Relay fault detection circuit and fault detection method

Abstract

The invention relates to a relay fault detection circuit and a fault detection method, the relay fault detection circuit comprises a relay driving circuit, a driving current sampling circuit, an amplifying circuit and a signal shaping circuit, the output end of the relay driving circuit is connected with a coil of a relay, and the other end of the coil of the relay is connected with the driving current sampling circuit; the output end of the driving current sampling circuit is connected with the amplifying circuit, and the output end of the amplifying circuit is connected with the input end of the signal shaping circuit; the output end of the signal shaping circuit is connected with a controller. The relay fault detection circuit is used for collecting the relay driving current signal and the relay pull-in current signal, the output square wave signal is combined with the relay fault detection method to carry out fault judgment on the relay, the relay does not need to be loaded, the safety is high, integration is convenient, and the universality is high.

Description

Technical Field

[0001] The present invention relates to the field of electrical control technology, and in particular to a relay fault detection circuit and a fault detection method. Background Art

[0002] In the field of automatic control, electromagnetic relay is a very common switch control device that controls strong current with weak current and high power with low power. Its basic structure generally includes an electromagnet composed of a coil, a reset spring, an armature and a contact. Its basic principle is that when the electromagnet is energized, it generates magnetic force, overcomes the pulling force of the reset spring, attracts the armature to move, and thus drives the moving contact to connect with the static contact, and the load end of the relay is connected. When the electromagnet is powered off, the magnetic force generated by the electromagnet disappears, and the armature drives the moving contact away from the static contact under the pull of the reset spring, and the load end of the relay is disconnected.

[0003] Common faults of electromagnetic relays are generally coil drive circuit failure, coil burnout and contact sticking. The first two will cause the electromagnet part of the electromagnetic relay to be unable to generate electromagnetic force, and thus unable to attract the armature to complete the action of connecting the load end of the relay. The latter is because the moving contact and static contact of the electromagnetic relay are generally made of metal, and there is contact resistance between them. Therefore, when the load power connected to the load end of the electromagnetic relay is too large, the current flowing through the contact surface of the moving contact and the static contact after the relay is attracted is too large, which will cause a lot of heat to be generated on the contact surface of the two, and eventually cause the static contact and the moving contact to melt, and the two stick together, causing the relay to have a contact sticking failure and unable to disconnect.

[0004] The general method of detecting relay failure is to add a detection circuit to the load end of the relay to detect whether the signal at the input load end appears at the output end, so as to determine whether the relay is connected. This detection scheme has two main disadvantages. First, the detection circuit must be adapted according to the type of relay load. For example, the detection circuit when the load is 220V AC and the load is 24V DC is not compatible, resulting in the same set of hardware being unable to control two or more loads and realize the relay's pull-in detection. Second, the detection circuit requires that the output end of the relay must intervene in the signal and cannot be left floating. For example, a relay circuit that controls a 220V AC load, when there is no 220V power input at the load end, since there is no signal flowing out of the load output end of the relay, the relay pull-in detection circuit at the load end cannot detect whether the relay is pulled in. Summary of the invention

[0005] In order to solve the problem that the existing relay fault detection needs to be performed on the load side, the present invention proposes a relay fault detection circuit and a fault detection method. The relay fault detection circuit is arranged to collect the relay drive current signal and the relay pull-in current signal, and the output square wave signal is combined with the relay fault detection method to perform relay fault judgment. The relay does not need to carry a load, has high safety, is easy to integrate and has high versatility.

[0006] To achieve the above-mentioned purpose, the first aspect of the present invention provides a relay fault detection circuit, comprising a relay drive circuit, a drive current sampling circuit, an amplification circuit and a signal shaping circuit, wherein the output end of the relay drive circuit is connected to a coil of a relay, and the other end of the coil of the relay is connected to the drive current sampling circuit; The output end of the driving current sampling circuit is connected to the amplifier circuit, and the output end of the amplifier circuit is connected to the input end of the signal shaping circuit; The output end of the signal shaping circuit is connected to a controller.

[0007] Furthermore, the relay drive circuit includes a first resistor, a second resistor and a transistor, the first resistor is respectively connected to the second resistor and the base of the transistor, the emitter of the transistor and the other end of the second resistor are connected and grounded, and the collector of the transistor is connected to the coil of the relay.

[0008] The relay drive circuit is set to turn the relay coil on and off.

