WO2009076564A1 - Amplificateur de jauge extensométrique programmable - Google Patents

Amplificateur de jauge extensométrique programmable Download PDF

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Publication number
WO2009076564A1
WO2009076564A1 PCT/US2008/086490 US2008086490W WO2009076564A1 WO 2009076564 A1 WO2009076564 A1 WO 2009076564A1 US 2008086490 W US2008086490 W US 2008086490W WO 2009076564 A1 WO2009076564 A1 WO 2009076564A1
Authority
WO
WIPO (PCT)
Prior art keywords
amplifier
strain gauge
assembly
board
gain
Prior art date
Application number
PCT/US2008/086490
Other languages
English (en)
Inventor
James C. Stevens
Original Assignee
Menard, Inc.
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 Menard, Inc. filed Critical Menard, Inc.
Publication of WO2009076564A1 publication Critical patent/WO2009076564A1/fr

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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
    • G01L1/2256—Measuring circuits therefor involving digital counting

Definitions

  • the present invention relates to data acquisition, and in particular, to a programmable strain gauge amplifier for facilitating setup and use of a strain gauge.
  • the variation is so significant that, after the time consuming part preparation and application of the strain gauge and its corresponding amplifier, the amplifier are calibrated, meaning they are tested to determine the offset and gain needed to zero out the load and to adjust the sensitivity, which adjustments are highly dependent on the part being monitored.
  • the appropriate offset and gain adjustments are made. Some adjustments can be made to the detached part on the bench, while others must be made on the part as attached to the car (or motorcycle, airplane, truck, boat, tractor or any other vehicle, machine or contraption for which strain measurements are desired).
  • a motorsports car i.e.
  • NASCAR, IRL, Formula One and many others may use only three or four or as many as 30 strain gauges and strain gauge amplifiers on the same car. After some use - perhaps as little as one lap around the track - the strain gauge and its amplifier may be tested and found to be needing further calibration. This may be due to general wear and tear or gradual deformation of the part. Worse and much too frequently, the strain gauges peel or break or stretch and the replacement rate is high.
  • the present invention relates to a data acquisition system for a facilitating the setup, adjusting and ongoing maintenance of strain gauge.
  • a strain gauge amplifier assembly for operationally connecting between a strain gauge having first and second differential voltage output values and a PC, including a board; an amplifier mounted to the board and configured for electrically connecting with first and second outputs of a strain gauge; a main controller mounted to the board and having data management elements including at least one controller core, a serial port, an A/D converter and an EEPROM, the amplifier being operationally connected with the main controller; a digital potentiometer assembly mounted to the board and operational to adjust at least one of the gain and offset values of the amplifier; and, a port assembly for connecting with a strain gauge and receiving first and second differential voltage values and with an external PC.
  • Fig. 1 is a schematic diagram of the strain gauge amplifier assembly 10 in accordance with one embodiment of the present invention.
  • FIG. 2 is a layout view showing the orientation of the partial views shown in FIGS. 2a-2b.
  • Fig. 3 is a filter block 49 for connection with the amplifier assembly 10 of Fig. 1 in accordance with another embodiment of the present invention.
  • Fig. 4 is a Main Page view 50 of one software program for facilitating connection and operation of the amplifier assembly 10 with an external PC.
  • Fig. 5 is a partial view of the Main Page 50 of Fig. 4 showing entered temperature compensation values.
  • Fig. 6 is a partial view of the Main Page 50 of Fig. 4 showing the temperature readout of temperature sensor 34.
  • Amplifier assembly 10 generally includes a main controller (or microprocessor) 11, a differential instrumentation amplifier (DIA) 12, a digital potentiometer assembly 13, and ports 14 and 15 for connecting with a strain gauge and with an external user computer (PC) and/or other devices, respectively, which elements are generally interconnected as shown, to connect with, and in some embodiments, include a strain gauge 16. All the elements shown in Fig. 1, except for strain gauge 16, are contemplated to be mounted on a common board 18, which may include a protective package (not shown).
  • board 18 contemplates any type of structure configured and operative to hold the components of amplifier assembly 10 thereon and includes, without limitation, a flex circuit. Alternative embodiments are also contemplated wherein the components of amplifier assembly 10 are all packaged into a single chip.
  • the various elements i.e. controller 11, DIA 12 and digital potentiometer assembly 13
  • the board are mounted to the board, meaning they are connected with or held by the board or other structure in any desirable manner sufficient to hold such elements in position to operate reliably as intended.
  • Controller 11 generally includes at least one controller core 21, a serial port (here a UART, a Universal Asynchronous Receiver Transmitter) 22 for serial communications, an A/D converter (to convert the signal from the amplifier for processing by controller 11 and transmission to the PC) 23, and an EEPROM (Electrically Erasable Programmable Read Only Memory) 24.
  • a serial port here a UART, a Universal Asynchronous Receiver Transmitter
  • A/D converter to convert the signal from the amplifier for processing by controller 11 and transmission to the PC
  • EEPROM Electrical Erasable Programmable Read Only Memory
  • Amplifier assembly 10 is configured for connection (at 25) via port 15 to an external PC (not shown) to enable a user to access, monitor and adjust the settings of the amplifier assembly 10 from the PC during the setup process.
  • the controller 11 waits for communications from the PC that may signal a change in either gain or desired amplifier offset. Such communications would come from the PC to the UART 22 of controller 11. If controller 11 determines the data from the PC is valid, a new set of gain and offset data is sent to the digital potentiometer assembly 13, which includes digital gain and offset potentiometers 28 and 29, respectively.
  • the gain digital pot 28 will be adjusted by the controller 11 to provide a new resistance value to the gain section of differential instrumentation amp 12. This will provide a new gain setting to the signal from the strain gauge.
  • the other offset digital pot 29 may be similarly adjusted by commands sent from the external PC (not shown) to provide a new offset voltage to the differential instrumentation amp 12, thereby changing the reference point of the amp 12.
  • the gain and offset pots 28 and 29 are provided on a dual digital pot at U2 (Fig. 2A).
  • the output of the amp 12 is directed to controller 11 through its A/D converter 23 (at 30) and provided for external use (at 31) by whatever data acquisition system is in use (such as an oscilloscope).
