JPS62165119A - Differential transformer interface circuit - Google Patents

Abstract

PURPOSE:To detect abnormality of a connection cable to a differential transformer, to obtain tolerance to a secular change and to further reduce the number of components by using the difference voltage between output sides of two rectifying circuits as a displacement signal. CONSTITUTION:Low-potential terminals 22L and 23L of the rectifying circuits 22 and 23 are connected with each other and the voltage between high-potential terminals 22H and 23H is supplied to a data processing circuit 7. Consequently, when the primary-side coil 3 of the differential transformer 2 is driven with the AC voltage of a driving circuit 1, AC voltages (f) and (g) proportional to the magnetic coupling with the coil 3 are induced at secondary-side coils 4 and 5 respectively. The voltages (f) and (g) are made into DC voltages by rectifying circuits 22 and 23 and signals (h) and (j) at the high-potential terminals 22H and 23H have positive potentials (voltage values V1 and V2) based on signals (i) at the low-potential terminals 22L and 23L. The voltage value V3 of the signal (h) for the signal (j) is the difference between the voltage values V1 and V2 according to the characteristics of the voltage values V1 and V2. When this voltage value V3 is supplied to an AD converter 24 and a voltage comparing circuit 25, it is converted 24 into a digital value as a displacement signal, which is supplied to a data processing circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a differential transformer interface circuit that converts an alternating current voltage obtained from the secondary side of a differential transformer into a predetermined sensor signal and supplies the signal to a data processing circuit.

(Conventional technology) Conventionally, as a technology in this field, Newton
Newton) Separate volume ``All about sensors'' (1989-4-2)
0) There was something described in Kyoikusha 2.69 etc. The configurations thereof will be explained below using figures.

FIG. 2 is a block diagram showing an example of the configuration of a conventional differential transformer interface circuit.

In FIG. 2, l is a drive circuit that outputs an alternating current voltage, and a differential transformer 2 is connected to this drive circuit l. As described in the above-mentioned document, the differential transformer 2 includes a primary coil 3 connected to the drive circuit 1;
It has a first secondary coil 4 and a second secondary coil 5, and a core 6 moves linearly in these coils 3 to 5, and the displacement X of the core 6 causes the primary Side coil 3 and 1st
．． The degree of magnetic coupling between the second secondary coils 4 and 5 changes differentially. An interface circuit is connected between the secondary side of the differential transformer 2 and the data processing circuit 7.

The interface circuit includes a first rectifier circuit 12 connected to the first secondary coil 4 via a cable 10, and a second rectifier circuit 13 connected to the second secondary coil 5 via a cable 11. It is equipped with A first high potential end 12H and a first low potential end 12L on the output side of the first rectifier circuit 12;
Of the second high potential end 13H and second low potential end 13L on the output side of the second rectifier circuit 13, the first and second high potential ends 12H and 13H have level shift circuits 14 and 15, respectively. are connected, and the first and second low potential ends! 2L and 13L are grounded. Each level shift circuit 14.15 has a level shift voltage generation circuit 1G connected to its input side, an AD converter 17.18 connected to its output side, and the AD converter 17.18 connected to the data processing circuit 7. It is connected.

Next, the operation will be explained.

When the primary coil 3 of the differential transformer 2 is driven by the AC voltage of the drive circuit l, the secondary coil 4 of the differential transformer 2
．． An alternating current voltage that differentially changes depending on the displacement X of the core 6 is induced in the core 5 . Each of these AC voltages is connected to the rectifier circuit 12.1.
3, the DC signal a.

It is converted to b.

The DC signals a and b have a relationship as shown in FIG. 3 with respect to the displacement X of the core 6. DC signal a.

Since b is largely biased with respect to the common ground potential, by setting the level shift voltage C generated by the level shift voltage generation circuit 16 to the value of signal a or b when the displacement X is zero, the level shift circuit 17.18 output signal d
, e, the signal characteristics shown in FIG. 4 are obtained. signal d,
e is converted into a digital value by AD converters 17 and 18, and then provided to the data processing circuit 7.

The data processing circuit 7 reads the outputs of the An converters 17 and 18, performs processing to obtain the difference between the digital value of the signal d and the digital value of the signal e, processes the processing result as displacement data, and converts the output of the core 6 into Find the displacement X, 1. Further, the data processing circuit 7 performs processing to calculate the sum of the digital value of the signal d and the digital value of the signal e, and when the processing result deviates significantly from zero, the differential transformer 2 and the cable 1.0 .11 It is determined that an abnormality has occurred in the connection with the device, and processing such as disabling the processing based on the displacement data at this time is performed.

