The daily maintenance of the instrument is a very important work, it is an indispensable part of many links to ensure production safety and smooth operation. The daily maintenance of the instrument reflects the idea of ​​total quality management and prevention first, and the instrument maintenance personnel should do the daily maintenance of the instrument to ensure the normal operation of the instrument. So how should the instrument be maintained? 1. Tour inspection Instrument maintenance personnel select the best inspection route based on the distribution of instruments in the area of ​​responsibility under their jurisdiction, and inspect at least once a day. During the patrol inspection, the operating personnel in the control room on duty should learn about the operation of the instrument and make a record of the patrol inspection. 1. Check whether the instrument indication and record are normal, whether the primary instrument (transmitter) indication on site is consistent with the indication value of the control room display instrument and regulating instrument, and whether the regulator output indication is consistent with the valve position of the regulating valve; 2. Check whether the power supply voltage of the instrument is within the specified range and whether the air source (0.14MPa) reaches the rated value; 3. Check the insulation and heat tracing conditions of the instrument; 4. Check the damage and corrosion of the instrument body and connecting parts; 5. Check the condition of the instrument, that is, the nameplate should be clear and correct, the parts should be intact and complete, the fasteners should be in good contact, the terminal wiring should be firm, the adjustable parts should be in the adjustable position, and the seals should be leak-free. 6. Check the equipment and environment to be tidy, clean, and meet the working requirements, that is, the whole machine should be clean and free of rust, the paint layer should be smooth, bright, and not falling off, the instrument pipelines and circuits should be neatly laid, and the pipelines and circuit numbers should be complete. Clear and accurate. 2. Regular sewage discharge There are two main tasks for regular sewage discharge, one is sewage discharge, and the other is regular blowdown. 1. Sewage Blowdown is mainly for pressure transmitters, differential pressure transmitters and other instruments. Because the measuring medium contains dust, grease, tiny particles, etc., which are deposited in the pressure guiding tube (or deposited in the pressure valve), it directly or indirectly affects the measurement. 2. Blowing Flushing is a method of using air blowing or flushing so that the measured medium does not directly contact the instrument components or the measuring pipeline, so as to protect the measuring instrument and implement the measurement. Attention should be paid to the following items during purging: ①The purge gas or liquid must be a fluid medium allowed by the tested process object, does not chemically react with the process medium, is clean, does not contain solid particles, is non-corrosive, and has good fluidity; ②The supply source of the purging liquid should be sufficient and reliable, and not affected by the process operation; ③The pressure of the purging fluid should be higher than the highest possible pressure at the measuring point during the process, to ensure that the purging fluid is continuously and stably purged at the flow rate required by the design; ④Use restrictive orifice or rotameter with adjustable resistance to measure and control the flow of purge liquid or gas; ⑤The inlet point of the purge fluid should be as close as possible to the source parts of the instrument, so as to keep the pressure drop of the purge fluid in the measuring pipeline to a minimum; ⑥In order to reduce the measurement error as much as possible, the flow rate of the purging fluid must be constant. 3. Regular lubrication and anti-corrosion process The daily maintenance of instrument workers can not be without regular lubrication and corrosion protection, but in specific work, these two items are often easy to overlook. The lubrication cycle should be determined according to the specific situation. The instruments and components that need regular lubrication and corrosion protection are as follows: 1. Pneumatic cam flex valve, pneumatic ball valve, pneumatic butterfly valve, rotating parts of electric actuator; 2. Protect the box, the door shaft of the incubator, and the fastening bolts of the junction box. 3. Fix the bolts and nuts of transmitters, regulating valves, valve positioners, and electrical converters in harsh environments to prevent the threads from corroding and difficult to disassemble. 4. The rotating part of the valve positioner feedback lever in harsh environments. 5. Thermal resistance, thermocouple junction box bolt or upper cover threaded part in harsh environment. 6. Flexible pipe and instrument connection part in harsh environment. Four, antifreeze inspection process Checking the anti-freezing measures of the meter is one of the contents of the daily maintenance of the meter. It is related to saving energy, preventing the meter from freezing damage, and ensuring the normal operation of the meter measurement system. It is an item that cannot be ignored in the maintenance of the meter. Five, fault handling process Fault handling is an important part of the daily maintenance of the instrument. Dealing with faults must be fast and effective, serious and serious, leaving no hidden dangers, and timely reporting and coordinating the handling of problems that cannot be handled. When dealing with faults and instrument overhaul, the instrument personnel must be safety first, and there must be no personal safety and the phenomenon that affects the normal operation of the production. The safety first idea must be established, and the process flow must be familiarized before the overhaul. Which instrument and equipment must be dismantled It can only be carried out under the supervision of the craftsman after contacting the craftsman for permission. Avoid safety accidents. Basic analysis and processing steps for field instrument system failures Field instrument measurement parameters are generally divided into four major parameters: temperature, pressure, flow, and liquid level. Now according to the different measurement parameters, to analyze the failure of different field instruments. 1. First of all, before analyzing on-site instrument failures, it is necessary to have a clearer understanding of the production process, production process and conditions of the relevant instrument system, understand the design plan, design intent of the instrument system, and the structure, characteristics, performance and parameter requirements of the instrument system Wait. 2. Before analyzing and checking the fault of the on-site instrument system, it is necessary to understand the production load and the parameter changes of the raw materials from the on-site operators, check the record curve of the faulty instrument, and conduct a comprehensive analysis to determine the cause of the instrument fault. 