A bidirectional digital input device with self-diagnosis function and a detection method thereof

Abstract

The application discloses a bidirectional digital quantity input device with a self-diagnosis function, which comprises a switching quantity input circuit and a switching quantity diagnosis circuit, wherein the switching quantity diagnosis circuit comprises a rectifier bridge, an excitation control unit, a voltage division and current limiting unit, a power amplification circuit, a first isolation unit and a second isolation unit, and the rectifier bridge, the excitation control unit, the voltage division and current limiting unit, the power amplification circuit, the first isolation unit and the second isolation unit are connected to realize the switching in and shielding of internal and external excitation through control switching; the switching quantity input circuit comprises a resistor and a switch, the two ends of the switch are connected with the two ends of the resistor respectively and are connected to the switching quantity diagnosis circuit; and the circuit further comprises a first input contact, a second input contact, a third input contact, at least one switching quantity signal input channel and at least one broken line detection channel; the application solves the defects of the existing digital quantity input circuit detection circuit, such as complexity and small coverage, and realizes the requirement of domestic self-controllable automation control field.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial automation, and in particular to a bidirectional digital quantity input device with a self-diagnosis function and a detection method thereof. BACKGROUND

[0002] With the improvement of automation, informatization and intelligentization level in the field of industrial control, the complexity of control systems is getting higher and higher. However, with the rise of personnel costs, the demand for unmanned operation and maintenance of control systems is becoming stronger. Control systems must implement channel-level self-diagnosis to reduce maintenance complexity. In the context of localization and self-control, using domestic devices to implement channel-level diagnosis has become an inevitable choice for domestic automation control manufacturers. This paper provides a low-cost, comprehensive digital quantity output circuit break detection method.

[0003] The prior art has made many attempts to detect the coverage of digital quantity input circuits. For example: Patent document CN112834957A provides a direct current active excitation switch quantity test method, which uses a voltage dividing resistor and an isolation amplification circuit to realize the diagnosis of I / O active excitation. However, this circuit cannot meet the needs of source type, drain type, passive input, and common circuits with alternating current input, and the isolation amplification circuit is currently difficult to replace. The break diagnosis scheme provided in CN112702054A document has some commonality with the break diagnosis method of this scheme, but it still cannot solve the problem of multiple signal input, and can only perform break diagnosis. Obviously, the diagnosis coverage cannot cover other fault states. The diagnosis method provided in CN112611983A document uses a Hall element and an analog-to-digital converter, which is obviously difficult to bear the cost compared to a switch quantity input channel. CN111813088A uses an external relay to control the excitation input relay to realize switching, which has high power consumption and slow switching, making it difficult to realize real-time detection. CN111624916A is a safety level input channel, although it increases excitation, it loses isolation. The DI channel described in CN111682872A document uses a rectifier bridge, but the subsequent processing circuit does not perform fault diagnosis.

[0004] In view of this, it is necessary to propose a bidirectional digital quantity input circuit with a self-diagnosis function, which solves the problems of switch quantity signal compatibility, channel monitoring, and external wiring fault monitoring in the field of industrial automation in the prior art. The existing digital quantity input circuit detection circuit is complex and has a small coverage. SUMMARY

[0005] The application aims to provide a bidirectional digital quantity input device with self-diagnosis function and a detection method thereof, which solves the defects of complex detection circuit and small coverage of the existing digital quantity input circuit, and realizes some domestic self-controllable requirements in the field of automatic control.

[0006] The application provides a bidirectional digital quantity input device with self-diagnosis function, which comprises a switch quantity input circuit and a switch quantity diagnosis circuit.

[0007] The excitation control unit comprises a first control component, a second control component, a third control component and a fourth control component, one end of each of the first control component, the second control component, the third control component and the fourth control component is connected with a power supply, the other end of the first control component is connected with the anode of a first diode, the other end of the second control component is connected with the anode of a second diode, the voltage dividing and current limiting unit, the power amplification circuit, the second isolation unit and the fourth control component and grounded, and the other end of the third control component is connected with the first isolation unit.

[0008] The switch quantity input circuit comprises a resistor and a switch, two ends of the switch are respectively connected with two ends of the resistor and connected into the switch quantity diagnosis circuit.

[0009] The circuit further comprises a first input contact, a second input contact, a third input contact, at least one switch quantity signal input channel and at least one wire break detection channel.