  • the DIA output is sampled by A/D converter 23, which converts the data to a digital stream that is outputted to the PC via pin 3 of port 15. This provides a means by which the setup person (user) can see the DIA output without the need for a separate piece of test equipment (oscilloscope, voltmeter, etc.) and make adjustments to the gain and offset pots 28 and 29 during setup of the DIA 12. Commands from the user and his/her computer are directed to controller 11 via pin 2 of port 15.
  • Amplifier assembly 10 also includes a temperature sensor 34, the output of which is directed to controller 11.
  • Temperature sensor 31 is mounted to the board 18, on which are mounted the various elements of amplifier assembly 10, and it allows the user to modulate both the gain and offset performance based on board temperatures.
  • the temperature sensor data can be very beneficial in optimizing the amplifier assembly's output.
  • temperature sensor 34 is mounted in close proximity to or with strain gauge 16, the gain and offset corrections can be even more accurate.
  • the instrumentation amplifier 12 is a differential type, suitable for use with any differential signal source, such as strain gauge 14. Alternative embodiments are contemplated wherein differential instrumentation amplifier 12 is replaced by one or more operational amplifiers. Amplifier assembly 10 further includes any suitable power supply (not shown) to supply regulated and stable power to both the circuits on the board and the strain gauge 14 itself.
  • Amplifier assembly 10 further includes a voltage regulator 36 (the power supply), a voltage follower 37, and reset circuitry 38.
  • Voltage regulator 36 connected with an outside power source via pin 1 of port 15, provides regulated and stable power to the board circuits, as well as to strain gauge 16.
  • strain gauge 16 is configured to draw its power from an alternative source.
  • Voltage follower 37 operates to improve the signal to noise ratio of DIA 12, and reset circuitry 38 protects temperature sensor 58 during initialization and setup of the controller 11.
  • controller 11 is programmed to operate as described herein, but any suitable software may be used.
  • the software requests the user to cycle the input between the maximum and minimum signal inputs that DIA 12 would see from strain gauge 16.
  • the amplifier then calculates the gain required to produce a 5V full-scale output. At that time, it also calculates a new center voltage setting, if required. Possibly, non-linear outputs can be realized, as well, using a derivative of this method. This highly desirable feature facilitates faster test setups.
  • the strain gauge amplifier assembly 10 includes all of the foregoing functions and features as shown in Figs. 2, 2A and 2B, but in addition includes another circuit block 44 shown in Fig. 3 to supply filtering of the output signal.
  • circuit block 44 is interposed between the output of DIA 12 and controller 11, as at point 45 (Fig. 2A) and provides the user with programmable filtering of the DIA output signal.
  • Circuit block 4 includes integrated circuits 7 and 8 as well as resistors R7 - R14 to provide this additional filter function. This filter is a low-pass filter. Programming of controller 11 will allow the user to adjust the corner frequency of the filter.
  • Other versions are contemplated to allow the user to adjust other parameters of the filter such as Q, secondary gain, number of poles, and possibly others.
  • the current "motorsports" amplifier assembly 10 with added circuit 44 allows for corner frequency adjustments only, but other amplifier assemblies are contemplated for more industrial customers that require additional adjustability.
  • this additionally filtered amplifier assembly would be similar. It may have to be slightly larger, but only by a small percentage. It is noted that the self- gain adjusting feature described above requires no hardware changes, and the same enclosures will be usable for amplifiers with and without the self-gain adjusting feature.
  • the first screen is the Main screen 50 (Fig. 4), which enables the user to ensure correct connection with the serial port (at 51) and to perform other connection parameters and initialization steps.
  • Main screen 50 also displays the voltage output of the DIA 12 in a scrolling real time graph 52 and in a digital readout window 53; displays the current gain and offset values in windows 56 and 57; and, displays the fill-in temperature compensation table 58.
  • the voltage output graph shows the voltage that is currently output to the Vsig wire. This is the wire that the data acquisition unit reads. In this manner, DIA 12 can be pre-set without needing a voltmeter or oscilloscope.
  • the software is designed to provide a set of tabular data to determine its operational states. It needs to receive the gain and offset values and any desired adjustment due to temperature.
  • the first step is thus to select the "Download Setup from Amp" button 61 when first connecting the PC with amplifier assembly 10. This retrieves all the setup data from the controller 11 of amplifier assembly 10, which data is intended to be pre-loaded onto the controller's EEPROM 24. When any setting is then changed on the screen (e.g. typing a value into the gain value window 56), the "Send Setup" button 64 should be pushed to send the current setup data on the screen to the controller 11 of amplifier assembly 10.
  • the "Save Setup to a File” button 65 can be clicked, and the PC software will allow the setup to be saved to a file.
  • the "Download Setup From File” button 66 should be clicked.
  • the load cell strain gauge
  • the value in the offset window is used to add or subtract to the amp output in order to provide the desired operating range. In most cases, the resulting range will be 0-5V outputs. Then save the setup by clicking the Send Setup button 64.
  • the gain and offset can be adjusted as a function of the temperature. Care should be used here as the amplifier cannot determine the temperature of the load cell directly. It only knows what its own PC board temperature is.
  • the temperature compensation table 58 on the right of Main screen 50 is where temperature compensations are entered. The units of these compensations are steps. In one embodiment, allowable values are -127 to +127 steps. For the offset compensations, these values are also in steps. Those values are -127 to +127 steps, as well. There is approximately 9.8 mV per step for offset compensation, so if it is needed to add 100 mV of offset at 90 degrees C, table 58 would be filled in as shown in Fig. 5. This assumes there would be some "tapering" of the effect as temperatures go up. This also shows one could decrease gain by entering a -1 into the table at the desired location. The calculations for determining the proper gain in view of the load cell are readily available and should be made carefully before entering the gain value into the window 56.
  • the temperature sensor 34 of amplifier assembly 10 provides the local temperature.
  • the components on amplifier assembly 10 will not self-heat to any great degree, but it must be remembered that the temperature reported is the temperature of amplifier assembly 10, not necessary the of the load cell (strain gauge), unless amplifier assembly 10 is mounted at or near the cell, which is desired.
  • the current amplifier assembly 10 temperature is reported by assembly 10 to the PC.
  • the temp is displayed in both degrees C and F, as shown for example in Fig. 6.
  • the table is graduated in degrees C.
  • the current table pointer vs. temperature is outlined by a box (see detail below in Fig. 6).

