JPH0619530A - Digital controller - Google Patents

Abstract

PURPOSE:To remove limitation due to the sampling period of the digital controller from a function connection programming quantity by providing a function which automatically adjust the sampling period. CONSTITUTION:A 1st storage part 1 is stored with a function connection program generated by combining control elements and arithmetic execution time information attached to the control elements is included. An adder 3 integrates the arithmetic execution time of the individual control elements to find the total control arithmetic time. A period derivation part 4 finds the sampling period from the total control arithmetic time. An output process start control part 5 sends out a signal for starting an output process in synchronism with the sampling period. Consequently, the function constitution for automatically finding the sampling period is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital controller used for process control of petroleum, chemical, steel, etc.
The present invention relates to a programmable digital controller that performs a control operation determined by a programming device externally connected to the controller, and more particularly to a digital controller that includes means for flexibly and automatically changing a sampling period that restricts the program amount.

[0002]

2. Description of the Related Art A digital controller, in addition to the completion of signal acquisition processing and signal output processing during a sampling period,
A control calculation must be executed based on the input data at the sampling time to determine the manipulated variable. Due to this limitation, the digital controller must execute all control calculations before saving the control calculation program in the storage medium of the controller so that the control calculation is completed within the sampling period (also referred to as the control period). Is being checked. The digital controller often has a fixed sampling period,
There is also a variable type that makes a large program variable. In the case of variable type, the change of sampling period must be declared in the control calculation program.

As described above, since the controller has to consider the execution speed, the usage limit is checked by recognizing the program execution speed. JP 59-98
In the 212 bulletin, the execution speed confirmation method of the sequence controller is described, but the same execution speed is confirmed in the digital controller mainly for PID calculation.

[0004]

As the capacity of the IC chip used in the digital controller is reduced and the processing speed is increased, the storage capacity is increased and the control calculation execution time is increased. Therefore, the controller is required to be able to perform various processes on a large scale. A large number of control operations are assembled into a series of control operation processes, which is called a function connection program. The number of steps of this program is limited in execution speed in addition to the storage capacity of the digital controller. As described above, although the problem of the storage capacity is being solved, the restriction of the execution speed by the sampling cycle necessitates the programmer who creates the function connection program to select whether or not the desired control operation can be constructed. So it's a problem. Normally, when the function connection program becomes too large to be installed, in the case of the variable sampling cycle type, set it as wide as possible.
Even so, it is necessary to consider the sampling period.

The problem that the present invention is to solve is as follows.
This is a troublesome procedure in which the programmer has to create the function connection program while being aware of the sampling cycle, and an object of the present invention is to eliminate such troublesome procedure and eliminate the modification after the program creation as much as possible. .

[0006]

The present invention is provided with a function for deriving a sampling period necessary for causing a digital controller to execute a control operation by a function connection program.
The object of the invention is achieved by adopting the function of automatically changing the sampling period.

The function connection program is created by combining blocked control elements such as PID control calculation and square root calculation, and these control elements have a pre-measured calculation execution time. The digital controller adds the calculation execution time from the beginning after loading the function connection program, and when the calculation times of all the control elements have been added, the total calculation time and the A of the first signal conversion unit are calculated.
A cycle deriving unit that derives a sampling cycle from a value obtained by adding the / D conversion processing time and the D / A conversion processing time of the second signal conversion unit operates, and is set and operates as the sampling cycle of the digital controller. As for the execution processing order between sampling cycles, after the input is taken in by A / D conversion, self-determination processing (memory check) of the controller is performed, and then control calculation processing is performed. In addition, self-diagnosis processing (watchdog timer for monitoring the microprocessor) is performed again, and then output processing by D / A conversion is performed. D /
Since the A conversion must be performed immediately before the next cycle, the D / A conversion process must also be shifted according to the sampling cycle. This is because there are integral calculation and differential calculation using the sampling period in the control calculation.
This is because a correct control calculation cannot be obtained unless the output is output at sampling cycle intervals. Since the D / A conversion processing time is a fixed time, the D / A conversion processing time
The time obtained by subtracting the conversion processing time is the start time of the D / A conversion processing in that cycle. The output processing start control unit
The start time of the D / A conversion process is obtained, and a trigger for starting the output process is given.

[0008]

Since the sampling period is obtained in the digital controller and the digital control is performed at the sampling period, the programmer of the functional calculation program does not have to worry about whether the control calculation is completed within the sampling period. Complex control operations can be written as far as the storage capacity allows. As a result, the programmer must be careful that the sampling period found inside the controller is
It is only a check to see if there is any problem in controlling the controlled object. In contrast to the flow rate control that needs to be controlled in units of tenths of a second, if a sampling cycle in units of seconds is set, the control amount of the control target cannot be controlled to be satisfactory by the controller. In addition, aliasing due to the sampling period may occur, and a correct signal may not be acquired. Therefore, the programmer can avoid the labor of forming a program while paying attention to the sampling cycle, but it is necessary to check whether or not the control target can be controlled at the sampling cycle obtained as a result of the program. These checks may be performed by a programming device or by displaying the sampling period on the display unit of the controller, and there is no great obstacle.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to FIG.

