CN111624916A - Functional safety type digital quantity input acquisition circuit and acquisition and diagnosis method thereof - Google Patents
Functional safety type digital quantity input acquisition circuit and acquisition and diagnosis method thereof Download PDFInfo
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- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B19/00—Programme-control systems
- G05B19/02—Programme-control systems electric
- G05B19/04—Programme control other than numerical control, i.e. in sequence controllers or logic controllers
- G05B19/042—Programme control other than numerical control, i.e. in sequence controllers or logic controllers using digital processors
- G05B19/0423—Input/output
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- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B2219/00—Program-control systems
- G05B2219/20—Pc systems
- G05B2219/21—Pc I-O input output
- G05B2219/21155—Over voltage protection
Abstract
The invention discloses a functional safety type digital input acquisition circuit and an acquisition and diagnosis method thereof in the technical field of electrical control, and aims to solve the technical problems of insufficient fault protection capability and no fault detection capability of the digital input acquisition circuit in the prior art. The acquisition circuit comprises a digital quantity input interface, a pull-up control circuit, a signal input circuit and a digital quantity acquisition MCU circuit, wherein the digital quantity input interface is electrically connected with the digital quantity acquisition MCU circuit through the pull-up control circuit and the signal input circuit respectively; the signal input circuit comprises a digital quantity input acquisition redundant forward channel and a digital quantity input acquisition redundant reverse channel which are mutually connected in parallel and are mutually reverse.
Description
Technical Field
The invention relates to a functional safety type digital quantity input acquisition circuit and acquisition and diagnosis methods thereof, belonging to the technical field of electrical control.
Background
With the continuous improvement of the functional safety requirements of special vehicles such as wheel cranes, aerial work platforms and the like in the engineering machinery industry, the common engineering machinery controller can not meet the requirements of functional safety design and certification of an engineering machinery electrical system, and the functional safety controller replaces a common controller to complete the functions related to functional safety besides the basic functions of the common controller.
The digital input acquisition module is widely applied to the controller, the digital input acquisition module of the common controller for the engineering machinery at present can only complete the basic input acquisition function, the safety of the circuit and the fault diagnosis capability are lacked, when the circuit of the digital acquisition module breaks down, the controller cannot identify the fault, the signal acquisition error is caused, and the potential safety hazard is brought to the operation of the engineering machinery. Therefore, it is urgently needed to provide a safe digital input acquisition circuit with a 1oo2 architecture.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a functional safety type digital quantity input acquisition circuit and an acquisition and diagnosis method thereof, so as to solve the technical problems of insufficient fault protection capability and no fault detection capability of the digital quantity input acquisition circuit in the prior art.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a functional safety digital input acquisition circuit comprises a digital input interface, a pull-up control circuit, a signal input circuit and a digital acquisition MCU circuit, wherein the digital input interface is electrically connected with the digital acquisition MCU circuit through the pull-up control circuit and the signal input circuit respectively; the signal input circuit comprises a digital quantity input acquisition redundant forward channel and a digital quantity input acquisition redundant reverse channel which are mutually connected in parallel and are mutually reverse.
Furthermore, the digital quantity input acquisition redundant forward channel or/and the digital quantity input acquisition redundant reverse channel comprise one-way switch circuits and voltage division current limiting circuits which are connected in series, the digital quantity input acquisition redundant forward channel is also connected in series with a forward Schmitt trigger, and the digital quantity input acquisition redundant reverse channel is also connected in series with a reverse Schmitt trigger.
Furthermore, the digital quantity input acquisition redundant forward channel or/and the digital quantity input acquisition redundant reverse channel are/is also connected in series with at least any one of a filter circuit, a current limiting circuit and an overvoltage protection circuit.
Furthermore, the pull-up control circuit adopts a pull-up reference voltage control circuit with a feedback circuit, and the pull-up reference voltage control circuit is electrically connected with the digital quantity acquisition MCU circuit through the feedback circuit.