3. If the instrument record curve is a dead line (the line with no change is called dead line), or the record curve originally fluctuates but suddenly becomes a straight line; the fault is probably in the instrument system. Because most of the current recording instruments are DCS computer systems, the sensitivity is very high, and the changes in parameters can be very sensitive to reflect. At this time, you can artificially change the process parameters to see the curve changes. If there is no change, it is basically concluded that there is a problem with the instrument system; if there is a normal change, it is basically concluded that there is no major problem with the instrument system. 4. When the process parameters are changed, it is found that the recording curve has a sudden change or jumps to the maximum or minimum. At this time, the fault is often in the instrument system. 5. The record curve of the instrument always behaves normally before the occurrence of the fault. After fluctuations, the record curve becomes irregular or makes the system difficult to control, even manual operation cannot be controlled. At this time, the fault may be caused by the process operating system. 6. When the DCS display instrument is found to be abnormal, you can go to the site to check the indication value of the same intuitive instrument. If they are very different, it is likely that the instrument system is malfunctioning. In short, when analyzing the causes of field instrument failures, special attention should be paid to changes in the characteristics of the measured control object and control valve, which may be the cause of the field instrument system failure. Therefore, it is necessary to comprehensively consider and analyze carefully from the two aspects of the field instrument system and the process operating system to check the reasons. Six, meter parking process The meter parking is relatively simple, and the precautions are as follows: 1. Work closely with craftsmen; 2. Understand the process shutdown time and chemical equipment maintenance plan; 3. Remove the instrument or detection element on the equipment according to the maintenance arrangement to prevent damage to the instrument during the maintenance of the equipment, and cut off the power supply and gas source before removing the instrument; 4. Dismantle the meter in time according to the maintenance plan. When dismantling the flange transmitter, be sure to make sure that the material in the storage tank is empty before proceeding; 5. Remove the thermal resistance, transmitter and other instruments, and place the signal cables properly after wrapping them with insulating tape. 6. When removing the pressure gauge and pressure transmitter, pay attention to the possible blockage of the pressure inlet, causing local pressure; the material rushes out and causes personal injury. The correct operation is to loosen the installation bolts, exhaust, and drain the remaining liquid. Remove the meter after the gas and liquid are drained; 7. For electrical valve positioners, disassemble after turning off the air source; 8. When removing the orifice plate of the ring chamber, pay attention to the direction of the orifice plate to prevent reverse installation; 9. Disassemble the meter should be clearly marked, and the number should be seated during installation to prevent the same type of meter from being mixed up due to different ranges and causing meter failure; 10. For instruments with interlock control, with the consent of the craftsman, switch to manual release of the interlock and then dismantle the instrument for maintenance. Seven, instrument start-up process 1. The instrument driving should be closely coordinated with the process. According to the process equipment and pipeline pressure test, the instrument should be installed in time, and the process start-up schedule will not be affected by the instrument; 2. Be sure to pay attention to the position number when installing the instrument, and check the number into the seat. 3. The instrument is powered. Turn on the corresponding power switch, check whether the 24v power supply voltage is normal, whether the power supply of each dcs power module and UPS is normal. 4. Air source sewage. Moisture and impurities will appear in the gas source pipeline after a period of operation. Due to the influence of startup and shutdown, there will be more impurities and moisture. It must be cleared before driving. Based on the principle of stem to branch, the dirt is removed successively to prevent the air source from blocking the constant orifice and causing instrument failure. 5. When installing orifice plates and other throttling devices, pay attention to the direction to prevent reverse installation. It is necessary to ensure that the front and rear straight pipe sections are smooth and clean, and any dirt is handled in time. The annular chamber should be in the center of the pipeline, and the pressure valve should be opened in time after the throttling device is installed to prevent the pressure signal from being driven when the vehicle is driven. It is recommended that the opening of the pressure valve is fully opened before returning to a half turn. 6. When installing the regulating valve, make sure that the arrow direction of the valve body is consistent with the flow direction. 7. When using full-scale negative migration to measure the liquid level, pay attention to filling up the negative pressure connecting pipe. 8. Differential pressure transmitters and pressure transmitters protected with isolating liquid should be filled with isolating liquid when restarting the vehicle. 9. Pay attention to the positive and negative polarity of the thermocouple compensation wire connection to prevent reverse connection. The thermal resistance should pay attention to the three wires not to be confused. 10. After the overhaul, the instrument should be linked and adjusted before driving, and the on-site primary instrument (transmitter, detection element, etc.) and the control room secondary instrument (panel mounting, rack mounting, computer display, etc.) should have the same instructions, or the primary meter output The value is consistent with the input value of the rack-mounted instrument (distributor, dcs input card) in the control room; check that the regulator, dcs output, manual controller output and the valve position indication of the regulating valve are consistent (or the electrical valve positioner input is consistent). The upper and lower strokes of the electric valve switch must be consistent. 11. For the instrument with interlock, switch to the automatic interlock position after the instrument is operating normally and the process is operating normally.
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