Analog input signal disconnection detection circuit

Abstract

The invention provides an analog input signal disconnection detection circuit, which comprises a front-end input circuit, a voltage following circuit and a dual-power negative voltage bias circuit, and is characterized in that the voltage following circuit is arranged between the front-end input circuit and the dual-power negative voltage bias circuit; the front-end input circuit is configured to realize analog quantity detection of a voltage single-ended signal, a voltage differential signal and a current signal; the voltage follower circuit is configured to be capable of realizing consistency of input voltage and output voltage; the dual-power-supply negative voltage bias circuit is configured to be capable of converting a single-end or differential voltage in a disconnection state into a voltage threshold different from a normal state. According to the invention, disconnection detection of single-ended or differential input of voltage or current analog signals is realized, the normal or disconnection state of the input signals can be accurately judged, the diagnosis requirement of an industrial field on detection equipment is met, and the reliability and safety of a system are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial control, in particular to a kind of analog input signal wire break detection circuit. BACKGROUND

[0002] In the field of industrial control, analog input signal is used for continuous monitoring of physical parameters (such as temperature, pressure, flow, etc.), and its input range needs to match the sensor, transmitter and PLC / DCS module. Common analog input range in industrial field includes voltage signal input and current signal input, among which voltage signal input range includes single polarity (0V~10V DC) and bipolar input (-10V~+10V DC), and current signal input range is 4~20mA DC.

[0003] When analog detection equipment is applied in industrial field, under the condition of vibration or impact, the external wiring of the equipment may be loose or fall off, etc. If the signal wire break is not detected, the system may misjudge as actual value abnormal, affecting monitoring accuracy or causing equipment malfunction, thereby affecting system safety, stability and reliability. Therefore, wire break detection of analog signal is the core function to ensure safe and stable operation of the system.

[0004] When the voltage signal input range is -10V~+10V DC, the detected signal voltage after wire break is 0V, which is equal to the normal 0V input signal voltage without wire break, and it cannot be distinguished whether it is wire break or real zero signal, resulting in blind area of voltage threshold detection, so wire break detection under "0V input" state cannot be performed.

[0005] Traditional analog quantity acquisition generally directly uses operational circuit, ADC conversion circuit and its peripheral circuit to realize, but the acquisition circuit can only detect wire break of voltage input analog quantity greater than 0V, and cannot effectively judge whether the device cable is broken under "0V input" state, so it cannot play a full range monitoring role for the device, and the application scenario is limited. SUMMARY

[0006] The present application aims to solve at least one of the technical problems existing in the prior art, and provides an analog input signal wire break detection circuit.

[0007] In a first aspect, an analog input signal wire break detection circuit is provided, which includes a front-end input circuit, a voltage follower circuit and a dual-power negative voltage bias circuit, the voltage follower circuit is arranged between the front-end input circuit and the dual-power negative voltage bias circuit;

[0008] The front-end input circuit is configured to realize analog detection of voltage single-ended signal, voltage differential signal and current signal;

[0009] The voltage follower circuit is configured to enable the input voltage to be consistent with the output voltage.

[0010] The dual-power negative voltage bias circuit is configured to convert the single-ended or differential voltage in the disconnected state into a voltage threshold different from the normal state.

[0011] In some embodiments, the analog input signal disconnection detection circuit of the present application further comprises a signal input positive terminal, a signal input negative terminal, a signal output positive terminal, and a signal output negative terminal, the voltage follower circuit comprises a first voltage follower and a second voltage follower, the dual-power negative voltage bias circuit has a first input terminal, a second input terminal, and a first output terminal and a second output terminal, the input terminal of the first voltage follower is connected to the signal input positive terminal, the output terminal of the first voltage follower is connected to the first input terminal of the dual-power negative voltage bias circuit, the first output terminal of the dual-power negative voltage bias circuit is connected to the signal output positive terminal, the input terminal of the second voltage follower is connected to the signal input negative terminal, the output terminal of the second voltage follower is connected to the second input terminal of the dual-power negative voltage bias circuit, and the second output terminal of the dual-power negative voltage bias circuit is connected to the signal output negative terminal.

[0012] The front-end input circuit is connected to the signal input positive terminal and the signal input negative terminal.

