Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1991-04-17
1995-08-22
O'Shea, Sandra L.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
32420712, G01R 2702
Patent
active
054443814
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is directed to a measuring circuit which can measure impedance values. An important application of such measuring circuits consists in determining, together with inductive displacement transmitters, regulating distances, whether in rotational or in linear movement, of any structural component parts. Conventional inductive displacement transmitters are half-differential short circuit ring displacement transmitters, differential choke displacement transmitters and differential transformer displacement transmitters.
In order to measure the impedance values of structural component parts not exclusively showing ohmic resistance, it is necessary to apply alternating voltage to the structural component parts. The amplitude and often also the phase of the voltage at the structural component part are then measured. The measurement signal is generally smoothed by a low-pass filter to obtain a direct voltage as final measurement value. Measuring circuits, such as are preferably used with inductive displacement transmitters, are generally constructed in such a way that the emitted direct voltage is proportional to the regulating distance of a final control element of the displacement transmitter. It is very difficult to achieve highly accurate results with conventional measuring circuits, since the low-pass filters which are employed lead to phase shifting which is difficult to take into account and/or since the obtained direct voltage still has a residual ripple.
Accordingly, it has long been a problem to further develop measuring circuits, which are particularly suited for evaluating the signals of inductive displacement transmitters, in such a way that they emit a measurement signal of particularly high accuracy which is a measure for the impedance value of a variable impedance.
SUMMARY OF THE INVENTION
The measuring circuit according to the invention comprises, as substantial function groups, a first oscillator means or device, a second oscillator means and an integrator which controls the amplitude of the alternating voltage put out by the second oscillator means or device. This alternating voltage is shifted in phase by 180.degree. relative to the alternating voltage of the first oscillator means or device. The frequency of the two voltages is constant. Moreover, the amplitude of the voltage from the first oscillator means or device is constant. The output signal of the integrator and accordingly the amplitude of the alternating voltage of the second oscillator means depends on the amplitude and phase of a signal which is fed to an input connection of the circuit. The integration, which takes into account the amplitude and phase, is made possible by a phase-controlled rectifier and a comparison device which obtains the output signal from the rectifier as actual value signal and compares it with a reference value signal. The actuating signal formed in the comparison is integrated.
In order to measure an impedance value, an impedance network containing that impedance whose value is to be measured is connected to the measuring circuit. The network is connected at a first point with the first alternating voltage, at a second point with the oppositely phased second alternating voltage of adjustable amplitude, and at a third point with the aforementioned phase-controlled rectifier. As long as an alternating voltage occurs at the third point, the integrator obtains an input signal which is not equal to zero, so that it integrates up or down, depending on the mathematical sign of the input signal, and accordingly adjusts the amplitude of the adjustable alternating voltage. When the network is suitably selected, the voltage at the third point finally becomes zero as a result of the adjustment of the amplitude of the second alternating voltage. The integrator then remains at the achieved value, so that the amplitude of the adjustable alternating voltage also no longer changes. The impedance value of a determined impedance can be calculated from this amplitude and known charact
REFERENCES:
patent: 3684961 (1912-08-01), Moir
patent: 4191922 (1980-03-01), Harris et al.
patent: 4866378 (1989-09-01), Redlich
patent: 5045786 (1991-09-01), Fischer
patent: 5202628 (1993-04-01), Locher et al.
Barth Joerg
Fischer Werner
Locher Johannes
O'Shea Sandra L.
Phillips R.
Robert & Bosch GmbH
Striker Michael J.
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