Analysis of instrument repair and system failure repair cases and instrument installation

First, the field instrument maintenance case:

1. In the existing plant of our factory, the part of the plant where crystallization of ammonium salt is likely to occur is the related instrument of hydrogenation desulfurization tower and the instrument of sulfur-containing gas. The treatment method is to use steam to heat and melt the ammonium salt. Make the instrument work normally, but the fundamental solution is to start from the process side and minimize the crystallization of ammonium salts.

2. When it is found that the field instrument is not working properly, it should start from the following aspects: (1) The water inlet phenomenon occurs in the field instrument junction box or the meter head and the threading pipe, so that the field instrument can not work normally (2) Poor wiring, check all wiring from the control room cabinet to the site (3) The safety barrier or isolation barrier is broken (4) Problems occur with the card or the card channel (5) The wire and the shield wire in the signal line are short-circuited, thereby attenuating the voltage , causing the scene to lose power. The treatment method can disconnect the shield wire from the ground wire.

3. What are the common faults of thermocouples (lower, smaller, unstable)?

The display value is low (the thermal potential is too small): 1) short circuit of the hot electrode; 2) short circuit of the compensation wire; 3) ash deposition of the thermocouple terminal, causing short circuit; 4) reverse polarity of the compensation wire and the thermocouple; 5) heat The thermal electrode is degraded; 6) The compensation wire is not matched with the thermocouple. 7) The thermocouple installation position or insertion depth does not meet the requirements; 8) The thermocouple temperature compensation does not meet the requirements; 9) The thermocouple does not match the display instrument.

The display value is too high: 1) The thermocouple is not matched with the display instrument; 2) The compensation wire is not matched with the thermocouple; 3) The interference of the DC signal.

The output of the thermocouple is unstable: .1) The thermocouple terminal is in poor contact with the electrode; 2) The thermal coupler measures the insulation damage of the circuit, causing intermittent short circuit and grounding; 3) The thermocouple is not installed securely or externally; 4) The hot electrode Will not break.

4. What are the common faults of electrical converters?

Common faults: 1. The linearity is not good: the nozzle and the baffle are not well matched, the baffle cover is not strict, and the baffle nozzle is damaged; 2. The backlash is large: mechanical friction, the moving coil is slightly stuck; 3. The range is not up to To, after repeated adjustments, the permanent magnet is demagnetized; 4. The input signal is not given, the output is maximum or the output is not returned to zero: the nozzle is clogged, the orifice seal ring is damaged, the amplifier is faulty; 5. The gas source is changed within 10%. The output changes too much: the orifice is too large, and the position of the baffle nozzle is not well matched.

5, test analysis of four-way valve common faults and treatment measures

(1) The four-way valve 380V is powered off, the motor does not operate, and the wiring is re-powered after processing; (2) The 9V battery is dead, the battery is replaced, and the four-way valve is re-commissioned; (3) the valve is closed or the valve is not in place, and the power is turned off. Reset the valve opening and closing limit; (4) The four-way valve cutting tower is not normal, check whether the four-way valve and the A/B tower blocking valve switch are in the remote and position switch is normal.

6. For measuring liquid level instruments:

For the buoy at the beginning of the construction phase due to the inconvenience of high pressure, 375 can be used to directly adjust the on-site buoy (high pressure buoy), first of all to ensure the accuracy of the glass plate and process production stability, as long as the boundary or liquid level calibration Find the 375 PVTRIM ZERO item to directly calibrate the pontoon. If the pontoon is high, just mark the PVTRIM ZERO to the corresponding position of the field glass plate. Otherwise, it is not necessary to perform 2-point calibration under normal conditions. For the on-site glass plate process Frequently reacting to the phenomenon, first check whether the upper and lower ball valves are in the proper position at the scene, generally open 3-4 turns after closing, do not open fully. In order to avoid blocking the liquid, it is mistaken to think that the upper and lower pressure points cannot be removed. If the medium is too dirty to block the glass plate, it is necessary to test the upper and lower valves, and then close the upper and lower hand valves to ventilate and drain the sewage. If it is no longer possible, it may be blocked. The glass plate needs to be removed.