[0013] In some embodiments, the front-end input circuit comprises a first pull-up branch, a first pull-down branch, and a current sampling branch, one end of the first pull-up branch is connected to the signal input positive terminal and the input terminal of the first voltage follower, the other end of the first pull-up branch is connected to a first positive power supply voltage, one end of the first pull-down branch is connected to the signal input negative terminal and the input terminal of the second voltage follower, the other end of the first pull-down branch is connected to a first negative power supply voltage, one end of the current sampling branch is connected to the signal input positive terminal and the input terminal of the first voltage follower, and the other end of the current sampling branch is connected to the signal input negative terminal and the input terminal of the first voltage follower.

[0014] In some embodiments, the first pull-up branch comprises a first resistor and a first switching switch SW1, and the first resistor and the first switching switch SW1 are connected in series on the first pull-up branch.

[0015] The first pull-down branch comprises a second resistor and a third switching switch, and the second resistor and the third switching switch are connected in series on the first pull-down branch.

[0016] The current sampling branch comprises an eleventh resistor and a second switching switch, and the eleventh resistor and the second switching switch are connected in series on the current sampling branch.

[0017] In some embodiments, the first switch is configured to receive a first control signal and, in response to the first control signal, perform an open or closed operation;

[0018] The second switch is configured to receive a second control signal and, in response to the second control signal, perform an open or closed operation.

[0019] The third switch is configured to receive a third control signal and, in response to the third control signal, perform an open or closed operation.

[0020] The first voltage follower includes a first operational amplifier, the non-inverting input terminal of the first operational amplifier is connected to the positive input terminal of the signal, the inverting input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier, the positive power supply terminal of the first operational amplifier is connected to a first positive power supply voltage, and the negative power supply terminal of the first operational amplifier is connected to a first negative power supply voltage.

[0021] The second voltage follower includes a second operational amplifier, the non-inverting input of the second operational amplifier is connected to the negative input terminal of the signal, the inverting input of the second operational amplifier is connected to the output terminal of the second operational amplifier, the positive power supply terminal of the second operational amplifier is connected to a first positive power supply voltage, and the negative power supply terminal of the second operational amplifier is connected to a first negative power supply voltage.

[0022] In some embodiments, the dual-power negative bias circuit includes a first signal transmission branch, a second signal transmission branch, a second pull-up branch, a second pull-down branch, a third pull-up branch, and a third pull-down branch. One end of the first signal transmission branch is connected to the output terminal of the first voltage follower, and the other end of the first signal transmission branch is connected to the positive signal output terminal. One end of the second pull-up branch is connected to the positive signal output terminal, and the other end of the second pull-up branch is connected to the second positive power supply voltage. One end of the second pull-down branch is connected to the positive signal output terminal, and the other end of the second pull-down branch is connected to the second negative power supply voltage. One end of the second signal transmission branch is connected to the output terminal of the second voltage follower, and the other end of the second signal transmission branch is connected to the negative signal output terminal. One end of the third pull-up branch is connected to the negative signal output terminal, and the other end of the third pull-up branch is connected to the second positive power supply voltage. One end of the third pull-down branch is connected to the negative signal output terminal, and the other end of the third pull-down branch is connected to the second negative power supply voltage.

[0023] In some embodiments, the first signal transmission branch includes a third resistor, which is connected in series in the first signal transmission branch;

[0024] The second signal transmission branch includes a fourth resistor, which is connected in series in the second signal transmission branch.

[0025] The second pull-up branch includes a fifth resistor, which is connected in series in the second pull-up branch;

[0026] The second pull-down branch includes a ninth resistor, which is connected in series in the second pull-down branch;

[0027] The third pull-up branch includes a sixth resistor, which is connected in series in the third pull-up branch;

[0028] The third pull-down branch includes a tenth resistor, which is connected in series in the third pull-down branch.

[0029] In some embodiments, the dual-power negative bias circuit includes a fourth pull-down branch and a fifth pull-down branch. One end of the fourth pull-down branch is connected to the output of the first voltage follower, and the other end of the fourth pull-down branch is connected to the second negative power supply voltage. One end of the fifth pull-down branch is connected to the output of the second voltage follower, and the other end of the fifth pull-down branch is connected to the second negative power supply voltage.

[0030] In some embodiments, the fourth pull-down branch includes a seventh resistor, which is connected in series in the fourth pull-down branch;

[0031] The fifth pull-down branch includes an eighth resistor, which is connected in series in the fifth pull-down branch.

[0032] In some embodiments, the analog input signal disconnection detection circuit of the present invention further includes an ADC conversion circuit, wherein the input terminal of the ADC conversion circuit is connected to the output terminal of the dual power supply negative voltage bias circuit, and the output terminal of the ADC conversion circuit is connected to the main control module.

