Calibration – American Magnetics 286 Multi-Sensor Liquid Level Instrument (CE-Marked) User Manual

Page 41

Calibration

Approximate calibration

While the sensor is submerged at the maximum depth, 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.

8. Measure the distance between the bottom hole of the sensor and

the location of the liquid level noted during step 7. This measured
length is L

dipped

9. The dielectric constant for the reference liquid,

, and the target

liquid,

, 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,
(

−

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

= 1.4336 for saturated liquid nitrogen 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 equilibrium temperature and pressure
maintained in the containing vessel.

10. Once the approximate calibration factor is calculated, it can be

entered into the instrument by placing the instrument in the
custom approximate calibration factor entry screen as documented
in paragraph 3.3.4.2 on page 31.

It will be necessary to

ESC

to the sensor input selection screen and

choose the

Select

option in order to traverse the calibration menu

tree and arrive at the custom approximate calibration factor entry
screen. Ensure that the same calibration used to this point of the
procedure is selected for the entry of a custom approximate
calibration factor.

1. Data from NIST Database 12.

Approximate Calibration Factor

–

--------------

100

active

dipped

-----------------