D-R 290 Measuring Principle The D-R 290 operates on the auto collimation (double-pass) principle. The light beam crosses the measurement path twice and the system measures the light attenuation from dust in the stack. A photo element alternately reads the measurement beam and a comparison light beam 2 minutes to insure accuracy. Since one joint amplifier is used for both the measuring and comparison light beams, temperature fluctuations and long-term amplifier drift are automatically compensated. The system generates light internally with the Super wideband Light Source to prevent distortions from sunlight or other sources. This LED also has a longer life span than traditional halogen lamps. The broad spectrum of emitted light means results are not distorted by temperature. This ensures a more stable measurement than a conventional narrow band LED.

Spectral Sensitivity with DURAG's new SWBD Technology

Special Features

The D-R 290 is equipped with two analog data outputs. Each output has an adjustable extinction or opacity range. Extinction measurements between 0.1 and 1.6 or opacity measurements from 20% to 100% can be selected. The opacity at the stack outlet can be computed using a correction factor for the D-R290 system location. To ensure it is functionally properly, the D-R 290 performs a periodic check cycle of the zero value and window dirtying to generate the reference value. the D-R 290 will then correct subsequent measurements. If the corrections exceed the value you have designated, the system will notify you. A heated plane within the system prevents condensation and deposits on the optics.

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Standard System

The standard system includes the following:

Mounting flanges
Measuring head
Reflector
Display and operating panel
One purge air fan

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Optional Accessories

Bus interfaces such as Modbus or CAN bus
Automatic fail-safe shutters to protect the measuring head and reflectors in the event of purge air outage
Weather protection hoods when the instrument is mounted in an unprotected area
Explosion-proof execution with EEx-p protection

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Transmission

Calibration of Dust Meters

Transmission T (=irradiation capability) measures the light attenuation when directed through a gas containing dust or other particles. Currently, several manufacturers have implemented a narrow-band LED light source with a spectral response between 500 and 600 nm using the light directly emitted from the LED. This gives a strongly temperature-dependent response. The DURAG Super wideband Light Source, with a greatly enlarged range of 400-700 nm, produces a more stable measurement with more constant results. A blue gallium nitrate diode, in connection with a fluorescent layer, produces a white light containing the broad band of wavelengths associated with the luminescence material as well as the emission band of a normal light emitting diode. The measured particulate load can then be displayed as either opacity, O, or as extinction (optical density), E.

Opacity
Opacity measures the percentage of absorbed light. It is used primarily in the USA and Asia. An advantage of opacity is that the measuring devices need not be calibrated. A disadvantage is that the results vary with the location of the monitor itself. However, the results can be recalculated for the distance from the monitor to the stack emission outlet. The influences of the color, shape, and surface structure of the dust particles are not taken into account, shown in the non-linear relationship between dust load and opacity. For example, opacity increases only about 15% when the dust load is doubled in the upper measurement ranges.

Optical Density (Extinction)
The extinction (optical density) has a linear relationship to the dust load because it is calculated logarithmically: doubling the dust load results in a doubled measurement. Extinction is used mainly in European countries and increasingly in Asia. A calibration curve is calculated for the measuring location according to VDI 2066 or EPA CFR 40 Part 60 #5 with the extinction coefficient k. Under normal operating conditions, however, the same dust load can lead to different readings depending on grain size and flow distribution, so the uncertainty ranges are also calculated, as shown in the figure above.

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