The liquid level gauge, especially the capillary pressure, if there is an abnormality between the long-term operation and normal, do not arbitrarily modify the range of the meter. First, check the zero point of the meter after normal. In winter, due to the poor mixing effect, the upper and lower pressure points may be Freezing, if it is not normal after heating with steam, there may be accumulation of dirty things to change the pressure and cause the pressure difference to be unstable. It is necessary to disassemble the hairlan to check whether there is any foreign matter inside, and pay attention to the full pressure and condensation after cutting. .

7, the chain speed valve, etc.:

For the valve of the solenoid valve, sometimes the valve does not work after being charged. First, check whether the relay in the cabinet has 24 volts output, and then go to the site to measure whether there is voltage. The voltage is there to prove that the circuit is no problem. If the wheel is better, it can be judged directly. If it can be shaken manually, it can be judged to be the problem of the solenoid valve gas path. Check whether the solenoid valve air passage is unblocked, whether there is any impurities inside, open the solenoid valve for corresponding cleaning, if the valve does not carry There are two ways to see if the valve is really stuck. First, the solenoid valve can be de-energized and the valve can be opened by manual control of the solenoid valve. (The actuators such as coking, hydrogenation and flue adjustment can only be lost after the site is de-energized. Manually check to see if the valve has a gas source output. If there is no output, the valve may be stuck. Then disassemble the valve to see if any foreign objects are stuck.

For the case of internal leakage of the valve; ball valve, disc valve, closing or closing will cause leakage inside the valve, and the corresponding phase adjustment is needed. If it is not possible, the ball valve core and the valve seat may be seriously worn or the sealing gasket may be damaged. . The regulating valve may be zero or too high, or the valve core and the valve seat may be stuck with foreign objects.

8. For temperature measuring instruments:

Thermocouples (resistors) generally have low temperature or fluctuations. First check whether the cable of the cabinet is firm. If the cabinet clamp has a low current string or short circuit, the voltage and resistance are unstable, and the temperature value changes. First, use the thermocouple. (Resistance) signal generator reads the value to see if the value on the DCS screen is consistent. Then use the generator to send the value to DCS to see if the value on the DCS screen is consistent with the value sent. If it is inconsistent, check it. For the problem of the card, you need to replace the new card. When replacing the card, be sure to contact the process whether the temperature is interlocked. If you accidentally pull it out, the temperature will be too high, which will cause the machine to stop. If it is consistent with the on-site problem, the wiring may be loose in the thermocouple. If the water is connected or the terminal is connected to the edge, the grounding or resistance is too large, resulting in temperature fluctuation. After cleaning, fix the terminal. If it is a short circuit of the instrumentation line, it is necessary to check whether the instrument junction box or the corner of the three-way junction box is short-circuited due to wear or rain, and the insulation rubber is used in the short-circuit. Package and tighten it also may be due for a long time into the lead at the junction with gas corrosion or bad, and then pick from the new cut.

9. For pressure measuring instruments:

Some transmitters are inconsistent with the data transmitted indoors and indoors. First, if the range of the DCS configuration is correct, (because some devices are modified by the range, the server is controlled, but the initial download is not completed before the start of the process.) Therefore, there will be a difference between the partially modified range and the actual table. Then check the line, there may be grounding of the line (for example, hydrogenation of PDT3109 reactor differential pressure, long-term rain may lead to grounding, because this table is From the DCS first to the on-site differential pressure display and then to the transmitter, the abnormal display of the pressure difference directly affects the display of the transmitter)

10. For a rotameter, the phenomenon of staying at a certain value often occurs, usually because some impurities (such as stones, welding slag, etc.) are stuck on the float, and the treatment method is to treat the rotor flow. Remove the system from the system, then remove the rotor flowmeter, clean it and reinstall it.

