Inclinometer sensing circuitry and operation
AssigneePrecision Navigation, Inc.
InventorChun-Foong Cheah
Life of this patent
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Abstract
Measurement circuitry for a biaxial inclinometer having electrolytic fluid incorporates a Schmitt trigger for measuring the resistance of each leg of the inclinometer by measuring the frequency output of the Schmitt trigger circuit while each leg is placed across input and output terminals. Switching is accomplished by cycling analog multiplexers as solid-state switches under control of a microprocessor. To minimize net dc current across any leg, legs are periodically reversed in polarity as they are switched into the Schmitt trigger circuit for measurement. Additionally, in the wiring of the switching multiplexers to the inclinometer legs, an additional analog multiplexer is switched to place a low clamp resistance in parallel with each leg not being measured in a cycle, to compensate for leakage current.
Claims16
A circuit for measuring resistance in legs of an inclinometer containing electrolytic fluid, comprising:
- a Schmitt trigger circuit for generating a signal with a frequency proportional to an electrical resistance placed across an input and an output lead of the Schmitt trigger circuit;
- and
- solid state switching circuitry connected to the legs of the inclinometer and controllable to connect each of the legs of the inclinometer individually across the Schmitt trigger input and output leads.
An inclinometer system comprising:
- a biaxial inclinometer having individual legs consisting of pairs of electrodes and containing electrolytic fluid in a manner that fluid level changes in the individual legs according to magnitude of tilt of the inclinometer;
- a Schmitt trigger circuit for generating a signal with a frequency proportional to an electrical resistance placed across an input and an output lead of the Schmitt trigger circuit;
- and
- solid state switching circuitry connected to the legs of the inclinometer and controllable to connect each of the legs of the inclinometer individually across the Schmitt trigger input and output leads.
A method for measuring resistance in legs of an inclinometer device for determining the orientation of the inclinometer, comprising the steps of:
- (a) connecting a first leg of the inclinometer device across an input and an output terminal of a Schmitt trigger circuit;
- (b) measuring frequency of the signal output by the Schmitt trigger circuit with the first leg connected;
- (c) disconnecting the first leg of the inclinometer from the input and output terminals of the Schmitt trigger circuit and connecting a second leg of the inclinometer to the input and output terminals of the Schmitt trigger circuit;
- (d) measuring frequency of the signal output by the Schmitt trigger circuit with the second leg connected;
- and
- (e) repeating steps (a) through (d) for other legs of the inclinometer until all legs are measured.
A method for minimizing net dc current through legs of an inclinometer during repeated measurements, comprising the steps of:
- (a) switching the legs of the inclinometer sequentially and individually across measurement circuitry and processing the output of the measurement circuitry;
- and
- (b) periodically reversing the polarity of the legs of the inclinometer across the measurement circuitry as the legs are switched into the measurement circuitry.
Dependencies are inferred from the claim text.