American Magnetics 185 & 186 Liquid Level Instruments (CE-Marked) - Manual (Page 31)

Rev. 3 21
Calibration
Open dewar calibration
3.3.1 Open dewar calibration
The instrument should be energized with the sensor connected to the
instrument via the oscillator (see the system diagram on page 7).
1. Slowly insert the sensor into the liquid until the level rests
approximately one inch below the top sensor hole and then press
the MAX push-button through the small hole provided on the
instrument front panel. When the calibration point has been
accepted, the display will show "bbb.b" and the push-button can
then be released. The location of the liquid level on the sensor when
the MAX button is pressed becomes the 100% level. The 100% level
should always be lower than the upper hole to ensure the
instrument will always reach 100% in the event the overall sensor
capacitance changes slightly due to component drift, pressure
variations, fluid impurities, etc.
2. Slowly withdraw the sensor out of the liquid to be measured until
the level is approximately even with the bottom hole in the sensor
and then press the MIN push-button through the small hole
provided in the instrument front panel. When the calibration point
has been accepted, the display will show "bbb.b" and the push-
button can then be released. The location of the liquid level on the
sensor when the MIN button is pressed becomes the 0% level. This
completes the calibration procedure.
Note
Having a small amount of liquid in contact with the sensor at the
MIN calibration level helps stabilize the sensor capacitance for 0%
level indication.
3. Permanently install the sensor in the vessel and proceed to the
Operation section for directions for configuring the instrument.
3.3.2 Closed dewar calibration
A calibration can be performed in a closed dewar system by monitoring the
liquid level while transferring the target liquid to an initially empty (or
near empty) dewar at a constant rate. In order to insure success with the
closed dewar technique, it is necessary to prepare the instrument by
presetting the calibration MIN and MAX points outside the estimated
level range. If the instrument is not prepared in this manner before the
calibration procedure, it is possible to reach the MAX calibration point of
the instrument before the target vessel is at the desired maximum level
point. If minimum and maximum liquid level indication is available via
some other means (e.g. flow calculation, visual determination, point
sensors, etc.), then the presetting of the instrument is not necessary.