GB2419670A - A strain gauge measuring circuit - Google Patents

A strain gauge measuring circuit Download PDF

Info

Publication number
GB2419670A
GB2419670A GB0423718A GB0423718A GB2419670A GB 2419670 A GB2419670 A GB 2419670A GB 0423718 A GB0423718 A GB 0423718A GB 0423718 A GB0423718 A GB 0423718A GB 2419670 A GB2419670 A GB 2419670A
Authority
GB
United Kingdom
Prior art keywords
resistive sensing
resistive
sensing element
arrangement according
terminal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB0423718A
Other versions
GB0423718D0 (en
Inventor
Robin Terence Albert Stevens
Industrial Dataloggers Limited
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Priority to GB0423718A priority Critical patent/GB2419670A/en
Publication of GB0423718D0 publication Critical patent/GB0423718D0/en
Priority to GB0506493A priority patent/GB2419672B/en
Priority to US11/259,012 priority patent/US20060087326A1/en
Publication of GB2419670A publication Critical patent/GB2419670A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
    • G01L1/225—Measuring circuits therefor

Abstract

The object of the invention is to provide a strain gauge measurement circuit to overcome the disadvantages of the Wheatstone bridge circuit. The invention is a strain gauge measuring circuit comprising a stabilized voltage supply Vg connected across one or more sets of strain gauges connected in series R1 and R2, R3 and R4, and Rn to the nth, with their junctions connected to a voltage source Vs which is varied until no current flows to or from the voltage source Vs, with the voltage source Vs remaining constant if one or more of the strain gauges are active then the total change in current through the strain gauges is equal to the current flowing to or from the voltage source Vs. The sensing current is linear even for large changes of the strain gauge resistance, simple, provides a large signal output and can function with precision with only a few components.