[0009] Furthermore, the drive current sampling circuit includes a sampling resistor and a DC blocking capacitor, one side of the sampling resistor is connected to a power supply, and the other side is respectively connected to the coil of the relay and the DC blocking capacitor, and the other end of the DC blocking capacitor is connected to an amplifier circuit.

[0010] Further, the amplifying circuit includes an amplifier, a third resistor, a fourth resistor, a fifth resistor and a sixth resistor; The DC blocking capacitor is connected to the in-phase end of the amplifier via the third resistor, the in-phase end of the amplifier is grounded via the fourth resistor, the inverting end of the amplifier is grounded via the fifth resistor, a sixth resistor is arranged between the inverting end of the amplifier and the output end of the amplifier, and the output end of the amplifier is connected to the signal shaping circuit.

[0011] The amplifier circuit amplifies the input current signal.

[0012] Furthermore, the signal shaping circuit includes a comparator, a potentiometer and a seventh resistor, wherein the non-inverting end of the comparator is connected to the potentiometer, the inverting end of the comparator is connected to the output end of the amplifier circuit, and the output end of the comparator is respectively connected to the seventh resistor and the controller.

[0013] The comparator is used to compare the relay drive current signal and the relay pull-in current signal with the threshold value set by the potentiometer, thereby shaping the continuous analog change signal into a jumping square wave signal, which is convenient for subsequent digital circuit processing.

[0014] Furthermore, the controller includes a combinational logic controller and a microprogram controller.

[0015] The relay fault detection circuit is easy to integrate and can be combined with a variety of controllers to provide judgment signals for relay fault detection.

[0016] A second aspect of the present invention provides a relay fault detection method, using a relay fault detection circuit: Step 1: Connect the controller to the relay drive circuit, and output a drive signal through the controller. The drive signal turns on the relay drive circuit, and the relay coil is energized; Step 2: The driving current sampling circuit collects the relay driving current signal and the relay pickup current signal, which are then amplified by the amplifier circuit and output as the relay operation status signal by the shaping circuit; Step 3: The output end of the shaping circuit is connected to the controller, and the controller determines the state of the relay according to the relay operation state signal; The states include: relay normal closure, relay coil failure and relay contact failure.

[0017] Furthermore, the step 3 comprises: If the controller receives two consecutive square wave signals, the relay will be normally energized; If the controller receives a square wave signal, the relay contacts are faulty; If the controller does not receive the square wave signal, the relay coil is faulty.

[0018] Through the above technical solution, the beneficial effects of the present invention are: 1 The present invention realizes the fault detection of the relay on the relay coil side. The relay does not need to carry a load, the detection is safe, and the detection is highly versatile. After the relay coil is energized, the coil pulls the armature, driving the contacts to move and complete the attraction. After the contacts are attracted, the armature is incorporated into the magnetic circuit of the relay coil, causing the magnetic flux of the coil to change transiently, and an induced electromotive force is generated inside the coil, thereby causing the current flowing through the coil to change transiently. A relay drive circuit, a drive current sampling circuit, an amplification circuit and a signal shaping circuit are set to collect, amplify and shape the relay drive current signal and the relay attraction current signal, and output a square wave signal to the controller according to the relay action situation. Relay fault detection is realized based on the change of current.

[0019] 2 The present invention proposes a relay fault detection method, which obtains the fault type of the relay by judging the signal output by the shaping circuit.

[0020] 3. The relay fault detection circuit of the present invention has a simple circuit structure and is easy to integrate, and can detect relay faults during the relay control process. The relay does not need to carry a load and has strong safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 One of the circuit diagrams of a relay fault detection circuit of the present invention; Figure 2 The second circuit diagram of a relay fault detection circuit of the present invention; Figure 3 A schematic diagram of a relay fault detection circuit of the present invention; Figure 4 One of the images of the oscilloscope during the detection of the present invention; Figure 5 This is the second image of the oscilloscope during the detection of the present invention.

[0022] Figure numbers: 1 is a relay driving circuit, 2 is a driving current sampling circuit, 3 is an amplifier circuit, 4 is a signal shaping circuit, 5 is a relay, 201 is a sampling resistor, 202 is a DC blocking capacitor, 301 is an amplifier, 302 is a third resistor, 303 is a fourth resistor, 304 is a fifth resistor, 305 is a sixth resistor, 401 is a comparator, 402 is a potentiometer, and 403 is a seventh resistor. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments: Example 1 like Figures 1 to 3 As shown, a relay fault detection circuit comprises a relay drive circuit 1, a drive current sampling circuit 2, an amplifier circuit 3 and a signal shaping circuit 4, wherein the output end of the relay drive circuit 1 is connected to a coil of a relay 5, and the other end of the coil of the relay 5 is connected to the drive current sampling circuit 2; The output end of the driving current sampling circuit 2 is connected to the amplifier circuit 3, and the output end of the amplifier circuit 3 is connected to the input end of the signal shaping circuit 4; The output end of the signal shaping circuit 4 is connected to a controller.