[0033] The present invention has at least the following beneficial effects:

[0034] The analog input signal disconnection detection circuit provided by this disclosure, through the use of a voltage follower, analog switch, and dual power supply negative voltage bias design, realizes disconnection detection of single-ended or differential input of voltage or current analog signals. It can accurately determine the normal or disconnection state of the input signal, meet the diagnostic needs of industrial field testing equipment, and improve the reliability and safety of the system. Attached Figure Description

[0035] Figure 1 A schematic block diagram of an analog input signal disconnection detection circuit provided in an embodiment of this disclosure;

[0036] Figure 2 A circuit diagram of an analog input signal disconnection detection circuit provided in an embodiment of this disclosure;

[0037] Figure 3 A circuit diagram (positive terminal voltage input) of an analog input signal disconnection detection circuit for realizing single-ended voltage signal detection is provided for an embodiment of this disclosure.

[0038] Figure 4 A circuit diagram (negative terminal voltage input) of another analog input signal disconnection detection circuit for realizing single-ended voltage signal detection is provided for an embodiment of this disclosure.

[0039] Figure 5 A circuit diagram of an analog input signal disconnection detection circuit for implementing differential voltage signal detection is provided in an embodiment of this disclosure;

[0040] Figure 6 This is a circuit diagram of an analog input signal disconnection detection circuit for realizing current signal detection, provided as an embodiment of the present disclosure. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solutions of the present invention, exemplary embodiments of the present invention are described below in conjunction with the accompanying drawings, including various details of the embodiments of the present invention to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0042] Where there is no conflict, the various embodiments of the present invention and the features thereof may be combined with each other.

[0043] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0044] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms “a” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded. Terms such as “connected” or “linked” are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect.

[0045] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meaning in the context of the relevant art and the invention, and will not be interpreted as having an idealized or overly formal meaning unless expressly so defined herein.

[0046] In the field of industrial control, analog input signals are used for continuous monitoring of physical parameters (such as temperature, pressure, flow rate, etc.), and their input range needs to be matched with sensors, transmitters, and PLC / DCS modules. Common analog input ranges in the industrial control industry are divided into voltage signal input and current signal input. Voltage signal input ranges include unipolar (0V~10V DC) and bipolar (-10V~+10V DC), while current signal input ranges are 4~20mA DC.

[0047] When analog signal detection equipment is used in industrial fields, vibration or impact conditions may cause poor contact or loosening of external wiring. If the signal disconnection is not detected, the system may misjudge the actual value as abnormal, affecting the monitoring accuracy or causing equipment malfunction, thus affecting the safety, stability and reliability of the system. Therefore, the detection of analog signal disconnection is a core function to ensure the safe and stable operation of the system.

[0048] When the voltage signal input range is -10V to +10V DC, the signal voltage detected after the wire is disconnected is 0V, which is equal to the normal 0V input signal voltage when the wire is not disconnected. It is impossible to distinguish between the disconnection and the true zero signal, resulting in a blind zone in the voltage threshold detection. Therefore, it is impossible to detect the disconnection under the "0V input" state.

[0049] Traditional analog signal acquisition typically uses arithmetic circuits, ADC conversion circuits, and their peripheral circuits. However, this acquisition circuit can only detect disconnections for analog input voltages greater than 0V. It cannot effectively determine whether the device connection cable is broken when the input voltage is 0V. Therefore, it cannot provide comprehensive monitoring of the device, and its application scenarios are somewhat limited.

[0050] As industrial control systems place higher demands on the diagnostic functions of analog input detection in programmable logic controllers (PLCs), this invention proposes an analog input signal disconnection detection circuit based on a voltage follower to achieve rapid response and diagnosis of analog signal disconnection in PLCs. This circuit can detect disconnections in analog input signals such as voltage or current in PLCs.

[0051] In order to effectively improve or even completely solve the above-mentioned problems in the related technologies, this disclosure provides corresponding solutions.

[0052] Figure 1 This is a schematic diagram of the circuit structure of an analog input signal disconnection detection circuit provided in an embodiment of this disclosure. Figure 1As shown, the analog input signal disconnection detection circuit includes: a front-end input circuit, a voltage follower circuit, and a dual-power negative voltage bias circuit. The voltage follower circuit is located between the front-end input circuit and the dual-power negative voltage bias circuit.

[0053] The front-end input circuit is configured to detect analog signals including single-ended voltage signals, differential voltage signals, and current signals.