Description

IMPROVED STRAIN GAUGE DEVICES
I
The invention relates to improved circuit for the measurement of strain.
The basic circuit used for the measurement of strain is the Wheatstone bridge circuit which produces a voltage output signal, it has become the international industrial standard even though it only produces a very small non-lineas signal, in response manufacturers have produced highly specialised designed cables and instrumentation to cope with the hazards this problem creates. The Wheatstone bridge limits the number of resistive sensing elements to four and even if strain gauge resistive sensing elements were to have a greater sensitivity the output signal from the Wheatstone bridge would be very non-linear.
It is the object of the invention to provide an alternative method for the measurement of strain which alleviates at least some of the problems set out above.
The principle of the invention is if a stabilized voltage supply is connected across one or more sets of two resistive sensing elements connected in series, with their junctions connected to a voltage source which its voltage is varied until no current is flowing to or from the voltage source then with the voltage source remaining constant if one or more of the resistive sensing elements change their resistance then the total change in current through the resistive sensing elements is equal to the current flowing to or from the voltage source.
The invention consists in a resistive sensing element circuit arrangement comprising one or more sets of two resistive sensing elements connected in series to form a resistive sensing element set or sets of which one terminal of the said resistive element set or sets is connected to the positive terminal of a voltage supply which can be a.c. or d.c. and the other terminal of the said resistive sensing element set or sets is connected to the negative terminal of the voltage supply, the junctions of the said resistive element set or sets is connected to a current sensing terminal for connection to a voltage source.
The principle and description of the invention is described by referring to the said resistive sensing element set or sets, the principle of the invention and the invention still applies to any star circuit combination of resistive sensing elements providing Kirchhoffs first law is satisfied.
Many possible ways of sensing the current flowing through the said current sensing terminal of the invention are envisaged and do not deviate from providing a said voltage source in accordance with the principle of the invention, the preferred embodiment is an electronic arrangement comprises a differential amplifier, the negative input of the differential amplifier is connected to the said current sensing terminal of the invention and the positive input of the differential amplifier is connected to a voltage source, the output of the differential amplifier is connected to a feedback resistor terminal, the other terminal of the feedback resistor is connected to the negative input of the differential amplifier It is preferred that the resistive sensing elements are initially of equal resistance.
The strain gauge is the preferred resistive sensing element however the invention also applies to any resistive sensing element that relies on the change in resistance for its measurement, examples include Platinum Resistance Thermometers, Piezo-Resistive sensors, Magneto-resistive sensors and liquid level sensors.
An arrangement constructed in accordance with the invention can be used with strain gauges as the resistive sensing element for strain measurement using single or multiple strain gauges or for transducers that have many industrial applications. The resistive sensing elements could be two precision resistors for the measurement of Resistance, Capacitance and Inductance.
The invention will now be described with reference to drawings, which schematically illustrates the preferred embodiments.
Figure 1 is a drawing showing the block schematic circuit of the invention with one set of resistive sensing elements.
Figure 2 is a drawing showing the block schematic circuit of the invention with one set of resistive sensing elements with only one resistive sensing element active, the current sensing circuit together with the other dummy resistive sensing element is located at a distance from the active resistive sensing element.
Figure 3 is a drawing showing the block schematic circuit of the invention as defined by the description of the invention.
Figure 4 is a drawing showing the block schematic circuit of the invention including the preferred current sensing circuit as defined by the
description.
Figure 1 shows the invention 1 with two resistive sensing elements RI and R2 with their junction connected to the current sensing terminal ib, the other terminal of Ri is connected to terminal I a, the other tenmnal of R2 is connected to terminal 1 c. The current sensing circuit 2 connects a positive supply voltage Vg from terminal 2a to terminal la, the current sensing circuit 2 connects a negative supply voltage Vg from terminal 2c to the terminal Ic, the voltage source Vs is connected to terminal 2b, terminal 2b is connected to the current sensing terminal ib, a Current Meter is connected in series so that the current can be measured.
If Ri and R2 are strain gauges with Ri active and R2 serving as a dummy gauge, Ri = R2 = 120 ohms with a K factor of 2 and Vg equal to 4.8 volts then by applying the principle of the invention that no current will be indicated on the meter when the voltage source Vs is equal to 2.4 volts, if the voltage source Vs remains constant at 2.4 volts, then if the active strain gauge changes its resistance by 2 percent which is equivalent to 10,000 micro-strain the Current Meter will indicate 0.4 milliamps.
Figure 2 Ri is the active strain gauge and R2 is a precision resistor of the same value as Ri located with the sensing circuit at a distance from the active strain gauge. At zero when Ri = R2 the current flowing from 2a to 1 a is equal to the current flowing from ic to 2d, providing the wires in the cable are the same then the voltage at terminal lb will be equal to Vg12 so no zero error will occur, the range error can be calibrated out by applying the Shunt resistor method across the active gauge.
Figure 3 shows the invention 1 as it is described and defined herein by 1 the statement of the principle and the description of the invention where Ri and R2 are the first set, R3 and R4 the second set and Rn the nth set. Two or more strain gauges are used with Transducers for various functions.
Figure 4 shows the preferred sensing circuit 2 as described herein, the sensing current flowing to or from lb to 2b is connected to the negative input of the differential amplifier 3 whose output is connected back to the negative input via the feedback resistor Rf the voltage source Vs is connected to the positive input of the differential amplifier, since no current can flow through the negative input of the differential amplifier the voltage output 2e will automatically change until the voltage at the negative input is equal to the voltage source Vs, if all the resistive sensing elements are equal then no current will flow to or from lb to 2e therefore the voltage at 2e will equal to Vs now if one of the resistive sensing elements change their resistance this will cause a current I to flow to or from lb to 2e causing a voltage change at 2e of a value equal to I x Rf Rf is chosen for the required output voltage span.
With reference to all the drawings the Invention 1 has many advantages over the Wheatstone bridge circuit of which will be defined: the invention us a current transmitting device which is less susceptible to EM interference, since the design of the sensing circuit 2 is simple and of low component count which makes it ideal to be located close to the active resistive sensing elements to provide an approved industrial voltage level, the current transmitted to or from the invention 1 is linear even for large changes of resistance, the invention 1 can have more than two sets of resistive sensing elements which is useful for transducers, the preferred strain gauge is the low cost 120 ohm strain gauge, the invention 1 is suitable for strain gauges of resistance values down to 12 ohms for simple applications.
Various modifications and amplifications may occur to those skilled in the art without departing from the true spirit and scope of the principle of the invention as defined by the claims.