[0024] The relay drive circuit 1 includes a first resistor 101, a second resistor 102 and a transistor 103, wherein the first resistor 101 is connected to the base of the second resistor 102 and the transistor 103 respectively, the emitter of the transistor 103 and the other end of the second resistor 102 are connected to ground, and the collector of the transistor 103 is connected to the coil of the relay 5.

[0025] The driving current sampling circuit 2 includes a sampling resistor 201 and a DC blocking capacitor 202 . One end of the sampling resistor 201 is connected to a power supply, and the other end is respectively connected to the coil of the relay 5 and the DC blocking capacitor 202 . The other end of the DC blocking capacitor 202 is connected to the amplifier circuit 3 .

[0026] The amplifying circuit 3 includes an amplifier 301, a third resistor 302, a fourth resistor 303, a fifth resistor 304 and a sixth resistor 305; The DC blocking capacitor 202 is connected to the in-phase end of the amplifier 301 via the third resistor 302, the in-phase end of the amplifier 301 is grounded via the fourth resistor 303, the inverting end of the amplifier 301 is grounded via the fifth resistor 304, a sixth resistor 305 is provided between the inverting end of the amplifier 301 and the output end of the amplifier 301, and the output end of the amplifier 301 is connected to the signal shaping circuit 4.

[0027] The signal shaping circuit 4 includes a comparator 401, a potentiometer 402 and a seventh resistor 403, the in-phase end of the comparator 401 is connected to the potentiometer 402, the inverting end of the comparator 401 is connected to the output end of the amplifier circuit 3, and the output end of the comparator 401 is respectively connected to the seventh resistor 403 and the controller.

[0028] The controller includes a combinational logic controller and a microprogram controller.

[0029] In this embodiment, the controller is a single chip microcomputer.

[0030] like Figure 2 As shown, the relay drive circuit 1 is connected to a controller. When in operation, the controller output signal SIG1 is valid, the transistor 103 (Q1) is turned on, the current passes through the sampling resistor 201 (R5), enters the coil of the relay 5 (K1), and is grounded through the transistor 103. The current signal increased by the sampling resistor 201 generates the first signal (relay drive current signal) through the DC blocking capacitor 202 (C3), and the coil of the relay 5 is energized.

[0031] When the armature of relay 5 pulls the contact to complete the attraction action, the armature is connected to the coil of relay 5, causing the coil magnetic flux to change, thereby generating an induced electromotive force, causing the current flowing through the coil to change. The current passes through the sampling resistor 201 and the DC blocking capacitor 202 to generate a second signal (relay attraction current signal).

[0032] The relay driving current signal and the relay pickup current signal are respectively output through the DC blocking capacitor 202, the sixth resistor 305 (R2), the fifth resistor 304 (R3), the third resistor 302 (R6), the fourth resistor 303 (R9) and the amplifier 301 (U1A).

[0033] After the relay driving current signal and the relay closing current signal are amplified, they are shaped and output to the controller via the potentiometer 402 (R11), the seventh resistor 403 (R7) and the comparator 401 (U2A).

[0034] Example 2 A relay fault detection method is described based on a relay fault detection circuit in Example 1: A relay fault detection method, comprising: Step 1: Connect the controller to the relay drive circuit 1, and output a drive signal through the controller. The drive signal turns on the relay drive circuit 1, and the coil of the relay 5 is energized; Step 2: The driving current sampling circuit 2 collects the relay driving current signal and the relay pickup current signal, which are then amplified by the amplifier circuit 3 and output as the relay operation status signal by the shaping circuit 4; Step 3: The output end of the shaping circuit 4 is connected to the controller, and the controller determines the state of the relay 5 according to the relay operation state signal; The states include: relay normal closure, relay coil failure and relay contact failure.

[0035] If the controller receives two consecutive square wave signals, the relay will be normally energized; If the controller receives a square wave signal, the relay contacts are faulty; If the controller does not receive the square wave signal, the relay coil is faulty.