[0054] The voltage follower circuit is configured to ensure that the input follower voltage and the output follower voltage are consistent. When the signal is not disconnected, the input voltage signal and the output voltage signal are consistent. After passing through the voltage follower, the differential voltage at the output signal terminal is within the normal operating voltage range, thereby achieving accurate measurement of the input voltage. When any input signal is disconnected, the differential input voltage is pulled up to a bias voltage through pull-up and pull-down resistors. After passing through the voltage follower, the differential voltage at the output signal terminal deviates from the normal operating voltage range. A threshold comparison can be used to determine if a disconnection has occurred.

[0055] The dual-power negative bias circuit is configured to convert single-ended or differential voltage in the disconnected state into a voltage threshold different from the normal state.

[0056] The dual-power negative bias circuit uses dual-power bias voltage and bias resistor to convert the open-circuit voltage signal into a voltage threshold different from the normal state, forming an abnormal voltage with significant identification, so that the ADC chip can detect this abnormal voltage and thus realize rapid diagnosis of open circuit.

[0057] In some embodiments, see Figure 2 The analog input signal disconnection detection circuit of the present invention further includes a positive input terminal AIN+, a negative input terminal AIN-, a positive output terminal ANINP, and a negative output terminal ANIMM. The voltage follower circuit includes a first voltage follower and a second voltage follower. The dual-power negative bias circuit has a first input terminal, a second input terminal, a first output terminal, and a second output terminal. The input terminal of the first voltage follower is connected to the positive input terminal, the output terminal of the first voltage follower is connected to the first input terminal of the dual-power negative bias circuit, the first output terminal of the dual-power negative bias circuit is connected to the positive output terminal, the input terminal of the second voltage follower is connected to the negative input terminal, the output terminal of the second voltage follower is connected to the second input terminal of the dual-power negative bias circuit, and the second output terminal of the dual-power negative bias circuit is connected to the negative output terminal.

[0058] The front-end input circuit is connected to the positive terminal and the negative terminal of the signal input.

[0059] The voltage follower circuit also includes a first positive power supply voltage VDD1 and a first negative power supply voltage VSS1.

[0060] The dual-power negative bias circuit also includes a second positive power supply voltage VDD2 and a second negative power supply voltage VSS2.

[0061] In some embodiments, the front-end input circuit includes a first pull-up branch, a first pull-down branch, and a current sampling branch. One end of the first pull-up branch is connected to the positive terminal of the signal input and the input terminal of the first voltage follower, and the other end of the first pull-up branch is connected to a first positive power supply voltage. One end of the first pull-down branch is connected to the negative terminal of the signal input and the input terminal of the second voltage follower, and the other end of the first pull-down branch is connected to a first negative power supply voltage. One end of the current sampling branch is connected to the positive terminal of the signal input and the input terminal of the first voltage follower, and the other end of the current sampling branch is connected to the negative terminal of the signal input and the input terminal of the first voltage follower.

[0062] In some embodiments, the first pull-up branch includes a first resistor R1 and a first switching switch SW1, wherein the first resistor R1 and the first switching switch SW1 are connected in series in the first pull-up branch.

[0063] The first pull-down branch includes a second resistor R2 and a third switch SW3, which are connected in series in the first pull-down branch;

[0064] The current sampling branch includes an eleventh resistor R11 and a second switching switch SW2, which are connected in series in the current sampling branch.

[0065] In some embodiments, the first switching switch SW1 is configured to receive a first control signal and, in response to the first control signal, perform an open or closed operation.

[0066] The second switch SW2 is configured to receive a second control signal and, in response to the second control signal, perform an open or closed operation.

[0067] The third switching switch SW3 is configured to receive a third control signal and, in response to the third control signal, perform an open or closed operation.

[0068] In some embodiments, the first switching switch SW1, the second switching switch SW2, and the third switching switch SW3 are all analog switches.

[0069] When a voltage signal is input, the first switch SW1 and the third switch SW3 are closed, and the second switch SW2 is opened, disconnecting resistor R11. Simultaneously, the pull-up resistors R1 and R2 at the differential signal input are connected to the circuit to provide a bias voltage for the voltage signal. When a current signal is input, the first switch SW1 and the third switch SW3 are opened, and the second switch SW2 is closed, disconnecting the pull-up resistors R1 and R2 at the differential signal input. Simultaneously, resistor R11 is connected to the circuit, thus achieving current detection. Resistor R11 is the current sensing resistor.