In order to achieve the above object, the present invention further provides a method for acquiring a functional safety digital input acquisition circuit, comprising the following steps:
based on a preset acquisition mode, extracting an external signal input by a digital quantity input interface through a digital quantity input acquisition redundant forward channel to obtain a forward conversion signal of the external signal;
extracting an external signal input by a digital input interface through a digital input acquisition redundant reverse channel to obtain a reverse conversion signal of the external signal;
comparing the forward conversion signal and the reverse conversion signal with a preset threshold respectively, and judging the level states of the forward conversion signal and the reverse conversion signal, wherein the judged level state is a low level or a high level;
if the level state of the forward conversion signal is opposite to that of the reverse conversion signal, the level state of the forward conversion signal is extracted as the level state of the external signal.
Furthermore, the acquisition mode comprises that the high level of the input external signal is effective, and the low level of the input external signal is effective.
Further, the method for setting the acquisition mode comprises the following steps:
the digital quantity acquisition MCU circuit sends a high-level or low-level control signal to the pull-up control circuit;
if the control signal is in a high level, the pull-up control circuit is opened in response to the high level control signal and corresponds to an effective acquisition mode of a low level of an input external signal;
if the control signal is at low level, the pull-up control circuit is closed in response to the low-level control signal, and the corresponding high-level effective acquisition mode of the input external signal is adopted.
In order to achieve the above object, the present invention further provides a diagnostic method for a functional safety digital input acquisition circuit, comprising the following steps:
extracting an external signal input by a digital input interface through a digital input acquisition redundant forward channel to obtain a forward conversion signal of the external signal;
extracting an external signal input by a digital input interface through a digital input acquisition redundant reverse channel to obtain a reverse conversion signal of the external signal;
comparing the forward conversion signal and the reverse conversion signal with a preset threshold respectively, and judging the level states of the forward conversion signal and the reverse conversion signal;
and if the level states of the forward conversion signal and the reverse conversion signal are the same, judging that the digital quantity input acquisition redundancy forward channel or/and the digital quantity input acquisition redundancy reverse channel have faults.
Further, still include:
sending a control signal to a pull-up reference voltage control circuit, extracting a feedback signal of the pull-up reference voltage control circuit through a feedback circuit, wherein the level states of the control signal and the feedback signal comprise a high level and a low level;
and if the level states of the feedback signal and the control signal are different, judging that the pull-up reference voltage control circuit has a fault.
Compared with the prior art, the invention has the following beneficial effects: the design has feedback circuit's pull-up reference voltage control circuit, and digital quantity gathers MCU circuit and sets for the collection mode through pull-up reference voltage control circuit, gathers redundant forward passageway and digital quantity input through parallelly connected each other and gathers redundant backward passageway and draw the forward transform signal and the reverse transform signal of external signal, when the level state of forward transform signal and reverse transform signal is opposite, draws the level state of forward transform signal and regards as the level state of external signal. When the level states of the forward conversion signal and the reverse conversion signal are the same, the signal input circuit can be judged to be in fault. Meanwhile, the control signal of the pull-up reference voltage control circuit and the feedback signal extracted by the feedback circuit can be compared, and if the level states of the control signal and the feedback signal are opposite, the pull-up reference voltage control circuit can be judged to have a fault. Specifically, the acquisition circuit and the acquisition and diagnosis method thereof have the following beneficial effects:
(1) the design accords with a 1oo2 architecture, and can be directly applied to the design of a functional safety type programmable logic controller;
(2) the device has the fault self-diagnosis capability, and can realize the functional safety under the condition of single channel fault;
(3) a pull-up control and feedback circuit is introduced, high-effective and low-effective input modes are compatible, and meanwhile, the state of the pull-up circuit is fed back to the MCU, so that fault detection is realized, and the reliability of the circuit is improved;
(4) the two mutually-reversed input channels are connected to two independent input modules of a main control chip MCU, so that the purpose of redundancy design can be realized, and the problems of complex circuit and high cost caused by using two MCUs in the traditional scheme are solved;
(5) two-stage current-limiting protection and overvoltage protection are introduced, so that the problem that a circuit is easily damaged when a fault occurs in the existing solution is solved, and the fault protection capability is improved.
Drawings
FIG. 1 is a digital value acquisition circuit of a general controller provided in a first prior art solution according to an embodiment of the present invention;
FIG. 2 is a diagram of a digital value acquisition circuit of a safety controller according to a second prior art of the present invention;
FIG. 3 is a circuit block diagram of an embodiment of the acquisition circuit of the present invention;
fig. 4 is a circuit schematic of an embodiment of the acquisition circuit of the present invention.
