Patent US3864959A successfully refreshed from Google Patents.
US3864959A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Thermal conductivity detector apparatus
Assignee: Pye Electronic Products Ltd
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Filing: 1971-12-16
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Granted: 1975-02-11
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Expires: 1991-12-16
Abstract
Abstract A thermal conductivity detector device for use as a gas chromatograph output detector includes a sensing filament and a reference filament connected in a bridge circuit which in turn is connected to a controllable filament heating current supply source. To prevent overheating of the reference filament, the resistance of the filament bridge circuit is measured and the heating current is controlled in response thereto so as to maintain the mean of the temperatures of the sensing and reference filaments substantially constant despite variations in the magnitude of the unbalance signal present across the detector terminals of the bridge circuit caused by the presence of substances to be detected near the sensing filament.
Inventors
- 👤 John Marshall Macdonald
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 19:57
CPC Classifications
G; G01; G01N; G01N30/00; G01N30/02; G01N30/62; G01N30/64; G01N30/66
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
151 words
Thermal conductivity detector apparatus comprising, at least one sensing filament and at least one reference filament connected in a katharometer bridge, circuit, supply means coupled to the katharometer bridge input supply terminals for supplying heating current to said katharometer bridge circuit, and detector means for detecting an unbalance in said katharometer bridge circuit between the resistance of said sensing and reference filaments and for providing an output signal representative of said unbalance, said supply means including current regulating means connected in series circuit with the katharometer bridge circuit and which regulates the heating current supplied to said katharometer bridge in response to variations in the resistance of said katharometer bridge appearing between the bridge input supply terminals for said heating current in such a way that the mean of the temperatures of said sensing and said reference filaments is maintained substantially constant despite variations in the magnitude of the detector unbalance.
Claim 2
Dependent Claim
151 words
Thermal conductivity detector apparatus comprising, at least one sensing filament and at least one reference filament connected in a katharometer bridge, circuit, supply means coupled to the katharometer bridge input supply terminals for supplying heating current to said katharometer bridge circuit, and detector means for detecting an unbalance in said katharometer bridge circuit between the resistance of said sensing and reference filaments and for providing an output signal representative of said unbalance, said supply means including current regulating means connected in series circuit with the katharometer bridge circuit and which regulates the heating current supplied to said katharometer bridge in response to variations in the resistance of said katharometer bridge appearing between the bridge input supply terminals for said heating current in such a way that the mean of the temperatures of said sensing and said reference filaments is maintained substantially constant despite variations in the magnitude of the detector unbalance.
Claim 3
Dependent Claim
63 words
Apparatus as claimed in claim 1 in which said current regulating means includes an amplifier connected in series with the katharometer bridge circuit and having a control electrode controlled by the voltage across the heater current supply terminals of said katharometer bridge circuit in such a manner that an increase in said voltage causes said current regulating means to reduce said heating current.
Claim 4
Dependent Claim
90 words
Apparatus as claimed in claim 1 wherein said current regulating means includes amplifier means and negative and positive feedback control loops which supply control signals to said amplifier means so as to regulate the heating current supplied to said katharometer bridge circuit, the control effect of said negative feedback control loop on the heating current being substantially greater than the control effect of said positive feedback control loop and wherein the time constant of said positive feedback control loop is longer than the thermal time constant of said katharometer bridge.
Claim 5
Dependent Claim
64 words
Apparatus as claimed in claim 3 in which the control signal applied via said negative feedback control loop comprises a signal representative of the voltage across the heater input supply terminals of said katharometer bridge and the control signal applied via said positive feedback control loop comprises a signal representative of the heater current supplied to the heater supply terminals of said katharometer bridge.
Claim 6
Dependent Claim
70 words
Apparatus as claimed in claim 1 wherein Said current regulating means includes a transistor amplifier having an input circuit which is connected to the heater current supply terminals of said katharometer bridge so as to draw a bleed current therefrom, and means for maintaining the bleed current drawn by the input circuit of said transistor amplifier at a substantially constant porportion of the output current of said current regulating means.
