity measurements
  • Calculating the dew point temperature

Tips for Dew Point Calculation:

The sensors Sewi Modbus calculate the ambient dew point temperature. This value can be used for dew point monitoring. This would require another sensor for measuring the surface temperature of the wall or pipe. Also, the dew point needs to be monitored (compare with temperatures) in the Modbus master.

Monitoring predetermines the possible condensate build-up on the surface, giving a chance for timely countermeasures.

ColourWhite (Cover glossy, skirting matt)
AssemblySurface, wall or ceiling installation
Protection categoryIP 30
DimensionsØ approx. 105mm, height approx. 32mm
WeightSewi AQS/TH Modbus: approx. 100g
Sewi TH Modbus: approx. 75g
Ambient temperatureOperation 0 …+50°C, Storage -20 …+70°C
Ambient humiditymax. 95% RH, avoid condensation
Operating voltage12 to 30V DC. An appropriate power supply unit can be purchased from Elsner Elektronik.
Cable cross-sectionSolid conductor up to 0.8mm2
Powermax. 15mA
RS485 bus load1/8 unit load according to the RS485 standard
RS485 drive outputmin. 2.4V at 54 Ohm bus load (according to the 32 standard RS485 unit loads)

Sewi TH Modbus (30175):

Temperature measurement range-40...+80°C
Humidity measurement range0% rH … 100% rH

Sewi AQS/TH Modbus (30174):

Temperature measurement range0°C…+50°C
Humidity measurement range0% rH…90% rH
CO2 measurement range0...2,000ppm