【 abstract 】 : now, along with petrochemical, steel, paper, food, pharmaceutical enterprise automation level unceasing enhancement, the instrument maintenance personnel to the technical level raised taller requirement. Reduce the processing time for instrument faults, ensure the safety production to improve the economic benefit, this paper published a little instrument site maintenance experience, for instrument maintenance personnel reference.
Now, along with petrochemical, steel, paper, food, pharmaceutical enterprise automation level unceasing enhancement, the instrument maintenance personnel to the technical level raised taller requirement. Reduce the processing time for instrument faults, ensure the safety production to improve the economic benefit, this paper published a little instrument site maintenance experience, for instrument maintenance personnel reference.
A, the field instruments system fault analysis of the basic steps
The instrument measuring parameters are generally divided into temperature, pressure, and flow, liquid level four parameters.
We, according to the different measuring parameters, to analyze the different field instruments for the source of the problems.
1. First of all, on the analysis of the fault before field instruments, have to compare a thorough understanding of relevant instrument system of production process, production process and conditions, understand the instrument system design scheme, design intention, the structure of the instrument system, properties, characteristics and parameters requirements, etc.
2. Check the field instruments on the analysis of the system failure before going to the operating workers know the load and the raw material production of parameter change, check the record curve fault instrument, and make comprehensive analysis to determine instrument faults the reason.
3. If meter records for a dead line curve (a little change also not line says dead line), or record original curve for wave, now suddenly become a straight line; Failure is likely in the instrument system. Because the current record instrument are mostly DCS computer system, the sensitivity is very high, the change of the parameters can very sensitive reaction comes out. At this point, people change process parameters, see curve changes. If you don’t change, basic concluded that is a problem instrument system; If have the normal change, basic judge instrumentation systems don’t have big problems.
4. Change process parameters, and found that mutations or jump to record curve maximum or minimum, at this time of failure often in the instrument system.
5. Fault was developed instrument document curve has been appear normal, volatile record curve have become law after or is difficult to control system, even in manual operation can’t control, this time the fault may be caused by the process operating system.
6. When found DCS display instrument is not normal, can go to the same visual inspection instrument instructions value, if they difference is very big, may be instrument system malfunction.
In short, analysis the field instruments when the cause of the problem, we must pay special attention to be measured and the characteristics of the control valve control object changes, all of these may cause the instrument system is the cause of the trouble. So, we should from the field instruments system and process operating system two comprehensive consideration, careful analysis, check the reason.
Two, four measuring parameters instrument control system fault analysis steps
1. The temperature control instrument system failure analysis steps
Temperature control instrument analysis system failure, you should pay attention to two points: the system with electric meter measuring instrument, the instructions, control; The system of measurement instruments often large time.
(1) temperature instruments system instructions value suddenly to a maximum or minimum, generally for instrument system failure. Because the temperature measurement instrument system lags behind larger, won’t happen suddenly change. At this time of the cause of the problem is more heat resistance, thermocouple, compensation conductor or transmitter amplifier caused by failure break.
(2) temperature control instrument systems instructions appeared fast oscillation phenomena, PID control parameter improper adjustment.
(3) temperature control instrument systems instructions face a slow wave, probably due to the change process operation, such as process operation at that time did not change, may be instrument control system itself fault.
(4) temperature control system itself the failure analysis steps: check the regulator input signal whether changes, the input signal does not change, the regulator movement, the regulator film head the diaphragm leak; Check the regulator locator input signal whether changes, the input signal does not change, change the output signal, the locator have fault; Check the locator input signal have change, look adjustment output for change, if the regulator input don’t change, output change, this is the fault regulator itself.
2. Pressure control instrument system failure analysis steps
(1) pressure control system instrument instructions appeared fast oscillation fluctuation, the first check process operation for change that is mostly process operation, and regulator PID parameters setting caused by bad.
(2) pressure control system instrument instructions appeared dead line, the pressure change process operation instructions or not to change, general fault appears in pressure measuring system, the first check the measuring pressure if there is lead ductal system of blocking phenomenon, not blocking, check pressure transmitter output system for change, change, fault in the controller measurement indicator system.
3. Flow control instrument system failure analysis steps
(1) flow control instrument system instructions to the value of hours, first check the field detection instrument, if the normal, the fault in the display instrument. When the field detection instrument instructions minimal, then check the regulator open degree, if the regulator opening is zero, it is often the regulator to fault between regulator. When the field detection instrument minimum instructions, the regulator opening normal, fault reason is quite likely the system pressure is not enough, system pipeline jams, pump not the quantity on the crystallization, medium, causes such as improper operation. If instrument malfunction, reasons for orifice plate differential pressure flow meter may be positive pressure led pressure catheter plugging; Differential pressure transmitter positive pressure chamber leak; Mechanical flowmeter is gear jammed or screen plugging, etc.
(2) flow control instrument system instructions to maximize value, the measurement instrument often instruction is the largest. This time can be manual remote control regulator open big or small shut, if can flow down is commonly for process operation causes. If flow value drop not come down, is the instrument system of the causes, check the flow control instrument system regulator is action; Check the meter measuring lead pressure system is normal; Inspection instrument signal transmission system is normal or not.
(3) flow control instrument system are more frequent fluctuations indicating value, can be changed to control manual, if fluctuations decrease, is the instrument of the reasons of the PID control parameters or instrument improper, if still frequent fluctuations, is the process operation causes.
4. Liquid level control instrument system failure analysis steps
(1) level control instrument system changes to the largest indicating value or the hours, can check to see if the normal inspection instruments, such as indicating normal, will level control to manual remote control level, see level changes. Such as liquid level can be stable in a certain range, the fault in the liquid level control system; If not steady level, it is commonly process system caused by fault, from the process to determine the cause.
(2) the differential pressure type fluid control instrument instructions and the direct reading type indicating meter on the instructions, the first check the direct reading type indicating meter is normal or not, such as indicating normal, check differential pressure type fluid instrument of negative pressure seal the liquid pressure pipe whether have leakage; If there is leaking, and to pouring sealant liquid, and the zero; No leakage, may be the negative transfer of instrument is wrong, readjust the traffics makes the gauge instructions to normal.
(3) liquid level control instrument systems instructions value change frequent fluctuations, the first analysis of liquid level control object size capacity, to the analysis of the cause of the failure, large capacity is usually caused by instrument faults. Capacity of the first small analysis process operation conditions are have change, if any change is likely to be caused by frequent fluctuations of the process. If no changes may be caused by instrument faults.
This article from the Hardware Appliances Exporters