JPH0375889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a process control method in a control computer system, and particularly to a process control method provided with an override function in a system that performs batch sequence control.

[Prior art and its problems]

In a computer system that performs sequence control, it is necessary to check whether the process status is maintained normally.
A constant monitoring function is required. For example, when starting a certain pump, the pump must operate (reflected on the digital input signal) within a certain fixed time after the start request (outputting the digital output signal). Further, once the pump is in operation, it continues to operate until the next stop request is issued. Thereafter, the operating state must be maintained until a stop request is issued.

In sequence control, even if any of these conditions is not satisfied, it is regarded as an abnormality in the process, and necessary abnormality processing is performed to bring the process into a safe state. Then, repair the malfunctioning device (equipment that makes up the process, such as a pump, valve, sensor, etc.), and resume necessary control after recovery.

Conventionally, various methods have been used to realize these functions, one example of which is shown in FIG. In this method, the process status is stored as bit information in the process status storage table 2 by the analog quantity conversion program 10 and the process status importing program 1, but this content is monitored by the process status monitoring program 4. . In FIG. 1, solid lines indicate program execution procedures and dotted lines indicate data flow. The method is to compare the contents of the monitoring status storage table 5 set in response to an output request with the command output program 7 and the contents of the process status storage table 2, and if they are the same, it is considered normal. If so, the contents of the mask data storage table 6 are checked, and if the mask is released, it is assumed that the process is abnormal, and a request is issued to the control program 8 to perform necessary abnormality processing.

Here, both the contents of the monitoring status storage table 5 and the mask data are stored in the command output program 7.
are created sequentially and dynamically according to commands from the control program 8. In particular, mask data is used after the output request is issued until devices such as valves and pumps are in a state that corresponds to the output request such as opening/closing or starting/stopping. This was created to prevent it from being judged as abnormal, and the mask is set at the same time as an output request is made, and is released when the state corresponding to the output request is reached. In this example, the process status is not only a digital input signal, but also data that is taken in as an analog signal. By comparing the magnitude with a set value and converting it to bit information (10), the data is the same as the digital input signal. Conditions are monitored using this method.

Here, in order to show the operation of the actual control program, an example of a simple process is shown in FIG. In this example, valve V1, pump P1 and level switch LS
1 is interfaced with a digital input signal, but the temperature T ₁ and level L ₁ of the tank on the left side of the figure are input as analog signals.
This analog quantity is converted into analog quantity conversion program 1.
0 is compared with the value in the set value storage table and converted into bit information, which is used in the control program.

FIG. 3 shows the processing procedure of a program that controls the process shown in FIG. 2. In the processing procedure of this control program, before starting control, a condition check process for starting is performed (step A).
That is, the valve is closed and the pump is at rest;
Check that the temperature and level of the left tank are within certain limits. Once this condition is met, proceed to the next step B to open the valve, start the pump in step C, wait for the level switch to turn on in steps D and E, and then proceed to steps F and G. The pump is stopped and the valve is closed to complete the process.

Regarding abnormality processing when an abnormality occurs, if the start conditions are not satisfied, the process goes into a waiting state at step H, and then checks the start conditions again (step A) upon the operator's restart request.
I do. Next, if any abnormality occurs while processing from Step B to Step G, the system jumps to Step I, closes the valve, stops the pump, and then asks the operator to Waits for a restart request (steps I to K). The operator requests restart after eliminating the cause of the abnormality, but the program does not immediately return to the routine that performs normal processing, but meets the conditions for restart at step L, that is, the valve closes and the pump stops. and check that the temperature and level are within certain values. Only when this condition is satisfied does the processing from step B onwards, which is a normal processing routine, begin.

In such an example, the limit switch that sends back the status of the valve with a digital input signal may fail.
If the valve is in the open state but the digital input signal (DI) of the valve is not in the open state, the control program 8 detects a process abnormality in step B, and executes steps I and J. After the abnormality processing is performed, the state becomes the holding state of step K. Even if there is a restart request from the operator,
An abnormality occurs when the valve is opened again in Step B, and it is not possible to proceed to Step C and subsequent steps until the limit switch is repaired. This situation occurs due to inadequate surrounding conditions even though the process itself is operating normally, and becomes an obstacle to increasing the operating efficiency.

