American Magnetics 185 & 186 Liquid Level Instruments (CE-Marked) - Manual (Page 34)

24 Rev. 3
Calibration
Closed dewar calibration
should decrease significantly when the liquid reaches the hole in
the top of the sensor.
When the break in the slope of the level trace occurs (i.e. the slope
of the level trace becomes 0 or horizontal), push the MAX push-
button through the small hole provided in the instrument front
panel. When the calibration data has been accepted, the display
will show "bbb.b" and the push-button can then be released. The
level on the sensor when the MAX button is pressed becomes the
100% level.
Note
If the instrument displayed a 100% reading before a break is
observed in the slope of the level trace, then the MAX calibration
point set prior to the current procedure has interfered. If this occurs,
the customer has two options: 1) stop the procedure, repeatedly enter
a value of
120 for C
adj
(see steps 4 and 5 of the presetting procedure)
until the current liquid level display falls below 100%, and then
continue the procedure; or 2) continue the liquid transfer until the
liquid level is determined to be 100% by means other than feedback
from the instrument and then pressing the MAX calibration push-
button.
6. To achieve a standard calibration of the sensor with the active
region located from the lower hole to one inch below the upper hole,
use the level data from the instrument to recalibrate the MAX point
when the percent level corresponds to one inch below the upper
hole. Use the following equation to determine the percent level at
which to reset the MAX calibration point:
where L
active
is the active length of the sensor in inches. This
technique can be used assuming the sensor was built as a standard
sensor. If the sensor was made in a custom configuration, refer to
the sensor documentation and/or drawing or contact AMI.
Example: 20" active length sensor:
When the sensor is calibrated by the closed dewar procedure, the
actual length of calibration will be 21" (distance between the
bottom and top holes in the sensor). When the liquid is 1" below the
upper hole, the display will show 95.2% [e.g. 100% − (1"/21" x 100%)
]. When the liquid level reaches this point during usage, push the
MAX calibrate button. The instrument and sensor are now
MAX
percent
100 100
1
L
active
--------------- – =