• Filter monitoring based on the triboelectric measuring principal
• Ideal for bag house monitoring
• Continuous in-situ measuring
• Adjustable integration time
• Compact design
• Sturdy construction; no moveable parts
• Easy, straight forward installation and operation
• Fast on-line performance check capability
• Minimal maintenance requirements
• Early detection of filter malfunction
• Reduces filter replacement costs

Applications

The DURAG D-FW 230 / D-FW 231 Filter Monitors may be used for continuous monitoring of filter installations in flue gas ducts, duct work for dust extraction, etc.

The filter monitor is placed on the clean-gas side, behind a filter, and will report any defect. By using filter monitors at the most important emissions sources or filter, appropriate action may be taken in the event of a malfunction to prevent or limit damage, i.e., by shutting down the defective filter chamber.

This system offers several advantages over comparable optical devices, including low purchase, installation and maintenance costs, as well as extremely high performance.

Principle of Operation

The DURAG filter monitors operate according to the principle of triboelectric measurement.

When dust particles collide with one another, they acquire an electrical charge. If these electrically charged particles strike the measuring probe, the charge is transferred. The current flowing through the probe is thus proportional to the number of particles colliding with it.

The result will accurately correspond to dust emissions, since it depends not only on dust concentration, but also accounts for the velocity of the particle flow.

Operation

A measuring probe inserted into the flue gas duct allows the sensor to record the electrical charge of the dust particles. Complete signal processing occurs in the sensor. The measured value is then transmitted as an interference resistant 4-20 mA signal and is available at the terminal strip.

Installation and operation are extremely simple: The sensitivity is set digitally using DIL switches in the sensor and on the request a integration to smooth out the measurement is available.

The D-FW 230 is designed for single applications. The control unit monitors the measured values digitally and uses a relay to signal any limit value accidence. The limit value threshold may be set anywhere from 4 to 20 mA. Zero testing may be carried out directly from the control unit with the flip of a switch.

The probe D-FW 231 is suitable for use in a multi-filter plant, where supervision of all filters is done by means of a central processing unit such as the DURAG D-IAS Information and Evaluation System. Limit value accidence, zero testing and measurements are analyzed computer-controlled

Choosing the Measuring Point

The length of the flow path prior to reaching the filter monitor must total at least 5 times the diameter of the channel.

To keep moisture away from the sensor isolator, the sensor should be mounted horizontally or with a downward slope.

If dust concentration is low, the selection of the measuring point is especially important to take full advantage of the triboelectric measuring principle. The chosen measuring point must be located at a site where both the flow velocity is high and the longest possible measuring probe may be used.