[0070] In some embodiments, the first voltage follower includes a first operational amplifier U1, the non-inverting input terminal of the first operational amplifier U1 is connected to the positive input terminal of the signal, the inverting input terminal of the first operational amplifier U1 is connected to the output terminal of the first operational amplifier U1, the positive power supply terminal of the first operational amplifier U1 is connected to a first positive power supply voltage, and the negative power supply terminal of the first operational amplifier U1 is connected to a first negative power supply voltage.

[0071] The second voltage follower includes a second operational amplifier U2. The non-inverting input terminal of the second operational amplifier U2 is connected to the negative input terminal of the signal, the inverting input terminal of the second operational amplifier U2 is connected to the output terminal of the second operational amplifier U2, the positive power supply terminal of the second operational amplifier U2 is connected to a first positive power supply voltage, and the negative power supply terminal of the second operational amplifier U2 is connected to a first negative power supply voltage.

[0072] In some embodiments, the dual-power negative bias circuit includes a first signal transmission branch, a second signal transmission branch, a second pull-up branch, a second pull-down branch, a third pull-up branch, and a third pull-down branch. One end of the first signal transmission branch is connected to the output terminal of the first voltage follower, and the other end of the first signal transmission branch is connected to the positive signal output terminal. One end of the second pull-up branch is connected to the positive signal output terminal, and the other end of the second pull-up branch is connected to the second positive power supply voltage. One end of the second pull-down branch is connected to the positive signal output terminal, and the other end of the second pull-down branch is connected to the second negative power supply voltage. One end of the second signal transmission branch is connected to the output terminal of the second voltage follower, and the other end of the second signal transmission branch is connected to the negative signal output terminal. One end of the third pull-up branch is connected to the negative signal output terminal, and the other end of the third pull-up branch is connected to the second positive power supply voltage. One end of the third pull-down branch is connected to the negative signal output terminal, and the other end of the third pull-down branch is connected to the second negative power supply voltage.

[0073] In some embodiments, the first signal transmission branch includes a third resistor R3, which is connected in series in the first signal transmission branch;

[0074] The second signal transmission branch includes a fourth resistor R4, which is connected in series in the second signal transmission branch.

[0075] The second pull-up branch includes a fifth resistor R5, which is connected in series in the second pull-up branch;

[0076] The second pull-down branch includes a ninth resistor R9, which is connected in series in the second pull-down branch;

[0077] The third pull-up branch includes a sixth resistor R6, which is connected in series in the third pull-up branch;

[0078] The third pull-down branch includes a tenth resistor R10, which is connected in series in the third pull-down branch.

[0079] In some embodiments, the dual-power negative bias circuit includes a fourth pull-down branch and a fifth pull-down branch. One end of the fourth pull-down branch is connected to the output of the first voltage follower, and the other end of the fourth pull-down branch is connected to the second negative power supply voltage. One end of the fifth pull-down branch is connected to the output of the second voltage follower, and the other end of the fifth pull-down branch is connected to the second negative power supply voltage.

[0080] In some embodiments, the fourth pull-down branch includes a seventh resistor R7, which is connected in series in the fourth pull-down branch;

[0081] The fifth pull-down branch includes an eighth resistor R8, which is connected in series in the fifth pull-down branch.

[0082] In some embodiments, the analog input signal disconnection detection circuit of the present invention further includes an ADC conversion circuit. The input terminal of the ADC conversion circuit is connected to the output terminal of the dual-power negative voltage bias circuit, and the output terminal of the ADC conversion circuit is connected to the main control module. The ADC conversion circuit is used to convert analog signals to digital signals.

[0083] The working principle of this invention is as follows: resistors R1, R2, R11, SW1, SW2 and SW3 form the front-end input circuit, voltages VDD2, VSS2 and operational amplifiers U1 and U2 form the voltage follower circuit, and resistors R3~R10 and voltages VDD2, VSS2 form the dual power supply negative voltage bias circuit. The positive input terminal AIN+ is connected to the non-inverting input terminal of operational amplifier U1, and is simultaneously pulled up to the positive power supply voltage VDD1 of operational amplifier U1 via switch SW1 and resistor R1. The output terminal of operational amplifier U1 is connected to the inverting input terminal of operational amplifier U1, forming the first voltage follower, and is simultaneously pulled down to the negative power supply voltage VSS2 of the dual power supply negative bias circuit via resistor R7. The output terminal 10 of operational amplifier U1 is also pulled up to the positive power supply voltage VDD2 of the dual power supply negative bias circuit via resistor R3 and resistor R5, and pulled down to the negative power supply voltage VSS2 of the dual power supply negative bias circuit via resistor R9. The positive input signal AIN+ is output as AINP after passing through the front-end input circuit, the first voltage follower, and the negative bias circuit.

