Method for Measuring Temperature and Digital Quantity Signals Simultaneously Using PLC Thermal Resistance Input Module

Abstract

The present invention discloses a method for detecting temperature and digital quantity signals by using a PLC thermal resistance input module, belonging to the technical field of automatic process detection and control. The method comprises the following steps: connecting the digital quantity contact signal in series into the thermal resistance signal loop; eliminating the influence of the access of the digital quantity contact signal into the thermal resistance signal loop on the temperature detection accuracy; adding a logic judgment and recognition method in the PLC to detect the temperature and the digital quantity contact signal simultaneously. This method solves the problem of insufficient channels of the DI digital input module in the existing PLC system, expands the input capacity of the digital quantity signals of the PLC system, reduces the cost of purchasing the DI digital input module and the cost of upgrading and transforming the PLC system, reduces the implementation operation time, quickly responds to the actual on-site requirements, has a wide application range and has extensive popularization value.

Description

Technical Field

[0001] The present invention relates to the technical field of automated process detection and control, and more particularly, to a method for simultaneously measuring temperature and digital signals using a PLC thermal resistance input module. Background Art

[0002] In the industrial production process, it is usually necessary to detect some process variables, such as analog and digital signals including temperature, pressure, differential pressure, flow rate, liquid level, purity, valve position, operating state temperature, operation instructions, etc., and adjust and control the above process variables to keep the production process running safely, continuously, and stably. Currently, the PLC (Programmable Logic Controller) system is widely used in the process control of industrial production. Among them, for the detection of temperature signals, primary detection is carried out using temperature sensors such as resistance temperature detectors (RTDs) or thermocouples (TCs) installed in the pipelines or containers of the measured medium at the site. The RTD uses the fact that the temperature change of the measured medium will cause a change in the resistance value of the RTD, while the thermocouple uses the fact that the temperature change causes a change in the electromotive force. Then, the signal measured by the temperature sensor is connected to the dedicated thermal resistance or thermocouple signal input module corresponding to the PLC system through a cable, and the control processor module at the back end converts and processes the resistance value of the thermal resistance or the electromotive force value of the thermocouple input at the front end to calculate the corresponding temperature value. For the detection of digital signals, the closing or opening of the lines of limit switches, operation buttons, and relay contacts coming from the site are connected to the digital input (DI) module of the PLC system, and an external power supply supplies power to the common terminal and input contacts of the DI module. When the contact is closed, the corresponding digital input module channel is powered on, and when the contact is open, the corresponding digital input module channel loses power. The control processor module at the back end judges the state of the on-site digital signal according to the voltage, which is mostly used for the detection of states such as the running or stopping state of the motor, the fully open or fully closed state of the valve, the start-stop operation instruction, and the opening and closing of the panel box door cabinet. Therefore, in the PLC control system, to detect different process variables, different types of variable input modules need to be used and cooperate with the control processor to work to achieve different variable detections, and one variable input module channel can only detect a specific type of process variable.

[0003] The wiring circuit diagram of the thermal resistance (RTD) input module of the PLC for detecting temperature signals is as shown in the attached Figure 1As shown in the figure, a thermal resistance temperature sensor generally adopts a three-wire connection method to access the RTD signal input module of the PLC. That is, the three phases A, B, and B of the thermal resistance are respectively connected to the terminal corresponding to a certain channel of the PLC thermal resistance signal input module. The resistance value between the A and B terminals is the thermal resistance value R0 plus the resistance values R1 and R2 of the two lines between the on-site terminal of the thermal resistance and the terminal of the PLC module, that is, RAB = R0 + R1 + R2. The resistance value between the B and B terminals is the sum of the resistance values R2 and R3 of the two lines between the on-site terminal of the thermal resistance and the terminal of the PLC module, that is, RBB = R2 + R3. And the actual resistance value RS measured by the temperature measurement algorithm of the PLC system is: the resistance value between the A and B terminals minus the line resistance between the B and B terminals, that is, RS = RAB - RBB, RS = R0 + R1 + R2 - (R2 + R3).