[0010] One end of the first input contact is connected with one end of the switch quantity input circuit, the other end of the first input contact is connected with the negative pole of the first diode, the first control component and the power supply, one end of the second input contact is connected with the other end of the switch quantity input circuit, the other end of the second input contact is connected with the first alternating current input end of the rectifier bridge, the third input contact is connected with the second alternating current input end of the rectifier bridge, the first direct current output end of the rectifier bridge is connected with the fourth control component and the ground, the second direct current output end of the rectifier bridge is connected with the negative pole of the second diode, the second control component and the power supply, the second direct current output end of the rectifier bridge is connected with the input end of the voltage division and current limiting unit and the input end of the power amplification circuit, and the output end of the power amplification circuit is connected with the first end of the first isolation unit, the second end of the first isolation unit is connected with the third control component and the power supply, the third end of the first isolation unit is connected with the disconnection detection channel, and the fourth end of the first isolation unit is grounded; the other output end of the power amplification circuit is connected with the fourth control component and the ground, and the output end of the voltage division and current limiting unit is respectively connected with the first end and the second end of the second isolation unit, the third end of the second isolation unit is connected with the switch quantity signal input channel, and the fourth end of the second isolation unit is grounded.

[0011] Preferably, the switch quantity input circuit further comprises a unidirectional conduction component, the unidirectional conduction component comprises a third diode and a fourth diode, the positive pole of the third diode is connected with the power supply, the negative pole of the third diode and the negative pole of the fourth diode are both connected with one end of a resistor, and the positive pole of the fourth diode is connected with the first input contact.

[0012] Preferably, the switch quantity input circuit is connected with the rectifier bridge at the input port, for adjusting the external input signal into a unidirectional direct current signal, driving the first isolation unit and the second isolation unit, monitoring the dry contact, open source, open drain and alternating current signal, and realizing the detection of alternating current, source type and drain type signals.

[0013] Preferably, the first control component, the second control end, the third control end and the fourth control end are a first switch, a second switch, a third switch and a fourth switch.

[0014] Preferably, the first control component, the second control end, the third control end and the fourth control end all comprise any one of a switch, a MOS tube, a triode, a relay and an optocoupler.

[0015] As preferably, the voltage division current limiting unit comprises a first resistor, a second resistor and a third resistor, the power amplification circuit comprises a triode, one end of the first resistor and one end of the second resistor are connected with the negative electrode of the second diode, the other end of the first resistor is connected with the base of the triode, the emitter of the triode is connected with the fourth control component and grounded, the collector of the triode is connected with the first end of the first isolation unit, the other end of the second resistor is connected with one end of the third resistor and the second end of the second isolation unit respectively, the other end of the third resistor is connected with the fourth control component and grounded.

[0016] As preferably, the power amplification circuit comprises any one of triode, MOS tube, operational amplifier and comparator.

[0017] As preferably, the first isolation unit and the second isolation unit each comprise any one of optical coupling, magnetic isolation or capacitive isolation device.

[0018] The application further provides a detection method of the bidirectional digital quantity input device with the self-diagnosis function, comprising:

[0019] A state table is established based on states generated when the external dry contact signal is input, and the working state of the channel is determined according to the state table.

[0020] The input channel, the diagnosis channel, the wiring and the excitation bypass health state diagnosis of the on-off quantity input channel are carried out through the input / output and the input / output corresponding relationship.

[0021] The third switch and the fourth switch are controlled to be closed to connect the power supply to the on-off quantity input channel, the dry contact signal is decomposed into the channel excitation signal with different duty cycles and the contact excitation signal by controlling the mutual exclusion of the first switch and the second switch to be closed and opened, the internal optical coupling is driven to output the square wave with different duty cycles, and thus the diagnosis of the channel is realized, and the diagnosis covers the external disconnection, the channel open circuit, the channel short circuit, the diagnosis channel open circuit and the diagnosis channel short circuit fault.