[0084] The negative input terminal AIN- is connected to the non-inverting input terminal of operational amplifier U2, and is simultaneously pulled down to the negative power supply voltage VSS1 of operational amplifier U2 via switch SW2 and resistor R2. The output terminal of operational amplifier U2 is connected to the inverting input terminal of operational amplifier U2, forming a second voltage follower, and is simultaneously pulled down to the negative power supply voltage VSS2 of the dual power supply negative bias circuit via resistor R8. The output terminal 10 of operational amplifier U2 is also pulled up to the positive power supply voltage VDD2 of the dual power supply negative bias circuit via resistor R4 and resistor R6, and pulled down to the negative power supply voltage VSS2 of the dual power supply negative bias circuit via resistor R10. The AIN- negative input signal is output as AIMM after passing through the front-end input circuit, the second voltage follower, and the negative bias circuit.

[0085] When the input analog signal is a voltage signal, switch SW1 and switch SW3 are closed, switch SW2 is open, resistors R1 and R2 are connected in the circuit, and resistor R11 is disconnected.

[0086] When the input voltage signal is a single-ended signal and ranges from 0V to 10V, the open circuit detection circuit is as follows: Figure 3 As shown, AIN- is 0V, and AIN+ is 0V~10V. It can be calculated that when the signal is not disconnected, the voltage of AIMN is 0V, and the voltage range of AINP is 0.1AIN+, that is, 0V~1V. Therefore, the differential signal voltage output by this circuit, AINP-AINM, is 0V~1V.

[0087] When the input signal line AIN+ is disconnected, the voltage at the negative terminal of AIN- remains unchanged at 0V. AIN+ is pulled up to VDD1 via R1, and the calculated voltage of AIMN is still 0V. The voltage of AINP is 2.1V. Therefore, the differential signal voltage of the output ADC, AINP-AINM, is 2.1V. When the line is disconnected, the differential voltage (2.1V) detected by the ADC is outside the normal operating voltage range (0~1V), and the disconnection state can be detected.

[0088] When the input voltage signal is a single-ended signal and its range is -10V to 0V, the open circuit detection circuit is as follows: Figure 4 As shown, AIN- is -10V to 0V, and AIN+ is 0V. It can be calculated that when the signal is not disconnected, the ANIPP voltage is 0V, and the ANIMM voltage range is 0.1AIN-, i.e., -1V to 0V. Therefore, the differential signal voltage ANIPP-AINM output by this circuit is -1V to 0V.

[0089] When the input signal line is disconnected, the voltage at the positive terminal of AIN+ remains unchanged at 0V. AIN- is pulled down to VSS1 via R2. It is calculated that the voltage of ANIP is still 0V, and the voltage of ANIMM is -2.1V. Therefore, the differential signal voltage of the output ADC, ANIP-AINM, is 2.1V. When the line is disconnected, the differential voltage (2.1V) detected by the ADC is outside the normal operating voltage range (-1V~0V), and the disconnection state can be detected.

[0090] When the input voltage signal is a differential signal and its range is -10V to +10V (absolute input voltage 0V to 10V), the disconnection detection circuit works as follows: Figure 5 As shown, the differential signal (AIN+ - AIN-) voltage is -10V to +10V. It can be calculated that when the signal is not disconnected, the differential signal voltage AINP-AINM output by this circuit is -1V to +1V.

[0091] When the positive input signal line AIN+ is disconnected, the voltage at the negative terminal of AIN- remains unchanged. AIN+ is pulled up to VDD1 via R1. The calculated voltage ANINP is 2.1V, and the voltage ANIMM is -1V to +1V. Therefore, the differential signal voltage ANINP-AINM output to the ADC is 1.1V to 3.1V. Thus, when the positive input signal line AIN+ is disconnected, the differential voltage (1.1V to 3.1V) detected by the ADC is outside the normal operating voltage range (0 to 1V), and the disconnection state can be detected.

[0092] When the negative input signal line AIN- is disconnected, the voltage at the positive terminal AIN+ remains unchanged. AIN- is pulled down to VSS1 via R2. The calculated voltage of AINN is -2.1V, and the voltage of AINP is -1V to +1V. Therefore, the differential signal voltage AINP-AINM output to the ADC is 1.1V to 3.1V. Thus, when the negative input signal line AIN- is disconnected, the differential voltage (1.1V to 3.1V) detected by the ADC is outside the normal operating voltage range (0 to 1V), and the disconnection state can be detected.