(Problems to be Solved by the Invention) However, the circuit having the configuration described above has the following problems. Output change of drive circuit 1, differential transformer 2
Due to changes in the characteristics of the secondary coil 4 of the differential transformer 2,
, 5 changes, the change directly affects the reliability d and e, resulting in a problem in that the performance deteriorates.

Furthermore, not only the level shift circuits 14 and 15 are required, but also the number of All converters 17 and 18 is two or more, so there is a problem that the amount of bird air increases.

The present invention provides a differential transformer interface circuit that solves the problems of the prior art, such as poor performance and a large number of components.

(Means for Solving the Problems) In order to solve the above-described problem, the present invention solves the above-mentioned problems at the first point of the differential transformer. The first. A differential transformer interface circuit comprising a second rectifier circuit and providing each output DC voltage of the first and second rectifier circuits to a data processing circuit as a sensor signal, wherein the first low potential of the first rectifier circuit is and a second low potential end of the second rectifier circuit, and a first high potential end of the first rectifier circuit and a second high potential end of the second rectifier circuit. The configuration is such that the voltage between them is subjected to a predetermined 0 conversion as a displacement signal and is then supplied to the data processing circuit. Furthermore, a voltage comparison circuit is provided which detects that the absolute value of the displacement signal is higher than the voltage that can be obtained during normal use and provides the detected signal to the data processing circuit.

(Function) According to the present invention, since the differential transformer interface circuit is configured as described above, two terminals appearing in the first and second secondary coils are connected between the first and second high potential terminals. Since the difference voltage of the signal appears and this is used as a displacement signal,
It is possible to reduce the effects of changes in the output of the drive circuit and changes in the characteristics of the differential transformer, and to simplify the circuit configuration. Since the voltage comparison circuit detects that the absolute value of the displacement signal exceeds a specified value, the detection signal can be used to detect an abnormality such as a disconnection or short circuit in the connection cable to the differential transformer. Therefore, the above-mentioned problem can be eliminated.

(Embodiment) FIG. 1 is a configuration block diagram of a differential transformer interface circuit showing an embodiment of the present invention. Note that the same elements as the conventional elements in FIG. 2 are given the same reference numerals.

This embodiment differs from the conventional one shown in FIG. 2 in that the circuit configuration of the interface circuit connected between the differential transformer 2 and the data processing circuit 7 is different.

That is, the interface circuit
A first rectifier circuit 22 is connected to the secondary coil 4 of the main unit by a cable 20, and a cable 21 is connected to the second secondary coil 5.
A second rectifier circuit 23 is connected to the second rectifier circuit 23. 1st
The first high potential end 22H on the output side in the rectifier circuit 22 of
and the first low potential end 22L, and the second high potential end 23) in the second rectifier circuit 23 and the second low potential end 23L.
Of these, an AD converter 24 and a voltage comparison circuit 25 are connected to the first high potential end 22H, and the first and second low potential ends 22H
2L and 23L are connected to each other, and a second high potential end 23H is grounded. The AD converter 24 is a circuit that converts the analog signal applied to the first high potential end 22H into a digital signal, and the voltage comparison circuit 25 is a circuit that compares the analog signal with a certain threshold value. The output sides of the AD converter 24 and the voltage comparison circuit 25 are connected to the data processing circuit 7.

Next, the operation will be explained.

When the primary coil 3 of the differential transformer 2 is driven by the AC voltage of the drive circuit 1, the first and second secondary coils 4, 5
AC voltages f and g, which are proportional to the degree of magnetic coupling with the primary coil 3, are respectively induced in the coils. The relationship between the magnitude of this AC voltage f9g and the displacement X of the core 6 is as shown in FIG.

The alternating current voltage f passes through the cable 20 to the first rectifier circuit 22
Similarly, the AC voltage g passes through the cable 21 and is converted to DC by the second rectifier circuit 23. Here, in the first rectifier circuit 22, the signal appearing at the high potential end 22H has a positive potential (voltage value Vl) with respect to the signal i appearing at the low potential end 22L, and in the second rectifier circuit 23, The signal j appearing at the high potential end 23H has a positive potential (voltage value V2) with respect to the signal i at the low potential end 23L.
becomes.

The voltage values Vl and V2 move in the same manner as the AC signals f and g with respect to the displacement X, as shown in FIG.

