Field instrument measuring parameters are generally divided into temperature, pressure, flow, liquid level four parameters, depending on the measuring parameters, to analyze different field instrument malfunction,
1. First of all, based on the analysis of field instruments before failure, want more thorough understanding of relevant instrument system production process, production process and conditions, understand instrument system design scheme, design intent, instrument system structure, characteristics, performance and parameter requirements, such as
2. On the analysis of the system fault before check the field instruments, to site operation workers understand the parameters of the production load and raw material, the changes of view fault instrument recording curve, make a comprehensive analysis, to determine the cause of the problem in instrument,
3. If the meter record curve as a dead line (no change of line said dead line), or record curve for the volatility, original now suddenly becomes a straight line; Failure may be in the instrument system, because most of the recording instrument is DCS computer system, the sensitivity is very high, the change of the parameters can be very sensitive response, this time can be artificially change of process parameters, see the curve changes, if not change, the basic is concluded that instrument system out of the question; If there are any changes in normal, basically decided that instrument system had no big problems,
4. Process parameters change, the found record curve mutations or jump to the maximum or minimum, at this time of failure is often in the instrument system,
5. Failure occurs before the instrument recording curve has been normal, fluctuate after record curve is no rule or make the system difficult to control, even the manual operation can not control, fault could be the result of a process operating system at this time,
6. When find DCS display instrument is not normal, can go to the site inspection indicated value of the same type of instrument, if they are difference is very big, is likely to be the instrument system malfunction,

Temperature control instrument system fault analysis step
Temperature control instrument system and analysis of the failure, the first to pay attention to two points: the system instrument adopts the electric meter, instructions, control; The system instrument measuring often lag is bigger,
(1) indicating value of the temperature instrument system suddenly to the maximum or minimum, generally for the instrument system failure, because of wide temperature measuring instrument system lag, does not happen suddenly change, at this time of the cause of the problem is more thermocouple, heat resistance, compensation wire break or transmitter amplifier failure cause,
(2) temperature control instrument systems instructions appear rapid oscillation phenomenon, many improper for adjusting the PID control parameters,
(3) temperature control instrument systems instructions appear sharply slow wave, is likely to be caused by the process change, such as the operation does not change, then is likely to be the fault of instrument control system itself,
(4) the failure analysis steps of the temperature control system itself: check whether the regulator input signal change, the change of the input signal, the regulator, valve film head diaphragm leakage; Check whether regulator input signal change, the change of the input signal, the output signal changes, defective; Check the input signal change, check regulator output without change, if you don't change controller input, output, at this time is the regulator itself fault,
Pressure control instrument system fault analysis steps
(1) the pressure control system there was a rapid oscillation wave instrument, first check whether there is any change on process operation, this change is mostly a poor process operation and controller PID parameters setting,
(2) instrument appear dead line pressure control system, technological operation changes the pressure indicator or not, the general failure occurs in the pressure measurement system, check first whether the measurement system for pressure pipe plugging phenomenon, not plugging, check whether there is any change on pressure transmitter output system, have change, fault in the controller measurement indicator system,
Flow control instrumentation system fault analysis step
(1) flow control instrumentation system to achieve the most hours, indicating value field detection instrument, first check if the normal, the fault in the display instrument of field detection instrument is minimum, when is the check valve opening, if the valve opening is zero, is often as the regulator between regulator failure, when the testing instrument, the smallest of the opening of the regulating valve is normal, the cause of the problem is likely to be the system pressure is not enough, the system pipeline blockage, pump volume, medium crystallization, improper operation, such as the cause, if the instrument failure, the reasons are: orifice differential pressure flowmeter may be positive pressure bring pressure pipe plugging; Positive pressure differential pressure transmitter room leak; Mechanical gear flowmeter is jammed or filter plugging,
(2) flow control instrumentation system indicated value maximum, detection instrument is often indicates the largest, manual and remote control regulator is up or down at this time, if the traffic can drop down the general reasons for process operation, if the flow values fall not come down, is the cause of the instrument system, check the valve flow control instrumentation system actions; Inspection instrument measuring system for pressure is normal; Check instrument signal transmission system is normal,
(3) flow control instrumentation system indicated value fluctuation is frequent, control can be switched to manual, if the fluctuation is reduced, the reason is the instrument or instrument control parameter PID is not appropriate, if still frequent fluctuations, is caused the process operation,
Liquid level control instrument system fault analysis steps
(1) indicating value of the liquid level control instrument system change to the largest or most hours, look to whether can check gauge is normal, such as the indication is normal, the liquid level control instead of manual remote control level, the liquid level changes, such as liquid level can be stable in a certain range, the breakdown in the liquid level control system; If not stable level, general process system for the fault, to find reasons from the aspects of technology,
(2) differential pressure type level control instrumentation, instructions and directions direct-reading meter site right, first check the scene direct-reading indicating instrument is normal, such as the indication is normal, check the pressure differential pressure type liquid level meter of negative pressure guide tube sealing liquid to see if there is leakage; If there is leakage, potting liquid again, and the zero point; No leakage, may be the instrument of negative transfer of the amount wrong, readjust the migration quantity make the instrument is normal,
(3) the liquid level control instrument system indicated value changes, frequent fluctuations of the first to analyze the capacity of the liquid level control object size, to analyze the cause of the failure, large capacity is commonly instrument failure, small capacity must first analysis process operating conditions change, such as the change is likely to be process caused by the frequent fluctuations, such as no change may be failure,
More than just the four parameters of single control instrument field failure analysis of the actual field and some complex control circuits, such as cascade control, process control, process control and interlocking control, etc., the fault analysis is more complex, to specific analysis,