Siemens LC 500 Interface Measurement, Switch action, Operation & Application, state Switch

Operation & Application

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	4 mA
100% product B	20 mA

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, For Vessels filled with Oil on page 91.)

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%.

Page 14 SITRANS LC 500 – INSTRUCTION MANUAL 7ML19985GE01