In the figure: 100. a digital quantity input interface; 200. a pull-up reference voltage control circuit; 300. inputting and acquiring a redundant forward channel by digital quantity; 301. a first unidirectional switch circuit; 302. a first voltage-dividing current-limiting circuit; 303. a first filter circuit; 304. a first current limiting circuit; 305. a first overvoltage protection circuit; 306. a forward Schmitt trigger; 400. the digital quantity is input into a redundant reverse channel; 401. a second unidirectional switch circuit; 402. a second voltage-dividing current-limiting circuit; 403. a second filter circuit; 404. a second current limiting circuit; 405. a second overvoltage protection circuit; 406. a reverse Schmitt trigger; 500. digital quantity acquisition MCU circuit.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
In the prior art, a common controller digital acquisition circuit and a safety controller digital acquisition circuit are generally adopted for digital acquisition. In order to make the technical content of the present invention more accurately understood by those skilled in the art and the related art, the following terms are first explained:
(1) digital quantity input module: DI module, generally used to collect high and low logic levels, such as on and off of a switch;
(2)1oo2 architecture: a redundant voting circuit structure includes two parallel channels, either of which is capable of performing a security function. The method can allow one channel to fail without affecting the execution of the safety function. Failure of the safety function only occurs when dangerous failures occur in both channels;
(3) MCU: the microcontroller unit or the single chip microcomputer refers to a chip integrating various IO interfaces, and comprises a GPIO interface, an ADC interface, a CPU, an SDRAM memory unit, a FLASH storage unit and the like, different operation control effects can be achieved by designing different program codes, and the conventional controller is designed by adding an external circuit on the basis of an MCU;
(4) schmitt trigger: for a standard schmitt trigger, when the input voltage is higher than the forward threshold voltage, the output is low; when the input voltage is lower than the negative threshold voltage, the output is high; when the input voltage is between the positive and negative threshold voltages, the output is unchanged, that is, the output is inverted from the high level to the low level, or from the low level to the high level, the corresponding threshold voltages are different. The output will change only when the input voltage changes enough;
(5) a clamping diode: the diode clamp circuit is characterized in that the forward conduction voltage drop of a diode is relatively stable and has a small value (sometimes, the value can be approximate to zero) to limit the potential of a certain point in the circuit, and the top or the bottom of a changed waveform is kept at a certain direct current level.
As shown in fig. 1, a digital quantity acquisition circuit of a general controller provided in a first technical solution mentioned in the detailed embodiment of the present invention includes a digital quantity acquisition circuit channel, which includes a voltage division and current limitation circuit (R1, R2), a filter circuit (R1, C1), an overvoltage clamp protection circuit (D1, D2), a signal input interface (DI), and a signal acquisition chip MCU, and its operating principle is as follows:
(1) the voltage dividing and current limiting circuits (R1, R2) are used for carrying out voltage reduction and current limitation on input voltage of the interface (DI), and then the input voltage is input to a General-purpose input/output port (GPIO) of the MCU for carrying out high-low logic level acquisition;
(2) the filter circuit (R1, C1) is used for filtering high-frequency interference signals superposed on the input voltage signals and preventing the high-frequency interference signals from causing errors in high-low logic level acquisition results;
(3) the voltage clamp protection circuits (D1, D2) are used for inputting the voltage V to the GPIO when the voltage value exceeds the supply Voltage (VCC) of the circuit after the input voltage passes through the voltage division Current limiting circuits (R1, R2)GPIOClamped to VCC + 0.7V; voltage V input to GPIO when voltage value is lower than Ground voltage (GND)GPIOClamped to GND-0.7V. Therefore, the clamping effect of the MCU input voltage is achieved, and the damage of the MCU caused by the voltage exceeding the limit is prevented;
(4) when the DI port has no voltage input, the voltage is set to be V by the on and off of a pull-down circuit in the MCU chipGPIOThe reference voltage value of (2). When the pull-up circuit is on and the pull-down circuit is off, VGPIOIs pulled high to VCC, at which time the DI port can be used for active low inputs. When pulling up circuitWhen closed and the pull-down circuit is open, VGPIOPulled down to GND, at which time the DI port can be used for active high input;
(5) digital quantity input acquisition and result judgment: reading the voltage of the GPIO port through the MCU to acquire a digital quantity input signal and judge a result, wherein the acquisition and the result judgment are as follows:
VGPIO＝[R2/(R1+R2)]*VDI，
when V isGPIOWhen the voltage is less than-0.3-0.8V, the DI input is judged to be low level;
when V isGPIOWhen the voltage is more than 2-VCC +0.3V, the DI input is judged to be high level.