In the digital controller of the present invention, an operation output is transmitted to the process to be controlled by an electric signal, and the process amount output by the process controlled by the operation output is fetched by the electric signal to perform PID control calculation and the like. , The operation signal is obtained, and the operation signal is converted into an electric signal again to give a process a periodic operation.
The period from the capture of the process amount to the output as the operation signal is called the sampling period. The operation output from when the process amount is captured to immediately before the operation signal is output is equal to the operation output output in the previous cycle. That is, the operation output output in the previous cycle is held. The digital controller normally performs this sample hold operation.
The process amount is taken in as an analog amount, but A / D
By conversion, it is converted into data handled by the microcomputer. This data is called a PV value. The digital controller derives an operation output value from these amounts so that the PV value matches the set value (SV value) set in the controller. The calculation algorithm used for derivation is called control calculation. The digital controller of the present invention is a programmable controller of the type in which this control calculation can be freely changed by a program. The program defining the control calculation is performed in the function connection program format shown in FIG. The function connection program is
Operands that represent control elements or operation elements and arguments that pass data to these operations. The calculation time obtained from the operand is automatically added by the programming device. The function connection program and the calculation time are written in the first storage unit having a user ROM as a medium. The user ROM is a removable ROM or an EEPROM. In the former case, the user ROM is attached to the programming device, and after writing the function connection program and the operation time, it is attached to the controller. In the latter case, the function connection program is set in the controller in a format in which the program device and the controller are connected via a communication line and downloaded. Since the function connection program only describes the operands of the operation elements, the control operation algorithm must be stored in advance in the operation processing routine indicated by the operands. This control calculation processing program is stored in a second storage section called a system ROM. The control operation decoding function unit 8 can be realized by a microprocessor. The control operation decoding function unit 8
The operand and the argument written in the user ROM are read, the argument is passed to the arithmetic processing routine indicated by the operand, and the arithmetic processing is executed.

The digital controller performs the processing shown in FIG. 2 during one sampling period. First, A / D conversion is performed to make the process amount into a data format that can be processed by a microprocessor. Next, a memory check is performed to increase the RAS function of the controller. After that, the control operation decoding function unit described above executes the control operation processing by an interpreter method. After the control calculation processing, self-diagnosis for program runaway monitoring by the watchdog timer is performed. Next, after idling to perform communication processing and the like, processing for D / A converting the operation output value obtained by the control calculation processing is performed. Since the D / A conversion process cannot perform a correct control calculation unless it is executed at a constant cycle, a trigger signal for starting the D / A conversion must be generated.

In the digital controller of the present invention, first, the adder that reads the operation time written in the user ROM from the beginning and adds it is operated. The added result is transmitted to the cycle deriving unit 4 as the total calculation time. The cycle deriving unit 4 obtains the minimum sampling cycle in which the processing shown in FIG. 2 can be performed within the sampling cycle, and sends the cycle to the cycle control unit 6 and the output processing start control unit 5. The cycle control unit 6 performs D / A conversion processing every time the sampling cycle is completed.
Control is performed so as to perform a series of processes up to the A conversion process. The output processing start control section 5 passes the sampling cycle minus the time required for the D / A conversion processing to the cycle control section as the output processing start time. The cycle control unit 6
The D / A conversion process is started based on this time.

The digital controller configured as described above increases the sampling cycle as the control calculation time increases, and therefore functions so that the control calculation process is always completed within the sampling cycle.

The obtained sampling period can be displayed on the display unit provided in the digital controller. This allows
It is possible to confirm how many sampling cycles the currently operating controller is performing the control operation.

Further, since the sampling period that can be set in the controller has a limit, it is more useful to prevent malfunction when the period deriving unit obtains a value equal to or larger than the limit sampling period. Therefore, it is kinder to the user to provide the function of displaying the sampling cycle setting error when such a case occurs. However, in practice, the error does not occur because a margin is set in the setting range of the sampling period so that such an error does not occur.

[0016]

In order for the digital controller to perform the desired control action, the programming amount limitation must be removed. The storage capacity of the program can be solved by a ROM that is smaller and larger in capacity, but the time for executing the program is limited by the sampling cycle (control cycle) of the digital controller.

Since the function of adjusting the sampling period according to the control calculation time is provided inside the digital controller, the control calculation execution process that increases as the program amount increases can be completed within the sampling period. It will be possible. This eliminates the troublesome procedure of limiting and adjusting the program amount while considering the sampling period.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a processing sequence performed by a digital controller in one sampling cycle.

FIG. 3 is an explanatory diagram of a function connection program.

[Explanation of symbols]

1 ... 1st memory | storage part, 2 ... 2nd memory | storage part, 3 ... adder, 4 ... period derivation | leading-out part, 5 ... output process start control part, 6 ... period control part, 7 ... 1st signal conversion part, 8 ... control Operation decoding function section, 9
... Second signal converter.

Claims (3)

[Claims] 1. A digital controller for controlling a process and subjecting sample values to control, a first storage unit storing a function connection program representing a control operation sequence of the digital controller, and the function connection program. A second storage unit for storing a control calculation processing program defined by the control calculation name and an A / D conversion of an electric signal applied to the input terminal of the digital controller, and a signal data which can be processed by a microcomputer. One signal conversion unit, conversely, a second signal conversion unit for D / A converting the processed data into an electric signal, and the function connection program stored in the first storage unit are decoded, and according to the control operation, A control operation decoding function unit for executing the control operation processing program stored in the second storage unit by an interprinter method, and the function connection program An addition unit that counts the calculation time associated with each of the constituent calculation elements, and a total calculation time obtained as a result of the addition, determines a sampling cycle for determining the sampling cycle for capturing the electrical signal by the first signal conversion unit. A digital controller, comprising: a cycle deriving unit for controlling the output of the second signal; and an output processing start control unit for shifting the processing start of the second signal converter based on the derived sampling cycle. 2. The digital controller according to claim 1, wherein the sampling period obtained by the period deriving unit is output to a display unit of the digital controller. 3. The digital controller according to claim 1, wherein when the sampling period obtained by the period deriving unit exceeds the maximum sampling period, a sampling period setting error is output to the display unit of the digital controller. .