Find the principle of instrument failure compliance.

Instrument fault occurs, if you want to quickly find the instrument failure cause of the problem, it is necessary to understand the production process, understand the instrument control system structure, characteristics, performance and parameters etc., this article to share with you the instrument maintenance, understand the process and control system of the premise condition, shall abide by the following seven principles for instrument failures.

1. Look at the instrument after the process.

Due to operator is the direct use of the instrument, so should ask to them before and after the instrument is out of order, understand the section before and after the production is normal, operation indicators have adjust or change etc., to determine the cause of the is process or instrument. In asking the operator at the same time, should observe the display of the changes, such as the record of the fault before the instrument has been a normal curve, but after record curve, make the system difficult to control, even the manual operation is difficult to control, it may be the cause of the process operation or equipment. Volatility if flow, liquid level control system, check the transmitter and found no problem, can be switched to manual operation, whether the flow or level stable, if the volatility is still very big, may be the reason for the process. If the pressure fluctuates a lot, it can be found from the process, such as load change, adding and reducing materials, switch backflow valve, improper operation, etc., will cause the change of internal pressure of the equipment.

2. Go to the control room first and then go to the scene.

When the appearance of the instrument fails, on the basis of inquiring the operator, the display status of the instrument can be observed, and the general judgment is where the problem is. Targeted available digital multimeter to measuring terminals, judging by measuring from the measuring element to control room wiring terminals, such as whether there is open circuit, short circuit and earth fault. If the thermocouple has no thermoelectric potential output, or with a pointed nose pliers to show the appearance of the receiver, see if the instrument can indicate room temperature. If the resistance value is changed by thermal resistance; Use pointed nose pliers to pick up the instrument's output terminals to see if the meter indicates sub-zero, or disconnect the terminals to see if it indicates the maximum or overflow. If the transmitter depends on the current output, it is more convenient to judge the fault by HRAT hand operator. For placement, automatic switch control system can check place whether correctly, can also cut the operator to manually when necessary, with manual observation actuator movement is normal, if there is a valve position feedback signal. It is suspected that there is no interference voltage and its size.

3. Look at the simple and complex first.

The first observation is that the single instrument is not normal or the meter is not normal, then check the power supply and power box of the meter, whether the fuse is broken or not; Check the relevant wiring to see if there is any contact or interruption, short circuit phenomenon, switch position is correct. Observe whether there is leakage in the guide tube and valve. For measuring micro - pressure gauges, check whether the hose or plastic pipe connected to the guide tube is removed or leaky. If the pressure, flow meter has no fluctuation and change, many times is due to the pressure pipe blockage.

4. Check the instrument after checking the instrument.

On the basis of the control room to observe, if you suspect an instrument has a problem, can waste was carried out on the field instruments, such as thermocouple, thermal resistance terminal connection is loose, with or without water phenomenon, if damaged, such as actuators is jammed or lack of oil, etc., can be in view of the problems for processing.

The pressure and differential pressure transmitter should be blow-down first, blow the guide tube, and check whether there are any clogging and leakage in the trivalve group and other valves. For the flow transmitter to close the positive and negative pressure valve of the three valve group, open the balance valve to observe whether the zero position of the transmitter is normal; Then in the open state, the fast switch is tube drain valve, observe whether the output current is to increase the direction of change, to quickly switch the negative tube drain valve, observe whether the output current to reduce the direction of change, if the current normal transmitter no big problem.

For liquid level transmitter closed three positive and negative pressure valve valve group, the balancing valve check transmitter output current no normal, the current related to migration, so negative transfer, the differential is zero, the output current should be 20 ma, so positive transfer, the differential is zero, the output current should be less than 4 ma. For negative transfer transmitter, in the condition of open table, quick switch is tube drain valve, observe the output current to reduce the direction of change, to quickly switch the negative tube drain valve, observe whether the output current is to increase the direction of change, if the current normal transmitter no big problem. When doing the above inspection, the action of the switch drain valve can be used to see that the output current is changed and the valve can be turned off immediately, so that the condensate will not be arranged too much.

For secondary instrument of fault diagnosis have rules to follow, lagging parameters such as temperature, so the instrument display value is impossible mutations, such as display suddenly ran to the maximum or minimum, ruled out a component problem, usually for fault detection. Temperature control system fluctuations are likely to be PID parameter tuning, or actuators have mechanical problems. If the pressure indication is not fluctuating, or the change is slow, the removal of the pressure pipe and the valve plug, should be the display of the instrument problem. If you can't wave approximation of linear flow recorder, this may be the instrument have fault, because of the traffic parameters fluctuation is bigger, the change of the parameters is more or less should be reflected on the recorder can. Display parameters of DCS or recorder when there is doubt, can see the regular backup instrument, or other instrument, such as transmitter indication of header, look at how much the display of the difference, in order to determine the fault. Check whether the controller is normal, can artificially change a given value to cause a new deviation, and then observe the change of the output current of the controller to determine whether the controller is normal.

5. Look outside and look inside the instrument.

In the first easy and difficult step, first check the external appearance of the instrument, such as whether the power supply is normal; Whether the pressure pipe has leakage point and observe whether the discharge is unobstructed to determine whether there is a blockage of the guide tube or valve; Check whether the wire connection and terminal are loose, corrosion contact is not good. In the case of thermocouple, a short circuit can be used to determine the fault location. Measuring the terminal or meter terminal voltage of the instrument panel to determine the fault. Based on this, it is necessary to determine whether to remove the instrument for processing.

6. Look in the dark after seeing the light.

When dealing with the instrument failure on the spot, check the terminal and wiring in the instrument panel, and no problem is found. However, if there is any problem with the wire, check the cable in the cable bridge and in the trench. A final inspection is also placed on the sewer pipe to the trench. In case of damage to the protective casing of thermocouple and thermal resistance, the inspection should be removed after checking that other parts have no problem.

7. First set up the software to check the hardware.

A large number of applications of smart meters, when dealing with the fault of the field instrument, can not only be limited to the original processing of the analog instruments. Intelligent instrument hardware can play a role relying on software support for the premise, leaving the software such instrument can not work. So in check when dealing with smart meters, should first check whether the instrument set is normal, the author has met due to lightning and electricity at night after complex instrument cannot work situation, found that after is instrument set parameters changed, reset is normal. Had met after replacing industrial computer network card, cannot be connected to the Internet, and install the driver, and in the network card, to nothing for a few hours, later found to be a computer CMOS setup item changed, reset is normal.