JPS5812452A - Detecting method for transmitter's fault - Google Patents

Abstract

PURPOSE:To eliminate such cases that control over a process variable is interrupted and a faulty oscillator can not be known immediately, by detecting abrupt variation in oscillator output and then deciding for the fault of the oscillator. CONSTITUTION:For example, an oscillator A measures a process variable. When the deviation of an output of the oscillator A from the normal output exceeds a prescribed value, it is judged that the oscillator A is faulty. When the oscillator A generates an output exceeding a prescribed value, a time delay element 5 finds its normal output and when the deviation of the abnormal output exceeds the certain prescribed value, a monitor relay is energized. Through the operation of this relay 7, the fault is displayed and at the same time, a changeover relay 9 is put in operation to change the oscillator A over to an oscillator B. Consequently, the control is continued without interrupting the measurement of the process variable. When the oscillator A is normal and the oscillator B is faulty, similar operation is performed. In this case, a differentiating element may be used as a substitute for the time delay element.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to failure detection of analog signals from transmitters that measure process quantities in measurement and control of thermal power plants and the like.

An example of the prior art is shown in FIG.

The conventional technique is to compare the outputs of two transmitters, and if the deviation of the outputs exceeds a certain specified value, it is determined that there is an abnormality in one of the transmitters. That is, the outputs of the transmitters (A) and (B) are input to the monitor relay 5, and if the deviation value exceeds the specified value, this monitor relay will
Operate. This action not only indicates a failure but also
The switching relay 7 automatically switches to the manual side. After switching to the manual side, the operator decides to switch the selector switch 6 to the normal transmitter and resume control, but it is impossible to immediately know which transmitter has failed. Moreover, there is a drawback that control is interrupted during the switching time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for detecting a failure in an oscillator, which eliminates the above-mentioned drawbacks and immediately determines which oscillator has a failure, immediately switches to a normal oscillator, and continues control.

The temporal change in the output of the oscillator used to measure the process amount tends to be as shown in FIG. 2 based on experience. In the figure, A and B show changes when the transmitter is normal, and C1D shows changes when it is abnormal. In other words, normal transmitter output shows gradual changes (although this gradualness varies depending on the measurement location and measurement point situation), and if an abnormality occurs in the transmitter such as power outage, disconnection, short circuit, etc., it will change suddenly. It will be a drastic change. The key point of the present invention is to use a time delay element or the like to detect this sudden change and determine whether there is an abnormality in the transmitter.

FIG. 3 shows an embodiment of the invention. Suppose that the transmitter (A
), it is assumed that the process amount is being measured. When the deviation of the output of the transmitter (A) from the normal output exceeds a specified value, it is determined that the transmitter (A) is abnormal. When an output greater than a specified value is output from the transmitter (A), the time delay element 5 captures the normal output, and if the deviation of the output from the abnormal output exceeds a certain specified value, the monitor Relay 7 operates. By operating this monitor relay, the switching relay 9 is immediately operated to switch to the transmitter (B) as soon as a failure is displayed, thereby making it possible to control the process amount without interruption.

In this case, even if the transmitter (A) is normal and the transmitter (B) is abnormal, detection is similarly performed and only the failure indication is displayed in full. In addition, even when the transmitter (B) measures the amount of purceme,
It can be detected similarly. Note that a differential element may be used instead of the time delay element, and if the differential value is greater than a certain specified value, it may be determined that the transmission is abnormal.

The present invention makes it possible to compensate for the drawbacks of the prior art, in which the control of process quantities with two transmitters is interrupted or it is not immediately possible to know which transmitter is faulty.

[Brief explanation of drawings]

FIG. 1 is a control system diagram of a conventional example, FIG. 2 is a change diagram of an oscillator output, and FIG. 3 is a control system diagram of the present invention. 1.2...transmitter 仄), (B), 3.4...
・mV/A 7verter 1A), (B)
, 5 - Monitor relay, 6... Selector switch, 7
... Switching relay ζB... Controller, 9... Manual operating device, 10... Switching relay, 11... Controller, 12... Manual operating device. V, 1st insert tsubohanaya 20

Claims (1)

[Claims] 1. A method for detecting a failure in a transmitter, which is characterized in that, in a transmitter that measures a process quantity, characteristic fluctuations in the output of the transmitter are detected using a time delay element, a differential element, etc., and an abnormality in the transmitter is determined.