JPS63120301A - One-loop controller - Google Patents

Abstract

PURPOSE:To secure the safe drive of a plant even with runaway of a control part by turning a switching means according to the AND conditions between the trouble signal of a diagnosis means and the normal signal of a watchdog timer. CONSTITUTION:When a control part 11 has no abnormality in an automatic mode, the trouble-free signal, the inverse of CD of a self-diagnosis part 11b is kept at a high level. At the same time, a watchdog timer 11c outputs a normal signal since each processing is carried out within a prescribed time at a digital arithmetic part 11a. Therefore an AND gate 18 outputs a signal of a high level and a one-shot circuit 19 outputs signals of high levels for a prescribed time. Thus a contact switch 14 is turned on and the output of an integration amplifier 15 follows the output of a holding amplifier 13. If the part 11 has runaway, the processing is not completed at the part 11a even though the timer 11c has a time-up. Thus no normal signal is outputted from the timer 11c and the output of the gate 18 does not rise up to a high level. Therefore the circuit 19 is not triggered and the switch 14 is not turned on either. As a result, the amplifier 15 holds its previous output and has no sudden change.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a one-loop controller used for process control and the like.

(b) Conventional technology In general, one-loop controllers used in process control, as shown in Fig. 3, receive input and perform predetermined digital calculations. 2, the signal is converted into an analog quantity, and is output via a hold amplifier 3, a contact switch 4 for automatic mode, and an integrating amplifier 5. Then, while operating in automatic mode, the self-diagnosis section 16 of the CPU
When WN is determined, the contact switch 4 is turned off in response to the signal CD, the mode is switched to manual mode, and manual adjustment is performed using the manual operation section 6 and operation switch 7.

(c) Problems to be solved by the invention In the above conventional one-loop controller, the CPU 1
When the CPU goes down, if the cause is a power supply abnormality that can be immediately detected, the automatic mode is switched from the manual mode to the manual mode as soon as the CPU goes down, and the contact switch 4 is turned off. Since the integrating amplifier 5 does not follow the data, there will be no erroneous output. However, if a CPU abnormality occurs while it takes time to detect the abnormality, such as when the CPU 1 goes out of control, the contact switch 4 may not turn off, resulting in an erroneous output and a sudden change in output.

In view of the above, it is an object of the present invention to provide a one-loop controller that can prevent sudden changes in output due to CPU runaway or the like.

(d) Means and operation for solving the problems The one-loop controller of the present invention includes a digital calculation section, a D/A converter that converts the output of the digital calculation section into an analog value, and a D/A converter that converts the output of the digital calculation section into an analog value. and an integrating amplifier that receives and integrates the output of the hold amplifier, the switching means being connected between the output of the hold amplifier and the input of the integrating amplifier, and the digital arithmetic unit. The present invention is characterized by a one-shot circuit that outputs a signal for a predetermined period of time when a logical product condition is satisfied between a means for diagnosing the presence or absence of a failure and a watchdog timer attached to the diagnosing means, and a no-failure signal from the diagnostic means and a normal signal from the watchdog timer. In preparation for this, the switching means is turned on by a signal from a one-shot circuit.

In this one-loop controller, when the digital calculation section is operating normally, the one-shot circuit outputs a signal for a predetermined time every sampling time due to no failure signal and a normal signal from the watchdog timer. is turned on, and the integrating amplifier follows the hold amplifier output. On the other hand, if the digital processing unit (CPU) goes out of control for some reason, the watchdog timer will not output a normal signal, and therefore the one-shot circuit will not output from the sampling time when the runaway started, and the switching means will turn on. The integral amplifier retains the output from one cycle before, that is, before the CPU goes out of control.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a circuit block diagram of a one-loop controller showing an embodiment of the present invention.

In the same figure, a digital output calculated by a digital calculation unit 11a of a control unit (consisting of a CPU) 11 is converted into an analog value by a D/A converter 12, held in analog value by a hold amplifier 13, and furthermore, an automatic mode The signal is input to an integrating amplifier 15 via a contact switch I4, and is integrated and output.

