JPS5985962A - Current detector - Google Patents

Abstract

PURPOSE:To simplify the equipment by combining a transformer, a rectifying/ smoothing circuit and a window comparator to act as a failsafe input/output circuit. CONSTITUTION:A transformer 3 is equipped with a primary winding 3a for current to be detected to a terminal 1 to be inputted into, a secondary winding 3b for detecting current and additionally, a third winding 3c for an excitation signal to be inputted into from a signal generator 2. A rectifying/smoothing circuit 4 comprises four diodes connected to a bridge and one 4-terminal capacitor and is a known failsafe circuit which generates no rectified output V1 regardless of short-circuiting and disconnection of a circuit part. A window comparator 5 has a window determined by upper and lower threshold levels and is a known circuit which oscillates to output an signal only when the level of the input signal is within the range of the window. It produces none of the oscillation signal when the level of the input signal is below the window, it above the window or a trouble occurs in the circuit and hence, has an output characteristic of non-symmetrical errors.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current detection device that can be used as a fail-safe input/output circuit in an information processing device.

2. Description of the Related Art In fail-safe information processing devices such as train detection devices, level crossing obstacle detection devices, and automatic train operation devices, relays are used to transmit and receive information. For this reason, this type of information processing device has drawbacks such as being complicated and expensive, and having a short lifespan due to wear of relay contacts.

An object of the present invention is to provide a current detection device that can be used as a fail-safe input/output circuit by using a transformer, a rectifying and smoothing circuit, and a window comparator.

Hereinafter, the present invention will be explained based on examples shown in the following.

In Figure 1, 1 is an input terminal for the current to be detected (current to be detected), 2 is a signal generator that generates an excitation signal for current detection, 3 is a transformer, and 4 is provided on the output side of the transformer 3. The rectifying and smoothing circuit 5 is a window comparator provided on the output side of the rectifying and smoothing circuit 4.

The transformer 3 includes a primary winding 3a to which the detected current is input to the terminal 1, a secondary winding 3b for current detection, and a tertiary winding 3C to which the excitation signal from the signal generator 2 is manually input. It is equipped with

The detected current input to the terminal 1 is a direct current or low frequency current that nearly saturates the transformer 3, and the excitation signal output from the signal generator 2 is a signal at a level that does not saturate the transformer 3. , excitation signals are constantly input.

Therefore, if the detected current is input to terminal 1, the signal obtained at winding 3b of transformer 3 will have a small amplitude and the same frequency as the excitation signal because the inductance of the lance will decrease. If the current to be detected is not input, the inductance of the transformer is large, so the signal has a large amplitude and the same frequency as the excitation signal.

As an example of the rectifying and smoothing circuit 4 is shown in FIG. is also a known fail-safe circuit that does not produce rectified output (1).

The window comparator 5 is a known circuit that has a window defined by upper and lower threshold levels and outputs a signal by oscillating only when the level of the input signal is within the range of the window. is greater than or equal to the window,
When it exceeds the window or when there is a circuit failure, no oscillation signal is obtained and the output characteristics are asymmetrical errors. Such a window comparator 5 is disclosed in Japanese Utility Model Application Publication No. 57-4764, etc., and an example thereof is shown in FIG.

In this example, the window comparator 5 in FIG. The terminal 43 is an input terminal for the output of the rectifying and smoothing circuit 4, and the terminal 44 is a power input terminal for the power supply (for example, 12 V) of the window comparator and is the power source for the transistor 32. The output of the transistor in the previous stage is connected to the base of each transistor by direct coupling. That is, the base of the L-transistor 31 is supplied with the output of the transistor 33 via the resistor 36 after being divided by the collector resistor 34.35, and the base of the transistor 32 is supplied with the output of the transistor 33.
The output of transistor 1 is divided and supplied by resistors 38 and 399 including the level shift of the power input to terminal 44, and the output of transistor 32 is divided and supplied to the base of transistor 33 by resistor 4041. . This window comparator constitutes a feedback controlled oscillator in which the output of each transistor is supplied in the order of transistor 31 - transistor 32 - transistor 33 - transistor 3-1 when a specific input voltage is applied to the input terminal. There is.

The input voltage range in which this window comparator can oscillate is based on the power supply voltage to the terminal 44 and the VO1 resistor 34.35.
The resistance values of 37, 38, and 39 are R34, R35, and R3, respectively.
7, R2O, 1 (39, the level of the input signal is Vl, the lower limit of the input terminal ■ when oscillating is V'1, the upper limit is V-2
When, V=I ・t< 3 9/ (R3z
+ R3θ 10 R39)=yo ・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・ (1) V-2・R35/ (R34
+R35)-VO・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・ （
2) is given by Here, the area between v=l and V-2 becomes the window of the window comparator.

When the input voltage V1 is lower than the lower limit V-1, the transistors 32 and 33 remain on and the transistor 31 remains off, so no oscillation occurs.

When the input voltage (1) becomes larger than the lower limit V-1, the transistors 32 and 33 are turned off, so that the transistor 31 is turned on. When the transistor 31 is turned on, the 1-transistors 32 and 33 are turned on.

When the transistors 32 and 33 turn on, the transistor 31 turns off, so the window comparator continues to oscillate.

Furthermore, if the input voltage V1 exceeds the upper limit V-2, even if the transistor 33 is turned on, the 1-transistor 3
1 does not turn off, the oscillation circuit becomes unable to oscillate.

