American Magnetics 187 Self-Compensating Liquid Level Controller - Manual (Page 28)

17
Operation
Sensor contamination
The fill timeout feature is enabled when the instrument is operated in the
AUTO mode with a fill timeout setting greater than zero. Once the liquid
level falls below the B setpoint, an internal fill timer (whose period is the
timeout setting) begins to increment. If the liquid level does not reach the
A setpoint before the timeout period expires, the FILL LED will begin
blinking and power to the rear panel controller output receptacle will be
interrupted. To reset this function the fill mode must be momentarily
changed to the ON state, the OFF state, or power to the instrument must
be momentarily turned off.
Note
The fill timeout function is disabled when the timeout setting is zero,
i.e. the Model 187 will continue to fill the target vessel until the A
setpoint is achieved. Adjusting the fill timeout setting to zero, while
an AUTO fill is in progress, will also terminate any in-progress
functions of the timer.
The instrument is shipped from the factory with a zero setting for the fill
timeout.
3.2 Sensor contamination
To ensure proper instrument calibration and operation, care must be
taken to ensure the sensor is kept free of contaminants and not subjected
to any force which would physically distort the sensor. Water or other
electrically conducting substances in the sensor will disturb the measured
capacitance and therefore instrument response. Physically distorting the
sensor in any way will also cause abnormal instrument operation by
introducing variations in the sensor capacitance not due to liquid level.
The absolute calibration of the instrument can be inaccurate if care is not
taken to ensure the sensor is in a proper environment.
Cold sensors exposed to humidified air can show erroneous high level
readings due to the fact that the air contains moisture which can condense
between the cold sensing tubes. A small film of water can cause a shorted
or partially shorted condition, which results in false level readings. As the
sensor warms, the moisture may evaporate and the sensor will again read
correctly. This is a physical phenomenon and does not indicate any
problem with your AMI level equipment. Limit or eliminate exposure of
cold sensors to humidified air to avoid this condition.
If a sensor should require cleaning, flushing with alcohol is recommended.
The sensor cannot be used again until all the alcohol has been evaporated.
Under no circumstances should the sensor be disassembled.