JPH06314962A - Static capacitance type sensor - Google Patents

Abstract

PURPOSE:To attain accurate detection by providing a phase detection circuit to the static capacitance type sensor, thereby outputting a positive or negative definite analog voltage without representing two states by a same voltage through the use of relation of quantity between a reference capacitor and a measured capacitor. CONSTITUTION:This sensor is provided with a phase detection circuit 6 and a comparator circuit 10. The phase detection circuit 6 receives an output of an oscillation circuit 1 via a coil L3, and is provided with a gate circuit such as an analog switch controlling whether or not an output of bridge circuit 4 is led out synchronously with the oscillation circuit 1 and activates the phase detection circuit 6 only when an oscillated voltage is positive. The analog switch is used to pass through only an AC signal whose period corresponds to a positive period of an oscillated voltage among outputs obtained by amplifying an output of the bridge circuit 4 by an AC amplifier circuit 5 and smoothes to output a DC voltage. Thus, a positive or a negative analog voltage is outputted from an output circuit 9 depending on the relation of the quantity of capacitors C1, C2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is based on a change in electrostatic capacitance between a detection electrode and a ground electrode facing it, which is caused by a detection object approaching the detection electrode, and the presence or absence of the detection object. The present invention relates to a capacitance type sensor that detects the number of sheets and the like and outputs them as an analog voltage.

[0002]

2. Description of the Related Art FIG. 5 shows an example of the configuration of a conventional capacitance type sensor.

Here, 1 is an oscillation circuit. Detection electrode 3
Is connected to the coil L2, the ground electrode 2 is connected to 0 V (ground potential) of the circuit, and both electrodes 2 and 3 form a capacitor C2. The capacitor C2, the reference capacitor C1, the coil L1, and the coil L2 form an LC bridge circuit 4. The output of the bridge circuit 4 is supplied to the AC amplification circuit 5, and the amplified output is converted into a DC voltage by the smoothing circuit 7, amplified by the DC amplification circuit 8, and output from the output circuit 9 as an analog voltage. A coil L3 connected to the output terminal of the oscillation circuit 1 is coupled to the coils L1 and L2, and the oscillation circuit 1 excites the coils L1 and L2 via the coil L3. Bridge circuit 4
From the above, an AC voltage signal having the same phase or a phase inversion with the oscillation voltage of the oscillation circuit 1 shown in FIG. 6 is output depending on the magnitude relationship between the electrostatic capacitances of the capacitors C1 and C2. As an output of the bridge circuit 4, when the capacitances of the capacitors C1 and C2 are equal to each other and a detection body (not shown) is inserted between the detection electrode 3 and the ground electrode 2 and C1 <C2, A waveform a indicated by a solid line in FIG. 7 is output. On the other hand, when the capacitance of the capacitor C2 is small and C1> C2 due to the setting deviation of both electrodes 1 and 2, a phase inverted from the output a as shown by the waveform b in FIG. 7 is obtained. The voltage signal that it has is output.

After the output of the bridge circuit 4 is amplified by the AC amplifier circuit 5, the voltage signal converted to DC through the smoothing circuit 7 is output. That is, as shown in FIG. 8, C1 <C
In either state of 2 or C1> C2, the output from the output circuit 9 becomes a positive voltage.

[0005]

As described above, in the conventional capacitance type sensor, whether the capacitance C2 between both electrodes is larger or smaller than the reference capacitor C1,
The output voltage is a positive voltage. That is, due to the deviation of the distance between the electrodes when the electrodes are installed, the output voltage becomes a positive voltage when the capacitance C2 is smaller than the reference capacitance C1 in the non-detection state, and the number of C, for example, inserted between the electrodes increases. As a result, the output voltage once drops to 0 V and then increases again, so that there is a problem that two states are represented by the same voltage value as shown in FIG.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a capacitance type sensor capable of obtaining a detection output without showing two states at the same voltage value.

[0007]

In order to solve this problem, the present invention according to claim 1 provides a measuring capacitor and a reference capacitor each comprising a detection electrode and a ground electrode provided so as to face the detection electrode. The oscillation output from the oscillation circuit is supplied to the bridge circuit including, the AC output from the bridge circuit is converted into the DC output, and the analog detection output is taken out between the detection electrode and the ground electrode. Capacitance sensor for detecting presence / absence, thickness, number, etc. of the detected object according to a change in electrostatic capacitance between the detection electrode and the ground electrode caused by the approach of the detected object. In, the phase of the oscillation output of the oscillation circuit is detected, a phase detection circuit that passes the AC output from the bridge circuit in synchronization with the detected phase is provided, and the output of the phase detection circuit is It is converted into flow output, characterized in that to obtain an analog detection output.

According to a second aspect of the present invention, a comparator circuit that produces an output only when the DC output is within a predetermined threshold value of the distance between the measurement electrode and the ground electrode, and the comparator circuit. And a display means for displaying only when the distance between the electrodes is within a predetermined threshold value.

[0009]

According to the present invention, since the phase detection circuit synchronized with the oscillation circuit is provided and whether the output of the bridge circuit is passed or not is controlled according to the positive / negative of the oscillation output of the oscillation circuit, the oscillation voltage is When positive, close the analog switch provided in the phase detection circuit and let the output of the bridge circuit pass,
On the contrary, when the oscillation voltage is negative, the analog switch is opened to block the output signal of the bridge circuit. That is, in order to determine whether the state of the bridge output is positive or negative in synchronization with the half cycle of the oscillation voltage, the reference capacitor C1
When the relationship between C1 and C2 is C1 <C2, the bridge output becomes positive when the oscillation is positive, and the positive bridge output is taken out from the phase detection circuit. On the other hand, C1> C2
In this case, when the oscillation is positive, the bridge output becomes negative, and the negative bridge output is taken out from the phase detection circuit.
Thus, according to the present invention, an analog output voltage having either a positive or negative output can be obtained depending on the size of both capacitors C1 and C2.

