Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1997-12-05
1999-11-30
Regan, Maura
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
324671, 331 65, G01R 2726
Patent
active
059949074
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus for measuring the capacitance between at least a conductive part of a wall of a vessel and a measuring electrode situated in the vessel and carrying a measuring voltage, comprising a measuring circuit and a compensating circuit for applying a compensating voltage as nearly as possible the same as the measuring voltage in the vicinity of the conductors carrying the measuring voltage.
Such apparatuses are known, for instance from EP-A-0 101 580.
As a consequence of these prior art steps the influence of parasitic capacities is eliminated to the greatest possible extent, so that the measuring range of the circuit becomes available to the greatest possible extent and accuracy is increased.
In this prior art circuit the measuring capacitance is measured by means of phase shift of the measuring signal. Phase shift is a quantity which is difficult to measure, so that measurement thereof is difficult, involves inaccuracies and a complicated measuring circuit using much power is required.
The object of the present invention is to avoid the above stated problems.
This object is achieved in that the capacitance between the measuring electrode and the vessel wall is connected as a frequency determining element in an oscillator, so that the frequency of the measuring signal is related to the value of the capacitance.
Frequency is a quantity which can be measured much better, can be determined much more precisely, requires less complicated circuits and can be largely implemented in integrated form.
According to a preferred embodiment the period of the measuring signal is substantially proportional to the capacitance and the measuring circuit is adapted to measure the period. This is a quantity which is likewise easy to measure and which is moreover proportional to the capacitance value for measuring.
Other attractive preferred embodiments will be found in the remaining claims.
The present invention will be elucidated hereinbelow with reference to annexed drawings, wherein:
FIG. 1 shows a partly broken away perspective view of a cylindrical measuring vessel with a centrally arranged electrode as part of the apparatus according to the invention;
FIG. 2 shows a sectional view of a cylindrical measuring vessel according to a second embodiment;
FIG. 3 shows a block diagram of the oscillator circuit which forms part of the apparatus according to the present invention;
FIG. 4 shows a block diagram of the full circuit according to the invention;
FIG. 5 is a sectional view of a variant of the first embodiment; and
FIG. 6 is a sectional view of an electrode construction according to the present invention.
FIG. 1 shows a measuring vessel 1 which is formed by a housing 2 on which is placed a cover 3. Placed on cover 3 is a casing 4 in which the circuit of the measuring apparatus according to the invention is arranged. The casing 4 is connected to an electrode body 5 which is arranged in the interior of housing 2 by means of a lead-through 6 through cover 4.
In this embodiment the vessel has the shape of a straight circular cylinder. It is also possible to use a vessel with a different cylinder shape, for instance a rectangular cylinder. It is even possible to use a non-cylindrical vessel.
The electrode body 5 comprises a housing 7 which is manufactured from insulating material and inside which is placed a measuring electrode 8 which is connected by means of a central rod 9 to the measuring circuit present in casing 4. Around the rod 9 but inside the housing 7 is arranged a guard electrode 10.
It will be apparent that the capacitance between measuring electrode 8 and housing 2, which is normally earthed for safety reasons, is influenced by the nature of the substance with which the vessel is filled and by the degree to which the vessel is filled. The nature of the substance here refers particularly to the electrical permittivity. The capacitance is thus a measure for the degree of filling of the vessel or the quality of the substance in the vessel.
This property will be used to perform measureme
REFERENCES:
patent: 2932970 (1960-04-01), Zito
patent: 3378638 (1968-04-01), Weingartner
patent: 4912976 (1990-04-01), Labriola
Mulder Richard
Schoenmakers Cornelis W. P.
Slezak Marian J. W.
Meridian Instruments B.V.
Regan Maura
LandOfFree
Apparatus for capacitive measurements does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for capacitive measurements, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for capacitive measurements will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1677374