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25 years of repair experience with faults in chemical process instruments: 01 Crystallization issues – In the existing plants, the instruments related to the hydrogenation desulfurization tower, as well as those used in the sulfur-containing gas handling section, are prone to ammonium salt crystallization. Treatment method: Steam is used for heating to melt the ammonium salts, thereby allowing the instruments to function properly. However, the fundamental solution is to address the issue at the process level by minimizing the formation of ammonium salt crystals. 02 Instrument out of power: When it is found that the instruments on site are not functioning properly due to a lack of power, the following aspects should be checked: (1) Water may have entered the wiring box of the instruments on site, or the instrument housings or wire conduits, which is causing the instruments to fail to operate correctly ； (2) Poor wiring; check all wiring from the control room cabinet to the field ； (3) The safety barrier or isolation barrier is damaged ； (4) There is a problem with the card holder or the card passage ； (5) A short circuit between the conductors and the shield wire in the signal line causes voltage attenuation, resulting in the meter on site running out of power. The solution is to disconnect the shield wire from the ground wire. 03 Thermocouple faults – Common faults of thermocouples (low readings, low values, instability). Guidelines for diagnosis: Low reading (low thermoelectromotive force): (1) Short circuit in the thermoelectric electrodes ； (2) Compensation wire short circuit ； (3) Dust accumulation on the thermocouple terminals causes a short circuit ； (4) Compensation wires and thermocouple polarities are connected reversely ； (5) Degradation of thermocouple thermoelectrodes ； (6) The compensation wire is not compatible with the thermocouple ； (7) The installation location or insertion depth of the thermocouple does not meet the requirements ； (8) The thermocouple temperature compensation does not meet the requirements ； (9) The thermocouple is not compatible with the display instrument. The displayed value is too high: (1) The thermocouple is not compatible with the display instrument ； (2) The compensation wire is not compatible with the thermocouple ； (3) Interference from DC signals. The thermocouple’s output is unstable: (1) Poor contact between the thermocouple terminals and the electrodes ； (2) Insulation damage in the thermocouple measurement circuit, causing intermittent short circuits and grounding ； (3) Thermocouple is poorly installed or there is external vibration ； (4) Whether the thermoelectric electrode is broken or not. 04 Electrical Converter Common faults of electrical converters: Common faults: (1) Poor linearity: Poor fit between the nozzle and the baffle, the baffle not sealing properly, damage to the baffle nozzle ； (2) Large backlash: mechanical friction, slight jamming of the moving coil ； (3) The measurement range cannot be achieved; after multiple adjustments, it is due to demagnetization of the permanent magnet ； (4) No input signal, maximum output, or output that does not return to zero: clogged nozzle, damaged throttle orifice seal ring, amplifier malfunction ； (5) If the air supply varies by less than 10% but the output still deviates from the specified range, it is due to an overly large throttle hole or improper alignment of the baffle nozzles. 05 Analysis of the four-way valve: Common faults of the four-way valve and corresponding solutions: (1) If the 380V power supply to the four-way valve is cut off, the motor will not operate; in this case, check the wiring and restore power supply ； (2) The 9V battery is dead; replace the battery and re-calibrate the four-way valve ； (3) The valve is not closed or opened properly; power off and reset the opening and closing limit positions ； (4) The four-way valve’s function for switching between towers is abnormal; check whether the switch for controlling the transition between the four-way valve and the isolation valves of towers A/B is set to remote mode, and whether the position switch is functioning properly. 06 Level gauges for measuring liquid levels: In the case of float gauges that are in use and subject to high pressures, it is not convenient to remove them; the 375 device can be used to adjust such float gauges directly on site. It is important first to ensure the accuracy of the glass panel as well as the stability of the production process. To calibrate the level or boundary point, one simply needs to use the PVTRIM ZERO function of the 375 device to adjust the float gauge accordingly. If the float gauge is set too high, simply adjust PVTRIM ZERO to the corresponding position on the glass panel; the same principle applies in reverse. Generally, no two-point calibration is required ； Regarding the issue of poor operation in the on-site glass plate process, the first thing to check is whether the upper and lower ball valves are in the correct position; generally, turning them 3-4 turns after closing them is sufficient, without needing to open them fully. To avoid blocking the liquid and mistakenly thinking that the pressure measurement points at the top