[0004] Since the routing lengths and environments of the three core wires in the cable from the on-site terminal of the thermal resistance to the RTD input module of the PLC are the same, the resistance values of the three lines are also the same, that is, R1 = R2 = R3. Therefore: RS = R0 + R1 + R2 - (R2 + R3) = R0 + R1 + R2 - R2 - R3 = R0. That is, the actual resistance value detected by the PLC module is the resistance value corresponding to the temperature of the measured medium sensed by the thermal resistance. Therefore, the purpose of the three-wire connection method of the thermal resistance is to eliminate the influence of the line resistance on the temperature detection accuracy; the wiring circuit diagram of the digital input (DI) module for detecting switch quantities is as shown in the appendix of the instruction manual. Figure 2 As shown in the figure, for the PLC digital input (DI) module, a DC 24V power supply is usually applied between the common ground terminal and each input channel terminal of the module. The positive pole is connected in series with the contacts of devices such as the operation switch, limit switch, and relay to be detected. When the contact is closed, the corresponding input channel detects a high level, that is, the "1" state; when the contact is open, the corresponding input channel detects a low level, that is, the "0" state, so as to judge the state of the input switch quantity signal.

[0005] At present, the production process of high-pressure nitrogen compressors is controlled by a PLC control system. The PLC modules and controllers are installed in the control cabinet to detect and control the production process data. The on-site PLC data is transmitted to the operation station in the central control room for display and alarm through the communication module. At the same time, operators can manually intervene in the on-site production process for setting and adjustment control according to needs. With the continuous strengthening of energy conservation, emission reduction, cost reduction, and efficiency improvement, the demand for production process management and control is also increasing year by year. Therefore, on the basis of the detection points required for the original designed production process control of these high-pressure nitrogen compressor PLC systems, many new measurement points have been added to monitor more production process parameters, resulting in the redundancy channels on the original process variable detection input modules (AI analog input, RTD thermocouple input, DI digital input, etc.) of the PLC system being all used up, and no new detection points can be added anymore. However, with the increase in extreme weather, such as typhoons and heavy rains, which lead to the phenomenon that the PLC control cabinet door is opened and not closed in a timely and reliable manner after maintenance, causing water ingress into the PLC cabinet, equipment damage, production shutdown, and the need for anti-theft, an alarm function when the on-site PLC control cabinet door is opened needs to be added. This requires installing a limit switch on the PLC control cabinet door to detect the open and closed states of the PLC control cabinet door. Normally, the PLC control cabinet door is closed, and the limit switch contact is closed. Once the PLC control cabinet door is opened, the limit switch contact will open. Then, the limit switch contact signal is input into a certain channel of the DI digital input module of the PLC system to identify whether the PLC control cabinet door is closed or open. Once the PLC system detects that the cabinet door is open, an alarm signal is sent on the operation station in the central control room to remind the operator to take corresponding measures. However, when adding new measured points, the PLC system must have a corresponding type of variable input module channel to access the PLC system for conversion and processing to obtain the required measured variable. Usually, the first consideration is to use the redundant channels of the existing DI digital input module of the PLC system for signal input. When all DI channels are used up, then consider adding a DI module to the PLC system to expand the number of input points. At present, all the DI module input channels of the existing PLC systems of each high-pressure nitrogen compressor have been used up, and due to limitations such as the physical slot number and system design capacity of the existing PLC system, it is also impossible to add a DI module to expand the number of input points. Only by upgrading the new PLC system can the number of input points be increased, but the transformation and upgrade cycle is long, the cost is high, and the downtime is long, which cannot meet the current on-site actual situation. Summary of the Invention

[0006] The object of the present invention is to provide a method for simultaneously measuring temperature and digital input signals by using a PLC thermal resistance input module. Without adding the hardware of the DI digital input module of the PLC system and without retrofitting and upgrading a new PLC system, by using an existing RTD temperature input module channel in use, the digital input contacts installed on the PLC control cabinet door are connected in series to the thermal resistance signal line, so as to realize the simultaneous detection of temperature signals and digital input signals, and an additional PLC logic judgment and recognition method is added. This method not only does not affect the existing functions of the thermal resistance for temperature detection, alarm, and interlock trip, but also can detect the opening and closing states of the PLC control cabinet door and give an alarm to remind the operator that the PLC cabinet door has been opened, so as to take corresponding measures in a timely manner.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] According to one aspect of the present invention, there is provided a method for simultaneously measuring temperature and digital input signals by using a PLC thermal resistance input module, including the following steps:

[0009] S1. Connect the digital input contact signal in series to the thermal resistance signal circuit;

[0010] S2. Eliminate the influence of the connection of the digital input contact signal to the thermal resistance signal circuit on the temperature detection accuracy;

[0011] S3. Add a logic judgment and recognition method in the PLC to simultaneously detect the temperature and the digital input contact signal.

