American Magnetics 185 & 186 Liquid Level Instruments (CE-Marked) - Manual (Page 36)

26 Rev. 3
Calibration
Approximate calibration
4. Measure the distance between the bottom hole of the sensor and
the location of the liquid level noted during step 3. This measured
length is L
dipped
.
5. The dielectric constant for the reference liquid, e
1
, and the target
liquid, e
2
, must be known to complete the approximate calibration.
These values must be placed in the equation:
where L
dipped
is the length of the sensor dipped in the reference
liquid and L
active
is the active sensor length.
Note
If the target liquid is available for dipping (i.e. the reference liquid
and target liquid are the same), then the dielectric ratio,
(e
2
− 1)/(e
1
−
1), becomes 1. If the full active length of the sensor can be dipped,
then the length ratio, L
active
/ L
dipped
, becomes
1.
Note that e
1
= 1.454 for liquid nitrogen at − 203 ° C at atmospheric
pressure. Dielectric constants for several liquids are provided in the
Appendix
. The dielectric constant varies with temperature and
pressure, therefore for best accuracy use the dielectric constant for
the target liquid at the temperature and pressure maintained in
the containing vessel.
6. Once the approximate calibration factor is calculated, it can be
entered 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,
you can adjust the approximate calibration factor 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.
7. Once the approximate calibration factor 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 calibration factor has been accepted, the display
will show "ddd.d" and the button can then be released. This
completes the approximate calibration procedure.
Approximate Calibration Factor
e
2
1 –
e
1
1 –
-------------- 100
×
L
active
L
dipped
----------------- =