Measuring system including thermal conductivity detector means

Claim 2

In a measuring system, the combination comprising: a bridge circuit including at least one reference thermally responsive element and a measuring thermally responsive element associated with each reference element, said bridge circuit having a pair of power nodes and a pair of output nodes; power means exciting a first of said power nodes of said bridge circuit with pulses of generally constant magnitude and alternating polarity; and feedback circuit means responsive to the common mode signal of said bridge for energizing the other of said power nodes of said bridge with pulses of a magnitude equal to the magnitude of the pulses energizing said first power node and having a polarity opposite to the pulses at said first node thereby to minimize the common mode signal to said bridge power nodes.

Claim 3

The system of claim 1 wherein said feedback circuit means for energizing the other of said power nodes includes summing circuit means responsive to the signal at the output signal nodes of said bridge circuit for generating a signal representative of the sum of said signals at the output nodes, said signal also being representative of the common mode signal to said bridge from said power means; and inverting amplifier means responsive to said summed signal for energizing said second power node of said bridge circuit with a signal of equal magnitude with the signal energizing said first power node and of opposite polarity.

Claim 4

The system of claim 1 further comprising clamping circuit means for clamping respectively the positive and negative voltage signals supplied to said first power node of said bridge circuit.

Claim 5

The system of claim 1 further comprising sensing circuit means responsive to the signals at the output nodes of said bridge circuit for generating a signal representative of the difference between said signals at said output nodes.

Claim 6

The system of claim 4 wherein said sensor means includes a differential amplifier responsive to the signals at the output nodes of said bridge, first and second switch means connected in circuit with the output signal of said differential amplifier, and delay circuit means for alternately actuating said switches to invert alternate half-cycles thereof a predetermined time after said power means has changed polarity.

Claim 7

In a system for measuring the thermal conductivity of a unknown fluid including at least one reference thermal conductivity detector immersed in a carrier fluid and a measuring thermal conductivity detector associated with each reference detector and immersed in a mixture of the carrier fluid and the unknown fluid, the improvement comprising: bridge circuit means including said measuring and said reference detectors for generating a signal representative of the difference in resistance between said detectors when said bridge circuit is energized, said bridge circuit having first and second power nodes for being energized; first source means for energizing one of said power nodes of said bridge circuit with a periodic voltage with alternate half cycles of generally constant magnitude relative to a reference voltage and opposite polarity; and second source means for energizing said second power terminal with a second periodic voltage synchronized with said first periodic voltage and of opposite polarity than said first periodic voltage, said second source means including feedback circuit means responsive to the common mode voltage fed to said bridge circuit for adjusting the magnitude of the voltage of said second source means to be equal to the magnitude of said first source means relative to said reference voltage.

Claim 8

In a system for measuring the thermal conductivity of a unknown fluid including at least one reference thermal conductivity detector immersed in a carrier fluid and a measuring thermal conductivity detector associated with each reference detector and immersed in a mixture of the carrier fluid and the unknown fluid, the improvement comprising: bridge circuit means including said measuring and said reference detectors for generating a signal representative of the difference in resistance between said detectors when said bridge circuit is energized, said bridge circuit having first and second power nodes for being energized; first source means for energizing one of said power nodes of said bridge circuit with a periodic voltage with alternate half cycles of generally constant magnitude relative to a reference voltage and opposite polarity; and second source means for energizing said second power terminal with a second periodic voltage synchronized with said first periodic voltage and of opposite polarity than said first periodic voltage, said second source means including feedback circuit means responsive to the common mode voltage fed to said bridge circuit for adjusting the magnitude of the voltage of said second source means to be equal to the magnitude of said first source means relative to said reference voltage.

Claim 9

In a system for measuring the thermal conductivity of an unknown gas including at least one reference thermal conductivity detector immersed in a carrier gas and a measuring thermal conductivity detector associated with each reference detector and immersed in a mixture of the carrier gas and the unknown gas, the improvement comprising: bridge circuit means including said measuring and said reference detectors for generating a signal representative of the difference in resistance between said detectors when said bridge circuit is energized, said bridge circuit having first and second power nodes for being energized; first source means including a multivibrator circuit for energizing one of said power nodes of said bridge circuit with a periodic voltage with alternate half cycles of constant magnitude and opposite polarity; and second source means including summing means summing the signal present at the output terminals of said bridge circuit and feedback means responsive to said summed signal for energizing the second power node of said bridge circuit with a second periodic voltage synchronized with said first periodic voltage and of opposite polarity, said feedback means being responsive to the summed signal of said signal node to vary the magnitude of the voltage at said second power node to be equal to the magnitude of the voltage at said first power node.