The technical scheme has the following defects:
1) no fault detection capability, and error judgment in fault
When R1 is open, MCU always judges DI as low level input;
when any one of R2, C1 and D2 is short-circuited, the MCU always judges the DI as low-level input;
when the D1 is short-circuited, the MCU always judges the DI as a high level input.
2) The fault protection capability is insufficient, and the circuit damage can occur in single fault
When R1 is short-circuited, D1 and/or MCU will be damaged when the DI input voltage is higher than VCC +0.7V voltage;
when R1 is shorted, D2 and/or the MCU may be damaged because the DI input voltage is lower than GND-0.7V.
As shown in fig. 2, the digital quantity collecting circuit of the safety controller provided in the second prior art mentioned in the specific embodiment of the present invention has two independent digital quantity collecting circuit channels, and the circuit composition and the operation principle of each digital quantity collecting circuit channel are the same as those of the digital quantity collecting circuit channel in the first prior art, specifically as follows:
(1) the MCU1 and the MCU2 synchronously acquire input voltage values of the DI1 and the DI2, acquisition results are compared through a communication interface between the MCU1 and the MCU2, and the design of a 1oo2 redundant structure digital quantity input acquisition circuit is achieved.
(2) And (3) judging a digital quantity input acquisition result:
set VGPIO1For the voltage input to the GPIO of the MCU1, set VGPIO2For the voltage input to the GPIO of the MCU2,
when V isGPIO1And VGPIO2When the voltage is all low level, the safety controller judges the voltage is low level;
when V isGPIO1And VGPIO2When the voltage is all high level, the safety controller judges the voltage is high level;
when V isGPIO1And VGPIO2When any one is high level and the other one is low level, the safety controller judges that the controller is in fault state, outputs fault alarm, and automatically enters into a safe working state.
The technical scheme has the following defects:
1) the fault protection capability is insufficient, and circuit damage can occur in single fault, which is the same as the 2 nd defect in the first scheme;
2) two processor chips (MCU1 and MCU2) are needed, the circuit design is complex, the circuit board is large in size and high in cost;
3) the communication between the two processors (MCU1 and MCU2) needs to contain a synchronous signal, so that the DI input signals collected at the same time can be ensured to be subjected to redundancy comparison, and the detection period is relatively long;
4) the two independent input ports (DI1, DI2) are designed, so that the components for requiring signals input from the outside are also independent, the number of external components is increased, and the system cost is increased.
In view of the above-mentioned defects in the prior art, a functional safety type digital input acquisition circuit is provided in the specific embodiment of the present invention, and as shown in fig. 3, the functional safety type digital input acquisition circuit provided in the embodiment of the present invention is a block diagram, and includes a digital input interface 100, a pull-up control circuit, a signal input circuit, and a digital acquisition MCU circuit 500, where the digital input interface 100 is electrically connected to the digital acquisition MCU circuit 500 through the pull-up control circuit and the signal input circuit, respectively. The pull-up control circuit is a pull-up reference voltage control circuit 200 with a feedback circuit, and the pull-up reference voltage control circuit 200 is electrically connected with a pin GPIO1 of the digital quantity acquisition MCU circuit 500 and is also electrically connected with a pin GPIO2 of the digital quantity acquisition MCU circuit 500 through the feedback circuit.