11. For the mass flowmeter, the empty pipe or two-phase reverse flow phenomenon often occurs, resulting in the mass flowmeter not showing or showing the inaccuracy. The treatment method is to close the rear hand valve of the mass flowmeter or the control valve behind it. , so that it is full and can be displayed normally.

12, the alarm process can not send oil in the process of oiling is: first check the actual situation on the scene to confirm the alarm, turn off the alarm, press the start to continue to send oil; wait for the oil to end and then follow the prompts to deal with. The general electrostatic alarm processing method is to check whether the electrostatic clamp is in good contact, and wipe the electrostatic clamp and the metal piece to make it contact well; the general treatment method of the oil spill alarm is to carefully clean the oil spill alarm probe.

13. When the loading and unloading truck batch controller crashes, first contact the craftsman to stop loading on the two cranes where the crash occurs, then power off the batch controller that has crashed, and then power it on. Restart to get it working.

14, PSA program control valve back to the wrong reasons are: (1) echo probe damage (2) echo cable disconnection or poor contact at the wiring (3) echo probe installation is not in place (4) power supply fuse short circuit (5) card The cause of burnout; the program control valve switch is not in place or does not move: (1) insufficient wind pressure (2) air line or membrane head air leakage (3) solenoid valve coil burnout (4) solenoid valve air source distribution block blocked ( 5) The card is burnt out (6) The power supply fuse is short-circuited (7) The program-controlled valve is stuck.

15. If it is found that the value displayed on the DCS is a certain multiple of the field instrument display value, it should be considered that the field instrument range does not correspond to the indoor range. The processing method is to log in the engineer level on the operator station and then DCS The range is modified correctly, or the field instrument can be modified.

16, the servo level gauge fails

If the servo level gauge and the gauge are not correct, first check whether the level gauge is working normally. Generally, the “reset failure” or “motor running timeout” may be static interference. You can check the running status of the level gauge in the debugging interface. After resetting the level gauge, after resetting, the liquid level is measured until the liquid level is found. If the measured value deviates from the actual value, the “level adjustment” can be performed.

17. The liquid level of the radar level gauge fluctuates greatly, there is no liquid level or there is deviation, and should start from the following aspects: (1) Whether the model of the radar matches the design of the radar of the crude oil tank requires the other of the waveguide (2) Whether the installation is reasonable, the liquid level measured by the radar is the required level, plus a horizontal reflector can solve the liquid level fluctuation problem; (3) the multiple gauges are different from the measured liquid level. The command line sets the reference height.

18, tank level or temperature can not be transmitted indoors, should start from the following aspects: (1) check the output signal of the level gauge is normal, generally 2.5V voltage output; (2) check the pre-can processor is normal Display if the replaceable circuit board is displayed abnormally; (3) Check whether the junction box to the indoor line is normal; finally, if the MOXA card of the upper computer server is working normally, there is generally a 5V voltage output.

Second, the system failure repair case:

1. How do you handle the main control and card replacement during normal start-up?

Card replacement is generally a bad channel. When changing the card, pay attention to whether the card is redundant. The DCS will accommodate 148R and 152, and the rest will not be spared. For the spare card, see if the other card is running, and the green light is displayed during normal operation. If it is normal, the bad card can be directly pulled out of the replacement card. For the card that is not enough, see if there are other links. The point that there is a chain must be contacted with a good process to remove the replacement card. If the master control is broken during the start of operation, it will switch to another. First, check that the master has to turn the DIP switch to ON, and then switch it to ON after the replacement, so as to prevent the main controller from being able to have another fault. Switch.

2, the operator station appears software disk can not be used or some buttons are not easy to use, how do you deal with?

In this case, there is no need to reboot the machine, and there is no need to unplug the connector from the software disk to the host. Just exit the operator station and re-enter it.