[0012] According to the method for simultaneously measuring temperature and digital input signals by using a PLC thermal resistance input module in the above aspect of the present invention, wherein S1 specifically includes the following steps:

[0013] S11. Among the three-phase lines in the temperature measurement circuit of the thermal resistance input module channel, select one of the three-phase lines as the first wiring line;

[0014] S12. Inside the PLC control cabinet, add a cable in the first wiring line and connect the digital input contact signal in series to the first wiring line.

[0015] According to the method for simultaneously measuring temperature and digital input signals by using a PLC thermal resistance input module in the above aspect of the present invention, wherein the other two of the three-phase lines in S11 are respectively the second wiring line and the third wiring line. A thermal resistance temperature sensor is provided on the first wiring line. Alarm units and trip protection interlock units are respectively provided on the first wiring line, the second wiring line, and the third wiring line, and the resistances of the first wiring line, the second wiring line, and the third wiring line are the same.

[0016] A method for simultaneously measuring temperature and digital input signals using a PLC thermal resistance input module according to the above aspect of the present invention, wherein S2 specifically includes the following steps:

[0017] S21. Compensate for the line resistance of the thermal resistance input module channel;

[0018] S22. Eliminate the influence of contact resistance on the temperature detection accuracy when the limit switch is closed.

[0019] A method for simultaneously measuring temperature and digital input signals using a PLC thermal resistance input module according to the above aspect of the present invention, wherein S21 specifically includes the following steps:

[0020] S211. Connect a cable with the same model, the same length, and the same resistance value as that in the first wiring line in series in the second wiring line;

[0021] S212. Connect a cable with the same model, the same length, and the same resistance value as that in the second wiring line in series in the third wiring line;

[0022] A method for simultaneously measuring temperature and digital input signals using a PLC thermal resistance input module according to the above aspect of the present invention, wherein S3 specifically includes the following steps:

[0023] S31. Set a logical judgment and identification program in the PLC to judge the temperature and digital input contact signals;

[0024] S32. Take corresponding measures according to different situations based on the logical judgment and identification program.

[0025] A method for simultaneously measuring temperature and digital input signals using a PLC thermal resistance input module according to the above aspect of the present invention, wherein the logical judgment and identification program in S31 specifically includes the following steps:

[0026] S311. Add a temperature value change rate judgment logic to the first wiring line to judge the accuracy of the temperature value detected by the thermal resistance temperature sensor;

[0027] S312. The PLC sends an alarm or interlock trip signal to the main motor according to the temperature value change rate judgment logic.

[0028] A method for simultaneously measuring temperature and digital input signals using a PLC thermal resistance input module according to the above aspect of the present invention, wherein the temperature value change rate judgment logic in S311 specifically includes the following steps:

[0029] S3111. When the temperature value does not change suddenly and the temperature value change rate ≤ 10 °C / s, determine that the temperature value detected by the thermal resistance temperature sensor is the true temperature value;

[0030] S31112. When the temperature value shows a sudden change and the rate of change of the temperature value is instantaneously ≥ 200 °C / s, it is determined that the temperature value detected by the thermal resistance temperature sensor is a false high temperature value.

[0031] According to the method for simultaneously measuring temperature and digital input signals using the PLC thermal resistance input module in the above aspect of the present invention, where S312 specifically includes the following steps:

[0032] S3121. When the PLC detects that the temperature value detected by the resistance temperature sensor ≥ the light fault alarm set value of 155 °C, the PLC operation station in the central control room issues a light fault alarm signal;

[0033] S3122. When the PLC detects that the temperature value detected by the resistance temperature sensor ≥ the heavy fault trip interlock value of 170 °C, the PLC operation station in the central control room issues a heavy fault alarm signal.

[0034] According to the method for simultaneously measuring temperature and digital input signals using the PLC thermal resistance input module in the above aspect of the present invention, where S32 specifically includes the following steps:

[0035] S321. When the PLC control cabinet door is closed and the digital input contact switch is closed, the PLC simultaneously sends an interlock trip signal to the motor main switch, and the PLC controls the motor main switch to trip and stop running;

[0036] S322. When the PLC control cabinet door is opened, the PLC issues an alarm signal prompt of "control cabinet door opened", and at the same time, the light fault alarm, heavy fault alarm and interlock trip signal are automatically cancelled. The operator promptly checks the reason for the opening of the PLC control cabinet door and resets the automatically cancelled function on the PLC operation station.