[0036] In order to prove that a relay fault detection circuit and a relay fault detection method have good detection effect: A first detection port TP1 and a second detection port TP2 are provided at the output ends of the amplifying circuit 3 and the shaping circuit 4 , and an oscilloscope is connected to the first detection port TP1 and the second detection port TP2 .

[0037] The oscilloscope image of the relay 5 under test that is normally energized is as follows: Figure 3 As shown, it can be observed that the second test port outputs the relay drive current signal ( Figure 4 The peak 1 in the figure) and the relay pickup current signal, ( Figure 4 2), and images of the two square wave signals output from the third test port.

[0038] The oscilloscope image of the faulty contact of relay 5 under test is as follows: Figure 4 As shown, it can be observed that the second test port outputs the relay drive current signal ( Figure 5 The peak 1 in the figure is shown in Figure 1), and a square wave signal is output from the third test port. No relay pickup current signal is output.

[0039] The coil of relay 5 under test is faulty and there is no image on the oscilloscope.

[0040] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, any equivalent changes or modifications made according to the structures, features and principles described in the patent scope of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A relay fault detection circuit, characterized in that: It comprises a relay drive circuit (1), a drive current sampling circuit (2), an amplification circuit (3) and a signal shaping circuit (4), wherein the output end of the relay drive circuit (1) is connected to the coil of a relay (5), and the other end of the coil of the relay (5) is connected to the drive current sampling circuit (2); The output end of the driving current sampling circuit (2) is connected to the amplifier circuit (3), and the output end of the amplifier circuit (3) is connected to the input end of the signal shaping circuit (4); The output end of the signal shaping circuit (4) is connected to a controller.

2. A relay fault detection circuit according to claim 1, characterized in that: The relay drive circuit (1) comprises a first resistor (101), a second resistor (102) and a transistor (103), wherein the first resistor (101) is connected to the base of the second resistor (102) and the transistor (103) respectively, the emitter of the transistor (103) and the other end of the second resistor (102) are connected and then grounded, and the collector of the transistor (103) is connected to the coil of the relay (5).

3. A relay fault detection circuit according to claim 1, characterized in that: The drive current sampling circuit (2) comprises a sampling resistor (201) and a DC blocking capacitor (202); one end of the sampling resistor (201) is connected to a power supply, and one end is respectively connected to the coil of the relay (5) and the DC blocking capacitor (202); the other end of the DC blocking capacitor (202) is connected to an amplifier circuit (3).

4. A relay fault detection circuit according to claim 3, characterized in that: The amplifying circuit (3) comprises an amplifier (301), a third resistor (302), a fourth resistor (303), a fifth resistor (304) and a sixth resistor (305); The DC blocking capacitor (202) is connected to the in-phase end of the amplifier (301) via the third resistor (302), the in-phase end of the amplifier (301) is grounded via the fourth resistor (303), the inverting end of the amplifier (301) is grounded via the fifth resistor (304), a sixth resistor (305) is provided between the inverting end of the amplifier (301) and the output end of the amplifier (301), and the output end of the amplifier (301) is connected to the signal shaping circuit (4).

5. A relay fault detection circuit according to claim 1, characterized in that: The signal shaping circuit (4) comprises a comparator (401), a potentiometer (402) and a seventh resistor (403); the in-phase end of the comparator (401) is connected to the potentiometer (402); the in-phase end of the comparator (401) is connected to the output end of the amplifier circuit (3); and the output end of the comparator (401) is respectively connected to the seventh resistor (403) and the controller.

6. A relay fault detection circuit according to claim 1, characterized in that: The controller includes a combinational logic controller and a microprogram controller.

7. A relay fault detection method, characterized in that: A relay fault detection circuit according to any one of claims 1 to 6, comprising: Step 1: Connect the controller to the relay drive circuit (1), and output an action signal through the controller to turn on the relay drive circuit (1), so that the coil of the relay (5) is energized; Step 2: The driving current sampling circuit (2) collects the relay driving current signal and the relay pickup current signal, which are then amplified by the amplifier circuit (3) and output as a relay operation status signal by the shaping circuit (4); Step 3: The output end of the shaping circuit (4) is connected to a controller, and the controller determines the state of the relay (5) according to the relay operation state signal; The states include: relay normal closure, relay coil failure and relay contact failure.

8. A relay fault detection method according to claim 7, characterized in that: The step 3 comprises: If the controller receives two consecutive square wave signals, the relay will be normally energized; If the controller receives a square wave signal, the relay contacts are faulty; If the controller does not receive the square wave signal, the relay coil is faulty.

Images