Claims (15)

  1. I CLAIMS: 1. A resistive sensing element circuit arrangement comprising
    one or more sets of two resistive sensing elements connected in series to form a resistive sensing element set or sets of which one terminal of the said resistive element set or sets is connected to the positive terminal of a voltage supply which can be a.c. or d.c. and the other terminal of the said resistive sensing element set or sets is connected to the negative terminal of the voltage supply, the junctions of the said resistive element set or sets is connected to a current sensing terminal for connection to a voltage source.
  2. 2. A resistive sensing element circuit arrangement according to claim 1 wherein the said resistive sensing element set or sets are in the form of a Star circuit configuration.
  3. 3. A resistive sensing element circuit arrangement according to Claim 1 or Claim 2 wherein the current sensing circuit comprising a power supply, voltage source and a current sensing circuit.
  4. 4. A resistive sensing element circuit arrangement according to Claim I or Claim 2 wherein the current sensing circuit comprising a differential amplifier, the negative input of the differential amplifier is connected to the said current sensing terminal of the invention and the positive input of the differential amplifier is connected to a voltage source, the output of the differential amplifier is connected to a feedback resistor terminal, the other terminal of the feedback resistor is connected to the negative input of the differential amplifier.
  5. 5. A current sensing circuit according to Claim 3 and Claim 4 the circuit is of conventional components or of surface mount form to be located close to the active resistive sensing elements or at a distance.
  6. 6. A resistive sensing element circuit arrangement according to Claim I or Claim 2 wherein the resistive sensing elements are Strain Gauges.
    1
  7. 7. A resistive sensing element circuit arrangement according to Claim I or Claim 2 wherein the resistive sensing elements are PCB Strain Gauges see Patent GB 2 360 361 B.
  8. 8. A resistive sensing element circuit arrangement according to Claim 1 or Claim 2 wherein a resistive sensing element is a Platinum Thermometer.
  9. 9. A resistive sensing element circuit arrangement according to Claim 1 or Claim 2 wherein the resistive sensing elements are Piezo- resistive sensors.
  10. 10. A resistive sensing element circuit arrangement according to Claim 1 or Claim 2 wherein the resistive sensing elements are Magneto- resistive sensors.
  11. 11. A resistive sensing element circuit arrangement according to Claim 1 or Claim 2 wherein two resistive sensing elements are a Liquid Level sensor.
  12. 12. A resistive sensing element circuit arrangement according to Claim 1 or Claim 2 wherein two resistive sensing elements are Precision Resistors.
  13. 13. A resistive sensing element circuit arrangement according to Claim 1 or Claim 2 wherein the resistive sensing elements are a resistive sensing element that uses a change in resistance for measurement purpose.
  14. 14. An arrangement as claimed in any of the preceding claims, bonded, bolted or adhesively attached close to the active resistive sensing element.
  15. 15. The arrangement substantially as herein-before described with reference to the accompanying drawings.
GB0423718A 2004-10-26 2004-10-26 A strain gauge measuring circuit Withdrawn GB2419670A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
GB0423718A GB2419670A (en) 2004-10-26 2004-10-26 A strain gauge measuring circuit
GB0506493A GB2419672B (en) 2004-10-26 2005-03-31 Improved strain gauge devices
US11/259,012 US20060087326A1 (en) 2004-10-26 2005-10-26 Resistive sensing element circuit

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0423718A GB2419670A (en) 2004-10-26 2004-10-26 A strain gauge measuring circuit

Publications (2)

Publication Number Publication Date
GB0423718D0 GB0423718D0 (en) 2004-11-24
GB2419670A true GB2419670A (en) 2006-05-03

Family

ID=33485199

Family Applications (2)

Application Number Title Priority Date Filing Date
GB0423718A Withdrawn GB2419670A (en) 2004-10-26 2004-10-26 A strain gauge measuring circuit
GB0506493A Expired - Fee Related GB2419672B (en) 2004-10-26 2005-03-31 Improved strain gauge devices

Family Applications After (1)

Application Number Title Priority Date Filing Date
GB0506493A Expired - Fee Related GB2419672B (en) 2004-10-26 2005-03-31 Improved strain gauge devices

Country Status (1)

Country Link
GB (2) GB2419670A (en)

