DURAG D-R 290, Operating Manual

Page: 44 / 202

4 | Product description
44 D-R 290
Zero point measurement
Comparison standard
Measuring section
Reflector
Zero point
reflector Transmitter
Turntable plate
50% splitter mirror
Receiver
Fig. 4.5: Zero point measurement
To check the correct operation of the D‑R 290 a checking cycle is performed at a peri­
odic interval configurable from 0 to 720 hours (0 = no control cycle). During this cycli­
cal check a zero point reflector is used to automatically check the contamination con­
trol of the optical surfaces. The zero point and a reference are also measured auto­
matically.
During the reference point measurement (
Fig. 4.6 ) a mesh filter (see Fig. 4.3 ) with a
defined light attenuation is moved into the measurement beam. A check is then made
that the measured attenuation corresponds with the defined value. For zero point
measurement ( Fig. 4.5 ) the measurement beam is reflected directly in front of the
measurement medium. It thus passes through all the lenses and relevant optical com­
ponents, just as in the real measurement procedure.
The measurement results for subsequent measurements are corrected to compensate
for the measured difference in value (contamination). If the contamination exceeds a
certain percentage (configurable between 0 and 10%), a warning is indicated. If the
contamination exceeds a higher percentage (>10%), an error message is indicated,
and the measured values from the device are thereafter no longer valid.
The evaluation electronics determines the transmission from the received measure­
ment light and the intensity of the comparison light. From this the opacity [
}
195] , or
alternatively the extinction [
}
195] is measured. The extinction can be calibrated and
can be specified as dust concentration in mg/m³.
Furthermore for a known measuring path length the extinction coefficient and the
Koschmieder visual range can be calculated.
All the calculated values can be freely assigned to the four digitial measuring chan­
nels.