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These "holes" in the instrument control system must be known.

Release date:2017-10-11 Author:Henan tranquil auspicious Click:

These "holes" in the instrument control system must be known.

The failure of any measuring instrument in a chemical plant will cause problems for the entire production process, and may even cause the production process to be interrupted or cause safety problems. So how can a large production system be maintained effectively to avoid a malfunction in the instrument control system? Check out these "holes" in the dashboard!

1. Do not mix the signal cable and power cable with a multi-core cable!

2. The oxygen pipeline instrumentation equipment should not be sticky, and the oil pressure transmitter and pressure gauge should not be mixed with ordinary table.

3。 When repairing the meter, make sure to wrap it up and prevent short circuit!

The cable should not have intermediate connections.

5. The shielding grounding of points is generally shielded and grounded on the side of the control room.

6. The protective hose must be lower than the meter inlet to prevent water inlet.

7。 The meter should be added to the meter protection box or wrapped in nylon plastic bag。

8. When the cable is laid in the rack, the cable, power cable and signal cable shall be separated by separator.

9。 In connection with the wiring, the compensation conductor shall not use the connection nose (piece) to avoid contact between two different conductors, causing the measurement error。

10. In production, if the meter is to deal with problems, including indoor and outdoor, it must be handled according to procedures or procedures, especially the operator, and sometimes the book must be signed in person.

11. In case of lightning protection area after surge protector access security gate field instruments and access control system such as DCS, SIS, indirect line to avoid redundant ark, the cabinet interior of surge protector and corresponding circuit safety barrier installed on the same side as far as possible in the cabinet.

12. The control room must be well protected against the small animals, because the rats urinate on the ESD card to cause the whole device to stop, and the loss is great.

13. Must complete the monomer debugging before the instrument installation, and must complete the circuit debugging after installation.

14。 During the operation of the device, the technician must be present for the maintenance of the instrument。 Remember, the problem is no small matter。

15 meter on-site maintenance must contact and technical personnel, inquire craft condition with power meter is disassembled must shut off the power first, then use a multimeter power is shut down, really want to know is your own life.

16. In the design of flow meters, it is necessary to choose the appropriate flowmeter type according to the measurement medium, temperature and pressure, and make the flow compensation. Attention should be paid to the special requirements of flow meter during installation.

17. In order to prevent rainwater from entering the control room when the instrument is designed into the control room, the upper and lower curves must be considered and sealed.

18. When the instrument wind is introduced from the main pipe, the valve must be above the center of the pipeline, preferably 90 degrees above the line, avoiding the booty in the wind line: into the meter valve.

19。 The shielding layer shall not be grounded at both ends; The outdoor cable protection pipe should be protected from rain。 The explosion-proof environment shall pay attention to the sealing of the nozzle。

20。 Alarm equipment, audio equipment must maintain good and normal putting-in-service proactively, otherwise once the process occur accident, instrument professional deathless also have to take off a layer of skin, the reason is because alarm is broken, the operator did not find。

21. In the case of ammonia, copper and copper alloys are prohibited; DCS system power supply, should design dual circuit power to enter!

22。 Thermal resistance temperature measurement, long-distance transmission can not be used two-wire system。

23. The insulation resistance of cables shall be greater than 5 megohm; The turning radius of the cable should be more than 10 times the diameter of the cable, and the cable is 15 times. The instrument cable should be kept at a distance (greater than 0.8 meters) in parallel with the electrical cable, and the spacing between the equipment and the pipe is greater than 150 mm.

24. The instrument pipe hydraulic test, experiment for austenitic stainless steel pipe, content of chloride ion in water shall not exceed 25 PPM (parts per million) instrument working grounding should be less than 1 ohm, other ground less than 4 ohm.

25。 The protection of the instrument should be made of fireproof cloth "asbestos cloth"。 You shouldn't use plastic bags。

26. The instrument used in the hydrogen unit must meet the explosion-proof grade and the protection level requirements. This ampere signal (cable) and the flameproof signal (cable) shall not enter the same live intermediate junction box.

27. The insulation resistance of cables shall be greater than 5 megohm; The turning radius of the cable should be more than 10 times the diameter of the cable, and the cable is 15 times. The instrument cable should be kept at a distance (greater than 0.8 meters) in parallel with the electrical cable, and the spacing between the equipment and the pipe is greater than 150 mm.

28. Instrument pipe hydraulic test, experiment for austenitic stainless steel pipe, content of chloride ion in water shall not exceed 25 PPM (parts per million) instrument working grounding should be less than 1 ohm, other ground less than 4 ohm.

29. The instrument used in the hydrogen unit must meet the explosion-proof grade and the protection level requirements. This ampere signal (cable) and the flameproof signal (cable) shall not enter the same live intermediate junction box.

30. When the FF bus is designed, the terminal of the power regulator and the field bus junction box shall be equipped with a terminal (resistance and capacitance series connection).

31。 The interlocking solenoid valve shall be operated in a fail-safe mode, which shall be charged in normal circumstances and without power during interlocking。

32. When the instrument is designed and installed, if the temperature meter is installed below DN80, use a thermometer expansion tube to expand the line to above 80.