In this embodiment, an external signal is input through the external digital input interface 100, and the external signal is divided into three levels, i.e., a high level, a low level, and a floating level. The digital quantity acquisition MCU circuit 500 can send a high-level or low-level control signal to the pull-up reference voltage control circuit 200 through a GPIO1 pin, when the control signal is high level, the pull-up reference voltage control circuit 200 is opened, at the moment, an effective acquisition mode of external signal low level is entered, and the pull-up reference voltage control circuit 200 performs pull-up control on the input external signal; when the control signal is at a low level, the pull-up reference voltage control circuit 200 is turned off, and at this time, the acquisition mode in which the external signal is at a high level is active is entered, and the pull-up reference voltage control circuit 200 does not perform pull-up control on the input external signal. After the digital quantity acquisition MCU circuit 500 sends the control signal to the pull-up reference voltage control circuit 200, the feedback signal of the pull-up reference voltage control circuit 200 is also extracted through the feedback circuit to detect whether it is the correct acquisition mode.
The signal input circuit adopts a redundancy design and is divided into two channels in total, and the two channels are connected in parallel and are opposite to each other, namely a digital quantity input acquisition redundancy forward channel 300 and a digital quantity input acquisition redundancy reverse channel 400. In this embodiment, the digital quantity input collection redundant forward channel 300 includes a first unidirectional switch circuit 301, a first voltage-dividing current-limiting circuit 302, a first filter circuit 303, a first current-limiting circuit 304, a first overvoltage protection circuit 305, and a forward schmitt trigger 306, which are connected in series, and the digital quantity input collection redundant reverse channel 400 includes a second unidirectional switch circuit 401, a second voltage-dividing current-limiting circuit 402, a second filter circuit 403, a second current-limiting circuit 404, a second overvoltage protection circuit 405, and a reverse schmitt trigger 406, which are connected in series. An external signal is subjected to voltage reduction and filtering through a digital quantity input acquisition redundancy forward channel 300 to obtain a forward conversion signal of the external signal, and the forward conversion signal is accessed to a GPIO3 pin of the digital quantity acquisition MCU circuit 500; the external signal is subjected to voltage reduction and filtering through the digital quantity input acquisition redundancy reverse channel 400, a reverse conversion signal of the external signal is obtained, and the external signal is accessed to a GPIO4 pin of the digital quantity acquisition MCU circuit 500. The forward conversion signal is in the same high-low level state as the external signal, and the reverse conversion signal is in the opposite high-low level state as the external signal. Finally, the digital quantity acquisition MCU circuit 500 determines the high-low level states of the forward transform signal and the reverse transform signal, and the determination method compares the forward transform signal and the reverse transform signal with a preset threshold respectively to obtain a determination result. If the level states of the forward conversion signal and the reverse conversion signal are just opposite, extracting the level state of the forward conversion signal as the level state of an external signal, namely the level signal state of the digital input; if the level states of the forward conversion signal and the reverse conversion signal are the same, the digital quantity input acquisition redundant forward channel 300 or the digital quantity input acquisition redundant reverse channel 400 is judged to have a fault.
More specifically, as shown in fig. 4, it is a schematic circuit diagram of an embodiment of the acquisition circuit of the present invention, and details are as follows:
digital quantity input interface 100: i.e., J1 in fig. 4;
pull-up reference voltage control circuit 200: the feedback circuit comprises R101, R102, R103, R104, R105, R106, Q101, Q102, D101 and C101, wherein a feedback circuit is formed by the connection circuit of the R105, R106 and C101 and the GPIO2 pin. The principle of the pull-up reference voltage control circuit 200 for pull-up controlling the input external signal is as follows: when the digital quantity acquisition MCU circuit 500 outputs a high-level control signal to the pull-up reference voltage control circuit 200 through a GPIO1 pin, Q101 is conducted and grounded, the pull-up power supply voltage is divided by R102 and R103 to control Q102 to be conducted, and at the moment, an external signal input by J1 is pulled up to VCC through Q102, R104 and D101. When the control signal output by the pin GPIO1 is at a low level, Q101 is turned off, the control terminal of Q102 is pulled up to VCC through R103, Q102 is controlled to be turned off, and at this time, the pull-up of the input terminal J1 is turned off, and the pull-up voltage is 0V. The pull-up state feedback principle is as follows: the pull-up power voltage is subjected to filter pressing by R105, R106 and C101 and then fed back to the input end GPIO2 of the digital quantity acquisition MCU circuit 500, when the pull-up control is opened, a feedback signal received by a pin of GPIO2 is in a high level state, at the moment, the pull-up reference voltage control circuit 200 works normally, otherwise, the pull-up reference voltage control circuit is in a failure state; when the pull-up control is turned off, the feedback signal received by the pin GPIO2 should be in a low level state, and at this time, the pull-up reference voltage control circuit 200 operates normally, otherwise it indicates that it is faulty.
