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Interface Measurement
The capacitance of the electrode system is dependent on the dielectric constant of the
product surrounding the probe. By comparing the capacitances resulting from different
products with different dielectric constants, it is possible to determine which product is
surrounding the probe.
For miscible products:
Contamination of one product by another can be measured:
100% product A
100% product B
Values in between 4 and 20 mA represent the ratio of the two products.
For immiscible products:
The interface between two products can be detected by the change in capacitance from
one to the other. (See example,
Switch action
2-state Switch
The mA output can be used as a 2-state switch set to either 4 or 20 mA. It can be set to go
to 4 mA if the probe is covered and 20 mA if the probe is uncovered, or the reverse.
Solid-state Switch
The solid-state output can be set to 'contact open' or 'contact closed' with a covered
probe.
Adjustable hysteresis and time delay
The adjustable hysteresis and time delay settings allow you to adjust the switch action for
applications with a lot of surface movement.
Examples:
With a moving surface that fluctuates between 79% and 80%, if the hysteresis is set
so that 80 is on and 79 is off, the alarm will constantly alternate between on and off.
Either set a time delay, or adjust the hysteresis:
•
Set the time delay to 10 seconds (for example): the alarm will be on only after
the surface has been at 80% for at least 10 seconds.
•
Reset the hysteresis for 70 (for example): the unit will ignore small surface
fluctuations between 79 and 80%.
7ML19985GE04
4 mA
20 mA
For Vessels filled with Oil
SITRANS LC500 – OPERATING INSTRUCTIONS
on page 101.)
Page 15
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