Furthermore, in batch sequence control, a certain set procedure is called one batch, and this batch is sequentially repeated to perform operation, but in a certain batch,
If you say that the temperature _T1 of the tank on the left side of Figure 2 is not within the originally planned specified value, but you want to run the control program 8 shown in Figure 3, you need to modify the control program. The only way to get the program working is to uncheck the temperature or widen the range of allowable settings.

As mentioned above, various condition checks and status monitoring in sequence control are absolutely necessary conditions for realizing safe plant operation, but on the other hand, various checks become obstacles and make flexible operation impossible. This has led to a decline in operational efficiency.

On the other hand, as a conventional technology for testing programs, a test mode function is provided to enable program execution without actually having valves, pumps, etc., without inputting the actual process status. Some machines have functions such as automatically creating process conditions according to output commands or ignoring all abnormal factors, but these are for testing purposes only and cannot be applied in actual operations. It was nothing like that.

[Purpose of the invention]

The purpose of the present invention is to provide a new override function to overcome the drawback that various condition checks in sequential control of a process often result in interruption of process operation and a decrease in operating efficiency, while ensuring safety. It is an object of the present invention to provide a process control method that resumes control from an interrupted state and continues operation of the process as necessary.

[Means to solve the problem]

The feature of the present invention is that in the process control method,
It is characterized by having the following steps.

(b) Process state storage step for inputting and storing process state signals; (b) Monitoring for comparing conditions set in advance corresponding to the process state with the stored process state signal and determining discrepancies between the two. Step (c) When the result of the determination is a discrepancy, refer to a mask set in advance for cases where the discrepancy is known to occur in a normal process state, and determine whether the mask is set for the process state. If so, proceed with normal control (d) Refer to the override to consider the process state to be in a matching state for the mismatched process state for which the mask is not set,
If an override has been set for the process state, an override step (e) that proceeds with normal control.If the override has been canceled for the process state by referring to the override, performs a predetermined safety process on the process. An interruption step (F) for interrupting the control by setting the override for the mismatched process state (f) A control restart step for resuming the normal control [Operation] Such the present invention According to , when a discrepancy occurs in the status signal input from a process with the setting conditions that cannot be avoided even with a mask, the process is temporarily interrupted after performing predetermined safety processing, and an override is performed for the discrepancy signal. The discrepancy can be ignored by setting , and normal control can be resumed immediately if the operator requests restarting.

According to the present invention, when a process state in which conditions do not match occurs, the necessary safety procedures are performed and control is interrupted, and during this period, the cause of the mismatch is investigated and the cause is determined to be, for example, a malfunction of a relay or sensor. (This frequently occurs in the field environment), and if it is confirmed that there are no obstacles to the progress of control, control can be immediately restarted and the failed equipment can be repaired while continuing process operation. Once the override is set, the cause of the mismatch is removed and the mismatch status signal is ignored until the override setting is canceled, so that control will not be interrupted again. As described above, the present invention has the effect of dramatically improving the operating rate while ensuring the safety of process control.

〔Example〕

FIG. 4 shows a configuration of functional blocks as an embodiment of the present invention having this override function. In this figure, the functional blocks having the same reference numerals or names as those shown in FIG. 1 are the same as the functions shown in FIG. 1 described above, and the following description will focus on the differences.

The difference from the conventional one in FIG. 4 is that an override setting state storage table is added. This improves the functionality of each program's processing as described below.

That is, the process status monitoring program 4
Captured process status (value of 2 captured in 1)
Even if the values in the monitoring state storage table 5 do not match and the mask data is canceled, if override is set for the corresponding device, it is treated as normal. In addition, in the control program 8,
When performing the condition check shown in step A or L in FIG. 3, if an override is set for the target device, it is taken from the actual input signal and is regarded as normal regardless of the state of the process storage state table 2.