[0037] Adopting the above technical solution, the present invention has the following advantages:

[0038] The present invention provides a method for simultaneously measuring temperature and digital input signals using the PLC thermal resistance input module. By connecting a digital input contact signal in series in the temperature measurement circuit of the PLC thermal resistance input module channel and cooperating with the corresponding logical judgment and recognition method, it plays the role of simultaneously detecting temperature signals and digital input signals using the PLC thermal resistance input module, solves the problem of insufficient channels of the DI digital input module in the existing PLC system, expands the input capacity of the digital input signals of the PLC system, reduces the cost of purchasing the DI digital input module and the cost of upgrading and transforming the PLC system, reduces the implementation operation time, quickly responds to the actual on-site requirements. This method has a wide range of applications and is applicable to automation detection and control industries such as metallurgy, petrochemical, gas production, and industrial manufacturing, and has broad popularization value. Description of the Drawings

[0039] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non - limiting embodiments read in conjunction with the accompanying drawings.

[0040] Figure 1 is the wiring circuit diagram of the PLC thermal resistance input module for detecting temperature signals in the prior art;

[0041] Figure 2 is the wiring circuit diagram of the digital input (DI) module for detecting digital quantities in the prior art;

[0042] Figure 3 is the flow chart of the present invention for simultaneously detecting temperature and digital quantity signals using the PLC thermal resistance input module;

[0043] Figure 4 is the wiring circuit diagram of the PLC thermal resistance input module in the present invention;

[0044] Figure 5 is the comparison table of thermal resistance temperature and resistance values in the present invention;

[0045] Figure 6 is the schematic flow diagram of the logic program in the present invention;

[0046] Figure 7 is the detailed step schematic diagram of the logic judgment and recognition method in the present invention. Detailed Embodiments

[0047] The technical solutions of the present invention will be specifically described below in conjunction with the accompanying drawings of the specification. The detailed features and advantages of the present invention are described in detail in the specific embodiments, and the content is sufficient for any person skilled in the art to understand the technical content of the present invention and implement it accordingly. According to the specification, claims, and drawings disclosed in this specification, those skilled in the art can easily understand the related purposes and advantages of the present invention.

[0048] Figure 3 shows the flow chart of the present invention for simultaneously detecting temperature and digital quantity signals using the PLC thermal resistance input module;

[0049] Figure 4 is the wiring circuit diagram of the PLC thermal resistance input module in the present invention.

[0050] A method for simultaneously measuring temperature and digital quantity signals using a PLC thermal resistance input module is as Figure 3 shown, and specifically includes the following steps:

[0051] S1. Connect the digital contact signal in series into the thermal resistance signal circuit; in a specific embodiment, connect the limit switch contact signal in series into the thermal resistance signal circuit, that is, in the PLC control cabinet, connect the contact of the limit switch LS-1 that detects the opening and closing state of the PLC control cabinet door in series to the A-phase line of the thermal resistance TE-41 for detecting the stator temperature of the main motor of the 1# high-pressure nitrogen compressor.

[0052] Wherein S1 specifically includes the following steps:

[0053] S11. In the three-phase lines of the temperature measurement circuit of the thermal resistance input module channel, select one of the three-phase lines as the first wiring line; in a specific embodiment, select the A-phase of the main motor of the 1# high-pressure nitrogen compressor as the first wiring line. The reason for selecting the A-phase stator temperature is that the main motor has three-phase stator temperatures of A, B, and C detected simultaneously, the three-phase temperatures are basically the same, and each of them has its own alarm and trip protection interlock functions. If the A-phase protection fails, there are still B-phase and C-phase stator temperature protection functions to provide reliable protection. The thermal resistance TE-41 is located in the A-phase line, and the thermal resistance TE-41 is a PT100 type thermal resistance.

[0054] S12. In the PLC control cabinet, add a cable in the first wiring line and connect the digital contact signal in series to the first wiring line. In a specific embodiment, due to the new wiring for connecting the contact of the limit switch LS-1 in series, a certain length of cable is added to the A-phase line in the first wiring line. The resistance value corresponding to this cable is denoted as Rp. This resistance value Rp increases the resistance value of the A-phase line of the thermal resistance. Since this resistance value Rp is a newly added value, it affects the temperature detection accuracy in the wiring circuit. Therefore, it is necessary to eliminate the influence of the newly added resistance value on the temperature detection accuracy in the wiring circuit.

