American Magnetics 185 & 186 Liquid Level Instruments (CE-Marked) - Manual (Page 32)

22 Rev. 3
Calibration
Closed dewar calibration
3.3.2.1 Presetting the MAX/MIN calibration points
The following procedure should be performed before installation of the
sensor in the target cryo-vessel.
1. Connect the extension and oscillator cables to the J5 coaxial
connector on the rear panel of the instrument (see page 7 for a
system diagram). Do not connect the sensor. Energize the
instrument. Press the MIN 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.
2. Connect the sensor to the oscillator cable (which is still connected
to the instrument via the extension cable). 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.
3. Calculate the factor C
adj
using the following equation:
where L
total
is the total sensor length in inches, L
active
is the active
sensor length in inches, and e is the dielectric constant of the target
liquid.
4. Enter C
adj
into the instrument by placing the front panel control
mode rotary switch in the SILENCE position. By using the RAISE/
LOWER toggle switch and holding it in the up or down position,
adjust the displayed value up or down. The display will move slowly
at first and then faster. Once near the desired value, simply release
the switch momentarily and then resume changing the factor at the
slower speed. Once the desired number has been reached, release
the toggle switch.
5. Once the value for C
adj
has been entered, momentarily press the
CAL push-button labeled as "~" (the tilde character) through the
small hole provided in the instrument front panel. When the value
has been accepted, the display will show "ddd.d" and the button can
then be released.
6. With the sensor connected, again press the MIN 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 presetting
procedure is complete. Proceed to the remainder of the closed dewar
calibration procedure as presented below.
C
adj
120 1
2.1 L
active
( )
5.2 L
total
( )
---------------------------- +
e 1 –
0.454
------------- =