STRAIN MEASURING SYSTEM

• US 3,847,017 A
• Filed: 02/21/1973
• Issued: 11/12/1974
• Est. Priority Date: 03/20/1972
• Status: Expired due to Term

• Current Assignee: Jack Watts
• Original Assignee: Jack Watts
• Inventors: Watts, Jack
• Primary Examiner(s): Gill, James J.
• Assistant Examiner(s): Kreitman, Stephen A.
• Application Number:
  US05/334,253
• Time in Patent Office: 629 Days
• Field of Search: 73/88.5R,141A 324/130,62,63,65R
• US Class Current: 73/765
• CPC Class Codes: G01L 1/225 Measuring circuits therefor

Abstract

A measuring device comprising the following: A. A Wheatstone bridge containing at least one resistance strain gauge adapted to measure stress or strain; B. MEANS FOR PROVIDING A DIRECT CURRENT VOLTAGE SUPPLY TO THE BRIDGE; C. MEANS FOR SENSING A VOLTAGE APPLIED TO THE BRIDGE AND FOR PROVIDING A REFERENCE VOLTAGE FOR A SIGNAL RESULTING FROM UNBALANCE IN THE BRIDGE DUE TO THE EFFECT OF STRAIN ON THE GAUGE, THE SIGNAL BEING AN AMPLIFIED OUTPUT VOLTAGE FROM THE BRIDGE; D. MEANS FOR CORRECTING FOR THE GAUGE FACTOR OF THE STRAIN GAUGE BY VARYING THE GAIN TO THE OUTPUT VOLTAGE FROM THE BRIDGE; AND E. MEANS FOR INDICATING THE RATIO BETWEEN THE SIGNAL AND THE REFERENCE VOLTAGE.

Claims

1. A measuring device comprising:

a. a Wheatstone bridge containing at least one resistance strain gauge adapted to produce an output voltage corresponding to unbalance in the bridge due to the effect of strain on the gauge;

b. means for providing a DC voltage to the bridge;

c. means for sensing the DC voltage applied to the bridge and producing a reference voltage therefrom;

d. means for amplifying said output voltage;

e. means for calibrating the device for different strain gauges by varying the gain in said amplifying means;

f. means for indicating the ratio between the output voltage and the reference voltage; and

g. means for compensating for bridge unbalance by summing the output voltage and a balance voltage derived from said reference voltage.

2. A measuring device according to claim 1 in which the means for sensing includes at least one amplifier and the means for calibrating is a variable gain control on the means for amplifying the output voltage.

3. A measuring device according to claim 1 in which said ratio is displayed on an indicator calibrated in units of strain and said indicating means is a digital indicator.

4. A measuring device according to claim 1 wherein the DC voltage is pulsed between zero and a positive value and further including means for correcting for a drift voltage produced in said measuring device during periods when the DC voltage is zero, including:

a. means for sampling said drift voltage when said DC voltage is zero, b. means for developing a voltage to correct for said drift voltage, c. means for storing the developed voltage, d. means for applying the developed voltage to the measuring device to correct for said drift voltage prior to said indicating means forming said ratio.

5. A measuring device according to claim 1 wherein the DC voltage is pulsed between zero and a positive value and further includes means for correcting for a drift voltage produced in said measuring device during periods when the DC voltage is zero, including:

a. means for sampling said drift voltage when said DC voltage is zero, b. means for developing a voltage to correct for said drift voltage, c. means for storing the developed voltage, d. means for applying the developed voltage to the measuring device to correct for said drift voltage prior to said indicating means forming said ratio.

6. A measuring device according to claim 4 in which the means for storing is a hold circuit including inverting means and the means for applying the developed voltage applies said voltage to a final stage of said amplifier means.

7. A measuring device comprising:

a. a Wheatstone bridge containing at least one resistance strain gauge adapted to produce an output voltage corresponding to unbalance in the bridge due to the effect of strain on the gauge, b. means for providing a DC voltage to the bridge, c. first amplifier means for sensing the DC voltage applied to the bridge and producing a reference voltage therefrom, d. second amplifier means for amplifying said output voltage, e. a gain control for calibrating the device for different strain gauges by varying the gain in said second amplifying means, and f. a digital indicator calibrated in units of strain for displaying the ratio between the output voltage and the reference voltage; and

g. summing amplifier means for compensating for bridge unbalance by summing the output voltage and a balance voltage derived from the reference voltage.

8. A measuring device according to claim 7 wherein the DC voltage is pulsed between zero and a positive value and further including means for correcting for a drift voltage produced in said measuring device during periods when the DC voltage is zero, including:

a. means for sampling said drift voltage when said DC voltage is zero, b. means for developing a voltage to correct for said drift voltage, c. means for storing the developed voltage, d. means for applying the developed voltage to the measuring device to correct for said drift voltage prior to said indicating means forming said ratio.

9. A measuring device according to claim 8, in which the means for storing is a hold circuit including inverting means and the means for applying the inverted developed voltage applies said voltage to a final stage of said second amplifier means.