[0093] When the positive input signal line AIN+ and the negative input signal line AIN- are simultaneously disconnected, AIN+ is pulled up to VDD1 via R1, and AIN- is pulled down to VSS1 via R2. The calculated voltage ANIP is 2.1V and the voltage ANIN is -2.1V. Therefore, the differential signal voltage ANIP-AINM output to the ADC is 4.2V. Thus, when the positive input signal line AIN+ and the negative input signal line AIN- are simultaneously disconnected, the differential voltage (4.2V) detected by the ADC is outside the normal operating voltage range (0~1V), and the disconnection state can be detected.

[0094] When the input analog signal is a current signal, the open circuit detection circuit is as follows: Figure 6 As shown, switches SW1 and SW2 are open, SW3 is closed, resistor R11 is connected in the circuit, and resistors R1 and R2 are disconnected. The input current signal range is 4mA~20mA. It can be calculated that when the signal is not disconnected, the positive input signal line AIN+ is 1V~10V, and the negative input signal line AIN- is 0V. After passing through the voltage follower circuit and the dual power supply negative voltage bias circuit, the ANIP voltage range is 0.1V~1V, and the ANIN voltage is 0V. Therefore, the differential signal voltage ANIP-AINM output to the ADC is 0.1V~1V.

[0095] When the input signal line is disconnected, the positive input signal line AIN+ suddenly drops to 0V, while the negative input signal line AIN- remains at 0V. After passing through the voltage follower circuit and the dual-power negative voltage bias circuit, the voltage of ANINP is 0V and the voltage of ANINN is 0V. Therefore, the differential signal voltage ANINP-AINM output to the ADC is 0V. When the current input is disconnected, the differential voltage (0V) detected by the ADC is outside the normal operating voltage range (0.1V~1V), and the disconnection state can be detected.

[0096] The technical solution disclosed herein provides an analog input signal disconnection detection circuit based on a voltage follower, including a voltage / current front-end input circuit, a voltage follower circuit, and a dual-power supply negative voltage bias circuit. By switching the connection mode of the pull-up / pull-down resistors and current sensing resistors of the voltage input signal through a switch, analog signal detection of single-ended voltage, differential signal, and current signal is realized. Through the voltage follower and the dual-power supply negative voltage bias circuit, the single-ended or differential voltage in the disconnection state forms a voltage threshold that is different from the normal state, thereby detecting abnormal voltage and realizing rapid disconnection diagnosis. This provides underlying perception protection for industrial sites and intelligent manufacturing, and improves the fault tolerance and stability of the system.

[0097] Based on the same inventive concept, embodiments of the present invention provide an analog input circuit, including the analog input signal disconnection detection circuit as described in any of the above embodiments.

[0098] Based on the same inventive concept, embodiments of the present invention provide a programmable logic controller, including the analog input circuit as described in any of the above embodiments.

[0099] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in conjunction with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in conjunction with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

1. An analog input signal open wire detection circuit, characterized by: The analog input signal line detection circuit comprises a front-end input circuit, a voltage follower circuit and a dual-power negative voltage bias circuit, the voltage follower circuit is arranged between the front-end input circuit and the dual-power negative voltage bias circuit; The front-end input circuit is configured to realize analog detection of voltage single-ended signals, voltage differential signals and current signals; The voltage follower circuit is configured to realize consistency between input voltage and output voltage; The dual-power negative voltage bias circuit is configured to convert single-ended or differential voltage in a broken state into a voltage threshold different from a normal state.

2. The analog input signal open-wire detection circuit of claim 1, wherein: The analog input signal line detection circuit further comprises a signal input positive terminal, a signal input negative terminal, a signal output positive terminal and a signal output negative terminal, the voltage follower circuit comprises a first voltage follower and a second voltage follower, the dual-power negative voltage bias circuit has a first input terminal, a second input terminal and a first output terminal and a second output terminal, the input terminal of the first voltage follower is connected with the signal input positive terminal, the output terminal of the first voltage follower is connected with the first input terminal of the dual-power negative voltage bias circuit, the first output terminal of the dual-power negative voltage bias circuit is connected with the signal output positive terminal, the input terminal of the second voltage follower is connected with the signal input negative terminal, the output terminal of the second voltage follower is connected with the second input terminal of the dual-power negative voltage bias circuit, and the second output terminal of the dual-power negative voltage bias circuit is connected with the signal output negative terminal. The front-end input circuit is connected with the signal input positive terminal and the signal input negative terminal.

