D-FW 231

Filter Monitor

Filter monitor to detect the efficiency and function of filters and filtration systems. Dust Monitor for qualitative measurement of dust concentration in dry process or flue gas.


  • In situ measurement, continuous measurement
  • Qualitative dust measurements for monitoring the functions of filters
  • Single-sided mounting on the channel
  • No moving parts within the duct
  • Easy installation, adjustment and maintenance without a PC

Your benefit

  • Compact and cost effective solution
    Small housing and low system cost
  • Space-saving and easy installation
    One-sided Installation without alignment and the simple measuring principle with analog output allows easy installation and setup
  • Low operation costs
    No purge air required
  • Suitable for harsh flue gas pressure conditions
    The filter monitor is suitable for flue gas pressure up to 500 hPa


  • Power Plants
  • Bag-filter of any kind
  • Dust in the manufacturing industry
  • Incinerators
  • Crematoria

The measurement principle is not suitable for use directly behind electrostatic filters.

Technical Data

Measured componentdust load
Flue gasair, flue gas, non flammable process gas
Flue gas dust concentration1 ... 25 to 20 ... 400 mg/m3
Flue gas flow velocity7 ... 40 m/s
Stack/ duct inner diameter> 0.15 m
Flue gas temperatureabove dew point,
up to 200 °C standard,
up to 500 °C option
Inner stack/duct pressure
(relative to ambient pressure)
-500 ... +500 hPa
Flue gas moisture20 ... 80% rel. humidity
Ambient temperature-20 ... +50 °C
Measuring principleMeasuring the transfer of electrical charge from dust particles to an electrode in flowing sample gas
Type, mounting location4 (7) wire transmitter, in situ, mounted at stack, probe is in contact with sample gas
System-ComponentsD-FW 231 M Measuring device
D-FW 231 P probe/electrode
Measuring ranges0 - 100% Tribo-value, 6 per micro DIP switch selectable ranges
Output range0- 100% Tribo value
Process connectionG1" Female thread, tube ID >= 36mm, L max. 100 (300*) mm
Analog outputs1 x 4–20 mA, 500 Ohm
Digital input2 x Transistor-Input for zero check, integration
Power supply18 - 36 V DC; 0.2A
IP protection class (IEC 60529)IP65
Dimensions (hxwxd)180 x 80 x 270 mm (Without D-FW 231 P Probe)
Weight1.9 kg
MaterialHousing: Al alloy, painted RAL 5017
Probe connector: 1.4571
Isolator: PTFE (standard), ceramic (option)
DimensionsLength: 80, 250, 400, 700, 1000 mm
  • The suitability of D-FW 231 for the listed ranges depends upon the kind of dust and its size distribution.
  • The measuring effect is dependant upon the flow speed. 
  • Subject to technical modifications!