and bottom are blocked, thus leading to disassembly. If the medium is too dirty and has blocked the glass plate, it is necessary to test the operation of the upper and lower valves; close the upper and lower manual valves in sequence to allow air to pass in and waste to be discharged. If flow still doesn’t occur, then there is likely a blockage. The glass panel needs to be removed. For level gauges, especially those that use capillary pressure sensing, if there is a sudden anomaly after normal operation for an extended period of time, do not alter the gauge’s range arbitrarily. First, check that the instrument’s zero point is functioning properly. In winter, poor heating effects may cause the pressure sensing points to freeze; if the problem persists even after thorough heating with steam, it could be that accumulated dirt is causing pressure fluctuations and unstable differential pressures. In such cases, the fitting needs to be disassembled to check for any foreign objects inside. Be sure to release pressure fully and allow condensation to occur before proceeding with further repairs. For the quick-close valves used in series 07, those equipped with solenoids may fail to operate when energized. First, check whether the relay inside the control cabinet is outputting 24 volts; then go to the site to measure if there is voltage present. The presence of voltage indicates that there is no problem with the circuit. If the valve has a handwheel, it’s easier to determine the issue – simply try operating it manually. If it can be turned manually, then the problem lies in the air supply circuit of the solenoid; check whether the air flow in that circuit is unobstructed and whether there are any impurities present. Open the solenoid and clean it accordingly. If the valve doesn’t have a handwheel, there are two ways to determine whether it’s truly stuck: first, de-energize the solenoid and then try to open the valve manually (as is the case with actuators used in coking, hydrogenation, and flue gas regulation, where manual operation is only possible after the power is cut off); check whether there is air supply coming from the valve. If there is no output, it’s possible the valve is indeed stuck. Then disassemble the valve to check if there are any foreign objects stuck inside. In the case of internal valve leakage ； For ball valves and disc valves, failure to close fully or properly can lead to internal leakage; corresponding phase adjustments are required. If that doesn’t work, it may be due to severe wear of the ball valve core and seat, or damaged sealing gaskets. Control valves may have an excessively high zero point, resulting in poor sealing, or foreign objects may be stuck between the valve core and the valve seat. For temperature instruments using thermocouples (resistors), problems such as abnormally low temperatures or fluctuations often occur. First, check whether the wires in the cabinet are secure; if there is a low-current leakage or short circuit in the cabinet’s components, it can lead to unstable voltage and resistance levels, which in turn causes changes in the temperature reading. Use a thermocouple (resistor) signal generator to read the values, and see if they match those displayed on the DCS screen. Then send the values from the generator to the DCS and check again whether the values on the DCS screen correspond to those sent. If they do not match, investigate the problem with the cabinet components and replace them with new ones. When replacing the components, make sure to confirm whether interlocks related to that temperature point are in place; removing the components carelessly could result in excessively high temperature readings, leading to shutdowns (for example, a shutdown occurs when the pressure of the gas tank exceeds 95 degrees) ； If it is necessary to check the issues on-site, it is possible that the wiring inside the thermocouple is loose, or that water has entered, or that the wiring terminals are not properly connected to the edges, resulting in grounding or excessive resistance and thus temperature fluctuations. In such cases, cleaning up and securing the wiring terminals will resolve the problem. If there is a short circuit in the instrument wires, it is necessary to check whether the instrument wiring box or the junction boxes at the bends have suffered short circuits due to wear or moisture from rain; in such cases, wrapping the faulty area with insulating tape will suffice. It is also possible that corrosion at the wiring connections has occurred due to prolonged use or the presence of gases, requiring the connections to be cut off and reconnected. 