Further, according to the present invention, if the output voltage is within a predetermined value, for example, a predetermined threshold value near 0V, by the comparator circuit having the analog output voltage thus obtained as an input, the display means It is possible to easily confirm that the set distance between the electrodes is within a predetermined threshold value by displaying, for example, turning on that effect.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In FIG. 1, the same parts as those in FIG. 5 are designated by the same reference numerals. That is, the oscillation circuit 1 having the coil L3, the reference capacitor C1, the capacitor C2 including the ground electrode 2 and the detection electrode 3, the bridge circuit 4 including the capacitors C1 and C2 and the coils L1 and L2,
The AC amplifier circuit 5, the smoothing circuit 7, the DC amplifier circuit 8 and the output circuit 9 are the same as those in the conventional case.

The circuit according to the present invention is different from the conventional one in that the phase detection circuit 6 and the comparator circuit 10 are provided.

The phase detection circuit 6 receives the output of the oscillating circuit 1 via the coil L3, and in synchronization with the oscillating circuit 1, an analog switch for controlling whether or not the output of the bridge circuit 4 is passed. 2A has a gate circuit such as
As shown in (B) of FIG. 2, only when the oscillation voltage is positive.
The phase detection circuit 6 is operated as shown in (1), and the output of the bridge circuit 4 is amplified by the AC amplification circuit 5 by using the analog switch thereof. Only the AC signal of the corresponding part is passed, smoothed, and the DC voltage is output.

In such a configuration, the capacitor C1
The output of the bridge circuit 4 becomes in phase with the oscillation circuit 1 as shown by the solid line a in the state of C1 <C2 as shown in FIG. , Only positive voltage is smoothed. C1> C
In the state of No. 2, as shown by the broken line b in FIG. 3, the phase is opposite to the oscillation voltage, and when the phase detection circuit 6 is operating, only the negative voltage is smoothed. As described above, as shown in FIG. 4, a positive or negative analog voltage can be output from the output circuit 9 depending on the magnitude relation between the capacitors C1 and C2.

The analog voltage from the output circuit 9 is supplied to the comparator circuit 10. The comparator circuit 10 is also supplied with the reference value of the resistors R1 and R2. Normal,
When the capacitances of the capacitors C1 and C2 are equal, the analog output voltage from the output circuit 9 is 0V, so this O
For the analog output voltage within a certain threshold with respect to the V output, that is, for the analog voltage near 0 V within the threshold, the indicator lamp 1 is output by the output of the comparator circuit 10.
By turning on 1, the distance between the ground electrode 2 and the detection electrode 3 can be easily set to C1 = C2.

[0018]

As is apparent from the above, according to the present invention, since the capacitance type sensor is provided with the phase detection circuit, the reference voltage C1 and the measurement capacity C2 have the same voltage value. Since it outputs a positive or negative unique analog voltage without representing two states, accurate detection can be performed. Furthermore, in the present invention, the indicator lamp can be turned on when the output voltage is near 0 V, which facilitates the setting of the inter-electrode distance.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

2 is an explanatory diagram of an output voltage (A) of an oscillation circuit and an output (B) of a phase detection circuit in FIG.

FIG. 3 is an explanatory diagram of an output voltage of the bridge circuit in FIG.

4 is an explanatory diagram of a relationship between capacitors C1 and C2 in FIG. 1 and a detection output voltage.

FIG. 5 is a block diagram showing an example of a conventional example.

6 is an explanatory diagram of an output voltage of the oscillation circuit in FIG.

7 is an explanatory diagram of an output voltage of the bridge circuit in FIG.

8 is an explanatory diagram of a relationship between capacitors C1 and C2 in FIG. 5 and a detection output voltage.

[Explanation of symbols]

 1 Oscillation circuit 2 Ground electrode 3 Detection electrode 4 Bridge circuit 5 AC amplification circuit 6 Phase detection circuit 7 Smoothing circuit 8 DC amplification circuit 9 Output circuit 10 Comparator circuit 11 Indicator light C1 Reference capacitor C2 Measurement capacitance R1, R2 Resistance

Claims (2)

[Claims] 1. A oscillating output from an oscillating circuit is supplied to a bridge circuit including a measuring capacitor and a reference capacitor which are composed of a detecting electrode and a ground electrode provided so as to face the detecting electrode, Convert the AC output to DC output and take out the analog detection output,
Presence / absence, thickness, number of objects to be detected, etc. according to a change in capacitance between the detection electrode and the ground electrode caused by an object to be detected approaching between the detection electrode and the ground electrode. In the electrostatic capacitance sensor configured to detect, a phase detection circuit that detects the phase of the oscillation output of the oscillation circuit and that allows the AC output from the bridge circuit to pass in synchronization with the detected phase is provided. A capacitance type sensor, wherein an output of the phase detection circuit is converted into a DC output to obtain an analog detection output. 2. A comparator circuit that produces an output only when the DC output is within a predetermined threshold value of the distance between the measurement electrode and the ground electrode, and is biased by the output of the comparator circuit. 2. The capacitance type sensor according to claim 1, further comprising: a display unit that displays only when the distance between the electrodes is within a predetermined threshold value.