K-Patents PR-03 - Manual (Page 62)

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56 PR-03 instruction manual
A good LED value is in the range 20-150. The most common reason to a LED value higher than 150 is
that prism is coated. It is also possible the prism has been destroyed with an overactive steam wash. Check
the wash times and the prism surface (especially if the wash time exceeds the maximum of 3 s). Replace
the prism if the surface is damaged (see Chapter 6 for instructions).
If the process is very hot, it is also possible that the light source LED wears out after many years’ constant
use and needs replacing. Also leakage into the sensor can destroy LEDs (and everything else inside the
sensor housing). However, normally the LEDs last as long as the sensor and high LED values indicate a
prism problem.
It is very unusual for the LED value to be lower than 20, but in theory this can be caused by light from
outside reaching the prism e.g. because the pipe is translucent.
7.2.2 Sensor temperature and humidity
Checking the conditions inside the sensor head will give you an idea whether there’s is a real physical
problem. The Scaled image (Calibrate / Optical image / Scaled image) shows you both
the internal sensor temperature and humidity.
A B C D
SCALED
OPTICAL
IMAGE
TEST: 115.9
51.2 °C
Endp: 21
L): 9.8
R): 25.9
HT: 20 °C
HH: 3%
Slope
Normal operation
Figure 7.2 Scaled image
The HT value gives you the sensor temperature and should be below 60 ◦ C. If the value is over this limit,
the measurement may not be accurate and the sensor needs to be cooled more effectively, see Section 2.2.1.
The HH value gives the humidity level inside the sensor and should be lower than 10 %. Most commonly
a higher humidity level indicates a leak in the sensor. If the sensor is subjected to big temperature changes,
condensate can cause humidity problems. If this is the case, the problem can be solved by replacing the
dryer unit inside the sensor, see Section 6.1.
7.2.3 Slope value
The Slope display (Calibrate / Optical image / Scaled image / Slope) shows you
the slope image and also gives the Slope value as a number. A good slope value is above 1.5. If the slope
value drops near 1.0, something is wrong with the prism:
− Prism is coated or
− Prism surface is not good or
− Prism gaskets leak and process liquid gets in by the prism sides