Furthermore, in the command output program 7, even if an answer request for an output request such as starting/stopping a pump is not returned within the time limit, if an override is set for the device such as the pump, it is not considered an error. First, assuming that the answer request has been returned normally, the control program terminates normally. This is to ensure time for the device to actually operate when the override is set, and when an output request is made, normal completion is not immediately reported even if the override is set.
Furthermore, if an answer call is returned within the time limit, it is treated as a normal end at that point, regardless of the override setting state.

The above-mentioned mask function is a function that prevents normally normal operations from being treated as "abnormal" due to transient responses or specific operations. Safety is related to speed and distance between vehicles, and it is known in advance that if the speed is slow even when approaching a vehicle, an abnormality in the distance signal will be avoided. In contrast, the override function of the present invention ignores the actual device status obtained from the status signal, such as device failures that cannot be avoided by masks or cannot be known in advance, and controls the device by assuming it as normal. This function is essentially different from that of a mask.

Further, as in the above embodiment, the override function of the present invention can be provided for each device. This means that digital input signals and devices do not necessarily have a one-to-one correspondence, and multiple signals
The state of one device may be detected (for example, a valve input signal DI consists of two relay contacts, one open and one closed), and an actual accident or change in operating conditions may be detected by this device. This is because it often occurs. Therefore, by setting overrides on a device-by-device basis, operator operations can be significantly reduced. Note that the override setting may be made for each digital input signal. Also,
Similar to DI, an override function can be provided for each point or device for analog input signals (AI).

In the system having the above-mentioned override function, operation time charts when the control procedure shown in FIG. 3 is executed are shown in FIGS. 5a to 5c in comparison with the conventional system. In this example, it is assumed that the limit switch of valve V1 fails and the limit switch remains closed even though the valve is opened. FIGS. 5a and 5b are time charts according to the prior art, showing that the program is in a waiting state and cannot operate until the limit switch of valve V1 is repaired. In the flowchart of Fig. 3, step A is performed normally, and since the V1 open signal is not input during the execution of "OPEN V1" in step B, it is determined that there is an abnormality and jumps to step I, and pumps P1, After processing to bring the process into a safe state by stopping and closing the output of the bubble V1, a so-called control suspension state is entered, in which the operator waits for a restart request.

On the other hand, FIG. 5c shows a case according to the present invention, in which the valve V1 jumps to step I in FIG.
After confirming that the limit switch is malfunctioning, the operator sets an override to V1 and issues a restart request, and control is immediately resumed. Even after restarting, the V1 open input signal cannot be obtained, so an abnormality is detected in step B. However, if the V1 override setting is confirmed, it will be treated as if there was an input to V1 (the broken line in cV1 in Figure 5). The actual limit switch state (indicated by ) is ignored and program 8 advances control to step C. Also, once the override is set, the signal is ignored until it is canceled, so V
Control will not be interrupted if 1 is checked repeatedly.

In fact, limit switches and other devices break down frequently in the field environment, and many of these devices are required for process control, so repairs,
Replacement will take a long time. However, failure of such sensors/switches is not an essential obstacle to the progress of control, and in such cases, if the present invention is applied, control can be resumed immediately after a failure of these devices is confirmed, making it easier to repair. During this period, actual control can be performed in parallel, and the fifth
As shown in the figure, UT (operability improvement time)
Operation efficiency can be significantly improved.

Although FIG. 5 shows the case where the limit switch of the valve fails, the effect of the present invention is exactly the same even if the pump fails. Even if you want to remove it, you can easily do so by simply setting an override.

In the above-mentioned embodiments, all override settings were made manually, but here an embodiment will be described in which a function is provided to automatically set the overrides using a computer. In this embodiment, the procedure from finding an abnormality in V1 to investigating the cause and setting an override when the present invention is applied as shown in Fig. 5c is automatically performed. Shown in Figures 6a-e. In this figure, the output procedure of output data, check data, and mask data (ON at low level) is exactly the same as the conventional one shown in FIG. In Figure 6, after the startup request,
This indicates when input data is not returned within the time limit set for the device. Conventionally, at this point, the mask is released and the device is considered to be abnormal, and the necessary abnormality processing is performed on the control program. However, in this embodiment, instead of immediately indicating an abnormality, by setting an override, it is treated as a normal termination, and after that, the device operates correctly according to various other input information. We will determine whether the input data was simply not reflected, or whether the device itself did not work, and if it is determined to be the former,
Control is continued with the override set, and then the override is canceled when the limit switch is restored to normal.