[0055] S2. Eliminate the influence of the digital contact signal access to the thermal resistance signal circuit on the temperature detection accuracy;

[0056] Wherein S2 specifically includes the following steps:

[0057] S21. Compensate the line resistances of the B and B phases of the thermal resistance input module channel;

[0058] Wherein S21 specifically includes the following steps:

[0059] S211. Connect a cable with the same model, the same length, and the same resistance value as that in the first wiring line in series to the second wiring line;

[0060] S212. Connect a cable with the same model, the same length, and the same resistance value as that in the second wiring line in series to the third wiring line;

[0061] In a specific embodiment, specifically asFigure 4 As shown, in the second and third wiring circuits of the thermal resistor, that is, in the B and B-phase wiring circuits, cables of the same model and the same length as those in the A phase are connected in series respectively, and their resistance values are both Rp, so as to offset the temperature detection error caused by the increase in the line resistance due to the increase in the cable Rp in the first wiring circuit, that is, in the A phase, when the limit switch is wired in series.

[0062] Figure 5 The comparison table of the temperature resistance values of the PT100 thermal resistor is shown.

[0063] S22. Eliminate the influence of the contact resistance on the temperature detection accuracy when the limit switch is closed.

[0064] In a specific embodiment, through actual measurement, the contact resistance value between the contacts when the limit switch LS-1 is closed is 0.01 Ω. The comparison table of the temperature resistance values of the PT100 thermal resistor is specifically as Figure 5 shown. From Figure 5 it can be seen that at any point within the working range of 0 to 200 °C of the TE-41 thermal resistor, when the resistance value is increased by 0.01 Ω, after conversion, the corresponding temperature value increases by about 0.025 °C. Therefore, the influence of the contact resistance value when the limit switch is closed on the temperature detection accuracy can be ignored and thus no treatment is required.

[0065] Figure 6 The flowchart of the logic program in the present invention is shown; Figure 7 The detailed step diagram of the logic judgment and recognition method in the present invention is shown.

[0066] In a specific embodiment, when the 1# high-pressure nitrogen compressor is running normally, the temperature of the stator of the main motor in the A phase is between 80 and 90 °C, and the temperature is the atmospheric temperature when it stops. Therefore, the temperature detection range of the thermal resistor TE-41 in the PLC is set to 0-200 °C. To protect the motor from being damaged due to overheating failure, this temperature is provided with a light high-temperature fault alarm, a high high-temperature heavy fault alarm and an interlock trip function. When the temperature of the thermal resistor TE-41 ≥ 155 °C, the PLC issues a light high-temperature fault alarm. When the temperature of TE-41 ≥ 170 °C, the PLC issues a high high-temperature alarm and, when the 1# high-pressure nitrogen compressor is in the running state, sends an interlock trip signal to the main motor of the 1# high-pressure nitrogen compressor. When the PLC control cabinet door is opened, the contact of the limit switch LS-1 is disconnected, the A-phase line of the thermal resistor TE-41 is disconnected, and the resistance value between the A and B phases is infinite. The PLC displays that the temperature will rise above 200 °C for high open-circuit overflow, and the PLC will issue an alarm and an interlock trip signal. Therefore, it is necessary to judge whether the increase in the temperature of the thermal resistor TE-41 is caused by the opening of the PLC control cabinet door or the actual increase in the temperature of the stator of the main motor in the A phase, so as to prevent false alarms and false trips, specifically as Figure 6 shown.

[0067] S3. Add a logic judgment and recognition method in the PLC to detect the temperature and digital input signal simultaneously. The logic judgment and recognition method in S31 is as Figure 7 shown, and specifically includes the following steps:

[0068] S31. Set a logic judgment and recognition method in the PLC to judge the temperature and digital input signal;

[0069] The logic judgment and recognition method in S31 specifically includes the following steps:

[0070] S311. Add a logic for judging the temperature change rate on the first wiring line to judge the accuracy of the temperature value detected by the thermal resistance temperature sensor;

[0071] In a specific embodiment, according to the actual situation of the 1# high-pressure nitrogen compressor equipment, whether the main motor is in the normal operation state or the stop state, the actual temperature value of the stator A-phase temperature of the motor will not change drastically. Therefore, a new logic for judging the temperature change rate is added to judge the authenticity of the temperature value measured by the thermal resistance TE-41.

