Electricity: measuring and testing – Conductor identification or location – Inaccessible
Patent
1981-03-27
1984-11-06
Krawczewicz, Stanley T.
Electricity: measuring and testing
Conductor identification or location
Inaccessible
G01R 1152, G01R 2726
Patent
active
044814658
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to capacitive measuring transducer apparatus, especially for small capacitive values, and more particularly to such apparatus with two bridge arms, each of which has at least one capacitor, and incorporating a differential amplifier connected on the input side with the bridge arms, each possibly having an amplifier, and the output of the differential amplifier is fed back to one of the bridge arms.
2. Prior Art
Such measuring transducer apparatus is disclosed in German OS No. 2 641 758. In case of this known measuring transducer, the two bridge arms, each of which has an amplifier, in the control circuit of which there is a capacitor or a parallel connection of capacitors and in the main circuits of which there always is a resistance combination for interconnecting terminal points of the bridge arms and an oscillator. The evaluation of capacitance changes of one or two of the capacitors disposed in different bridge arms takes place in the known case by way of the amplifiers acting as charge amplifiers, -which may be, for example, d.c. current operational amplifiers with a capacitive feedback, which may produce an output voltage, which is directly proportional to the change of the charge at the input connections. The differential amplifiers evaluate the output signals, to which a filter and a phase demodulator is series connected, the second input of which is connected with the oscillator, as well as a differential amplifier series connected to the phase demodulator, and a wave-band filter. The output voltage of the wave-band filter, at the same time, is fed back to a bridge arm via an analog multiplier, which precedes the latter.
The disadvantage of this known transducer lies in the fact that the individual parts of the circuit are very expensive and that the consequent costs are very high, to which the analog-multiplier also contributes considerably. Another disadvantage of this transducer, which operates according to the carrier-frequency method, also results from the fact that a sinusoidal generator is needed, in case somewhat higher demands are made, and this likewise results in a considerable expense.
SUMMARY OF THE INVENTION
It is the goal of the invention to propose a transducer of the initially mentioned type which is distinguished by a simple construction and nevertheless has a high degree of stability.
This will be achieved according to the invention by connecting a control element in series with each bridge arm. One of the terminals of the control elements is connected together and this common point is connected to the output of a square wave generator. The other terminals of the control elements, along with their respective bridge arms are each connected through at least one passive circuit element to a potential source. A feed-back circuit is provided, consisting of essentially passive circuit elements and which is connected to one of the capacitors in one of the bridge arms, whereas the corresponding capacitor in the other bridge arm is connected, via a passive circuit element to a fixed potential or to a potential which is determined by the differential amplifier and which varies in an inverse manner with the output of the differential amplifier.
The potential at the bridge arms is changed by way of the control elements by the pulse train delivered from the oscillator, in correspondence with the pulse train, whereby potential changes on the electrodes of the capacitors occur, and charge transferring currents develop in the bridge arms, corresponding to the capacitance values of the capacitors. Differences in the currents of the bridge arms or voltage differences at certain points of the two bridge arms are amplified by the differential amplifier and are fedback to a bridge arm via the feedback circuit to influence the extent of the potential variations on the basis of the pulse train coming from the oscillator in one bridge arm, whereas the second bridge arm is influenced during the off period of the control elem
REFERENCES:
patent: 3519923 (1970-07-01), Martin et al.
Phillips, "Capacitive Ink Level Detector"-IBM Bulletin, Mar. 1974.
Fredericks George E.
Preschern Horst
Krawczewicz Stanley T.
List Hans
Solis Jose M.
LandOfFree
Capacitive measuring transducer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Capacitive measuring transducer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Capacitive measuring transducer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1044189