The signal input circuit with redundant design comprises a digital quantity input acquisition redundant forward channel 300 and a digital quantity input acquisition redundant backward channel 400, wherein,
the digital quantity input acquisition redundancy forward channel 300 comprises D201, R202, R203, C201, D202 and K203; the digital quantity input acquisition redundant backchannel 400 includes D301, R302, C301, R303, D302, K303. The method comprises the following specific steps:
d201 and D301 are unidirectional conducting devices, which respectively correspond to the first unidirectional switching circuit 301 and the second unidirectional switching circuit 401, external signals input by J1 can normally pass through, and isolation of two channels is formed at the same time, so that a fault protection effect is achieved, and when any one channel fails, the other channel cannot be affected;
r201 and R203 or R301 and R303 play a role in limiting input current, and prevent the digital quantity acquisition MCU circuit 500 from being burnt out due to overlarge input current, wherein the R201 and the R203 correspond to the first current limiting circuit 304. Wherein, R301 and R303 correspond to the second current limiting circuit 404;
r201 and R202 or R301 and R302 play a role in reducing input voltage and preventing the digital quantity acquisition MCU circuit 500 from being burnt out due to overlarge input voltage. Wherein, R201 and R202 correspond to the first voltage-dividing current-limiting circuit 302, and R301 and R302 correspond to the second voltage-dividing current-limiting circuit 402;
r201 and C201 or R301 and C301 play a role in filtering, and can filter input high-frequency interference signals. Wherein, R201 and C201 correspond to the first filter circuit 303, and R301 and C301 correspond to the second filter circuit 403;
the D202 or D302 plays a role of overvoltage protection, and when the input voltage is greater than VCC1 or VCC2 and less than GND, the voltage input to GPIO3 or GPIO4 of the digital quantity acquisition MCU circuit 500 is clamped to VCC1+0.7V or VCC2+0.7V or GND-0.7V. Wherein D202 corresponds to the first overvoltage protection circuit 305, and D302 corresponds to the second overvoltage protection circuit 405;
k203 and K303 are Schmitt triggers, the level state of the output of the K203 is the same as that of the input signal, and the level state of the output of the K303 is opposite to that of the input signal, so that the K203 and the K303 are used for redundant comparison and fault judgment of external signals. Where K203 corresponds to the forward schmitt trigger 306 and K303 corresponds to the reverse schmitt trigger 406.
Digital quantity acquisition MCU circuit 500: for controlling the pull-up reference voltage control circuit 200, diagnosing whether it is malfunctioning according to its feedback signal, detecting a digital quantity input, and diagnosing whether the signal input circuit is malfunctioning. In this embodiment, the model of the digital quantity acquisition MCU circuit 500 is TMS570LS3137, two digital quantity input channels must be connected to independent input modules inside the digital quantity acquisition MCU circuit 500, that is, the two digital quantity input channels are respectively connected to GPIO3 and GPIO4 pins, and when a single input module fails, no mutual influence is caused. The processing control and determination result of the digital quantity acquisition MCU circuit 500 for the external signal is specifically shown in table 1:
table 1: the invention relates to digital quantity acquisition circuit control and result judgment
Based on the aforementioned acquisition circuit of the present invention, the specific embodiment of the present invention further provides a method for acquiring a functionally safe digital input acquisition circuit, which comprises the following steps:
based on a preset acquisition mode, the digital quantity acquisition MCU circuit 500 extracts an external signal input by the digital quantity input interface 100 through the digital quantity input acquisition redundant forward channel 300 to obtain a forward conversion signal of the external signal; the external signal input from the digital input interface 100 is extracted through the digital input acquisition redundant backward channel 400, and a backward converted signal of the external signal is obtained. The acquisition mode comprises two modes of high level validity of the input external signal and low level validity of the input external signal, and the setting method comprises the following steps:
the digital quantity acquisition MCU circuit 500 sends a control signal of high level or low level to the pull-up reference voltage control circuit 200;
if the control signal is at a high level, the pull-up reference voltage control circuit 200 is turned on in response to the high-level control signal to perform pull-up control on the input external signal, and at this time, corresponding to an effective acquisition mode of a low level of the input external signal, in the acquisition mode, a forward conversion signal converted from the external signal at the low level is still at a low level state, and forward conversion signals converted from the external signal at a floating or high level are all at a high level state;
if the control signal is at a low level, the pull-up reference voltage control circuit 200 is turned off in response to the low level control signal, and does not perform pull-up control on the input external signal, i.e., corresponds to an effective acquisition mode of the high level of the input external signal.
