Application

The D-RX 250 Combined Sample Probe is used for continuous monitoring of dust concentrations in flue gas ducts, dust extraction pipes, etc. In addition to the measurement of dust concentration, the volume flow, temperature and the absolute pressure in the flue is measured. These measurements enable the figures to be converted to normal conditions.

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Measuring Method

The combined probe measures four different quantities simultaneously.

• The dust concentration is determined according to the tribo-electric measuring principle. The tribological probe measures the charge on the particles that strike the rod. Due to the measurement principle, this charge flow is, without any compensation calculation, dependent on the flow velocity and the concentration of the dust in the flue gas.

• The measurement of the volume flow works on the differential-pressure principle. For this the probe has two chambers separated from one another, between which a pressure difference is established in the directional approaching flow. Due to the special shape of the probe, the largest possible differential pressure is produced and the linearity of the measurement signal referred to the flow is guaranteed.

• The absolute pressure in the flue gas is sampled in one chamber of the probe and measured by a piezoresistive pressure transmitter.

• The temperature is measured in a separate chamber within the probe directly in the core flow of the flue gas by a Pt100 resistance thermometer.

The raw data is processed locally at the measuring point and transferred via a bus interface (Modbus, CAN-Bus or similar) up to 1000 m to an operating and evaluation unit with display or to a process control system.

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Computation Principles

The dust concentration is calculated from the tribo-electric measuring signal and the volume flow. The parameters necessary for this in the relevant velocity ranges are obtained during calibration and these then form the basis for the computation of the dust concentration. The normalized dust concentration as well as the normalized volume flow can then be computed from the similarly measured raw values for the gas temperature and the absolute pressure.

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Construction

• Probe
  The probe consists of a probe profile according to VDI 2066-1, mounted in the stack path using a flange that is connected to the stack. The probe is built in isolation due to the tribo-electric measurement and contains two chambers for the measurement of differential and absolute pressure. In a third chamber, the gas temperature is measured.
   
• Differential Pressure Transducer
  The measurement transducer detects the flow speed of the gas and transmits this as a 20 mA measurement signal to the transmitter.
   
• Transmitter
  The transmitter is connected to the probe and modifies the tribo-electric current, the signal of the temperature sensor, the absolute pressure, as well as the volumetric flow value from the differential pressure transducer to raw values and transmits these over a bus interface to the control and evaluation unit.
   
• Operating and evaluation unit
  The operating and evaluation unit receives the raw values and computes the normalized dust concentration from them. The measurements are available as 20 mA current signals for dust concentration, volume flow, temperature and absolute pressure together with a series of associated status signals, e.g. for servicing, faults, etc.

  Operation is menu-guided using four keys and a four-line display. The measurements are displayed in various menus in German and English. For improved readability the measurements can be shown in large characters.

The transmitter is mounted at the measuring point and with transmission of the raw data via the bus interface, the mounting location of the operating and evaluation unit can be positioned up to 1000 m from the measuring point. Alternatively the raw data can also be computed by an emission computer (e.g. DURAG D-MS 500) or a process control system.

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Measurement ranges

D-RX 250 S Probe

Differential Pressure Measuring Transducer (root extractor)

D-RX 250 T Transmitter

D-RX 250 D Operating and Evaluation Unit

Options

• Weather-protecting roof
• Manual switching valve for purging / zero-point check
• Automatic cyclic probe purging
• Condensate drain / collection vessel