Patent US3845385A successfully refreshed from Google Patents.
US3845385A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Circuit arrangement for converting a bridge unbalance into a frequency variation
Assignee: US Philips Corp
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Filing: 1973-03-16
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Granted: 1974-10-29
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Expires: 1993-03-16
Abstract
Abstract The unbalance of a measuring bridge is measured by means of a frequency variation or period variation of an oscillator. The measuring bridge may, for example, be a four-arm strain-gage bridge. In order to assure a linear conversion of the unbalance, which represents the quantity to be measured, into a frequency or period variation two control loops are required. One loop injects an unbalance compensation current into the bridge via a null balancing system. The variations in the latter system cause a variation of the frequency of an oscillator via, for example, the resistance variation of a photo-sensitive resistor. The second loop ensures that a second equivalent impedance in the frequencydetermining network influences the oscillator in the same way, so that the square root of the two impedances yields the linear relationship. The invention indicates how by the choice of the oscillator the control loops can be simplified, for example, by using multiplier circuits as variable potentiometers, and how in a simple manner either a frequency variation or a period variation can be obtained as a measuring result.
Inventors
- 👤 D Ebrecht
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 12:37
CPC Classifications
H; H03; H03B; H03B5/00; H03B5/20; H03B5/26; H03B5/30; H03B5/32; H03B5/38; H03K; H03K3/00; H03K3/02; H03K3/023; H03K3/0231
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
196 words
A circuit for converting a resistance variation into a proportional variation of the oscillation frequency of an oscillator comprising, a resistance bridge having input terminals supplied by the oscillation signal of the oscillator, said oscillator including a frequency determining network that includes a variable gain device, a compensation amplifier with its input connected to the bridge output terminals and its output connected to control the variable gain device, a resistor coupling the variable gain device to an output terminal of said bridge to supply a compensation signal for any bridge unbalance so that the ratio of the compensation signal to the oscillation signal is in a linear relationship to the bridge unbalance, said oscillator further comprising, a variable resistor and a reactance element in series circuit, an amplifier with its input coupled to the reactance element and its output connected to the input of an integrator, means connecting the integrator output to the input of the variable gain device and the output of the variable gain device to said series circuit, and means responsive to the integrator output signal for varying said variable resistor in a manner to maintain the amplitude of the integrator signal constant.
Claim 2
Dependent Claim
196 words
A circuit for converting a resistance variation into a proportional variation of the oscillation frequency of an oscillator comprising, a resistance bridge having input terminals supplied by the oscillation signal of the oscillator, said oscillator including a frequency determining network that includes a variable gain device, a compensation amplifier with its input connected to the bridge output terminals and its output connected to control the variable gain device, a resistor coupling the variable gain device to an output terminal of said bridge to supply a compensation signal for any bridge unbalance so that the ratio of the compensation signal to the oscillation signal is in a linear relationship to the bridge unbalance, said oscillator further comprising, a variable resistor and a reactance element in series circuit, an amplifier with its input coupled to the reactance element and its output connected to the input of an integrator, means connecting the integrator output to the input of the variable gain device and the output of the variable gain device to said series circuit, and means responsive to the integrator output signal for varying said variable resistor in a manner to maintain the amplitude of the integrator signal constant.
Claim 3
Dependent Claim
37 words
A circuit as claimed in claim 1 wherein the oscillation signal for said resistance bridge is derived at the output of said integrator and the compensation signal is developed at the output of said variable gain device.
Claim 4
Dependent Claim
63 words
A circuit as claimed in claim 1 wherein said series circuit comprises one branch of a second bridge circuit, the second branch of said second bridge circuit comprising first and second series connected resistors, and wherein the output of the variable gain device is coupled to the second bridge input terminals and the amplifier input is coupled to the second bridge output terminals.
Claim 5
Dependent Claim
45 words
A circuit as claimed in claim 1 wherein said variable gain device comprises a multiplier circuit having first and second inputs connected to the output of the integrator and to the output of the compensation amplifier, respectively, and an output connected to said series circuit.
