JP2001033507A - Disconnection detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect disconnection of a primary coil or a secondary coil of a differential transformer in the case that long distance wiring, e.g., several ten meters wiring is performed between the differential transformer and a differential transformer type detecting circuit, and wiring stray capacitance is increased. SOLUTION: A DC/AC switching contact 7 and a primary coil side DC current detecting circuit constituted of a DC power source 9, a DC current detecting resistance 10, a differential amplifier 11 and a flip-flop 12 are arranged on the output side of an excitating circuit 5. A DC power source drive switching contact 7 and a secondary coil side DC current detecting circuit constituted of a DC power source 13, a DC current detecting resistor 14, a differential amplifier 15 and a flip-flop 16 are arranged on the input side of a detecting circuit detecting an output waveform voltage from a secondary coil of a differential transformer. When detection of disconnection is performed, switching is performed from normal operation to disconnection detecting operation driven by a DC current, and disconnection can be detected without being affected by a differential transformer 3 and wring stray capacitance 1 of a differential transformer type detecting circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disconnection detecting circuit for detecting a disconnection of a differential transformer in a differential transformer type detector.

[0002]

2. Description of the Related Art As a disconnection detecting circuit for detecting disconnection of a differential transformer in a differential transformer type detector, there is a conventional one disclosed in Japanese Patent Application Laid-Open No. 7-128388, for example. This conventional disconnection detection circuit is designed to operate when the differential transformer is disconnected.
Utilizing that the output voltage waveform of the next coil becomes 0V,
A disconnection detection operation is performed.

[0003]

In the conventional disconnection detecting circuit, it is possible to detect when the connecting line connecting the differential transformer and the differential transformer type detecting circuit is at a short distance. However, when the differential transformer and the differential transformer type detection circuit are wirings of equal length of several tens of meters, the stray capacitance of the wiring as shown in FIG.
Is increased, and even if the primary or secondary coil of the differential transformer 3 is disconnected, the current (IAC) 2 flows into the detection circuit through the floating capacitance 1 of the wiring, and the differential transformer 3 is not disconnected. Since the normal voltage waveform 4 is detected,
There is a problem that it is not possible to determine whether the primary or secondary coil of the differential transformer 3 has been disconnected.

[0004]

SUMMARY OF THE INVENTION A differential transformer type detector having an excitation circuit for outputting a sine wave to a primary coil of a differential transformer and a detection circuit for detecting an output waveform voltage from a secondary coil of the differential transformer. At the output of the excitation circuit
An AC switching circuit and a DC current detection circuit are connected to a differential transformer 2
A DC power supply drive switching circuit and a DC current detection circuit are provided on the input side of the detection circuit that detects the output waveform voltage from the next coil, and when a disconnection is detected, the normal operation is switched to the DC current drive disconnection detection operation. Disconnection can be detected without being affected by the stray capacitance.

[0005]

FIG. 2 shows an embodiment of the present invention. In a differential transformer type detector having an excitation circuit 5 for outputting a sine wave to a primary coil of the differential transformer 3 and a detection circuit 6 for detecting an output waveform voltage from a secondary coil of the differential transformer 3, A DC / AC switching contact 7 and a primary coil-side DC current detection circuit including a DC power supply 9, a DC current detection resistor 10, a differential amplifier 11, and a flip-flop 12 are provided on the excitation circuit 5 side. On the side of the detection circuit 6 for detecting the output waveform voltage from the coil, a contact 7 for DC power supply drive switching, and a secondary coil side comprising a DC power supply 13, a DC current detection resistor 14, a differential amplifier 15, and a flip-flop 16 DC current detection circuit and DC / AC switching contact 7
Is provided with a period timer 8 for switching the connection.

A differential transformer detector is a differential transformer 3
This is a detector for detecting the position of the core 17 of FIG. The operation of the differential transformer detector is performed when the contact of the DC / AC switching contact 7 is connected to the side (a).

[0007] The excitation circuit 3 applies a sine wave of a certain voltage and frequency to the primary coil of the differential transformer 3. At this time, a voltage is applied to the secondary coil of the differential transformer 3 by applying a voltage to the primary coil.
, The secondary coil voltage of the differential transformer 3 is detected.
The core 17 of the differential transformer 3 is movable, and the secondary coil voltage of the differential transformer 3 changes according to the position of the core 17 so that the position of the core 17 can be observed.