In the control unit 11, the CPU d of the digital calculation unit 11a
In addition to a self-diagnosis section 11b that self-diagnoses whether the device is own or the like, it is equipped with a watchdog timer IIC. As shown in Fig. 2, this watchdog timer IIC starts every time the real-time clock RTC is input and is reset at a predetermined time.Normally, the digital calculation is completed before the watchdog timer ILC performs time amplification. Part 11a
In such a case, the watchdog timer llc outputs a normal signal.

However, if the series of input, calculation, and output processing is not completed even after the watchdog timer IIc times out, this corresponds to so-called runaway, and in this case, an abnormal signal is output.

The no-failure signal τ of the self-diagnosis unit 11b and the normal signal of the watchdog timer llc are input to the AND gate 18, and when a logic "1" signal is obtained at the output of the AND gate 18, a one-shot signal is activated by No. 13. The circuit 19 is triggered and outputs a signal "1" for a certain period of time, and the contact switch 14 is turned on during this period. This on-operation period is set to such an extent that the output of the integrating amplifier 15 can follow the output of the hold amplifier 13.

If the control unit 11 is currently in automatic mode and there is no abnormality, the self-diagnosis unit 11b will not output the failure signal CD, so τ■ is high, and the digital calculation unit 11
Since the input, calculation, and output processes are executed in a predetermined time in a, the watched timer ila also outputs a normal signal. Therefore, the AND gate 18 outputs a high output, and the one-shot circuit 19 responds to this by outputting a high signal for a predetermined period of time. This signal turns on the contact switch 14, and the output of the integrating amplifier 15 follows the output of the hold amplifier 13. Then, as long as the control unit 11 continues to operate normally, the contact switch 14 is turned on when the watchdog timer IIC is reset at each sampling time, and the same operation continues until 1! Continued.

Here, if the CPU of the control unit 11 goes out of control, the input/calculation/output processing will not be completed even if the watchdog timer lie times out, and in this case, the watchdog timer IIC will send a normal signal to the AND gate 18. is not input, the output of the AND gate 18 does not rise to high, and therefore the one-shot circuit 19 is not triggered, therefore,
Contact switch 14 is also not turned on. Therefore, the integrating amplifier 15 will hold the output from one sampling time ago, and even if the output of the hold amplifier 13 suddenly changes due to a runaway of the CPU, the output of the integrating amplifier 15 will not suddenly change.
Does not interfere with plant operation.

(F) Effects of the Invention According to the present invention, a switching means is provided between the hold amplifier and the integrating amplifier, and a one-shot circuit is provided which is triggered by the AND condition of the no-failure signal and the normal signal of the watched timer. Since the switching means is turned on by the output, if the CPU goes out of control, the switching means will not be turned on and the output of the integrating amplifier will be maintained at the value before the sampling time, ensuring safe plant operation. can.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a one-loop controller showing an embodiment of the present invention, Fig. 2 is an explanatory diagram for explaining the operation of the one-loop controller, and Fig. 3 is a block diagram of a conventional one-loop controller. be. 11: Control unit, 11a: Digital calculation unit, 11
b: Self-diagnosis section, 11C: Watchdog timer, 12: D/A converter, 13: Hold amplifier, 14
: Contact switch, 15: Integrating amplifier, 1B=AND gate, I9: One-shot circuit.

Claims (1)

[Claims] (1) A digital calculation section, a D/A converter that converts the output of this digital calculation section into an analog value, a hold amplifier that holds the analog output of this D/A converter, and a hold amplifier that receives the output of this hold amplifier. In the one-loop controller, the one-loop controller is provided with an integrating amplifier that integrates the hold amplifier, further comprising a switching means between the output of the hold amplifier and the input of the integrating amplifier, a means for diagnosing the presence or absence of a failure in the digital arithmetic unit, and a watchdog timer. A one-shot circuit is attached to the digital arithmetic unit and outputs a signal for a predetermined time under the AND condition of the no failure signal of the diagnostic means and the normal signal of the watchdog timer, and the signal of this one-shot circuit is used to activate the switching means. A one-loop controller that turns on.