Guarded capacitance probe and related measurement circuit
US5546005A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jan 9, 1995 |
| Grant date | Aug 13, 1996 |
| Priority date | — |
| Expiry date | Jan 9, 2015 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01F23/266
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A continuous liquid level measuring system having a guarded capacitance probe and related drive circuit for providing accurate level measurements, even when measuring the level of ionic and highly viscous fluids. The capacitance probe has two parallel electrodes, each constructed of a half-tube section, that are separated from each other by an insulated guard wire. The probe is excited by a 1 MHz excitation signal applied across the electrodes. The current through the electrodes is a function of the capacitance between the electrodes, which is affected by the relative permitivity of the surrounding liquid. The effects of highly viscous ionic liquids that adhere to the probe are reduced by exciting the guard wire with a guard signal that is 180.degree. out of phase from the probe's excitation signal. The guard signal changes the electric field existing in the space adjacent the junctions of the two electrodes to reduce any liquid coating effects on the level measurement. The capacitance probe is connected to a capacitance measurement circuit through at least one 1:1 ratio pulse transformer for isolation, effectively eliminating the effects of noise currents on the probe's capacitanc…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.