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2513295A (en) * 1947-07-31 1950-07-04 Eisenberg Phillip Tension dynamometer
GB1411993A (en) * 1971-09-30 1975-10-29 Licentia Gmbh Method of and device for measuring a given force acting on a body
GB2042188A (en) * 1979-01-29 1980-09-17 Anderson G B Pressure sensitive mats
GB2206211A (en) * 1987-06-12 1988-12-29 Turnright Controls Sensor circuit
GB2326719A (en) * 1997-06-19 1998-12-30 John Karl Atkinson Force sensitive devices
EP0905725A1 (en) * 1997-08-29 1999-03-31 Eaton Corporation Muliple-function selector utilizing a force sensitive variable impedance device
GB2372817A (en) * 2000-10-05 2002-09-04 Ind Dataloggers Ltd Strain gauge having matching metallic layer patterns on opposite sides of a substrate

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB859630A (en) * 1959-10-14 1961-01-25 Streeter Amet Co Weighing apparatus
GB1517157A (en) * 1975-07-30 1978-07-12 G V Planer Ltd Amplifier circuits
US4167869A (en) * 1977-10-07 1979-09-18 The Gillette Company Apparatus for measuring hair grooming force
IT206726Z2 (en) * 1985-09-17 1987-10-01 Marelli Autronica PRESSURE METER DEVICE
AU657016B2 (en) * 1991-12-16 1995-02-23 Sharp Kabushiki Kaisha A circuit for humidity detection
JP3727133B2 (en) * 1997-03-14 2005-12-14 日本たばこ産業株式会社 Load measuring method and load measuring apparatus
RU2223507C2 (en) * 2001-10-12 2004-02-10 Открытое акционерное общество Раменское приборостроительное конструкторское бюро Circuit to process signal from strain-gauge transducer to serial code

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2513295A (en) * 1947-07-31 1950-07-04 Eisenberg Phillip Tension dynamometer
GB1411993A (en) * 1971-09-30 1975-10-29 Licentia Gmbh Method of and device for measuring a given force acting on a body
GB2042188A (en) * 1979-01-29 1980-09-17 Anderson G B Pressure sensitive mats
GB2206211A (en) * 1987-06-12 1988-12-29 Turnright Controls Sensor circuit
GB2326719A (en) * 1997-06-19 1998-12-30 John Karl Atkinson Force sensitive devices
EP0905725A1 (en) * 1997-08-29 1999-03-31 Eaton Corporation Muliple-function selector utilizing a force sensitive variable impedance device
GB2372817A (en) * 2000-10-05 2002-09-04 Ind Dataloggers Ltd Strain gauge having matching metallic layer patterns on opposite sides of a substrate

Also Published As

Publication number Publication date
GB0506493D0 (en) 2005-05-04
GB2419672A (en) 2006-05-03
GB2419672B (en) 2007-11-07
GB0423718D0 (en) 2004-11-24

Similar Documents

Publication Publication Date Title
US7775711B2 (en) Temperature measurement device and measurement method
US20100020842A1 (en) System and method for temperature measurement
CA2145698C (en) Electronic circuit for a transducer
US4169243A (en) Remote sensing apparatus
CN106443159B (en) Current detection chip
Anderson The new current loop: An instrumentation and measurement circuit topology
GB1569150A (en) Strain gauge arrangements
US7301352B1 (en) High sensitivity single or multi sensor interface circuit with constant voltage operation
US2974279A (en) Voltage compensated resistance bridge
CN101120264B (en) Millivolt output circuit for use with programmable sensor compensation integrated circuits
US20130043892A1 (en) Resistance measurement circuit
US20060087326A1 (en) Resistive sensing element circuit
US6107861A (en) Circuit for self compensation of silicon strain gauge pressure transmitters
GB2419670A (en) A strain gauge measuring circuit
US8893554B2 (en) System and method for passively compensating pressure sensors
CN106840287B (en) Flow sensor, flowmeter and flow detection method
CN102012279A (en) Dual-constant current source temperature measurement system for thermal resistor
JP2002131159A (en) Sensor circuit
Maiti et al. Novel remote measurement technique using resistive sensor as grounded load in an opamp based V-to-I converter
CN110967548B (en) Program-controlled variable resistor device with current detection function and working method
US5096303A (en) Electronic circuit arrangement for temperature measurement based on a platinum resistor as a temperature sensing resistor
RU2395060C1 (en) Frequency converter for disbalance signal of strain gauge bridge with low temperature error
Anderson The new current loop: NASA's successor to the Wheatstone bridge
RU2380714C1 (en) Method for processing of strain sensor signal and device for its realisation
US7141991B2 (en) Instrumentation current loop

Legal Events

Date Code Title Description
WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)