Claim 7
Independent Claim
155 words
A system for measuring thermal conductivity comprising, a bridge circuit having input terminals and output terminals and including a thermal sensing element and a thermal reference element in respective arms of the bridge, power supply means coupled to said bridge input terminals for supplying current to the bridge circuit, said supply means comprising current regulating means connected in series with the bridge circuit and responsive to resistance variations appearing across the bridge input terminals for regulating the current supplied to the bridge circuit in a sense to hold substantially constant the mean value of the temperatures of said sensing and said reference elements despite a variation in the magnitude of the unbalance signal appearing at the bridge output terminals, and detector means coupled to the bridge output terminals for providing an output signal proportional to an unbalance signal produced at the output terminals by an unbalance in the resistance of said sensing and reference elements.
Claim 8
Independent Claim
155 words
A system for measuring thermal conductivity comprising, a bridge circuit having input terminals and output terminals and including a thermal sensing element and a thermal reference element in respective arms of the bridge, power supply means coupled to said bridge input terminals for supplying current to the bridge circuit, said supply means comprising current regulating means connected in series with the bridge circuit and responsive to resistance variations appearing across the bridge input terminals for regulating the current supplied to the bridge circuit in a sense to hold substantially constant the mean value of the temperatures of said sensing and said reference elements despite a variation in the magnitude of the unbalance signal appearing at the bridge output terminals, and detector means coupled to the bridge output terminals for providing an output signal proportional to an unbalance signal produced at the output terminals by an unbalance in the resistance of said sensing and reference elements.
Claim 9
Dependent Claim
56 words
A system as claimed in claim 6 wherein said current regulating means comprises amplifier means having input circuit means controlled by the voltage across the bridge input terminals so as to produce a negative feedback effect by said current regulating means whereby an increase in the bridge input voltage causes a decrease in the bridge current.
Claim 10
Dependent Claim
48 words
A system as claimed in claim 7 further comprising means responsive to the bridge current for supplying a positive feedback signal to said amplifier input circuit means whereby the current regulating means responds to a decrease in bridge current to cause a further decrease in said bridge current.
Claim 11
Dependent Claim
59 words
A system as claimed in claim 6 wherein said current regulating means comprises amplifier means having negative and positive feedback control loops which supply control signals to said amplifier means for regulating the current supplied to said bridge circuit, said negative feedback control loop producing a greater control effect on said bridge current than said positive feedback control loop.
Claim 12
Dependent Claim
35 words
A system as claimed in claim 9 wherein said positive feedback control loop includes a resistor and capacitor providing an RC time constant that is longer than the thermal time constant of the bridge circuit.
Claim 13
Dependent Claim
52 words
A system as claimed in claim 9 wherein said negative feedback control loop includes means for deriving a control signal that is determined by the voltage across the bridge input terminals and said positive feedback control loop includes means for deriving a control signal that is a function of the bridge current.
Claim 14
Dependent Claim
107 words
A system as claimed in claim 6 wherein said current regulating means comprises, a first transistor amplifier connected in series with the bridge circuit across a source of voltage, a second transistor amplifier with its control input circuit connected in circuit to receive a control signal indicative of the voltage across the bridge input terminals and an output circuit coupled to the control electrode of the first transistor amplifier, said control signal producing a negative feedback control on the bridge current, and means responsive to the bridge current for deriving a positive feedback control signal that is applied to the control electrode of the first transistor amplifier.
Claim 15
Dependent Claim
69 words
A system as claimed in claim 12 further comprising an operational amplifier having a first input coupled to the output circuit of the second transistor amplifier and a second input coupled via an RC circuit to the positive feedback control signal deriving means, the output of said operational amplifieR being coupled to the control electrode of the first transistor amplifier to apply thereto the negative and positive control signals.
Claim 16
Dependent Claim
102 words
A system as claimed in claim 6 wherein said current regulating means comprises an amplifier connected in circuit to regulate the bridge current and having an input control circuit, means for deriving a negative feedback voltage proportional to the voltage across the bridge input terminals, means responsive to the bridge current for deriving a positive feedback voltage, and means for coupling said negative and positive feedback voltages to the input control circuit of said amplifier so as to control the bridge current as a function thereof, said negative feedback voltage being arranged to have a greater control effect than said positive-feedback voltage.
Claim 17
Dependent Claim
38 words
A system as claimed in claim 6 wherein said power supply means comprises a pair of DC voltage supply terminals and said current regulating means is connected in series with the bridge circuit across said DC supply terminals.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-02-10 | 1978-08-12 | 1979-02-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-02-10 | 1982-08-12 | 1983-02-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-02-10 | 1986-08-12 | 1987-02-11 | $7700.00 | Window Closed / Lapsed |