When the primary or secondary coil of the differential transformer 3 is disconnected, if the floating stray capacitance 1 between the excitation circuit 5 / detection circuit 6 and the differential amplifier 3 is small, the voltage detected by the detection circuit 6 Is 0, which is easily detectable. However, when the differential transformer and the differential transformer type detection circuit are wirings having a long distance of several tens of meters, the wiring stray capacitance 1 becomes large and the detection is performed through the wiring stray capacitance 1 described above. Since a voltage is generated on the circuit 6 side, it cannot be determined whether or not the wire is disconnected.

The disconnection detecting operation of the present invention will be described.

The operation of the differential transformer detector and the operation of detecting the disconnection of the differential transformer are periodically switched by a periodic timer 8. During operation of the differential transformer detector, when the DC / AC switching contact 7 is connected to (a),
The differential transformer disconnection detection operation is performed when the DC / AC switching contact 7 is connected to (b).

When the DC / AC switching contact 7 is connected to (b), the DC power supply 9 on the primary coil side of the differential transformer 3
Then, a current flows through the DC current detection resistor 10 to the primary coil of the differential transformer 3. At this time, since the DC power is applied, the impedance of the wiring stray capacitance 1 is very large, and the influence of the wiring stray capacitance can be ignored. Therefore, if the primary coil of the differential transformer 3 is not disconnected, a voltage is observed at the input terminal of the differential amplifier 11, and if disconnected, the voltage becomes 0 at the input terminal of the differential amplifier 11. Since the voltage applied to the primary coil of the differential transformer 3 is DC,
Detection can be performed without being affected by the wiring stray capacitance 1. Also,
The output of the differential amplifier 11 is
VO1 = HIGH output when there is no disconnection, and VO1 = LOW output when there is a disconnection. The disconnection of the secondary coil of the differential transformer 3 is detected by the same operation.

The above operation will be described with reference to a time chart shown in FIG.

The period timer 8 generates two signals TOUT1 and TOUT2. TOUT1 is a signal for switching connection of the DC / AC switching contact 7, and TOUT2 is a signal for latching the output signal of the differential amplifier to the flip-flop at the time of disconnection detection operation.

When TOUT1 becomes HIGH, the DC / AC switching contact 7 is connected to the (b) side, and a DC voltage is applied to the primary coil side of the differential transformer 3. At this time, if the primary coil of the differential transformer 3 is not disconnected, the DC current ID
C1 continues to flow through the primary coil of the differential transformer 3, and if the primary coil of the differential transformer 3 is disconnected, the DC current
IDC1 is 0A after flowing through wiring stray capacitance 1 momentarily
Becomes The flip-flop that latches the output of the differential amplifier 11 when the disconnection occurs is latched by TOUT2 when the DC current IDC1 instantaneously flows through the wiring stray capacitance 1 and then becomes close to 0. The signal goes LOW. The same operation is performed when disconnection of the secondary coil of the differential transformer 3 is detected.

[0015]

According to the disconnection detection circuit of the present invention, even if the differential transformer and the differential transformer type detection circuit are wired as long as several tens of meters and the wiring stray capacitance becomes large, the differential transformer can be used. Disconnection of the primary or secondary coil can be detected.

[Brief description of the drawings]

FIG. 1 is an equivalent diagram of a wiring stray capacitance in a differential transformer and a differential transformer type detector.

FIG. 2 is a diagram showing one embodiment of the present invention.

FIG. 3 is an operation time chart of one embodiment of the present invention.

[Explanation of symbols]

1: Floating capacitance of wiring, 2: Current IA flowing through floating capacitance of wiring
C, 3 ... differential transformer, 4 ... detector input voltage waveform, 5
... Excitation circuit, 6 ... Detection circuit, 7 ... DC / AC switching contact, 8 ... Period timer, 9 ... DC power supply on primary coil side, 1
0 ... DC current detection resistor on primary coil side, 11 ... Differential amplifier on primary coil side, 12 ... Flip-flop on primary coil side, 13 ... DC power supply on secondary coil side, 14 ... DC power supply on secondary coil side DC current detection resistor, 15: differential amplifier on secondary coil side, 16: flip-flop on primary coil side, 17 ...
Differential transformer core.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomohiko 5-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside the Omika Plant, Hitachi, Ltd. No.2 F-term in Hitachi Engineering Co., Ltd. (Reference) 2G014 AA02 AB04 AC18

Claims (1)

[Claims] 1. A differential transformer type detector having an excitation circuit for outputting a sine wave to a primary coil of a differential transformer and a detection circuit for detecting an output waveform voltage from a secondary coil of the differential transformer. A DC / AC switching circuit and a DC current detection circuit are provided on the output side of the circuit, and a DC power supply drive switching circuit and a DC current detection circuit are provided on the input side of the detection circuit for detecting an output waveform voltage from the differential transformer secondary coil. Disconnection detection circuit characterized by the above-mentioned.