3. From the system side, if the interlock valve or pump is not turned on or started. Or the feedback point on the screen after the pump starts, how do you find the problem? ,

First, you can try to log in to the main control. If there is output, check the corresponding solenoid valve fuse or the relay on the appliance. If there is output valve, the output should be viewed. The output on the appliance is the cause of the appliance. If the relay is not available. Output, check if the fuse is burnt short, if the fuse is not broken, the relay may be broken. After the pump starts, the feedback point does not come. First, find the channel corresponding to the cabinet and use the short wiring to short-circuit to see if the echo is normal. If the normal description is the cause of the appliance or the fault of the appliance to the DCS line.

4. If you need to turn off the solenoid valve according to the safety requirements, and you are doing the power off, how do you change it from the system or cabinet?

In the configuration, only the chain output DO point needs to be reversed before it will affect the operation of the system. If the cabinet is changed from the cabinet, the normally open or normally closed point of the relay can be reversed.

5. In the ESD system, some actuators (such as quick-opening dampers, flue baffles, etc.) may be in the wrong state when they meet the chain condition or release the chain condition, which may be caused by the following aspects: (1) Engineer In the station ELOPII, the point is in the forcible state, the lifting method is to open the ELOPII software, click to find the modified program (that is, the blue triangle symbol represents), then right click on the blue triangle symbol, select the ONLINE-TEST option to open Log in to the online state, and then find the point (must be DO or DI point, can not be the intermediate variable point), left-click and hold out a small yellow frame (there are two upper and lower columns), double-click to move the black small block to the top, you can Unforced. (2) In the cabinet, the fuse at the corresponding point is burned out, the processing method is to replace the fuse (3) in the cabinet, the corresponding relay is faulty, and the processing method is to replace the corresponding type of relay (4) in the cabinet, on the terminal block The corresponding small knife gate is not closed.

In addition, when dealing with instruments related to ESD systems (such as those related to coking instrument cabinets), special care should be taken to notify the relevant process personnel before handling the problem, and to remove the interlocks involved in the instrument to be repaired. After the lock is removed, repairs are carried out to avoid unnecessary chain parking accidents.

6, SNETB network card problem

The Macsv system server or operating station exchanges data from the A network (128 segments or 130 segments) during normal operation. The system automatically disables the B network card for a long time. At this point, the system status map will show that a machine or all B networks are red, but can be pinged.

Processing: Desktop - My Computer - Right click - Management - Click on "Device Management" - click on "Network Card" in the right area - Intel Pro100 (or Dlink) - Right click "Properties" - Power Management -- Remove the 前 before "Allow the computer to turn off this device to save power" and restart the computer to return to normal.

16. When the process personnel report that the corresponding valve position output is incorrect after a certain PID circuit is automatically injected, it may be because the positive and negative effects in the PID parameter are reversed. The processing method is to log in to the engineer on the operator station. After the level, you can modify the positive and negative items in the PID panel.

Third, instrument installation knowledge

1, temperature instrument installation

Temperature measuring components (such as thermocouples, RTDs, bimetal thermometers, pressure thermometers, etc.) should be installed at locations that accurately reflect the temperature of the media. The temperature measuring element installed on the process pipe should be perpendicular to the pipe centerline or inclined 450, the insertion depth should be greater than 250mm or at the center of the pipe, and the insertion direction should be reverse or perpendicular to the measured medium. When the pipe nominal diameter is less than 80mm, it can be installed at the elbow or the enlarged tube. When the bimetal thermometer is installed, the dial surface should be easy to observe, and the straight mercury thermometer should not be installed horizontally.

2, pressure gauge installation

Pressure gauges installed on high-voltage equipment and pipelines, such as near the operating position, should be installed at a height of more than 1.8m from the ground. Otherwise, a protective cover should be placed on the front of the instrument. Pressure gauges should not be installed on equipment and pipelines with high vibration. When the pressure of the measured medium fluctuates greatly, the pressure gauge should take buffer measures. When measuring media with high viscosity, high corrosivity or easy to vaporize. Pressure gauge installation should be installed with isolation tank or diaphragm pressure gauge, sealed capillary diaphragm pressure gauge. A purge or sintered metal filter should be added to the measurement of solid particles or dust media.

