JPH0231404B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inspection circuit for a process control device that controls a controlled object whose state changes slowly.

Conventionally, the method of inspecting this type of equipment is to have a skilled worker start the inspection as soon as he/she confirms that the controlled object is stable. It was necessary to supply an alternative process signal in an appropriate manner so as not to cause

In this way, conventional technology is not easy to inspect;
There was a drawback that it was not possible to respond promptly even if new changes occurred in the controlled object during inspection.

This invention was made in order to solve the conventional problems as described above.Inspections can be easily started, and if a change exceeding a predetermined value occurs during an inspection, the inspection can be stopped immediately. An object of the present invention is to provide a process control inspection circuit that does not adversely affect a process control device when the inspection circuit malfunctions.

An embodiment of the present invention will be described below with reference to the drawings. In the figure, a controller 1 is a process control device and is an object to be inspected. The process signal PCI, which is the input of controller 1, is connected to switch 2.
is supplied to the controller 1 via.

The process control inspection circuit of the present invention for inspecting the function of the controller 1 is broadly divided into an inspection device 4, a memory circuit 5, and a switching control section 6. The inspection device 4 supplies various inspection signals TPCI that simulate the process signal PCI to the controller 1 via the switch 2, and feeds back control signals that are the response results to the inspection device 4. Check the functions of controller 1 from

The memory circuit 5 stores the control signal output from the controller 1 immediately before the start of the inspection via the switch 7 and outputs it via the switch 3 in order to maintain the function of the process device even during the inspection. Consists of a sample and hold circuit.

The switching control circuit 6 is used to control the switching of the switching devices 2, 3, and 7 that function as a signal selection circuit, and includes a sample hold circuit 8 that inputs the process signal PCI, and an output signal 8a of the sample hold circuit 8 and the process signal. A discriminator 9 that compares the signal PCI and outputs a signal 9a indicating that there is no transient change in the process signal PCI when the difference between the two becomes less than a predetermined value, and a signal 10 that is obtained by delaying the signal 9a by a certain time period.
A timer 10 that outputs a and an inspection start signal
It has a switching control circuit 11 that sets the switching devices 2, 3, and 7 to positions opposite to those shown in the figure when STR and signal 10a are input.

During non-inspection operations, the switches 2, 3, and 7 are in the positions shown, and the controller 1 normally functions as a process control device.

Here, when the start signal STR is input to the switching control circuit 11 to check the controller 1, if the timer 10 is outputting the signal 10a at that time, the switching control circuit 11 Switch to the opposite position as shown. If the timer 10 is not outputting the signal 10a at that point, it means that the process signal PCI input to the controller 1 is undergoing a transient change. , 7, and 3 maintain the positions shown. In other words, if the control system including the process control device has not reached an equilibrium state, the inspection will not start even if the start signal STR is applied to the circuit.
The control system is stable.

If the switch 7 is opened during inspection, the memory circuit 5
Since the contents are no longer updated, the control signal PCO outputted from this retains the value immediately before the inspection started. Since the process control system is stable when the switch 3 is switched, the control signal PCO output from the memory circuit 5 is essentially the same as the control signal PCO output from the controller 1 during non-inspection. is the same as If the process signal is
When a change occurs in the PCI, the discriminator 9 no longer outputs the signal 9a, so as is clear from the foregoing, the switches 2, 3, and 7 return to the positions shown, and the inspection is discontinued.

Note that the sample and hold circuit 8 in the above embodiment may be replaced with a delay circuit. Further, the set time of the timer 10 may be set to an appropriate amount within a range that guarantees determination of the equilibrium state depending on the nature of the process signal PCI.

As described above, according to the present invention, even when the process control device is online, when it is detected that the controlled object is stable, the process control signal of the control amount stored immediately before the start of inspection is sent to the process control device. This makes it easy to inspect the process control equipment, and since the inspection equipment is connected in parallel with the process control equipment, there is no risk of adverse effects on the process control equipment if the inspection equipment malfunctions. effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a process control inspection circuit according to an embodiment of the present invention. 1... Controller, 4... Inspection device, 5...
Memory circuit, 6... switching control section.

Claims (1)

[Claims] 1. At the time of inspection, an inspection device that outputs an inspection signal that simulates a process signal, a first switch that selectively switches the inspection signal or process signal output from this inspection device and supplies it to the process control device, A hold circuit that temporarily holds the hold circuit, a discrimination circuit that compares the output of this hold circuit with the above process signal and outputs an output when the difference between the two is less than a predetermined value, and an inspection start signal generated during inspection and the output of the above discrimination circuit. a switching control circuit that operates based on the above, a storage circuit that stores and updates the control signal output from the process control device, and outputs the control signal; a switching control circuit that selectively switches and outputs the output of the storage circuit or the output of the process control device; Under normal conditions, the switching control circuit switches the first switching device to the process signal side and the second switching device to the process control device side. During inspection, the switching control circuit switches the first switching device to the process signal side and the second switching device to the process control device side. A process control inspection circuit characterized in that, by operation, the first switch is switched to the inspection device side, the second switch is switched to the storage circuit side, and the stored value of the memory circuit is held.