And step two, the digital quantity acquisition MCU circuit 500 compares the forward conversion signal and the reverse conversion signal with a preset threshold respectively, and judges the level states of the forward conversion signal and the reverse conversion signal to be low level or high level. If the level states of the forward conversion signal and the reverse conversion signal are opposite, the signal input circuit works normally, and the level state of the forward conversion signal is extracted as the level state of the external signal.
Based on the aforementioned acquisition circuit of the present invention, the specific embodiment of the present invention further provides a diagnostic method for a functional safety digital input acquisition circuit, which comprises the following steps:
step one, the digital quantity acquisition MCU circuit 500 sends a high level or low level control signal to the pull-up reference voltage control circuit 200 to set an acquisition mode, and meanwhile, extracts a feedback signal of the pull-up reference voltage control circuit 200 through a feedback circuit. Based on the set acquisition mode, the digital quantity acquisition MCU circuit 500 extracts the external signal input by the digital quantity input interface 100 through the digital quantity input acquisition redundant forward channel 300 to obtain the forward conversion signal of the external signal; the external signal input from the digital input interface 100 is extracted through the digital input acquisition redundant backward channel 400, and a backward converted signal of the external signal is obtained.
Step two, the digital quantity acquisition MCU circuit 500 compares the feedback signal with the control signal, and if the level states of the feedback signal and the control signal are different, the pull-up reference voltage control circuit 200 is judged to have a fault; if the two signals are the same, the pull-up reference voltage control circuit 200 is judged to work normally.
And step three, comparing the forward conversion signal and the reverse conversion signal with a preset threshold value respectively by the digital quantity acquisition MCU circuit 500, and judging the level states of the forward conversion signal and the reverse conversion signal. And if the level states of the forward conversion signal and the reverse conversion signal are the same, judging that the digital quantity input acquisition redundant forward channel 300 or/and the digital quantity input acquisition redundant reverse channel 400 have faults. If the level states of the forward conversion signal and the reverse conversion signal are opposite, the signal input circuit can be judged to work normally.
In summary, the embodiment of the invention provides a functional safety digital input acquisition circuit and an acquisition and diagnosis method thereof, and the acquisition circuit can realize the digital input acquisition and acquisition circuit diagnosis functions. Specifically, compared with the prior art, the method has the following technical effects:
(1) the acquisition circuit of the invention conforms to the architecture of 1oo2, reaches the levels of ISO 61508SIL2 and EN 13849PLd, passes the functional safety certification of the Germany TUV south Deutsche group company and can be directly applied to the design of a functional safety type programmable logic controller;
(2) the circuit has the fault self-diagnosis capability, and can realize the functional safety under the condition of single channel fault;
(3) the invention introduces the pull-up control and feedback circuit, is compatible with high-effective and low-effective input modes through software configuration, and simultaneously feeds back the pull-up circuit state to the MCU, thereby realizing fault detection and improving the reliability of the circuit;
(4) the two mutually-reversed input channels are connected to two independent input modules of a main control chip MCU, so that the purpose of redundancy design can be realized, and the problems of complex circuit and high cost caused by using two MCUs in the traditional scheme are solved;
(5) two-stage current-limiting protection and overvoltage protection are introduced into the circuit, so that the problem that the circuit is easily damaged when a fault occurs in the existing solution is solved, the fault protection capability is improved, and the permanent damage of the circuit caused by a single fault is prevented.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (9)
1. A functional safety type digital input acquisition circuit is characterized by comprising a digital input interface (100), a pull-up control circuit, a signal input circuit and a digital acquisition MCU circuit (500), wherein the digital input interface (100) is electrically connected with the digital acquisition MCU circuit (500) through the pull-up control circuit and the signal input circuit respectively; the signal input circuit comprises a digital quantity input acquisition redundant forward channel (300) and a digital quantity input acquisition redundant reverse channel (400) which are connected in parallel and are opposite to each other.