3. The analog input signal open-wire detection circuit of claim 2, wherein: The front-end input circuit comprises a first pull-up branch, a first pull-down branch and a current sampling branch, one end of the first pull-up branch is connected with the signal input positive terminal and the input terminal of the first voltage follower, the other end of the first pull-up branch is connected with a first positive power voltage, one end of the first pull-down branch is connected with the signal input negative terminal and the input terminal of the second voltage follower, the other end of the first pull-down branch is connected with a first negative power voltage, one end of the current sampling branch is connected with the signal input positive terminal and the input terminal of the first voltage follower, and the other end of the current sampling branch is connected with the signal input negative terminal and the input terminal of the first voltage follower.

4. The analog input signal open-wire detection circuit of claim 3, wherein: The first pull-up branch comprises a first resistor and a first switch, the first resistor and the first switch SW1 are connected in series on the first pull-up branch; The first pull-down branch comprises a second resistor and a third switch, the second resistor and the third switch are connected in series on the first pull-down branch; The current sampling branch comprises an eleventh resistor and a second switch, the eleventh resistor and the second switch are connected in series on the current sampling branch.

5. The analog input signal line detection circuit according to claim 4, wherein: The first switch is configured to receive a first control signal and perform an opening or closing operation in response to the first control signal; The second switch is configured to receive a second control signal and perform an opening or closing operation in response to the second control signal; The third switch is configured to receive a third control signal and perform an opening or closing operation in response to the third control signal.

6. The analog input signal open-wire detection circuit of claim 2, wherein: The double power supply negative voltage bias circuit comprises a first signal transmission branch, a second signal transmission branch, a second pull-up branch and a second pull-down branch, a third pull-up branch and a third pull-down branch, one end of the first signal transmission branch is connected with the output end of the first voltage follower, the other end of the first signal transmission branch is connected with the signal output positive end, one end of the second pull-up branch is connected with the signal output positive end, the other end of the second pull-up branch is connected with the second positive power supply voltage, one end of the second pull-down branch is connected with the signal output positive end, the other end of the second pull-down branch is connected with the second negative power supply voltage, one end of the second signal transmission branch is connected with the output end of the second voltage follower, the other end of the second signal transmission branch is connected with the signal output negative end, one end of the third pull-up branch is connected with the signal output negative end, the other end of the third pull-up branch is connected with the second positive power supply voltage, one end of the third pull-down branch is connected with the signal output negative end, and the other end of the third pull-down branch is connected with the second negative power supply voltage.

7. The analog input signal open-wire detection circuit of claim 6, wherein: The first signal transmission branch comprises a third resistor, and the third resistor is connected in series on the first signal transmission branch. The second signal transmission branch comprises a fourth resistor, and the fourth resistor is connected in series on the second signal transmission branch. The second pull-up branch comprises a fifth resistor, and the fifth resistor is connected in series on the second pull-up branch. The second pull-down branch comprises a ninth resistor, and the ninth resistor is connected in series on the second pull-down branch. The third pull-up branch comprises a sixth resistor, and the sixth resistor is connected in series on the third pull-up branch. The third pull-down branch comprises a tenth resistor, and the tenth resistor is connected in series on the third pull-down branch.

8. The analog input signal open wire detection circuit of claim 6 or 7, wherein: The double power supply negative voltage bias circuit comprises a fourth pull-down branch and a fifth pull-down branch, one end of the fourth pull-down branch is connected with the output end of the first voltage follower, the other end of the fourth pull-down branch is connected with the second negative power supply voltage, one end of the fifth pull-down branch is connected with the output end of the second voltage follower, and the other end of the fifth pull-down branch is connected with the second negative power supply voltage.

9. The analog input signal open wire detection circuit of claim 8, wherein: The fourth pull-down branch comprises a seventh resistor, and the seventh resistor is connected in series on the fourth pull-down branch. The fifth pull-down branch comprises an eighth resistor, and the eighth resistor is connected in series on the fifth pull-down branch.

10. The analog input signal open-wire detection circuit of claim 1, wherein: An ADC conversion circuit is further included, an input end of the ADC conversion circuit is connected with the output end of the double power supply negative voltage bias circuit, and an output end of the ADC conversion circuit is connected with the main control module.

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