Troubleshooting Other Problems - Emerson Clarity II Instruction Manual

MODEL CLARITY II

8.4 TROUBLESHOOTING OTHER PROBLEMS

Problem
Readings are erratic
Readings drift
Analyzer responds too slowly to changes in turbidity
Flow is too low
Readings are lower or higher than expected
Current output is too low
Alarm relays do not operate when setpoint is exceeded
Display is unreadable-too faint or all pixels dark
8.4.1 Readings are erratic
Erratic readings are usually caused by air bubbles drifting through the measurement zone of the sensor. Air bub-
bles reflect light onto the detector and cause spikes in the turbidity reading. A debubbling chamber helps remove
large bubbles. An orifice in the outlet of the debubbler helps eliminate outgassing by putting back pressure on the
debubbler. Outgassing can occur when the pressure of the sample is reduced or when a cold sample warms up.
A bubble rejection filter in the analyzer software also helps reduce the effect of bubbles.
A. Be sure the bubble rejection filter is on and increase the signal averaging time. See Section 5.5.
B. If the inlet pressure is high enough, increase the back pressure on the debubbler using a valve or a valved
rotameter (PN 24103-00) installed in the outlet of the debubbler. Do not exceed 30 psig (308 kPa abs).
Increasing the back pressure reduces the sample flow and increases the system response time. If the inlet
pressure is too low, increasing the back pressure might not be feasible.
C. If bubbles persist, increase the back pressure and use a sample pump to increase the inlet pressure.
8.4.2 Readings drift
Gradual downward drift in readings is caused by dirt accumulating on the lamp or detector windows. The dirt
reduces the amount of light entering the measuring zone in the sample and blocks scattered light from reaching
the detector. Upward drift is usually caused by bubbles adhering to the lamp or detector windows. The bubbles,
which act like lenses, direct light onto the detector and increase the apparent turbidity reading. Once the bubbles
get large enough, they break away from the surface of the detector and the turbidity reading drops.
A. If downward drift is occurring, inspect the sensor windows for cleanliness. See Section 7.2.1 for cleaning
instructions.
B. If upward drift is occurring, remove the sensor completely from the debubbler and then replace it. If readings
drop back to normal or expected values, then the upward drift was probably caused by bubbles accumulating
on the sensor. (Removing the sensor from the debubbler causes the air bubbles to break.) To reduce bubble
accumulation, increase the back pressure on the debubbler using a valve or valved rotameter (PN 24103-00)
installed in the outlet of the debubbler. Do not exceed 30 psig (308 kPa abs). Increasing the back pressure
reduces the sample flow and increases the system response time. If the inlet pressure is too low, increasing
the back pressure might not be feasible.
C. If bubbles persist, increase the back pressure and use a sample pump to increase the inlet pressure.
54
SECTION 8.0
TROUBLESHOOTING
Section
8.4.1
8.4.2
8.4.3
8.4.4
8.4.5
8.4.6
8.4.7
8.4.8