[0022] As preferably, the input channel, the diagnosis channel, the wiring and the excitation bypass health state diagnosis of the on-off quantity input channel carried out through the input / output and the input / output corresponding relationship further comprise:

[0023] When the measured sensor has no output, the first switch and the fourth switch are controlled to be closed to provide the excitation signal for the sensor channel, and thus the circuit integrity of the channel except the rectifier bridge is detected; and / or,

[0024] When the preset branch is provided at the sensor position to be detected, the first switch and the second switch are controlled to be opened and closed alternately, so that the sensor output is excited, the internal isolation unit keeps outputting high, the sensor does not output, the internal broken line detection first isolation unit outputs high, the channel detection second isolation unit outputs a square wave, the internal broken line isolation unit outputs a square wave when the sensor power fails, and / or

[0025] A third switch is arranged on the broken line detection first isolation unit, and when an external signal is accessed, the third switch is opened to determine whether the broken line detection circuit is short-circuited.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] The present application provides a low-cost broken line detection method for a digital quantity output circuit with comprehensive diagnostic coverage. A small number of devices are used to solve the access and diagnosis of multiple signals, solve the switch quantity signal compatibility problem, channel monitoring problem and external wiring fault monitoring problem of multiple signal systems in the field of industrial automation, and effectively improve the diagnostic coverage of the product.

[0028] The switch quantity input circuit of the present application adds a rectifier bridge at the input channel port part, adjusts the external input signal to a unidirectional direct current signal for driving the isolation devices OP1 and OP2, and realizes the monitoring of dry contacts, open sources, open leaks and alternating current signals. By controlling the switch, the channel fault diagnosis and broken line diagnosis are realized.

[0029] The present application can meet the switch quantity access of multiple signal systems in the field of industrial control, support the measurement of channel fault states when supporting signal access, realize channel level fault diagnosis, and the diagnostic state covers channel broken line, sensor power failure, channel open circuit, channel short circuit and even the fault detection of the diagnostic circuit. The diagnostic coverage far exceeds that of the existing switch quantity fault diagnosis circuit. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Fig. 1 is a schematic diagram of the principle when a dry contact signal is accessed in the embodiment of the present application;

[0031] Figure 2 Fig. 2 is a schematic diagram of the principle when an open source, open leak and alternating current signal are accessed in the embodiment of the present application. DETAILED DESCRIPTION

[0032] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0033] Embodiment one

[0034] As Figures 1-2 described, the present application provides a bidirectional digital input device with self-diagnosis function, comprising: on-off input circuit and on-off diagnosis circuit, the on-off diagnosis circuit comprises rectifier bridge B1, excitation control unit, voltage division and current limiting unit, power amplifier circuit, first isolation unit OP1 and second isolation unit OP2, the rectifier bridge B1, excitation control unit, voltage division and current limiting unit, power amplifier circuit, first isolation unit OP1 and second isolation unit OP2 are connected, for realizing the cut-in and shielding of internal and external excitation by controlling switch; the excitation control unit used in the embodiment refers to the external excitation control unit of the equivalent input circuit of the first switch K1, the second switch K2, the third switch K3 and the fourth switch K4, and the excitation control unit can also be other devices other than MOS tube, triode, relay and optocoupler; the voltage division and current limiting unit used in the embodiment is the voltage division, current division and current limiting unit of the input circuit composed of the first resistor R1, the second resistor R2 and the third resistor R3, including but not limited to resistors, capacitors and other devices; the power amplifier circuit used in the embodiment is the power amplifier circuit of the broken line signal composed of the triode T1, and the power amplifier circuit can also be triode, MOS tube, operational amplifier and comparator; the first isolation unit OP1 and the second isolation unit OP2 can be but are not limited to optocoupler, magnetic isolation and capacitive isolation devices.

[0035] The excitation control unit comprises a first control component, a second control component, a third control component and a fourth control component, one end of the first control component, the second control component, the third control component and the fourth control component is connected with the power supply, the other end of the first control component is connected with the anode of the first diode, the other end of the second control component is connected with the anode of the second diode, the voltage division and current limiting unit, the power amplifier circuit, the second isolation unit and the fourth control component are connected and grounded, the other end of the third control component is connected with the first isolation unit;

[0036] The first control component, the second control end, the third control end and the fourth control end used in the embodiment are the first switch K1, the second switch K2, the third switch K3 and the fourth switch K4. The first control component, the second control end, the third control end and the fourth control end all include any one of a switch, a MOS tube, a triode, a relay and an optocoupler.

[0037] The switch quantity input circuit includes a resistor and a switch, and two ends of the switch are connected with two ends of the resistor respectively and are connected to the switch quantity diagnosis circuit.