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Amplifiers (AREA)
  • Measurement Of Force In General (AREA)

Abstract

La présente invention concerne un ensemble amplificateur de jauge extensométrique pour une connexion opérationnelle entre une jauge extensométrique présentant des première et seconde valeurs de sortie de tension différentielle et un PC, comprenant un panneau; un amplificateur monté sur le panneau et conçu pour se relier électriquement aux première et seconde sorties d'une jauge extensométrique; un dispositif de commande principal monté sur le panneau et comportant des éléments de gestion de données comprenant au moins un cœur de contrôleur, un port série, un convertisseur A/N et une mémoire EEPROM, l'amplificateur étant relié de façon opérationnelle au dispositif de commande principal; un ensemble potentiomètre numérique monté sur le panneau et opérationnel pour ajuster les valeurs de gain et/ou les valeurs d'écart de l'amplificateur; et un ensemble port pour une connexion à une jauge extensométrique et la réception de première et seconde valeurs de tension différentielle et pour une connexion à un PC externe.
PCT/US2008/086490 2007-12-11 2008-12-11 Amplificateur de jauge extensométrique programmable WO2009076564A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US716407P 2007-12-11 2007-12-11
US61/007,164 2007-12-11

Publications (1)

Publication Number Publication Date
WO2009076564A1 true WO2009076564A1 (fr) 2009-06-18

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5300736A (en) * 1992-03-12 1994-04-05 Hi-Speed Checkweigher Co., Inc. Adaptive timing in-motion checkweigher
US5448662A (en) * 1992-02-12 1995-09-05 Hughes Aircraft Company Apparatus for coupling an optical fiber to a structure at a desired angle
GB2342720A (en) * 1998-10-15 2000-04-19 Takata Corp Offset compensation for a seat load measuring apparatus
US7256505B2 (en) * 2003-03-05 2007-08-14 Microstrain, Inc. Shaft mounted energy harvesting for wireless sensor operation and data transmission

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5448662A (en) * 1992-02-12 1995-09-05 Hughes Aircraft Company Apparatus for coupling an optical fiber to a structure at a desired angle
US5300736A (en) * 1992-03-12 1994-04-05 Hi-Speed Checkweigher Co., Inc. Adaptive timing in-motion checkweigher
GB2342720A (en) * 1998-10-15 2000-04-19 Takata Corp Offset compensation for a seat load measuring apparatus
US7256505B2 (en) * 2003-03-05 2007-08-14 Microstrain, Inc. Shaft mounted energy harvesting for wireless sensor operation and data transmission

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