JPS6024428B2 - Change amount detection method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reliably detecting the amount of change in a measured quantity or a process quantity, and in particular, the method of detecting the amount of change in a measured quantity or a process quantity, etc. The present invention relates to a change detection method and apparatus suitable for detecting a change in a measured quantity whose degree of change is extremely gradual.

Detecting a change in a measured quantity such as a process quantity is extremely important in the case of loop control, as seen in D control in PID control, for example.

Furthermore, various abnormalities in the process can also be detected based on this amount of change. For example, FIGS. 2 and 3 show a conventional method for detecting the amount of change in a process variable as shown in FIG. 1. Figure 2 shows an analog method, with a capacitor C, a resistor R, and an operational amplifier A.
This is a so-called differential circuit consisting of: This is for example PID
This circuit is used in the ○ calculation section of the controller. Although this circuit has the advantage of being simple and inexpensive, it has the disadvantage that it is not practical in places where the input changes slowly, for example, by only a few percent on the order of minutes, as the required capacitance of the capacitor becomes large. In many cases, the process quantity that is the measured quantity contains ripples, and the circuit shown in Figure 2 also differentiates these ripples, making it impossible to obtain an output signal with sufficient reliability. At present, it has not been put into practical use for gradual changes such as . A conventional method used as an alternative in such a case is a method using a digital computer as shown in FIG.

This is done by closing the sampling switch S at times t2, . This is stored in the memory in the CPU, and a change is detected by finding the difference between the previous value en and the current value en-. However, this circuit has '
1' When the input measured quantity changes slowly, for example, when it changes by only about 1% of the full scale, the error of the analog-to-digital converter A/○ will be superimposed, so calculate the deviation that is practically necessary. In addition, since the difference between instantaneous values is used, it is necessary to shorten the sampling period and capture a large amount of data in order to improve accuracy, but in this case, a dedicated digital computer is required. It has disadvantages such as requiring a The present invention has been made in response to the above points,
The purpose is to provide a method and apparatus for detecting a change amount, which can accurately detect a change amount in a slowly changing measured quantity J with a simple configuration.

The feature of the present invention is to sample the measured quantity at predetermined time intervals, detect it, and store it, compare this stored value with the measured quantity, integrate the difference between the two within the sampling period, and calculate this integral value. The purpose is to detect the amount of change in the measured quantity based on the size. The operating principle of the present invention will be explained below with reference to FIGS. 4 and 5.

4, 1 is a sampling switch that is closed at a predetermined period as shown in FIG. 5b, and 2 is an analog value of the input signal e when the sampling switch is closed (for example, (a, e, e2, etc.) (Fig. 5c). The analog memory 2 may be one that digitally holds the input and holds the analog value through D/A conversion, one that holds the analog value using a capacitor, one that uses a servo type, or any other type of principle. The resistors 3, 4, the operational amplifier 5, and the capacitor 6 constitute an integrator, and the difference between the previously stored analog value (e,, e2, ..., etc.) and the subsequent input signal e (Fig. 5d) ) has an integrating function, and 7 is an integrator 5 in synchronization with the sampling switch 1.
This is a reset switch that has the function of resetting to 0. 8 is an output switch that takes out the output of the integrator (Fig. 5 e), and is opened just before switch 7 is opened, that is, just before the measured quantity e is sampled and stored in analog memory 2, and the integrated value is stored. It is output from the terminal 9 as the amount of change in the input signal e.

It is now assumed that the input to be measured e changes as shown in FIG. 5a. At time L'b, the switch 1 is closed and the input e at that time is taken into the analog memory 2 (c in the same figure), and at the same time, the reset switch 7 sets the integrator 5 to 0.
'Reset this. From time t to time t2, the integrator integrates the difference (d in the figure) between the memory value e in the analog memory 2 and the constantly changing input signal e. Next, at the time immediately before closing switch 1, the output switch 8 is closed (e in the same figure), and the integrator output at that time (f in the same figure) is
) is output to the terminal 9 as the change value of the measured quantity e, as shown in g in the figure. Note that FIG. 5 shows an example in which the input signal to be measured e does not change between times Ut2 and t3; in this case, the output of the integrator is 0, and the output from terminal 9 is
produces no output. As is clear from the above explanation, according to the method of the present invention, it is possible to easily measure and detect the amount of change in a measurand that has a gradual change, that is, a large time constant, which could not be measured using conventional methods. Become so.

According to experiments conducted by the present inventor, good results were obtained when the integration period was set to about 3 minutes for fluctuations in the measured quantity with a time constant of about 20 minutes. As explained above, the present invention integrates the deviation obtained by comparing the detected value of the measured quantity at the time of sampling and the measured quantity after that within the sampling period, and detects the amount of change in the measured quantity from the integrated value. Therefore, even if the change is gradual, the amount of change can be detected with high accuracy, and it can also be detected with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the state of change of the measured process quantity,
2 and 3 are block diagrams for explaining the conventional variation detection method, FIG. 4 is a block diagram for explaining one embodiment of the present invention, and FIG. 5 is a waveform for explaining its operation. It is a diagram. 1... Sampling suite, 2... Analog memory,
5...Operation amplifier, 6...Capacitor, 7...Reset switch, 8...Output switch. 1 box of fins * 3 boxes of bacteria fins Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1. The quantity to be measured is sampled at predetermined time intervals, detected and stored, and this stored value is compared with the quantity to be measured thereafter, and the difference between the two within the sampling period is integrated. A method for detecting a change amount, characterized in that the amount of change in the amount to be measured is detected based on the magnitude of the value. 2. A sampling means for sampling and detecting the quantity to be measured at predetermined time intervals, a storage means for storing the value of the quantity to be measured detected by this sampling means, and a storage means for storing the value of the quantity to be measured and the subsequent quantity to be measured. and integrating means for comparing the values and integrating the difference between the two within a sampling period, and detecting the amount of change in the measured quantity based on the magnitude of the integrated value of the integrating means. Change amount detection device.