Siemens Sitrans The SITRANS LC 500 electrode, Operation & Application, The stilling well

Operation & Application

In a non-conductive or irregular tank

Where the vessel contents are non-conductive:

•a reference electrode parallel to the measurement electrode is required

•the reference electrode must be grounded to the instrument

•a stilling well can form the reference electrode.

Where the vessel contents are conductive:

•the interface between the contents and the electrode insulation acts as the reference electrode

•a connection from the vessel contents to the instrument ground is required

•a stilling well can provide a means of connecting the contents to the instrument ground.

The stilling well

The stilling well is a metal tube concentric with the electrode, with vent openings to facilitate level equalization. Its diameter is somewhat larger than that of the electrode, depending on the application. The stilling well can either be integral to the SITRANS LC 500, or it may be part of the tank1.

The SITRANS LC 500 electrode

The SITRANS LC 500 electrode, comprising a measurement section and an active shield section, is the primary sensor of the system. It supplies the electrical capacitance value of the measurement section relative to the environment (tank wall or stilling well).

The SITRANS LC 500 patented Active-Shield Technology electrically isolates the measurement section and prevents any non-measurement capacitance from interfering with the measurement. (Capacitance changes could result from uncontrolled variations occurring in the connection cable, process connection, and non-active parts of the probe). This results in a better ratio of initial capacitance to total capacitance, resulting in higher accuracy.

1.The tank wall, or the stilling well if it is part of the tank, must be grounded.

Page 10 SITRANS LC 500 – INSTRUCTION MANUAL 7ML19985GE01