[0072] The method of the logic for judging the temperature change rate in S311 specifically includes the following steps:

[0073] S3111. When the temperature value does not show a sudden change and the temperature change rate ≤ 10°C / s, determine that the temperature value detected by the thermal resistance temperature sensor is the true temperature value;

[0074] S31112. When the temperature value shows a sudden change and the temperature change rate instantaneously ≥ 200°C / s, determine that the temperature value detected by the thermal resistance temperature sensor is a false high temperature value.

[0075] S312. The PLC sends an alarm or interlock trip signal to the main motor according to the logic for judging the temperature change rate.

[0076] S312 specifically includes the following steps:

[0077] S3121. When the PLC detects that the temperature value detected by the resistance temperature sensor ≥ the light fault alarm set value of 155°C, the PLC operation station in the central control room sends a light fault alarm signal;

[0078] S3122. When the PLC detects that the temperature value detected by the resistance temperature sensor ≥ the heavy fault trip interlock value of 170°C, the PLC operation station in the central control room sends a heavy fault alarm signal.

[0079] In a specific embodiment, when the PLC control cabinet door is closed, the normally open contact of the limit switch LS-1 closes, and the TE-41 thermal resistor is in a normal temperature detection state. The temperature value does not show a sudden change phenomenon, that is, on the premise that the temperature value change per second does not exceed 10 °C, when the TE-41 temperature value detected by the PLC ≥ the light fault alarm setting value of 155 °C, the PLC operation station in the central control room issues a light fault sound and light alarm prompt; when the TE-41 temperature value ≥ the heavy fault tripping interlock value of 170 °C, the PLC operation station in the central control room issues a heavy fault sound and light alarm prompt.

[0080] S32. According to the logical judgment and recognition method, take corresponding measures in different situations.

[0081] Among them, S32 specifically includes the following steps:

[0082] S321. When the PLC control cabinet door is closed and the digital quantity contact switch is closed, the PLC simultaneously sends an interlock tripping signal to the motor main switch, and the PLC controls the motor main switch to trip and stop running; in a specific embodiment, if the 1# high-pressure nitrogen compressor is in the running state, the PLC simultaneously sends an interlock tripping signal to the 1# high-pressure nitrogen compressor motor main switch to make it trip and stop running.

[0083] S322. When the PLC control cabinet door is opened, the PLC issues an alarm signal prompt of "control cabinet door opened", and at the same time, the light fault alarm, heavy fault alarm and interlock tripping signal are automatically cancelled. The operator timely checks the reason for the opening of the PLC control cabinet door and resets the automatically cancelled function on the PLC operation station.

[0084] In a specific embodiment, when the PLC control cabinet door is opened, at the moment of opening, the normally open contact of the limit switch LS-1 changes from the closed state to the open state. Utilizing the characteristic that the resistance value is 0 when the switch contact is closed and infinite when it is open, the temperature signal is normally detected when the limit switch is closed, and when it is open, the temperature signal steps up to the full-scale value overflow. The resistance value between the A and B lines of the temperature measuring thermal resistor TE-41 instantaneously becomes infinite, and the temperature value of TE-41 changes abruptly, that is, the change amount of the temperature value per second must exceed 10 °C, and the temperature value instantaneously rises from the previous normal detection value to above 200 °C with high open circuit overflow. It can be judged that after the PLC control cabinet door is opened, the limit switch LS-1 operates, causing the A-phase line of the temperature measuring thermal resistor TE-41 to break, resulting in a sudden rise in the temperature detection value. The PLC sends the "OPEN" alarm signal of the control cabinet door to the central control room PLC operation station to remind the operator that the on-site PLC control cabinet door is opened. At the same time, since the temperature measuring thermal resistor TE-41 detects a false high temperature value, to avoid mis-tripping the machine and misleading the operator, the light fault alarm, heavy fault alarm, and interlock tripping functions of the temperature measuring thermal resistor TE-41 will be automatically bypassed at this time. It is necessary to go to the on-site PLC control cabinet to check and confirm the reason for the opening of the control cabinet door and take corresponding treatment measures. After the treatment and recovery, the operator confirms and resets at the PLC operation station to make the light fault alarm, heavy fault alarm, and tripping functions of this temperature return to the normal state.