09 For pressure instruments, some transmitters transmit inconsistent data indoors and outdoors. First, check whether the range set in the DCS configuration is correct; since all such devices have had their ranges modified before being connected to the server controller, and no thorough reset was performed prior to initialization, this results in discrepancies between the modified ranges and the actual values shown by the instruments. Then check the wiring; it’s possible that there is a ground fault in the wiring. (For example, in the case of the differential pressure of the hydrogenation PDT3109 reactor, prolonged rainfall may cause the wiring to become grounded, as this gauge sends the pressure data from the DCS to the field display unit before it reaches the transmitter, and any abnormal readings at the field level directly affect the transmitter’s display.) As for rotor flowmeters, it’s common for them to stay fixed at a certain value, usually due to foreign objects such as stones or slag getting stuck in the float. The solution is to disconnect the rotor flowmeter from the system, take it apart, clean it, and then reinstall it. 11 Mass flow meters: For mass flow meters, it is common for there to be empty tubes or two-phase backflow, which results in no reading or inaccurate readings on the meter. The solution is to reduce the size of the back valve or the control valve behind the mass flow meter, so that the tube is filled and normal readings can be obtained. If an alarm occurs during the oil dispensing process and dispensing cannot proceed, the solution is to first check the actual situation on site, disable the alarm once confirmed, and then restart the process to continue dispensing the oil ； Wait until the hair serum application is complete, then proceed according to the instructions. The common method for dealing with static electricity alarms is to check whether the static clamps are in good contact, and to wipe the static clamps and the metal plates to ensure proper contact ； The general approach to dealing with an oil spill alarm is to carefully clean the oil spill alarm sensor. 13 When the batch controller for loading and unloading freezes, first contact the process engineers and ask them to stop loading operations at the two cranes where this freezing issue is occurring. Next, power off the frozen batch controller, and then power it on again to restore normal operation. 14. The incorrect feedback from the programmable valve for the PSA is caused by: (1) Damaged feedback probe ； (2) The return cable is open or the connection at the terminal is poor ； (3) The reply probe is not installed properly ； (4) Short circuit in the power supply fuse ； (5) Card component burned out ； The reasons why the programmable valve does not operate properly or remains stationary are: (1) Insufficient air pressure ； (2) Air leakage at the air duct or diaphragm head ； (3) The solenoid coil is burned out ； (4) Blockage in the solenoid valve air supply distributor ； (5) Card component burned out ； (6) Short circuit in power supply fuse ； (7) The programmable valve is stuck. If the values displayed on the DCS are at a certain multiple of the values shown on the field instruments, it may be due to a mismatch between the range of the field instruments and that of the DCS. To resolve this issue, one should log in as an engineer on the operator station, adjust the range of the DCS to the correct value, or modify the field instruments accordingly. 16. The servo level gauge is not functioning properly; there is a mismatch between the servo level gauge and the level measurement device. First, it is necessary to check whether the level gauge is working correctly. Common issues include “reset failure” or “motor operation timeout”; static interference may also be a cause. The operating status of the level gauge can be viewed on the debugging interface. After resolving these issues, reset the level gauge. Once it has been reset, measure the level again until the correct value is obtained. If there is a discrepancy between the measured value and the actual value, “level adjustment” can be performed. 17. If the radar level gauge exhibits large fluctuations or inaccuracies – that is, if the level fluctuates greatly, there is no level detected, or the readings are inaccurate – the following aspects should be checked: (1) Whether the model of the radar matches the design requirements; radar levels in crude oil tanks require the use of waveguides, while those in other types of tanks do not ； (2) Is the installation proper? The liquid level measured by the radar is supposed to be horizontal; adding a horizontal reflector can resolve the issue of fluctuations in the liquid level ； (3) If multiple level measurements show deviations from the actual liquid level, the reference height can be set via the command line. If the parameters of the 18-tank area cannot be transmitted to the indoor tank area, or if the liquid level or temperature there cannot be sent indoors, the following aspects should be checked: (1) Verify whether the output signal from the level gauge is normal; generally, it should produce a voltage of 2.5V ； (2) Check whether the tank pre-processor displays properly; if there is an abnormal display, the circuit board can be replaced ； (3) Check whether the wiring from the junction box to the indoor circuits is normal ； Finally, check whether the MOXA card on the host server is working properly; it usually has a 5V voltage output. During the operation of the 19-system, the replacement of the main controller and cards is carried out as usual. During normal operation, it is necessary to replace the main controller and cards: card replacement is usually required when a channel fails; when replacing a card, it is important to check whether that card is redundant – in the DCS system, the 148R and 152 cards are redundant, while all