Fault Analysis of Field Instrument System
63-160mm PE/PP pipe extruder, Exporting Tritube Extrusion Line Machinery, China 63-160mm PE/PP pipe extruder KERKE Extrusion Equipment Co.Ltd. , http://www.kerkeextrusion.com
According to the different measurement parameters, different field instrument faults are analyzed.
1. First of all, before analyzing the failure of the field instrument, it is necessary to thoroughly understand the production process, production process conditions and conditions of the relevant instrument system, understand the design scheme and design intent of the instrument system, and the structure, characteristics, performance and parameter requirements of the instrument system. Wait.
2. Before analyzing and inspecting the fault of the field instrument system, the operating personnel of the site shall be informed of the changes in the production load and the parameters of the raw materials, and the record curves of the faulty instruments shall be checked and a comprehensive analysis shall be conducted to determine the cause of the instrument malfunction.
3. If the meter records a dead line (a line with no changes in the line is called a dead line), or the record curve originally fluctuates, it suddenly becomes a straight line; the fault is likely to be in the instrument system. Because the current recording instruments are mostly DCS computer systems, the sensitivity is very high, and the change of parameters can be very sensitive to the reaction. At this point can artificially change the process parameters to see the curve changes. If it does not change, the basic conclusion is that the instrument system has a problem; if there is a normal change, it is basically determined that the instrument system has no major problems.
4. When the process parameters are changed, it is found that the recorded curve has abruptly changed or jumped to the maximum or minimum. At this time, the fault is often in the instrument system.
5. Before the failure occurs, the instrument record curve has been performed normally. After the fluctuation, the recording curve becomes irregular or the system is difficult to control. Even the manual operation cannot be controlled. At this time, the failure may be caused by the process operating system.
6. When it is found that the DCS display instrument is not normal, you can go to the scene to check the indicator value of the same intuitive instrument. If they are very different, it is likely that the instrument system has failed.
In short, when analyzing the causes of field instrument failures, special attention must be paid to the changes in the characteristics of the measured control object and the control valve, which may be the cause of the failure of the field instrument system. Therefore, we must comprehensively consider and carefully analyze the field instrument system and the process operating system to check the reason.
Second, the four major measurement parameters Instrument Control System Failure Analysis Steps 1. Temperature Control Instrumentation System Failure Analysis Step Analysis Temperature Control Instrumentation System Failure, we must first pay attention to two points: The system instrument uses electric meters to measure, indicate, control; Meters often lag behind.
(1) The indicator value of the temperature meter system suddenly changes to the maximum or minimum, which is generally a failure of the instrument system. Because the temperature meter system measures large lags, sudden changes do not occur. Most of the faults at this time are due to the thermocouple, thermal resistance, wire breakage in the compensation lead, or malfunction of the transmitter amplifier.
(2) Temperature control instrumentation system indicates rapid oscillation, which is mostly caused by improper adjustment of control parameter PID.
(3) The temperature control instrumentation system indicates the occurrence of large and slow fluctuations, which may be due to changes in process operations. If the process operation does not change at that time, it is likely that the instrument control system itself has failed.
(4) Failure analysis procedure of the temperature control system itself: Check whether the input signal of the regulating valve changes, the input signal does not change, the regulating valve is actuated, and the diaphragm of the valve membrane is adjusted to leak; Check whether the input signal of the regulating valve positioner changes or not. No change, the output signal changes, the positioner has a fault; check the positioner input signal changes, and then check whether the regulator output changes, if the regulator input does not change, the output changes, this time is the fault of the regulator itself.
2. Pressure analysis instrument system failure analysis steps (1) pressure control system instrument indicates rapid oscillation fluctuations, first check whether the process operation changes, this change is mostly caused by the process operation and regulator PID parameter setting is not good.
(2) The pressure control system instrument indicates dead line, the process operation changes the pressure indication or does not change, the general failure occurs in the pressure measurement system, first check whether the measurement pressure piping system has a plugging phenomenon, no plugging, check the pressure change The transmitter output system has no change, there are changes, the fault is in the controller measurement indicator system.
3. Flow Control Instrumentation System Failure Analysis Steps (1) When the indicated value of the flow control instrumentation system reaches a minimum, the site inspection instrument is first checked, and if it is normal, the failure is displayed on the instrument. When the on-site detection instrument indicator is also the smallest, check the opening degree of the regulating valve. If the opening degree of the regulating valve is zero, it is often a fault between the regulating valve and the regulator. When the on-site detection instrument indicates the minimum and the opening of the regulating valve is normal, the cause of the malfunction is likely to be caused by insufficient system pressure, blockage of the system piping, loss of the pump volume, crystallization of the medium, improper operation, and the like. If the instrument is faulty, the reasons are: the orifice differential pressure flowmeter may be a positive pressure induction conduit plug; the differential pressure transmitter positive pressure chamber leakage; the mechanical flowmeter is a gear stuck or a filter plug.
(2) When the indicated value of the flow control instrument system reaches the maximum, the detection instrument will often indicate the maximum value. At this point you can manually control the valve to open large or small, if the flow can be reduced, it is generally caused by the process operation. If the flow rate does not fall, it is the cause of the instrument system. Check whether the regulating valve of the flow control instrumentation system operates; check whether the instrument measures the pressure stimulating system is normal; check whether the instrument signal transmission system is normal.
(3) The flow control instrumentation system indicates that the value fluctuates more frequently. The control can be changed to manual. If the fluctuation is reduced, it is the cause of the instrument or the instrument control parameter PID is not suitable. If the fluctuation is still frequent, it is the process operation. Caused by.
4. Level control instrument system failure analysis steps (1) liquid level control instrument system indicator value changes to the maximum or minimum, you can first check the instrument to see if it is normal, if the instructions are normal, change the liquid level control to manual remote liquid level To see the level change. If the liquid level can be stabilized in a certain range, the fault is in the liquid level control system; if the liquid level cannot be stabilized, it is generally a fault caused by the process system, and the cause must be looked up from the process.
(2) When the differential pressure type liquid level control instrument indicator and on-site direct-reading indicator instrument indicator are not on, first check whether the direct-reading indicator instrument is normal. If the indicator is normal, check the negative pressure guide of the differential pressure level indicator. If there is leakage, refill the liquid and adjust the zero point; if there is no leakage, the negative migration amount of the instrument may be wrong. Adjust the migration amount to make the indicator normal.
(3) When the indicating value of the liquid level control instrumentation system changes frequently and fluctuates frequently, it is necessary to first analyze the capacity of the liquid level control object to analyze the cause of the failure. The large capacity is generally caused by instrument failure. The first thing to do is to analyze whether there is any change in the process operation. If there is any change, it is likely that the process will cause frequent fluctuations. If no change may be caused by instrument failure.
The above is only the on-site four-parameter control parameters of the instrument's field failure analysis, the actual site there are some complex control loops, such as cascade control, split control, program control, interlock control and so on. The analysis of these failures is more complex and requires detailed analysis.