Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-11-20
2001-03-20
Oda, Christine (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207190, C324S654000
Reexamination Certificate
active
06204659
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inductance change detection circuit for detecting a change in the inductance of a coil. More specifically, the invention relates to an inductance change detection circuit for detecting a change in the position of an object based on a change in the inductance of a coil due to a change of a magnetic flux.
2. Description of the Related Art
A change in the position of an object that disrupts or indirectly changes the magnetic flux of a coil when the position of the object changes also results in a change in the inductance of the coil. It is therefore possible to detect a change in the object's position by detecting this inductance change as a DC signal, and devices used for this purpose are known from the literature. It is particularly desirable for such devices to detect this inductance change as a DC signal using a simple circuit design.
FIG. 8
shows a typical inductance change detection circuit according to the prior art as taught in Japanese Patent Laid-Open Publication No. 7-332910.
FIG. 8A
is a circuit diagram of this inductance change detection circuit, and
FIG. 8B
is a graph illustrating relationship between output pulses from a pulse power supply, and the output waveforms from a resistor R
F
in the inductance change detection circuit. Shown in
FIG. 8A
are a coil L of which the inductance changes according to the position of an object; a resistor R
F
having one end connected in series with the coil L and the other end to ground; and a pulse power supply
101
.
The inductance change detection circuit shown in
FIG. 8A
detects the output from the output terminal, that is, the voltage between the resistor R
F
and ground, as an output voltage. When the position of the detected object has not changed from an initial position (referred to as the reference position below), this output voltage has a waveform as indicated by a solid line in FIG.
8
B. When the position changes, however, the coil inductance L also changes, and the output voltage waveform changes as indicated by a dotted line in FIG.
8
B. Because the output wave thus changes before and after the object changes position, it is possible to measure the voltage V
0
and V
01
at a specific time t
k
, and to detect the inductance change from this voltage difference.
A typical inductance change detection circuit of this type, however, has difficulty in detecting an inductance change with good precision when the signal amplitude from the output terminal drops or varies, however, because the change in coil inductance is detected from output voltage values detected at specific discrete points in time.
There is therefore a need for an inductance change detection circuit whereby a change in coil inductance can be detected with good precision using a simple circuit configuration.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a simple inductance change detection circuit for detecting a change in coil inductance with good precision.
It is a further object of the invention to provide an inductance change detection circuit for outputting the inductance change detection signal as a DC signal.
To achieve these objects, an inductance change detection circuit according to the present invention comprises: a series circuit element comprising a resistor and a coil of which an inductance changes according to a position of an object; a pulse power supply for applying a pulse voltage to the series circuit element; a first signal generating means for generating a first signal according to when an output voltage of the resistor in the series circuit element becomes a specific voltage level; a second signal generating means for generating a second signal according to a pulse voltage of the pulse power supply; and a comparison pulse generating means for generating a pulse signal having a duty ratio according to the coil inductance based on the first signal supplied from the first signal generating means and the second signal supplied from the second signal generating means.
In an inductance change detection circuit thus comprised, the second signal is preferably a pulse voltage from the pulse power supply, and the comparison pulse generating means is a phase comparator for comparing the phase of the first signal and the phase of the second signal.
Further preferably, the second signal generating means outputs a signal according to when an output voltage from the resistor of the series circuit element becomes a specific voltage, and the comparison pulse generating means is an operator for obtaining the exclusive OR of the first signal and second signal.
Alternatively, the signal generating means generate a signal according to the time an output voltage of the resistor in the series circuit element is between a first voltage level and a second voltage level.
In this case, the first and second voltage levels are preferably half the amplitude of the pulse voltage. The first and second voltage levels can also be different. Yet alternatively, the difference between the first voltage level and the low level of the pulse voltage, and the difference between the second voltage level and the high level of the pulse voltage, are the same.
Yet further alternatively, the signal generating means for generating a signal based on when the output voltage of the resistor in the series circuit element becomes a specific voltage is a comparator.
A yet further version of the inductance change detection circuit additionally comprises an integrator for integrating a pulse signal generated by the comparison pulse generating means, and converting the integrated pulse signal to a DC signal.
Any of the preceding inductance change detection circuits can yet further comprise a detection circuit connected to the series circuit element for detecting a resistance component of the coil. The inductance change detection circuit in this case detects displacement of an object by considering the detection result from the detection circuit.
The detection circuit can also measure a total voltage of the series circuit element and a voltage between the resistor and coil of the series circuit element. In this case, both measured voltage levels are integrated, and the resistance component of the coil is detected based on a difference between the integrated values.
REFERENCES:
patent: 4626621 (1986-12-01), Hiyama et al.
patent: 43 34 844 (1994-10-01), None
patent: 43 13 273 (1994-10-01), None
patent: 195 21 531 (1995-12-01), None
Jolly Anthony
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Oda Christine
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