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


  • 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
sample gasair, flue gas, non flammable process gas
dust concentration**
(typical values)
1 - 25 / 2-50 / 5 - 100 / 10 -200 / 20 - 400 mg/m3
flow velocity***7-40 m/s
duct diameter> 0.15 m
sample gas temperature-20°C - 200°C / 500°C*
sample gas pressure
(relative to ambient pressure)
-500 to +500 hPa, others on request
sample gas moisture20 ... 80% rel. humidity
ambient temperature-20 to +50 °C
measuring principlemeasuring the transfer of electrical charge from dust particles to an electrode in flowing sample gas
type4 (7) wire transmitter, in situ, mounted at stack, probe is in contact with sample gas
system-ComponentsD-FW 231 M Measuring head
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
Adapters for flanges already mounted at the site on request
measurement output1 x 4–20 mA / 500 Ohm
control input2 x transistor-Input
zero check, integration
supply18 - 36 V DC; 0.2A
IP protectionIP65
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 / ceramic*
available rods (length)80, 250, 400, 700, 1000 mm
material1.4571, others on request
remarks* Variations
** 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!

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