8 Troubleshoong
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8.2.4 Message OUTSIDE LIGHT TO PRISM
Cause: Some light from the outside reaches the sensor and may disturb the measure-
ment.
Action: Identify the light source (for example sun shining into an open tank or a
translucent pipe) and block the light from getting to the prism at the sensor tip.
8.2.5 Message LOW IMAGE QUALITY
Cause: The most likely cause for this message is scaling on the prism. There still is a
optical image available, but the measurement quality may not be optimal.
Action: Clean the prism, see Section 8.2.3 above.
8.2.6 Message NO SAMPLE
The operation of the equipment is OK but there is no process liquid on the prism. The
optical image looks like the left image in Figure 5.8 or Figure 5.6.
8.2.7 Message TEMP MEASUREMENT FAULT
Indicates faulty temperature element. Disconnect the temperature sensor leads from
the screw terminals at the processor card, Section 7.3.1, “Disassembling the sensor”.
The resistance value of the Pt-1000 element should be close to 1000 Ω
. To change the
temperature element, see Section 7.3.3 “Replacing the prism and prism gaskets”.
Note: The prism gasket must be replaced, too.
Note: A difference to some other process temperature measurement is not a fault.
PR-23 measures the true temperature of the prism surface.
8.2.8 Concentraon dri during NORMAL OPERATION
For drift upward, suspect prism coating, Section 4.1, “Prism coating”. Otherwise check
calibration (Section 6.4, “Calibrating the concentration measurement”) and sensor
veriication (Chapter 13, “Sensor veriication”).
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