2. The functionally safe digital quantity input acquisition circuit according to claim 1, wherein the digital quantity input acquisition redundant forward channel (300) and/or the digital quantity input acquisition redundant reverse channel (400) comprise a unidirectional switch circuit and a voltage division current limiting circuit which are connected in series with each other, the digital quantity input acquisition redundant forward channel (300) is further connected in series with a forward Schmitt trigger (306), and the digital quantity input acquisition redundant reverse channel (400) is further connected in series with a reverse Schmitt trigger (406).
3. The functional safety digital input acquisition circuit according to claim 2, wherein the digital input acquisition redundant forward channel (300) or/and the digital input acquisition redundant reverse channel (400) are further connected in series with at least one of a filter circuit, a current limiting circuit and an overvoltage protection circuit.
4. The functional safety type digital quantity input acquisition circuit according to claim 1, wherein the pull-up control circuit adopts a pull-up reference voltage control circuit (200) with a feedback circuit, and the pull-up reference voltage control circuit (200) is further electrically connected with the digital quantity acquisition MCU circuit (500) through the feedback circuit.
5. A method for acquiring a functional safety digital input acquisition circuit is characterized by comprising the following steps:
based on a preset acquisition mode, extracting an external signal input by a digital quantity input interface (100) through a digital quantity input acquisition redundancy forward channel (300) to obtain a forward conversion signal of the external signal;
extracting an external signal input by a digital input interface (100) through a digital input acquisition redundant reverse channel (400) to obtain a reverse conversion signal of the external signal;
comparing the forward conversion signal and the reverse conversion signal with a preset threshold respectively, and judging the level states of the forward conversion signal and the reverse conversion signal, wherein the judged level state is a low level or a high level;
if the level state of the forward conversion signal is opposite to that of the reverse conversion signal, the level state of the forward conversion signal is extracted as the level state of the external signal.
6. The method as claimed in claim 5, wherein the sampling mode includes that the input external signal is active at high level and the input external signal is active at low level.
7. The method for acquiring the functional safety type digital quantity input acquisition circuit according to claim 6, wherein the method for setting the acquisition mode comprises the following steps:
the digital quantity acquisition MCU circuit (500) pulls the control circuit upwards to send a control signal of high level or low level;
if the control signal is in a high level, the pull-up control circuit is opened in response to the high level control signal and corresponds to an effective acquisition mode of a low level of an input external signal;
if the control signal is at low level, the pull-up control circuit is closed in response to the low-level control signal, and the corresponding high-level effective acquisition mode of the input external signal is adopted.
8. A diagnostic method of a functional safety digital input acquisition circuit is characterized by comprising the following steps:
extracting an external signal input by a digital input interface (100) through a digital input acquisition redundancy forward channel (300) to obtain a forward conversion signal of the external signal;
extracting an external signal input by a digital input interface (100) through a digital input acquisition redundant reverse channel (400) to obtain a reverse conversion signal of the external signal;
comparing the forward conversion signal and the reverse conversion signal with a preset threshold respectively, and judging the level states of the forward conversion signal and the reverse conversion signal;
and if the level states of the forward conversion signal and the reverse conversion signal are the same, judging that the digital quantity input acquisition redundant forward channel (300) or/and the digital quantity input acquisition redundant reverse channel (400) have faults.
9. The method of claim 8, further comprising:
sending a control signal to a pull-up reference voltage control circuit (200), extracting a feedback signal of the pull-up reference voltage control circuit (200) through a feedback circuit, wherein the level states of the control signal and the feedback signal comprise a high level and a low level;
if the feedback signal is different from the control signal in level state, it is determined that the pull-up reference voltage control circuit (200) is malfunctioning.
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