JPS6210707A - Program controller - Google Patents

Abstract

PURPOSE:To grasp the input signal condition before and after the change-over and to generate the abnormal signal by generating the abnormal signal when the first and second holding means to hold the first and second input signals before and after the change-over and the difference between two held signals are the prescribed comparing value of above. CONSTITUTION:When the program control is started, an input signal T1 of the first sensor 11 is inputted to a control means 4, compared with the set value of a program pattern generating means 3, and the adjusting output signal is outputted to the controlled system. At the time of a change-over temperature T0, a change-over means 2 is changed over from the first input signal T1 of the first sensor 11 to the second input signal T2 of the second sensor 12, and supplied to the control means 4. A value T0 of the first input signal T1 before and after the change-over of the change-over means 2 and a value T0' of the second input signal T2 are held respectively at holding means 51 and 52, the difference between both signals T0 and T0' is taken by a subtracting means 6, when the difference is the prescribed comparing value or above, a comparing means 7 generates an abnormal signal, generates the program stopping signal and sets the control condition to a safety side. Thus, even when the sensor is abnormal, the safe program control can be always executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a program controller that performs program control of process variables such as temperature of a controlled object such as an electric furnace.

[Prior art] As a programmable meter for program-controlling a controlled object, different sensors are used, such as a thermocouple to measure the low-temperature state of the controlled object and a radiation thermometer to measure the high-temperature state. Some devices automatically switch input signals and perform program control.

[Problems to be solved by this inventionJ However,
When the sensor is switched as shown in Fig. 3, both measurement values TO and T are inevitably obtained.

- There may be some differences between the two. Further, in some cases, the sensor after switching is abnormal and its measurement input signal is abnormal, resulting in a large difference between the input signals before and after switching, which causes a problem that normal control cannot be performed.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a program controller that can grasp the input signal state before and after switching and generate an abnormal signal.

Means for Solving Problem E] The present invention provides a program controller that performs control according to a predetermined program pattern.
a switching means for switching the input signal, first and second holding means for holding the first and second input signals before and after this switching, and two holding means held by the first and second holding means. The program controller is equipped with a comparison means that generates an abnormal signal when the difference between the signals is equal to or greater than a predetermined comparison value.

[Embodiment] FIG. 1 is a configuration explanatory diagram showing an embodiment of the present invention.

In the figure, 11 is a first sensor such as a thermocouple that measures a relatively low temperature of a controlled object (not shown), and 12 is a second sensor such as a radiation thermometer that measures a relatively high temperature of the same controlled object. sensor 2 is the first and second sensor 11.1
2, a switching means for switching the first and second input signals T1 and T2; 3, a program pattern generation means for generating a predetermined program pattern; 4, switching the switching means 2 and switching the input signal and the program pattern; This control means compares the program setting value of the generating means 3, performs P10 calculation, etc., and generates an adjustment output signal. 51.5
2 indicates a first sensor 11 and a second sensor before and after switching of the switching means 2.
The first sensor 12 holds input signals T1 and T2 of the sensor 12,
, second holding means, 6 are the first and second holding means 51.
A subtraction means 7 for taking the difference between the signals held in the subtraction means 6 compares the difference signal of the subtraction means 6 with a predetermined comparison value, and when the difference signal is larger than the comparison value, generates an abnormal signal, and generates a program stop signal, etc. It is a means of comparison that generates Note that the above configuration is usually realized as a function of a microcomputer.

Next, the operation will be explained with reference to FIG.

The program pattern generating means 3 generates the trapezoidal pattern shown in FIG. 2 P, and switches from the first input signal T1 of the first sensor 11 to the second input signal T2 of the second sensor 12 at the temperature TO. shall be taken as a thing.

That is, when program control is started, the input signal T1 of the first sensor 11 is inputted to the control means 4 via the switching means 2, compared with the set value of the program pattern generation means 3, and a predetermined adjustment calculation is performed. and the adjusted output signal is output to the controlled object.

The program control progresses with the passage of time t, and when the switching temperature TO is reached, the switching means 2 is switched from the first input signal T1 of the first sensor 11 to the second input input signal T2 of the second sensor 12. The signal is switched and supplied to the control means 4. The value To of the first input signal T1 and the value To' of the second input signal T2 before and after switching of the switching means 2 are held in the holding means 51 and 52, respectively. Then, the subtraction means 6 calculates the difference between the two signals To, To=, and when the difference between these two signals is greater than a predetermined comparison value, the comparison means 7 generates an abnormal signal and generates a program stop signal, Take necessary measures such as changing the control state to the safe side.

It should be noted that an alarm signal can be generated in the same way when switching from the second input signal to the first input signal when the program pattern is falling as well as when the program pattern is rising.

[Effects of the Invention] As described above, the present invention makes it possible to always perform program control before and after switching, and is highly reliable.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are explanatory diagrams showing one embodiment of the present invention,
FIG. 3 is an explanatory diagram showing a conventional example.

Claims (1)

[Claims] 1. In a program controller that performs control according to a predetermined program pattern, a switching means for switching between a first input signal and a second input signal, and a first input signal before and after the switching,
Generates an abnormal signal when the difference between the first and second holding means holding the second input signal and the two signals held by the first and second holding means is greater than or equal to a predetermined comparison value. A program controller characterized by comprising a comparison means.