Claim 10

In a system for measuring the thermal conductivity of an unknown gas including at least one reference thermal conductivity detector immersed in a carrier gas and a measuring thermal conductivity detector associated with each reference detector and immersed in a mixture of the carrier gas and the unknown gas, the improvement comprising: bridge circuit means including said measuring and said reference detectors for generating a signal representative of the difference in resistance between said detectors when said bridge circuit is energized, said bridge circuit having first and second power nodes for being energized; first source means including a multivibrator circuit for energizing one of said power nodes of said bridge circuit with a periodic voltage with alternate half cycles of constant magnitude and opposite polarity; and second source means including summing means summing the signal present at the output terminals of said bridge circuit and feedback means responsive to said summed signal for energizing the second power node of said bridge circuit with a second periodic voltage synchronized with said first periodic voltage and of opposite polarity, said feedback means being responsive to the summed signal of said signal node to vary the magnitude of the voltage at said second power node to be equal to the magnitude of the voltage at said first power node.

Claim 11

In a system for measuring the thermal conductivity of an unknown gas including at least one reference thermal conductivity detector immersed in a carrier gas and a measuring thermal conductivity detector associated with each reference detector and immersed in a mixture of the carrier gas and the unknown gas, the improvement comprising: bridge circuit means including said measuring and said reference detectors for generating a signal representative of the difference in resistance between said detectors when said bridge circuit is energized, said bridge circuit having first and second power nodes for being energized; first source means for generating a first clamped voltage of one polarity; second source means for generating a second clamped voltage of opposite polarity than the first clamped voltage; switching circuit means For alternately connecting said first clamped voltage to said first and second power nodes of said bridge periodically and for alternately connecting said second clamped voltage to said second and said first power nodes of said bridge periodically and mutually exclusively with the connection of said first clamped voltage; and summing circuit means sensing the sum of voltages applied to said bridge by one of said source means for adjusting the magnitude of the other of said source means to be equal to the magnitude of said first source means and thereby to substantially reduce the common mode signal fed to said bridge power nodes.

Claim 12

In a system for measuring the thermal conductivity of an unknown gas including at least one reference thermal conductivity detector immersed in a carrier gas and a measuring thermal conductivity detector associated with each reference detector and immersed in a mixture of the carrier gas and the unknown gas, the improvement comprising: bridge circuit means including said measuring and said reference detectors for generating a signal representative of the difference in resistance between said detectors when said bridge circuit is energized, said bridge circuit having first and second power nodes for being energized; first source means for generating a first clamped voltage of one polarity; second source means for generating a second clamped voltage of opposite polarity than the first clamped voltage; switching circuit means For alternately connecting said first clamped voltage to said first and second power nodes of said bridge periodically and for alternately connecting said second clamped voltage to said second and said first power nodes of said bridge periodically and mutually exclusively with the connection of said first clamped voltage; and summing circuit means sensing the sum of voltages applied to said bridge by one of said source means for adjusting the magnitude of the other of said source means to be equal to the magnitude of said first source means and thereby to substantially reduce the common mode signal fed to said bridge power nodes.

Claim 13

In a measuring system, the combination comprising: a bridge circuit including at least one reference thermally responsive element and a measuring thermally responsive element, said bridge circuit having first and second power nodes and first and second output nodes; a first pair of switching circuits for selectively connecting said first and second power nodes of said bridge circuit respectively to a high clamp node and a low clamp node when actuated; a second pair of switching circuits for selectively connecting said first and second power nodes of said bridge circuit respectively to said high clamp node and said low clamp node when actuated; means for actuating said first and second pairs of switches to operate mutually exclusively, whereby said first and second power nodes of said bridge circuit are coupled alternately to said high and low clamp nodes; clamping circuit means for calmping one of said high clamp and low clamp nodes to a predetermined constant voltage; summing circuit means for generating a signal representative of the common mode signal of said bridge circuit; and feedback circuit means responsive to said summing circuit means for energizing the other of said high clamp and low clamp nodes with a signal of opposite polarity while minimizing the common mode signal supplied to said bridge.

Claim 14

In a measuring system, the combination comprising: a bridge circuit including at least one reference thermally responsive element and a measuring thermally responsive element, said bridge circuit having first and second power nodes and first and second output nodes; a first pair of switching circuits for selectively connecting said first and second power nodes of said bridge circuit respectively to a high clamp node and a low clamp node when actuated; a second pair of switching circuits for selectively connecting said first and second power nodes of said bridge circuit respectively to said high clamp node and said low clamp node when actuated; means for actuating said first and second pairs of switches to operate mutually exclusively, whereby said first and second power nodes of said bridge circuit are coupled alternately to said high and low clamp nodes; clamping circuit means for calmping one of said high clamp and low clamp nodes to a predetermined constant voltage; summing circuit means for generating a signal representative of the common mode signal of said bridge circuit; and feedback circuit means responsive to said summing circuit means for energizing the other of said high clamp and low clamp nodes with a signal of opposite polarity while minimizing the common mode signal supplied to said bridge.