American Magnetics 286 Multi-Sensor Liquid Level Instrument (CE-Marked) - Manual (Page 36)

22
Calibration
Closed dewar calibration
3.2.2 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.
3.2.2.1 Presetting the MAX/MIN calibration points
The following procedure should be performed before installation of the
sensor in the target cryo-vessel.
1. Enter the calibration menu by using the passcode, and select the
appropriate sensor input to calibrate as documented in paragraph
3.3.2 on page 30.
2. Choose the Perform option and select the desired calibration to
perform as documented in paragraph 3.3.5.1 on page 33.
3. Enter the appropriate active length value as documented in
paragraph 3.3.5.2 on page 33.
4. Place the instrument in the MIN/MAX entry screen as documented
in paragraph 3.3.5.3 on page 34.
5. Connect the extension and oscillator cable to the C or D coaxial
sensor input connector on the rear panel of the instrument (see
page 5 for a system diagram). If using sensor input A or B, simply
connect the sensor cable to the Model 286. Do not connect the
actual sensor.
6. Press the MIN button as prompted by the display. When the
calibration point has been accepted, the display will change to
Entered and the Model 286 will beep once.
7. Connect the sensor to the oscillator cable for sensor inputs C or D,
or connect the sensor to the single sensor cable for sensor inputs A
or B.
8. Press the MAX button as prompted by the display. When the
calibration point has been accepted, the display will change to
Entered and the Model 286 will beep once.