Measurement circuit for load cell

Abstract

The strain gauge bridge circuit located in .[.the.]. .Iadd.a .Iaddend.load cell .[.of a load cell mass comparator.]. is modified to provide temperature stability by coupling a remotely located temperature compensating circuit between the two normally connected output ends of strain gauges in adjacent arms of the bridge. The compensating circuit is comprised of a pair of series connected low noise, drift-free precision resistors of relatively low resistance value compared to the resistance of the strain gauges. The precision resistors are shunted by relatively high valued potentiometers which operate to balance the bridge. One potentiometer additionally includes a series connected high value precision resistor for providing fine balance while the other potentiometer is used for coarse balance.

I claim: 
     
       1. A temperature compensated load sensing circuit for a load cell mass comparator including a load cell containing a plurality of strain gauges connected to form arms of a bridge circuit connected to a measuring circuit, comprising the combination of: a pair of series connected resistance means coupled between the output side of the strain gauges in a first of two adjacent arms of said bridge circuit, said resistance means being of a relatively low resistance value compared to the resistance value of said strain gauges;   potentiometer means shunted across at least one of said pair of series connected resistance means, said potentiometer means having a relatively large resistance value compared to the resistance value of said resistance means and further including an adjustable voltage output terminal; and   means connecting said output terminal of said potentiometer means and the output side of the strain gauges in the second of two adjacent arms of said bridge circuit to said measuring circuit.   
     
     
       2. The load sensing circuit according to claim 1 wherein said pair of series connected resistance means comprises a first and second precision resistor. 
     
     
       3. The load sensing circuit according to claim 2 wherein said first and second precision resistors further exhibit a low noise and low temperature drift operating characteristic. 
     
     
       4. The load sensing circuit according to claim 3 wherein said first and second precision resistors and said potentiometer means are located remotely from said load cell. 
     
     
       5. The load sensing circuit according to claim 1 and including additional .Iadd.bridge balancing .Iaddend.potentiometer means shunted across the other of said pair of series connected resistance means, said additional potentiometer means also having a relatively large resistance value compared to the resistance value of said resistance means. 
     
     
       6. The load sensing circuit according to claim 5 and further including resistance means coupled in series with said additional potentiometer means whereby the first recited said potentiometer means is operable to provide a coarse balance of said bridge and said additional potentiometer means is operable to provide a fine balance of said bridge. 
     
     
       7. The load sensing circuit according to claim 6 wherein said pair of series connected resistance means and said resistance means connected in series with said other potentiometer means are comprised of precision resistors. 
     
     
       8. The load sensing circuit according to claim 7 wherein said precision resistors are comprised of resistors having a low noise and low temperature drift characteristic. 
     
     
       9. The load sensing circuit according to claim 8 wherein said precision resistors and both said potentiometer means are located remoately from said load cell. 
     
     
       10. The load sensing circuit according to claim 9 wherein said remotely located precision resistors and potentiometer means are located in close proximity to said measuring circuit. 
     
     
       11. The load sensing circuit according to claim 9 wherein said remotely located precision resistors and potentiometer means are integrated with said measuring circuit. 
     
     
       12. The load sensing circuit according to claim 9 wherein said precision resistors are fixed value resistors. .Iadd. 
     
     
       13.  A circuit for providing temperature stabilization of a load cell containing a plurality of strain gauges connected to form arms of a bridge circuit connected to a measuring circuit, comprising the combination of: a pair of series connected impedances coupled between the output side of the strain gauges in a first of two adjacent arms of said bridge circuit, said pair of impedances being of a relatively low impedance value compared to the impedance value of said strain gauges;   variable impedance means for balancing said bridge circuit shunted across at least one of said pair of series connected impedances, said variable impedance means having a relatively large impedance value compared to the impedance value of said pair of impedances and further including an adjustable voltage output terminal; and   means connecting said output terminal of said variable impedance means and the output side of the strain gauges in the second of two adjacent arms of said bridge circuit to said measuring circuit..Iaddend. .Iadd.14. The circuit according to claim 13 wherein said pair of series connected impedances comprises a first and second precision resistor..Iaddend. .Iadd.15. The circuit according to claim 14 wherein said first and second precision resistors further exhibit a low noise and low temperature drift   
     
     
        operating characteristic..Iaddend. .Iadd.16.  The circuit according to claim 15 wherein said variable impedance means comprises potentiometer means and wherein said first and second precision resistors and said potentiometer means are located remotely from said load cell..Iaddend. .Iadd.17. The circuit according to claim 13 and including additional variable impedance means for further balancing said bridge circuit shunted across the other of said pair of series connected impedances, said additional variable impedance means also having a relatively large impedance value compared to the impedance value of said impedances..Iaddend. .Iadd.18. The load sensing circuit according to claim 17 and further including impedance means coupled in series with said additional variable impedance means whereby the first recited said variable impedance means is operable to provide a coarse balance of said bridge and said additional variable impedance means is operable to provide a fine balance of said bridge..Iaddend. .Iadd.19. The circuit according to claim 18 wherein both said variable impedance means are comprised of potentiometer means and wherein said pair of series connected impedances and said impedance means connected in series with said other variable impedance means are comprised of precision resistors..Iaddend. .Iadd.20. The circuit according to claim 19 wherein said precision resistors are comprised of resistors having a low noise and low temperature drift 
     
     
        characteristic..Iaddend. .Iadd.21.  The circuit according to claim 20 wherein said precision resistors and both said potentiometer means are located remotely from said load cell..Iaddend. .Iadd.22. The circuit according to claim 21 wherein said remotely located precision resistors and potentiometer means are located in close proximity to said measuring circuit..Iaddend. .Iadd.23. The circuit according to claim 21 wherein said remotely located precision resistors and potentiometer means are integrated with said measuring circuit..Iaddend. .Iadd.24. A circuit for providing temperature stabilization of a bridge circuit including a plurality of impedance means connected to form arms of a bridge circuit connected to a measuring circuit, comprising the combination of: a pair of series connected impedances coupled between the output side of the impedance means in a first of two adjacent arms of said bridge circuit, said pair of impedances being of a relatively low impedance value compared to the impedance value of said impedance means;   variable impedance means for balancing said bridge circuit shunted across at least one of said pair of series connected impedances, said variable impedance means having a relatively large impedance value compared to the impedance value of said pair of impedances and further including an adjustable voltage output terminal; and   means connecting said output terminal of said variable impedance means and the output side of the impedance means in the second of two adjacent arms   
     
     
        of said bridge circuit to said measuring circuit..Iaddend. .Iadd.25.  The circuit according to claim 24 wherein said bridge circuit comprises a load sensing circuit..Iaddend. .Iadd.26. The circuit according to claim 24 wherein said bridge circuit comprises a load sensing circuit included in a load cell..Iaddend. .Iadd.27. The circuit according to claim 24 wherein said plurality of impedance means comprises a plurality of strain gauges included in a load cell..Iaddend.