20
Calibration
Approximate Calibration
If the target liquid is not available for dipping, a substitute
non-conducting
reference
liquid can be used. If the full length of the sensor cannot be dipped, then a partial
length dip can be performed. If both situations are encountered, then a partial length
dip can be performed in a substitute reference liquid.
1. First, cool the sensor as much as possible by dipping the sensor as far as
possible in the available reference liquid.
2. Slowly withdraw the sensor out of the reference liquid 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.
Note
Having a small amount of liquid on the sensor at the MIN calibration level
helps stabilize the sensor capacitance for 0% level indication.
3. Reinsert the sensor in the reference liquid as far as possible, but not exceeding
1" below the top hole. Note the physical location of the liquid level on the
sensor at the maximum insertion depth. While the sensor is submerged at the
maximum depth, press the MAX 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.
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
Approximate Calibration Factor
e
2
1
–
e
1
1
–
--------------
100
×
L
active
L
dipped
------------------
=
Summary of Contents for 186
Page 3: ...2 Introduction ...
Page 13: ...12 Installation Configuring power ...
Page 23: ...22 Calibration Approximate Calibration ...
Page 29: ...28 Operation Sensor contamination ...
Page 37: ...36 RS 232 Communication Data Logger Option Error Codes ...
Page 47: ...46 IEEE 488 Communication Option Serial Poll Status Byte ...
Page 55: ...54 Virtual Instrument Operation Running multiple GPIB devices ...
Page 65: ...64 Index ...