As is clear from conditional expressions (1) and (2), the input voltage range in which the window comparator oscillates, that is, ■
The lower limit V-1 and upper limit V-2 of 1 are 1, resistance 34.35.
37, 38, and 39, and by appropriately selecting these resistance values, the oscillation start voltage can be freely set.

The window of the window comparator 5 used in the current detection device has a narrow window that includes the level of the output of the rectifying and smoothing circuit 4 when the current to be detected is input to the terminal 1 and a signal with a small amplitude is output to the winding 3b. It has been decided that

In the current detection device described above, when the current to be detected is input to the terminal 1, a low amplitude signal is obtained at the winding 3b of the transformer 3, and the level of the output of the rectifying and smoothing circuit 4 falls within the window of the window comparator 5. Therefore, the window comparator 5 oscillates.

However, if the current to be detected is not input to the terminal 1 or the winding 3a is disconnected, the output of the winding 3 of the transformer 3 becomes high amplitude, and the level of the output of the rectifier and smoothing circuit 4 changes from the window of the window comparator 5. , the window comparator 5 does not oscillate.

Also, if the excitation signal is not input to the winding 3a or the winding 3b
, 3c are disconnected or short-circuited and no AC signal is input to the rectifying and smoothing circuit 4. Since the output of the rectifying and smoothing circuit 4 does not reach the window of the window comparator 5, the in-to comparator 5 does not oscillate.

Furthermore, if the window comparator 5 fails, the window comparator 5 will not oscillate.

In other words, the above-described current detection device can obtain an oscillation signal at the output of the window comparator 5 only when each circuit is normal and the current to be detected is input to the terminal 1. However, if any of the circuits is malfunctioning, When this happens and when the current to be detected is not input, an oscillation output cannot be obtained as the output of the window comparator 5.

Therefore, in order to use the above-described current detection device as an input circuit of a fail-safe device, the time when there is no current to be detected is used as detection information of the sensor or control information corresponding to a control command. That is, the output when the window comparator 5 does not oscillate can be used as the non-safe control output, and the output when it oscillates can be used as the safe control output. In this way, it is not possible to obtain an oscillation output as the output of the window comparator 5 both when there is a control command and when the device malfunctions. Therefore, for example, in a railroad crossing obstacle detection device, it is possible to detect an obstacle due to a malfunction of the device. The output of the device can be used to make the device 7-ale safe.

The current detection device shown in Fig. 4 has resistors 6 and 7 connected to both sides of the secondary winding 3b of the transformer 3, a signal generator 2 for an excitation signal connected between the resistor 6 and the ground, and a resistor 7 connected to the signal generator 2 for generating an excitation signal. Secondary winding 3b
The opposite side is connected to ground, and the voltage between the terminals of the resistor 7 is input to the rectifying and smoothing circuit 4.

In the current detection device shown in FIG. 4, if the current to be detected is manually applied to the terminal 1, a signal with a small amplitude and the same frequency as the excitation signal is obtained between the terminals of the resistor 7. When the level of the input signal falls within the window range, the window comparator 5 oscillates.

However, if the detected current is not input to terminal 1, winding 3b
As the voltage drop increases, the amplitude of the signal obtained between the terminals of the resistor 7 becomes smaller and the level of the input signal to the window comparator 5 falls outside the window where it can oscillate, so the window comparator 5 does not oscillate. .

Furthermore, if the primary winding 3a or the resistor 7 is disconnected or the resistor 6 is short-circuited, the amplitude of the signal obtained between the terminals of the resistor 7 increases, and the level of the input signal to the window comparator 5 exceeds the window. , the window comparator 5 does not oscillate.

Furthermore, if the secondary winding 3b or the resistor 7 is short-circuited or the resistor 6 is disconnected, the level of the signal 19 applied between the terminals of the resistor 7 will not reach the window of the window comparator 5, so the window comparator 5 will not oscillate.

゛In other words, each circuit of the current detection device in Fig. 4 is normal,
However, since the oscillation output can be obtained from the window comparator 5 only when the current to be detected is input to terminal 1, by using it in the same way as the current detection device shown in Fig. 1, a fail-safe input device can be obtained. It can be done.

As described above, the present invention uses a transformer, a rectifying and smoothing circuit, and a window comparator to create a safe input circuit without using a relay, which simplifies the device and makes maintenance work extremely easy. Become. In addition, the rectifying and smoothing circuit and the window comparator can be made into semiconductor integrated circuits, making the device simpler and cheaper.
Become.

[Brief explanation of the drawing]

FIG. 1 is an embodiment of the current detection device according to the present invention, FIG. 2 is an embodiment of the rectifying and smoothing circuit, FIG. 3 is an embodiment of the window comparator, and FIG. 4 is the current detection device. It is another Example figure. 1: Input terminal, 2: Signal generator, 3 Nidorance, 4: Rectifier and smoothing circuit, 5: Window comparator, 3a,
3b: Winding wire. Patent applicant Nippon Signal Co., Ltd. Figure 1 O Figure 2 jla Figure 4

Claims (1)

[Claims] (1) A transformer having a winding through which a current to be detected flows and a winding for current export, and means for applying an excitation signal for current detection to the transformer, and an output of the winding for current detection. A current detection device consisting of a rectifying and smoothing circuit connected to the side and a window comparator connected to the output side of this rectifying and smoothing circuit.