[0038] The circuit further includes a first input contact, a second input contact, a third input contact, at least one switch quantity signal input channel and at least one disconnection detection channel.

[0039] One end of the first input contact is connected with one end of the switch quantity input circuit, and the other end of the first input contact is connected with a negative electrode of the first diode, the first control component such as K1 and a power supply. One end of the second input contact is connected with the other end of the switch quantity input circuit, and the other end of the second input contact is connected with a first alternating current input end of the rectifier bridge B1. The third input contact is connected with a second alternating current input end of the rectifier bridge B1. A first direct current output end of the rectifier bridge B1 is connected with the fourth control component such as K4 and grounded. A second direct current output end of the rectifier bridge B1 is connected with a negative electrode of the second diode, the second control component such as K2 and a power supply. The second direct current output end of the rectifier bridge B1 is connected with an input end of the voltage division and current limiting unit and an input end of the power amplification circuit. An output end of the power amplification circuit is connected with a first end of the first isolation unit OP1. A second end of the first isolation unit OP1 is connected with the third control component such as K3 and a power supply. A third end of the first isolation unit OP1 is connected with the disconnection detection channel. A fourth end of the first isolation unit is grounded. The other output end of the power amplification circuit is connected with the fourth control component such as K4 and grounded. Output ends of the voltage division and current limiting unit are connected with a first end and a second end of the second isolation unit respectively. A third end of the second isolation unit OP2 is connected with the switch quantity signal input channel. A fourth end of the second isolation unit OP2 is grounded.

[0040] The first AC input end and the second AC input end of the rectifier bridge B1 refer to the upper pins of the rectifier bridge B1, and the first DC output end and the second DC output end of the rectifier bridge B1 refer to the left pin and the right pin of the rectifier bridge B1. The first end, the second end, the third end and the fourth end of the first isolation unit OP1 refer to the lower left pin, the upper left pin, the upper right pin and the lower right pin on the OP1 module. The first end, the second end, the third end and the fourth end of the second isolation unit OP2 refer to the lower left pin, the upper left pin, the upper right pin and the lower right pin on the OP2 module.

[0041] The voltage division and current limiting unit comprises a first resistor R1, a second resistor R2 and a third resistor R3, and the power amplification circuit comprises a triode T1, one end of the first resistor R1 and one end of the second resistor R2 are connected with the negative electrode of the second diode, the other end of the first resistor R1 is connected with the base of the triode, the emitter of the triode is connected with the fourth control component such as K4 and grounded, the collector of the triode is connected with the first end of the first isolation unit OP1, the other end of the second resistor R2 is connected with one end of the third resistor R3 and the second end of the second isolation unit OP2 respectively, and the other end of the third resistor R3 is connected with the fourth control component such as K4 and grounded.

[0042] The switch quantity input circuit further comprises a one-way conduction component, the one-way conduction component comprises a third diode and a fourth diode, the positive electrode of the third diode is connected with a power supply, the negative electrode of the third diode and the negative electrode of the fourth diode are connected with one end of a resistor, and the positive electrode of the fourth diode is connected with the first input contact.

[0043] The switch quantity input circuit is connected with the rectifier bridge B1 at the input port, is used for adjusting an external input signal into a one-way DC signal, driving the first isolation unit OP1 and the second isolation unit OP2, monitoring dry contacts, open sources, open leaks and AC signals, and realizing detection of AC, source type and drain type signals.

[0044] The power amplification circuit comprises any one of a triode, a MOS tube, an operational amplifier and a comparator.

[0045] The first isolation unit OP1 and the second isolation unit OP2 each comprise any one of an optical coupler, a magnetic isolation device or a capacitive isolation device.

[0046] The switch quantity input circuit of the present application adds a rectifier bridge B1 at the input channel port part, adjusts an external input signal into a one-way DC signal for driving the first isolation unit OP1 and the second isolation unit OP2, realizes monitoring of dry contacts, open sources, open leaks and AC signals, and realizes channel fault diagnosis and broken wire diagnosis through control of switches to realize cutting in and shielding of internal and external excitation.

[0047] The scheme provided by the application can be realized by using domestic discrete components, and on one hand, the scheme solves the defects of the existing digital input circuit detection circuit, such as complexity and small coverage; on the other hand, the scheme realizes some domestic self-controllable requirements in the field of automatic control.