From the polarity of voltage values Vl and V2, common ground potential (signal j)
If the voltage value of the signal is v3, then V3=Vl-
V2, and its relationship with the displacement X of V3 is as shown in FIG.

When the voltage value v3 is applied to the AD converter 24 and the voltage comparator circuit 25, the An converter 24 converts the voltage value v3 into a digital value as a displacement signal and provides it to the data processing circuit 7. Then, the data processing circuit 7 performs processing using the digital value.

Here, consider a case where the cable 20.21 connecting the differential transformer 2 and the rectifier circuit 22.23 is disconnected or short-circuited.

(i) When the cable 20 or 21 is disconnected or short-circuited When the cable 20 breaks down, the voltage value Vt=O, and the voltage value V3=-V2.

Further, when the cable 21 fails, the voltage value V2 becomes 0, and the voltage value V3 becomes V1.

Generally, the magnitudes of the voltage values Vl and V2 in a normal connection state are sufficiently larger than the possible range of the voltage value (displacement signal) V3, so the absolute value of the displacement signal v3 is used as the threshold value of the voltage comparison circuit 25. , it is easy to set the value to a value that is greater than the maximum value that can be taken in a normal connection state, and smaller than the voltage value Vl or v2 that would occur in the event of a disconnection or short circuit. Therefore, if the data processing circuit 7 is notified by the signal k that the displacement signal v3 exceeds the threshold value in the voltage comparison circuit 25, the data processing circuit 7
processing can be disabled.

(2) When the cables 20 and 21 are disconnected or short-circuited, the voltage comparison circuit 25 does not operate, but since the displacement signal v3 is originally zero, the data processing circuit 7 does not process the displacement X.

The advantages of the present invention are as follows.

■ On the output side of the rectifier circuits 22 and 23, the difference in the magnitude of the two signals appearing on the first and second secondary coil sides of the differential transformer 2 is calculated, so the change in the output of the drive circuit l and Even if there is a change in the characteristics of the differential transformer 2, the influence on the displacement signal v3 can be reduced.

(2) Since the displacement signal v3 obtained by taking the difference between the two signals is AD converted, one AD converter 24 is sufficient. moreover,
Since the voltage comparator circuit 25 does not need to be highly accurate, it can be easily constructed.

In this way, it is possible to realize a circuit that is resistant to aging and has a configuration with a small number of parts, and has the same ability to detect disconnections and short circuits in differential transformer connection cables as the conventional circuit.

(Effects of the Invention) As described above in detail, according to the present invention, the difference voltage on the output side of the first and second rectifier circuits is used as a displacement signal, and the absolute value of the displacement signal is By detecting that the value exceeds the specified value and sending it to the data processing circuit, it is not only possible to detect abnormalities such as disconnections and short circuits in the connecting cable to the differential transformer, but it is also resistant to changes over time. Furthermore, the effect of reducing the number of parts can be expected.

[Brief explanation of drawings]

Figure 1 is a configuration block diagram of a differential transformer interface circuit showing an embodiment of the present invention, Figure 2 is a configuration block diagram of a conventional differential transformer interface circuit, and Figures 3 and 4 are displacements in Figure 2. Signal characteristic diagram for 5th
7 to 7 are signal characteristic diagrams with respect to the displacement in FIG. 1. 1... Drive circuit, 2... Differential transformer, 3... Primary coil, 4, 5...
・First. Second secondary coil, 6...Core, 7
...Data processing circuit, 20.21...
Cable, 22.23... 1st, 2nd rectifier circuit, 22H, 23H... 1st. Second high potential end, 22L, 23L... 1st. a second low potential end;
24...AD converter, 25...Voltage comparison circuit. Applicant's agent Kyo Moto Signal diagram of Seikyo 2 diagram

Claims (1)

[Claims] In a differential transformer having a primary coil and first and second secondary coils, first and second coils are connected to the first and second secondary coils by cables, respectively. Equipped with 2 rectifier circuits,
DC voltage at a first high potential end and a first low potential end of the rectified output in the first rectifier circuit, and a second high potential end and second low potential end of the rectified output in the second rectifier circuit. In a differential transformer interface circuit that supplies a DC voltage at an end to a data processing circuit as a sensor signal, the first and second low potential ends are connected, and the potential between the first and second high potential ends is A voltage that performs a predetermined signal conversion as a displacement signal and supplies it to the data processing circuit, detects that the absolute value of the displacement signal is higher than a voltage that can be taken during normal use, and supplies the detection signal to the data processing circuit. A differential transformer interface circuit characterized by being provided with a comparison circuit.