Claim 6
Dependent Claim
179 words
A measuring circuit comprising, an oscillator, a compensation amplifier, a resistance bridge comprising four resistors, means connecting the bridge output terminals to the compensation amplifier which in turn controls a variable gain device, means connecting at least one of the bridge output terminals through a resistor to the variable gain device in order to supply a compensation voltage for the bridge unbalance, means connecting the variable gain device as a part of the frequency-determining network of the oscillator, said oscillator including a closed loop comprising, in this order, an all-pass network including a series connection of a variable resistor and a reactance element and a first amplifier, an integrator connected between the first amplifier and the variable gain device, means connecting an amplitude detector to the integrator output, said detector comparing the integrator signal to a reference quantity to derive a control signal, means for coupling the control signal to the variable resistor so as to maintain the amplitude of said integrator signal constant, and means for coupling the oscillator signal to the input terminals of the resistance bridge.
Claim 7
Dependent Claim
179 words
A measuring circuit comprising, an oscillator, a compensation amplifier, a resistance bridge comprising four resistors, means connecting the bridge output terminals to the compensation amplifier which in turn controls a variable gain device, means connecting at least one of the bridge output terminals through a resistor to the variable gain device in order to supply a compensation voltage for the bridge unbalance, means connecting the variable gain device as a part of the frequency-determining network of the oscillator, said oscillator including a closed loop comprising, in this order, an all-pass network including a series connection of a variable resistor and a reactance element and a first amplifier, an integrator connected between the first amplifier and the variable gain device, means connecting an amplitude detector to the integrator output, said detector comparing the integrator signal to a reference quantity to derive a control signal, means for coupling the control signal to the variable resistor so as to maintain the amplitude of said integrator signal constant, and means for coupling the oscillator signal to the input terminals of the resistance bridge.
Claim 8
Dependent Claim
58 words
A circuit as claimed in claim 5 wherein to convert the bridge unbalance into a frequency variation of the oscillator signal the circuit includes means connecting the bridge to the output of the integrator, and said one of the output terminals of the resistance bridge is connected to the output of the variable gain device through said resistor.
Claim 9
Dependent Claim
61 words
A circuit as claimed in claim 5, characterized in that for the conversion of the bridge unbalance into a variation of the period of the oscillator signal the bridge is connected to the output of the variable gain device and said one of the output terminals of the resistance bridge iS connected to the output of the integrator through said resistor.
Claim 10
Dependent Claim
59 words
A circuit as claimed in claim 5 wherein said variable gain device comprises, a voltage dividing network controlled by the compensation amplifier and connected to the output of the integrator, and an amplifier with constant gain factor having an input connected to a voltage division tap of the voltage dividing network and an output connected to the all-pass filter.
Claim 11
Dependent Claim
52 words
A circuit as claimed in claim 5 wherein said variable gain device comprises, a first multiplier circuit having one input connected to the output of the integrator and a second input connected to the output of the compensation amplifier, and means connecting the output of the multiplier circuit to the all-pass network.
Claim 12
Dependent Claim
92 words
A circuit as claimed in claim 5 wherein the all-pass filter network comprises, a second bridge circuit having a pair of input terminals which forms the input of the filter, one branch of the bridge circuit between the input terminals includes two equal resistors and the other branch comprises said reactance element and the variable resistor, and the first amplifier comprises a differential amplifier having input terminals connected to the output terminals of the second bridge circuit and an output connected to the integrator input, and said reactance element includes a capacitor.
Claim 13
Dependent Claim
133 words
A circuit as claimed in claim 5 wherein the all-pass filter network, the first amplifier and the integrator comprise, means connecting a capacitor reactance element to the input of the filter and to the variable resistor and to the input of the first amplifier which has a gain factor -V1, means connecting the output of the first amplifier via a first integrating resistor of the value Ri to one input of an operational amplifier, whose other input is connected to ground and whose output is the output of the integrator, means connecting the input of the filter to the one input of the operational amplifier by means of a second integrating resistor of the value 2 Ri/V1, and an integrating capacitor connected between said one input and the output of the operational amplifier.
Claim 14
Dependent Claim
69 words
A circuit as claimed in claim 11, characterized in that the variable resistor comprises a resistor of constant value, one end of which is connected to the input of the first amplifier and the other end to the output of a multiplier stage having two inputs, means connecting one multiplier input to the output of the first amplifier and the other input to the output of the amplitude detector.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-10-28 | 1978-04-29 | 1978-10-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-10-28 | 1982-04-29 | 1982-10-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-10-28 | 1986-04-29 | 1986-10-29 | $7700.00 | Window Closed / Lapsed |