Here, as an example of a method for determining whether or not the device itself is normal but is not reflected in the input data, a case will be shown in which an abnormality is detected in the pump in the process shown in FIG. In this process, if the pump operates, it will appear as a change in the liquid level in the left tank, so monitor the output (analog amount) of level sensor L1 with a meter (not shown), and if there is no change, , it is a failure of the pump itself, and if there is a change, it is determined that only the input signal system is abnormal.

By the way, the automatic override setting function of this embodiment is not necessarily applicable to all devices to be controlled. In the process example shown in Figure 3, there is a restriction that the pump must be started after the valve is opened, and simply opening the valve will not cause a change in the tank level. If an abnormality in V1 is detected,
As shown in the procedure shown in Figure 5, after confirming that the limit switch is malfunctioning, the override should be set manually.

According to this embodiment, the automatic override setting function further improves the plant operating efficiency.

As yet another embodiment, a case will be described below in which a check function is provided for the manual or automatic override setting shown above.

Generally, in plant control, the level of abnormality of each device changes dynamically depending on the control steps or the state of the plant. Here, in a control that has three "processes": raw material charging, reaction, and product unloading, abnormalities in devices related to raw material loading are not very important while the product unloading process is being executed; In a control system where an abnormality in a device for product removal can be determined to be serious, override settings for a device for product removal can only be set manually by a plant engineer rather than a general operator, whereas In contrast, the computer system is provided with a judgment function that enables automatic override setting and manual setting by general operators.

Further, as yet another embodiment, an example in which the override setting state is constantly monitored and the override is forcibly canceled as necessary will be described below.
In this example, in the target plant,
If a certain device that plays an extremely important role is set, it will be canceled immediately, and for other devices, if it remains set for a certain period of time, Forcibly,
This is a "cancellation". In this example, these functions prevent overrides from being left unintentionally set, and together with the previous example, they have extremely significant implications in terms of product quality and safe plant operation. It is something that has.

[Effects of the Invention] According to the present invention, when a process differs from the desired state, safety processing is performed to interrupt control, and an override function is used to "deem it normal" or "in a certain state". As a result, control can be restarted from an interrupted state, resulting in significant improvements in plant operation and the ability to ensure safe operation.

[Brief explanation of drawings]

Fig. 1 is a functional configuration diagram showing a conventional system, Fig. 2 is an example of a simple process, Fig. 3 is a flowchart showing the processing flow of the conventional system and the present invention, and Fig. 4 is a functional block diagram showing a conventional system.
5 is a functional block diagram of the system of the present invention, FIG. 5 is an operation time chart in one embodiment of the present invention, and FIG. 6 is an operation time chart explaining an override automatic setting function in another embodiment. 1...Process state capture program, 2...Process state storage table, 4...Process state monitoring program, 5...Monitoring state storage file,
6... Mask data storage table, 7... Command output program, 10... Analog amount conversion program.

Claims (1)

[Claims] 1. In a process control method for sequentially controlling a process, (a) a process state storage step for inputting and storing a process state signal; (b) a step set in advance in accordance with the process state; a monitoring step of comparing the condition with the stored process state signal and determining a mismatch between the two; (c) when the result of the judgment is a mismatch, a case where it is known that the mismatch occurs in a normal process state; (d) a masking step that refers to a preset mask and proceeds with normal control if the mask is set for the process state; (d) for the mismatched process state for which the mask is not set; refer to an override that considers the process state to be in a matching state,
(e) If the override has been canceled for the process state by referring to the override, perform a predetermined safety process on the process. (f) following the suspending step, setting the override for the mismatched process state and resuming the normal control; Characteristic process control method.