[0085] Finally, it should be pointed out that although the present invention has been described with reference to the current specific embodiments, those of ordinary skill in the art in this technical field should recognize that the above embodiments are only used to illustrate the present invention and are not used as a limitation to the present invention. Various equivalent changes or substitutions can be made without departing from the inventive concept of the present invention. Therefore, as long as the changes and variations of the above embodiments are within the scope of the spirit of the present invention, they will fall within the scope of the claims of the present invention.

Claims

1. A method for simultaneously measuring temperature and digital quantity signals by using a PLC thermal resistance input module, characterized in that, Including the following steps: S1. Connect the digital contact signal in series to the thermal resistance signal circuit; The specific steps of S1 include the following: S11. In the three-phase lines of the temperature measurement circuit of the thermal resistance input module channel, select one of the three-phase lines as the first wiring line; S12. Inside the PLC control cabinet, add a cable in the first wiring line and connect the digital contact signal in series to the first wiring line; S2. Eliminate the influence of the digital contact signal connected to the thermal resistance signal circuit on the temperature detection accuracy; The specific steps of S2 include the following: S21. Compensate the line resistance of the thermal resistance input module channel; S22. Eliminate the influence of the contact resistance on the temperature detection accuracy when the limit switch is closed; S3. Add a logic judgment and recognition method in the PLC to detect the temperature and digital contact signal simultaneously, The specific steps of S3 include the following: S31. Set a logic judgment and recognition program in the PLC to judge the temperature and digital contact signal; The specific steps of the logic judgment and recognition program include the following: S311. Add a temperature value change rate judgment logic on the first wiring line to judge the accuracy of the temperature value detected by the thermal resistance temperature sensor; S312. According to the temperature value change rate judgment logic, the PLC sends an alarm or interlock trip signal to the main motor; S32. According to the logic judgment and recognition program, take corresponding measures according to different situations.

2. A method for simultaneously measuring temperature and digital input signals using a PLC thermal resistance input module as claimed in claim 1, characterized in that The other two-phase lines in the three-phase lines in S11 are the second wiring line and the third wiring line respectively. A thermal resistance temperature sensor is provided on the first wiring line. Alarm units and trip protection interlock units are provided on the first wiring line, the second wiring line, and the third wiring line respectively. The resistances of the first wiring line, the second wiring line, and the third wiring line are the same.

3. A method for simultaneously measuring temperature and digital input signals using a PLC thermal resistance input module as claimed in claim 2, characterized in that, The specific steps of S21 include the following: S211. Connect a cable with the same model, the same length, and the same resistance value as that in the first wiring line in series to the second wiring line; S212. Connect a cable with the same model, the same length, and the same resistance value as that in the second wiring line in series to the third wiring line.

4. A method for simultaneously measuring temperature and digital quantity signals using a PLC thermal resistance input module as described in claim 1, characterized in that, The specific steps of the temperature value change rate judgment logic in S311 include the following: S3111. When the temperature value does not change suddenly and the temperature value change rate ≤ 10°C / s, judge that the temperature value detected by the thermal resistance temperature sensor is the true temperature value; S31112. When the temperature value changes suddenly and the temperature value change rate is instantaneously ≥ 200°C / s, judge that the temperature value detected by the thermal resistance temperature sensor is a false high temperature value.

5. The method for simultaneously measuring temperature and digital input signals using a PLC thermal resistance input module as claimed in claim 4, wherein The specific steps of S312 include the following: S3121. When the PLC detects that the temperature value detected by the resistance temperature sensor ≥ the light fault alarm set value of 155°C, the PLC operation station in the central control room sends a light fault alarm signal; S3122. When the PLC detects that the temperature value detected by the resistance temperature sensor ≥ the heavy fault trip interlock value of 170°C, the PLC operation station in the central control room sends a heavy fault alarm signal.

6. A method for simultaneously measuring temperature and digital input signals using a PLC thermal resistance input module as described in claim 5, characterized in that The specific steps of S32 include the following: S321. When the PLC control cabinet door is closed and the switch contact switch is closed, the PLC simultaneously sends an interlock trip signal to the motor main switch, and the PLC controls the motor main switch to trip and stop the machine; S322. When the PLC control cabinet door is opened, the PLC sends out a "control cabinet door open" alarm signal prompt, and at the same time, the minor fault alarm, major fault alarm and interlock trip signal are automatically released. The operator promptly checks the reason why the PLC control cabinet door is open and resets the automatic release function on the PLC operation station.

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