Setting The Dielectric Constant Of Upper Media; Configuring Gas Phase Compensation - ABB LWT300 Series User Manual

Setting the dielectric constant of upper media

When your application involves measurement of the interface between liquids (e.g., oil on top of water), you
must indicate the dielectric constant (DC) of the first liquid that the pulse will encounter (in this case, oil).
To do so:
1 Select Device Setup > Sensor Setup > Upper Media DC.
2 Press Edit.
3 Set the proper dielectric constant (between 1.4 and 10) and press OK.
You can find the dielectric constant of most common liquids in "Appendix D" on page D95.

Configuring gas phase compensation

Different substances have different dielectric constants (DC), and even a single substance has
different DCs depending of its state (phase): solid vs. liquid vs. gaseous. When measuring the level
of a substance in a vessel, inaccuracies can appear if that substance is present in two phases at the
same time (e.g., liquid and vapor [gas]) The gas phase compensation (GPC) feature takes into account
the variation of DC brought about by the presence of a substance in gas phase inside a vessel, thus
considerably improving level measurement accuracy.
GPC generally applies to high-pressure, high-temperature (HPHT) applications (e.g., boilers), but it can
be used in any application where a substance in gas phase is present.
GPC is configured from the Device Setup menu.
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Figure 35 The Device Setup menu
Activating GPC
LWT instruments offer two modes for dealing with GPC: static, if you know exactly the percentage
variation between the two phases present in the vessel, and dynamic, if you prefer to let the instrument
calculate a proper compensation.
To activate the gas-phase compensation function:
1 Select Device Setup > Sensor Setup > Gas Phase comp. > GPC Mode.
2 Press Edit.
3 Highlight Static and press OK.
NOTICE
The menu also contains a Dynamic option. Dynamic-related options are used specifically
with high-pressure, high-temperature hardware options not offered at the time of writing.
Configuring the instrument
47