[0048] When the circuit is externally connected with the dry contact signal, the circuit specifically operates as follows:

[0049] State 1: K1, K2, K3 and K4 are kept open: OP1 and OP2 have no output, it is confirmed that the broken line diagnosis channel and the input channel have normal output state, and the output indicates that the channel is faulty, and the subsequent processing after the joint can locate the fault point;

[0050] State 2: K2, K3 and K4 are closed, OP1 and OP2 output, it is confirmed that the broken line diagnosis channel and the input channel have normal output state, otherwise the output indicates that the channel is faulty, and the subsequent processing after the joint can locate the fault point;

[0051] State 3: K2 and K4 are kept closed, and K3 is open: OP1 has no output, and OP2 outputs, it is confirmed that the broken line diagnosis channel correctly reacts to the input state, and OP1 cannot react to the input state, which indicates that the broken line diagnosis channel is faulty, and the diagnosis information is not reliable;

[0052] State 4: K1, K3 and K4 are closed, and K2 is open:

[0053] State 41: when the bypass circuit is good and the wiring is correct: the dry contact is closed, OP1 and OP2 output, the dry contact is broken, OP1 keeps output, and OP2 has no output, which indicates that the wiring is correct, and the rectifier bridge B1 is good

[0054] State 42: when the bypass circuit is faulty, the wiring is disconnected or the rectifier bridge is open: the dry contact is closed, OP1 and OP2 output, the dry contact is broken, and OP1 and OP2 have no output, the diagnosis results of states 2 and 3 after the joint can confirm the broken line fault or the diagnosis fault.

[0055] When the active signal is externally connected, the circuit adopts the circuit shown in Figure 2 The specific operation is as follows:

[0056] State 5: K1, K2, K3 and K4 are open: external excitation output: OP1 has no output, and OP2 outputs; there is no excitation, and OP1 and OP2 have no output, which correctly reacts to the excitation. If OP1 has output, it indicates that the diagnosis branch K3 has short circuit fault, and the diagnosis is not reliable, and if OP2 has output when there is no excitation, the channel circuit is faulty.

[0057] State 6: K1 is disconnected, K2, K3, K4 are closed: whether there is an excitation or not, OP1 and OP2 are outputted; if OP1 is not outputted, the open circuit fault of the detection channel is detected, and if OP2 is not outputted, the channel circuit fault is detected;

[0058] State 7: K1 and K2 are disconnected, K3 and K4 are conducted:

[0059] State 71: when the external circuit is correct and the power excitation is correct, the external excitation output is outputted, OP1 and OP2 are outputted, and when the external excitation is not outputted, OP1 is outputted and OP2 is not outputted;

[0060] State 72: when the external circuit is correct and the power excitation is faulty, the external excitation output is outputted, OP1 and OP2 are outputted, and when the external excitation is not outputted, OP1 and OP2 are not outputted.

[0061] State 8: K1, K3 and K4 are closed, and K2 is disconnected: the external excitation output is outputted, OP1 and OP2 are outputted, and when the external excitation is not outputted, OP1 is outputted and OP2 is not outputted, but when the external excitation is not outputted, OP1 and OP2 are not outputted; internal output to the outside

[0062] According to the above states, a state table is established, the working state of the channel can be determined through the state table, and the input channel, the diagnosis channel, the wiring and the excitation bypass health state diagnosis of the on-off quantity input channel can be carried out through the input / output and the corresponding relationship.

[0063] The application further provides a bidirectional digital quantity input system / module with a self-diagnosis function, which comprises the bidirectional digital quantity input device with a self-diagnosis function as described in the embodiments of the application.

[0064] The application further provides a bidirectional digital quantity input device with a self-diagnosis function, which comprises the bidirectional digital quantity input circuit with a self-diagnosis function as described in the embodiments of the application. The functional principles are as described in the first embodiment of the application, and are not described here again.

[0065] Embodiment two

[0066] Based on the same concept, the application further provides a detection method of the bidirectional digital quantity input device with a self-diagnosis function, which comprises:

[0067] Step S1: a state table is established based on the state generated when the external dry contact signal is outputted, and the working state of the channel is determined according to the state table;

[0068] Step S2: the input channel, the diagnosis channel, the wiring and the excitation bypass health state diagnosis of the on-off quantity input channel are carried out through the input / output and the corresponding relationship between the input and the output;

[0069] Wherein, the control third switch K3, fourth switch K4 closed will power access switch quantity input channel, through in control first switch K1 and second switch K2 mutual exclusion closed, open, the continuous input dry contact signal is decomposed into duty cycle different channel excitation signal and contact excitation signal, drive internal optical coupling output duty cycle different square wave, thereby realizing the diagnosis of channel, diagnosis covers external broken line, channel open circuit, channel short circuit, diagnosis channel open circuit, diagnosis channel short circuit fault.