3, flow meter installation

The rotameter must be installed on a vertical pipe without vibration. The allowable deviation of the verticality is 2/1000, the flow direction of the measured medium should be from bottom to top, and the length of the upstream straight pipe section should be greater than 5 times the inner diameter of the process pipe.

The electromagnetic flowmeter (transmitter) can be installed on horizontal or vertical pipes without strong magnetic fields and should meet the following requirements: (1) When the transmitter is installed on a vertical pipe. The flow direction of the medium should be from bottom to top. (2) The length of the straight pipe section upstream of the flowmeter should be greater than 5 times the inner diameter of the process pipe. (3) The electromagnetic flowmeter (transmitter), the measured medium and the process pipeline should be connected to equipotential. And should have a good grounding (4) electromagnetic flowmeter converter should be installed in an environment free of vibration, normal temperature, dry, where the local installer should be loaded or added protection box (cover) (5) when the pipe nominal diameter is greater than When 300mm, special support should be added.

The vortex flowmeter should be installed on a vibration-free pipe and meet the following requirements: (1) Choice of installation location: electromagnetic interference should be avoided. The installation location of the flowmeter should be as far away as possible from strong electromagnetic fields, such as high-power motors, transformers, and inverter equipment. (2) Pay attention to the flow direction mark on the flowmeter casing during installation, and do not install it. (3) Straight pipe section: The upstream and downstream of the vortex flowmeter are required to have a straight pipe section of a certain length. Upstream generally requires a straight pipe section of about 40D, and a downstream straight pipe section of 5D is required. (4) The center of the process pipe should be aligned (no obvious deviation from the naked eye). Do not use the flowmeter to straighten the upstream and downstream process piping during installation to avoid damage to the flowmeter. There should be support at the near flange of the upstream and downstream process piping to prevent vibration and affect measurement accuracy.

Throttling devices such as orifice plates, nozzles and venturis should be inspected for appearance and size before installation. The processing size should meet the design requirements, and the orifice plate, nozzle inlet edge and inner wall should be smooth and burr-free. No scratches and visible damage. The installation of orifice plate, nozzle and venturi shall comply with the following requirements: (1) The sharp edge of the orifice plate or the curved side of the nozzle shall greet the flow direction of the measured medium (2) the orifice plate, the nozzle and both sides of the venturi The length of the straight pipe section should meet the design requirements. (3) The end face of the orifice plate and the orifice flange should be perpendicular to the axis, and the deviation should not be greater than l0 (4) The positive pressure chamber, the negative pressure chamber and the orifice plate of the differential pressure transmitter The positive and negative signs on the nozzle correspond, and the transmitter should be installed for easy operation and maintenance.

4, liquid level instrument installation

The height of the float level gauge should be such that the normal level or boundary level is at the center of the float and is easy to set up and repair. The pontoon should be mounted vertically with a tolerance of 2/1000 for the verticality.

The glass plate level gauge should be installed in a position that is easy to observe and repair. If it is used together with the float level gauge, the liquid level indication should be installed in the direction of easy observation. The level gauge installation should be vertical with a vertical tolerance of 5/1000. Install the glass tube liquid level timing, and use a wrench to gently tighten the filler to prevent the glass tube from breaking.

The installation height of the differential pressure liquid level transmitter should not be higher than the lower pressure receiving port of the liquid surface, but it is not affected by the flange type differential pressure transmitter, the air blowing method and the method of measuring the liquid level by using the low-boiling liquid vaporization pressure. limit. Flange type differential pressure transmitter should be protected when capillary is laid. The bending radius should be greater than 50mm, and the ambient temperature of the installation site should not be too large. Otherwise, heat insulation measures should be taken.