33. The flow measurement element does not participate in the hydraulic test of the power plant.

34。 When measuring the steam flow, the installation height of two condensing tanks should be consistent when using the condenser。

35. The steeling of the field instrument guide tube is cooled and simmered, and the heat of gas welding can not be used.

36. In the process of design and selection of control valves, design pipelines and determination of pressure distribution, flash evaporation should be fully considered. From the control valve, attention should be paid to the following items.

(1) improve the hardness of the material。

(2) reduce fluid flow velocity.

(3) select the appropriate control valve type and flow direction. For example, for a fluid that is easy to vaporize, a ball with high pressure recovery should not be selected.

37. Valves and butterfly valves can be selected with low pressure recovery single seat valves. Measures to eliminate and reduce the actual occurrence:

(1) control pressure drop, and do not occur. For example, the pressure drop of the control valve can be divided into several levels by means of multi-stage step-down.

(2) reduce the influence of cavitation erosion. A similar method is used to prevent flash evaporation. For example, increase the hardness of the material, reduce the flow rate, etc., reduce the influence of the cavitation.

(3) reasonable distribution of pipe pressure and upward pressure.

38。 The problems to be noticed in the control room of cable and wire overhead are:

(1) before entering the control room, a fixed support shall be given to the slot plate to prevent climate change, and the force should be used for indoor equipment;

(2) when the slot plate enters the control room, it shall have a slope of more than 1/100, and the slope shall be outside to prevent the flow of rainwater into the control room;

(3) the wall in and out of the control room shall be sealed to prevent the entry of mice and mosquitoes。

39. The selection of pressure gauges in place must clearly distinguish the nature of the pressure source: whether it is impact load or general pressure, there are not many meters in time, and the replacement can be disastrous. The installation dimension of the local thermometer must be communicated with the process, and the size should be selected when measuring the liquid of the dissatisfied pipe. The material choice of high temperature and high pressure must be different from normal pressure. Can not be charged to dismantle the equipment, carry a test pen, to prevent electric shock hazard.

40. Can not be charged with demolition and construction equipment, with a test pen, to prevent electric shock hazard.

41.DCS must work against static electricity, and do not cause accidents due to static electricity.

42。 The maintenance chain must require DCS to be forced to act。

43. The solenoid coil shall not be unplugged in the case of electricity, otherwise the coil will be burnt.

44. When the rotor and wheel flow meter are installed vertically, be sure to pay attention to the fluid from the bottom up.

45. After the newly installed regulating valve, the gas source line shall be released for a period of time before connecting to the valve locator to prevent the oil entering into the damage locator.

46。 The acetylene gas is also prohibited from copper, so it should be noted that in the case of acetylene gas, in addition to the requirement of explosion protection level, the nameplate of the device should be marked "not suitable for acetylene gas"。

47. Current signals between DCS and electric. For general electric sent is active, after an isolator isolating the best, on the one hand not to put the electric circuits of the instrument I/O card into, on the one hand is if there is no isolator, may the debugging.

48. The steam tracing to the gauge pipe is hot, and the heat pipe is better than 12 O.D., otherwise, once the route is long, it is easy to have the steam not hot and the heat effect is not good.

49。 Correct an error in a design that, regardless of the system, is a security fence。 In fact, the safety grid is used for the security system。 Safety protection system:

(1) the field instrument must be the instrument;

(2) the side of the control room must have a security fence。

(3) the intermediate cable must be an ampere signal cable.

50。 Signal isolation is necessary for the addition of instrumentation and explosive devices if necessary。

51。 The zener security grid must pay attention to the grounding problem。

52. In fact, the instrument and process are inseparable instruments online maintenance must pay attention to minimize the interference to the process process.

53。 Selection of flow meters: when the conductivity of the tested medium is low, the electromagnetic flowmeter cannot be selected; The quality flowmeter should be used when the measurement requirements are high。

54. When measuring media pressure, the temperature of the measured medium is greater than 60 degrees with a condensation pipe or siphon gas.

55. After the installation of the pneumatic regulating valve, it is important to pay attention to the action Settings of the air opening and the gas closed on the DCS.

56。 The indicator value of the temperature instrument system suddenly changes to the maximum or minimum, which is generally the fault of the instrument system。 Because the measurement of temperature meter system is lagging behind, it will not change suddenly。 At this time, the cause of failure is mainly thermocouple, thermal resistance, compensation wire breakage or transmitter amplifier failure。

57。 Make sure that the line number is marked on the instrument wiring! At the beginning of the work made such a low error, the recovery of a good trouble temperature once the parts installed in the bend of the pipe or inclined installation, should reverse the flow。

58. If there is a pressure point or temperature at the same time on the same pipe line, the pressure point should be at the upstream side of the temperature point at a time.

59. The rotor flow meter must be installed vertically on the pipe and the flow direction must be downward.

60。 The straight pipe requires the upstream side 5DN and the downstream 3DN (DN is the diameter of the pipe)。


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