[0070] Specifically, the input channel, diagnosis channel, wiring, excitation bypass health status diagnosis of the switch quantity input channel through the input / output and input / output corresponding relationship further comprises:

[0071] When the measured sensor has no output, the closure of the first switch K1 and the fourth switch K4 provides an excitation signal for the sensor channel, thereby detecting the integrity of the circuit except the rectifier bridge; and / or,

[0072] When the measured sensor position provides a preset branch, during testing, the closure of the first switch K1 and the second switch K2 in mutual exclusion realizes the output of the internal isolation unit when the sensor outputs excitation, realizes the output of the internal broken line detection first isolation unit OP1 when the sensor does not output, realizes the output of the channel detection second isolation unit OP2, realizes the output of the internal broken line isolation unit when the sensor power fails; and / or, the branch is composed of current limiting devices and unidirectional conduction devices.

[0073] A third switch K3 is arranged on the broken line detection first isolation unit OP1, and when an external signal is accessed, the third switch K3 is opened to determine whether the broken line detection circuit is short-circuited.

[0074] The present application can meet the switch quantity access of various signal systems in the field of industrial control, support the measurement of channel fault status when supporting signal access, realize channel level fault diagnosis, and the diagnosis state covers channel broken line, sensor power failure, channel open circuit, channel short circuit, and even the diagnosis circuit is also developed for fault detection, and the diagnosis coverage rate far exceeds that of the existing switch quantity fault diagnosis circuit.

[0075] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A bidirectional digital input device with self-diagnostic function, characterized in that, include: The circuit includes a switch input circuit and a switch diagnostic circuit. The switch diagnostic circuit includes a rectifier bridge, an excitation control unit, a voltage divider and current limiting unit, a power amplifier circuit, a first isolation unit, and a second isolation unit. The rectifier bridge, excitation control unit, voltage divider and current limiting unit, power amplifier circuit, first isolation unit, and second isolation unit are connected to achieve the input and shielding of internal and external excitations through a control switch. The excitation control unit includes a first control component, a second control component, a third control component, and a fourth control component. One end of each of the first, second, third, and fourth control components is connected to a power supply. The other end of the first control component is connected to the anode of a first diode. The other end of the second control component is connected to the anode of a second diode, the voltage divider and current limiting unit, the power amplifier circuit, the second isolation unit, and the fourth control component, and is grounded. The other end of the third control component is connected to the first isolation unit. The digital input circuit includes a resistor and a switch, with the two ends of the switch connected to the two ends of the resistor and connected to the digital diagnostic circuit. Furthermore, the circuit also includes a first input contact, a second input contact, a third input contact, at least one switch signal input channel, and at least one open circuit detection channel. One end of the first input contact is connected to one end of the digital input circuit, and the other end of the first input contact is connected to the cathode of the first diode, the first control component, and a power supply. One end of the second input contact is connected to the other end of the digital input circuit, and the other end of the second input contact is connected to the first AC input terminal of the rectifier bridge. The third input contact is connected to the second AC input terminal of the rectifier bridge. The first DC output terminal of the rectifier bridge is connected to the fourth control component and grounded. The second DC output terminal of the rectifier bridge is connected to the cathode of the second diode, the second control component, and a power supply. The voltage divider and current limiting unit is connected to the input terminal of the voltage divider and current limiting unit and the input terminal of the power amplifier circuit. The output terminal of the power amplifier circuit is connected to the first terminal of the first isolation unit. The second terminal of the first isolation unit is connected to the third control component and connected to the power supply. The third terminal of the first isolation unit is connected to the open circuit detection channel. The fourth terminal of the first isolation unit is grounded. The other output terminal of the power amplifier circuit is connected to the fourth control component and grounded. The output terminal of the voltage divider and current limiting unit is connected to the first and second terminals of the second isolation unit. The third terminal of the second isolation unit is connected to the switch signal input channel. The fourth terminal of the second isolation unit is grounded. A status table is established according to the preset status. The working status of the channel is determined by the status table. The health status diagnosis of the input channel, diagnostic channel, wiring, and excitation bypass of the switch input channel is carried out by input / output and their corresponding relationship.

