Appendix A: Technical References; Operating Principles; High Frequency Oscillator; Detection Range - Siemens Pointek CLS200 Operating Instructions Manual

Appendix A: Technical References

Operating Principles

In capacitance measurement
vessel wall) acts as the reference electrode of a variable capacitor, and the probe
supplies the measurement electrode. The dielectric
(air, vapor, liquid, solid, or a combination) and, if the measurement electrode is insulated,
the insulating layer.
The capacitance when the probe is uncovered (capacitance in air) will be different from
the capacitance when the probe is covered (for example, capacitance in water). If the
product is two immiscible liquids with different relative dielectric constants, (for example,
oil and water) the capacitance will change at the interface between the two liquids.

High Frequency Oscillator

The Pointek CLS200/300 probe is equipped with a high frequency oscillator which
responds to the capacitance. The inverse of frequency is proportional to the capacitance.
A small change in capacitance results in a large change in frequency which is easy to
detect, resulting in high resolution and accuracy.

Detection Range

The functional detection range depends on the relative dielectric constant of the material
monitored. The detection range will be shorter when the material has a lower relative
dielectric constant, and longer when it has a higher relative dielectric constant.
1.
For definitions relating to capacitance, see the glossary, page 71
2.
The relative dielectric constant of air (vacuum) is 1: all other materials have a higher value.
Page 32 Pointek CLS200/300 Standard – INSTRUCTION MANUAL
1
inside a vessel or silo, the environment (typically, the
dielectric = contents plus insulation (non-conductive contents)
dielectric = insulation (conductive contents)
probe
dia. (d)
(insulation)
internal
probe
vessel
sleeve
wall
internal vessel dia. (D)
2
is composed of the vessel contents
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