1. Simple fault determination of liquid level instrument

First, the substitution method. It is required to have two instruments of the same model UQC series magnetic plate level gauge or have enough spare parts. Replace a good spare with the same component on the faulty machine to see if the fault is eliminated.

Second, the exclusion method. The method of judging the cause of the fault by plugging and unplugging some plug-in boards and devices in the machine. When the instrument returns to normal after a plug-in board or device is removed, it means that the fault occurs there.

Third, the parallel method. Put a good IC chip on the chip to be checked, or connect good components (resistor capacitors, diodes, transistors, etc.) in parallel with the components to be checked, and keep good contact. If the fault comes from the internal open circuit of the device or Reasons such as poor contact can be ruled out by this method.

Fourth, the comparison method. It is required to have two instruments of the same model, and one magnetic plate level gauge is in normal operation. Using this method also requires the necessary equipment, such as a multimeter, oscilloscope, etc. According to the nature of comparison, there are voltage comparison, waveform comparison, static impedance comparison, output result comparison, current comparison and so on.

Fifth, the observation method. Use sight, smell, touch. Sometimes, damaged components will discolor, blister or have burnt spots; burnt components will produce some special odor; shorted chips will become hot; virtual soldering or desoldering can also be observed with the naked eye. . This method is more suitable for experienced workers.

Sixth, percussion hand pressure method. When encountering the situation that the glass plate liquid level gauge is running good and bad, Shanghai Automation Instrument Co., Ltd. believes that the best method is to apply the tapping hand pressure method. The so-called "knock" is to tap the board or component lightly with a small rubber cockroach or other percussion object to see if it will cause an error or downtime. The so-called "hand pressure" means that when a fault occurs, after turning off the power, press the plugged parts, plugs and sockets firmly by hand, and then start the machine again to try whether the fault will be eliminated. If you find that tapping on the casing is normal, and hitting it again is abnormal, it is best to re-insert all the connectors and try again.

2. Analysis and judgment of on-site instrumentation system failures

Field instrument measurement parameters are generally divided into four parameters: temperature, pressure, flow, and liquid level. Now according to the different measurement parameters, to analyze the faults of different field instruments:

First, before analyzing the failure of the on-site instrument, it is necessary to have a thorough understanding of the production process, production process and conditions of the relevant instrument system, understand the design scheme, design intention, structure, characteristics, performance and parameter requirements of the instrument system, etc. .

Second, before analyzing and checking the failure of the on-site instrumentation system, it is necessary to understand the production load and the parameter changes of the raw materials from the on-site operators, check the recording curve of the faulty instrument, and conduct a comprehensive analysis to determine the cause of the instrument failure.

Third, if the instrument recording curve is a dead line (a line that has no change at all is called a dead line), or the recording curve was originally a fluctuation, but now suddenly becomes a straight line; the fault is likely to be in the instrument system. Because most of the current recording instruments are DCS computer systems, the sensitivity is very high, and the changes of parameters can be very sensitively reflected. At this time, the process parameters can be changed artificially to see the curve changes. If there is no change, it is basically concluded that there is a problem with the instrumentation system; if there is a normal change, it is basically concluded that there is no major problem with the instrumentation system.

Fourth, when changing the process parameters, it is found that the recording curve has a sudden change or jumped to the maximum or minimum, and the fault at this time is often in the instrument system.

Fifth, before the fault occurs, the instrument recording curve has been performing normally. After the fluctuation occurs, the recording curve becomes irregular or makes the system difficult to control, and even manual operation cannot be controlled. At this time, the fault may be caused by the process operating system.

Sixth, when it is found that the DCS display instrument is abnormal, you can go to the site to check the indicated values of the same intuitive instrument. If they are very different, it is likely that the instrument system is faulty.