other cards are not. For cards with redundancy, check whether the other card is functioning; if it is working properly, a green light will be displayed. In such cases, the faulty card can be removed and replaced with a new one directly. For cards without redundancy, check if there are any interconnected points; if there are such points, it is necessary to coordinate with the technical team to remove them before the card can be taken out and replaced. If the main controller fails during operation, it will switch to another one. First, check that the main controller’s dial switch is set to ON; after replacing it, also set it to ON so that the controller can switch automatically in case another one fails. On the 20 operation station, the soft keyboard does not work; on the operator station, the software disk is unusable or some of the buttons do not function properly. In such cases, there is no need to restart the machine, nor is it necessary to remove the software disk from its connection to the main unit. All you need to do is exit the operator station and re-enter it. If the 21-system indicates that the valve or pump is not open or running, try logging in to the main control unit first. If there is a signal output, check whether the fuse of the solenoid valve corresponding to that channel, or the relay associated with it, is sending a signal. If the valve does respond to the signal, then an on-site inspection is necessary; if the electrical components are sending a signal, the problem lies with those components. If the relay does not send any signal, check whether the fuse has been burned out. If the fuse is intact, it’s likely that the relay is damaged. After the pump starts, if no feedback is received, first check the corresponding channel in the cabinet by using a short circuit to see if there is normal feedback. If feedback is present, then the issue lies with the electrical components or there is a fault in the connection from the electrical components to the DCS. 22. How to make changes from the system or cabinet: If, for safety reasons, it is required that the solenoid valve shut off when power is cut off, but you currently cause it to shut off while power is still supplied, then to make the change from the system or cabinet, simply invert the logic at the interlock output DO point in the configuration – this will not affect the operation of the system. When making the change from the cabinet, simply reverse the normally open or normally closed state of the relay. 23 ESD system error: In the ESD system, some actuators (such as quick-opening dampers and flue dampers) may end up in an incorrect state when the interlock conditions are met or removed. This can be caused by the following reasons: (1) At the engineer station ELOPII, that particular point is in a forced state. To resolve this, open the ELOPII software, locate the corresponding program (indicated by the blue small triangle symbol), right-click on that blue triangle, select the ONLINE-TEST option to enter online mode, then find that point (it must be a DO or DI point; it cannot be an intermediate variable point). Hold down the left mouse button to draw a small yellow box with two columns; double-click to move the black square to the upper column, thereby releasing the forced state ； (2) In the cabinet, the fuse at the corresponding point is blown; the solution is to replace the fuse ； (3) In the cabinet, in the case of a fault with the corresponding relay, the solution is to replace it with a relay of the appropriate model ； (4) In the cabinet, the corresponding knife switch on the terminal block is not closed. Furthermore, when dealing with instruments related to the ESD system (such as those associated with the coking instrument panel), special care must be taken. Before addressing any issues, the relevant process personnel should be informed, and the interlocks related to the instrument that needs repair should be disabled. Repair work should only be carried out after confirming that the interlocks have been disabled, in order to avoid unnecessary chain-stop incidents. With the 24SNETB network card issue, when the Macsv system server or workstation is running normally, data exchange takes place over Network A (segments 128 or 130). Over time, the system will automatically disable Network B. At this point, the system status diagram will show a particular machine or all machines in network B in red, but ping requests can still be sent to them. Solution: Desktop – My Computer – right-click – Manage – click on \"Device Manager\" – in the right-hand area, select \"Network adapters\" – Intel Pro100 (or Dlink) – right-click and choose \"Properties\" – Power Management – remove the checkmark from \"Allow the computer to turn off this device to save power\", then restart the computer to restore normal operation. After a PID loop is set to automatic mode, the valve position output becomes inaccurate. When process engineers report that the valve position output for a particular PID loop is incorrect after it is set to automatic mode, it may be due to the reverse action setting in the PID parameters being incorrect. The solution is to log in to the operator station as an engineer and then modify the reverse action setting on the PID panel.