2. The bidirectional digital input device with self-diagnostic function as described in claim 1, characterized in that, The switch input circuit also includes a unidirectional conduction component, which includes a third diode and a fourth diode. The positive terminal of the third diode is connected to a power supply, and the negative terminals of the third diode and the fourth diode are both connected to one end of a resistor. The positive terminal of the fourth diode is connected to the first input contact.

3. A bidirectional digital input device with self-diagnostic function as described in claim 1 or 2, characterized in that, The digital input circuit is connected to the rectifier bridge at the input port to adjust the external input signal into a unidirectional DC signal, drive the first isolation unit and the second isolation unit, and monitor dry contacts, open source, open drain and AC signals to realize the detection of AC, source type and drain type signals.

4. A bidirectional digital input device with self-diagnostic function as described in claim 1, characterized in that, The first control component, the second control terminal, the third control terminal, and the fourth control terminal are the first switch, the second switch, the third switch, and the fourth switch.

5. A bidirectional digital input device with self-diagnostic function as described in claim 1, characterized in that, The first control component, the second control terminal, the third control terminal, and the fourth control terminal are all included as any one of the following: switch, MOSFET, transistor, relay, and optocoupler.

6. A bidirectional digital input device with self-diagnostic function as described in claim 1, characterized in that, The voltage divider and current limiting unit includes a first resistor, a second resistor, and a third resistor. The power amplifier circuit includes a transistor. One end of the first resistor and one end of the second resistor are both connected to the negative terminal of the second diode. The other end of the first resistor is connected to the base of the transistor. The emitter of the transistor is connected to the fourth control component and grounded. The collector of the transistor is connected to the first end of the first isolation unit. The other end of the second resistor is connected to one end of the third resistor and the second end of the second isolation unit, respectively. The other end of the third resistor is connected to the fourth control component and grounded.

7. A bidirectional digital input device with self-diagnostic function as described in claim 1, characterized in that, The power amplifier circuit includes any one of transistors, MOSFETs, operational amplifiers, and comparators.

8. A bidirectional digital input device with self-diagnostic function as described in claim 1, characterized in that, Both the first isolation unit and the second isolation unit include any one of optocouplers, magnetic isolation devices, or capacitive isolation devices.

9. A detection method for a bidirectional digital input device with self-diagnostic function, characterized in that, A bidirectional digital input device with self-diagnostic function as described in claim 1, comprising: A status table is established based on the status generated by the external dry contact signal, and the channel working status is determined according to the status table. Health status diagnosis of digital input channels, diagnostic channels, wiring, and excitation bypass is carried out by input / output and input / output correspondence. Specifically, controlling the closing of the third and fourth switches connects the power supply to the switch input channel. By controlling the mutual exclusion of the first and second switches to close and open, the continuously input dry contact signal is decomposed into channel excitation signals and contact excitation signals with different duty cycles, driving the internal optocoupler to output square waves with different duty cycles, thereby realizing the diagnosis of the channel. The diagnosis covers external open circuit, channel open circuit, channel short circuit, and diagnoses channel open circuit and channel short circuit faults.

10. The detection method for a bidirectional digital input device with self-diagnostic function as described in claim 9, characterized in that, The method of conducting health status diagnosis of input channels, diagnostic channels, wiring, and excitation bypass of digital input channels through input / output and input / output correspondence also includes: When the sensor under test has no output, the opening and closing of the first and fourth switches are controlled to provide an excitation signal to the sensor channel, thereby detecting the integrity of the channel circuit except for the rectifier bridge; and / or, When a preset branch is provided at the location of the sensor under test, by controlling the closing of the mutually exclusive switches of the first and second switches, the internal isolation unit maintains a high output when the sensor is outputting an excitation; when the sensor is not outputting, the internal disconnection detection first isolation unit outputs a high output, and the channel detection second isolation unit outputs a square wave; when the sensor power supply fails, the internal disconnection isolation unit outputs a square wave; and / or, A third switch is installed on the first isolation unit for disconnection detection. When an external signal is input, the disconnection detection circuit is short-circuited by disconnecting the third switch.

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