1. Lesson 28 CONTROL SYSTEMS ICONTROL SYSTEMS I

2. Control systems on board ship are either automatic or remote or a combination of these.Control systems on board ship are either automatic or remote or a combination of these.

3. The term ‘automation’, or automatic control, generally is taken to mean the operation of a machine by a self- regulating mechanism thatThe term ‘automation’, or automatic control, generally is taken to mean the operation of a machine by a self- regulating mechanism that

4. that senses the performance of the machine and, using a process called feedback, compares it with the intended performance,that senses the performance of the machine and, using a process called feedback, compares it with the intended performance,

5. and then adjusts the machine to reduce the difference between actual and intended performance.and then adjusts the machine to reduce the difference between actual and intended performance.

6. In a full automatic control system, a computer is used to supervise, analyze, record and display the conditions of the machines,In a full automatic control system, a computer is used to supervise, analyze, record and display the conditions of the machines,

7. and then to make necessary decisions and take necessary actions.and then to make necessary decisions and take necessary actions.

8. Remote control means that the system is being controlled by the operator who is situated remote from the system.Remote control means that the system is being controlled by the operator who is situated remote from the system.

9. Examples are steering gear, watertight door system, tanker cargo control, bridge control of engine, etc.Examples are steering gear, watertight door system, tanker cargo control, bridge control of engine, etc.

10. The combination of automatic control and remote control results in the centralized control( 集中的控制 ) of main and auxiliary machinery.The combination of automatic control and remote control results in the centralized control( 集中的控制 ) of main and auxiliary machinery.

11. Modern engine room has machinery control rooms from where every possible operation will be performed remotely.Modern engine room has machinery control rooms from where every possible operation will be performed remotely.

12. The operation state and parameters of working condition of machines can be recorded, displayed and controlled automatically or manually in the rooms.The operation state and parameters of working condition of machines can be recorded, displayed and controlled automatically or manually in the rooms.

13. An alarm system enables the monitoring of certain measured variables( 变量 ).An alarm system enables the monitoring of certain measured variables( 变量 ).

14. Where a fault condition is located, audible and visual alarms are given and a print-out of the fault and the time of occurrence is produced.Where a fault condition is located, audible and visual alarms are given and a print-out of the fault and the time of occurrence is produced.

15. The modern improvement of control systems and the reliability of the equipment used have resulted in machinery space remaining unattended( 无人看管的 ) for long periods.The modern improvement of control systems and the reliability of the equipment used have resulted in machinery space remaining unattended( 无人看管的 ) for long periods.

16. In order to ensure the safety of the ship and its equipment during UMS (Unattended Machinery Spaces 无人机舱 ) operation, certain essential functions must be provided.In order to ensure the safety of the ship and its equipment during UMS (Unattended Machinery Spaces 无人机舱 ) operation, certain essential functions must be provided.

17. Those are bridge control, machinery control room control, alarm and fire protection, and emergency power.Those are bridge control, machinery control room control, alarm and fire protection, and emergency power.

18. UMS are mainly unattended overnight and during this time the bridge officer on watch should have control of the main engine.UMS are mainly unattended overnight and during this time the bridge officer on watch should have control of the main engine.

19. In the event of minor( 较轻的 ) emergencies when the machinery spaces unattended the engineer on cabin watch will be informed of malfunctions in the machinery by his cabin monitor.In the event of minor( 较轻的 ) emergencies when the machinery spaces unattended the engineer on cabin watch will be informed of malfunctions in the machinery by his cabin monitor.

20. READING MATERIAL A. LUBRICATING OIL SYSTEM CONTROLA. LUBRICATING OIL SYSTEM CONTROL

21. The lubricating oil is pumped from the drain tank, very often with a magnetic filter in the suction line, via main suction filters, fitted with a differential pressure alarm.The lubricating oil is pumped from the drain tank, very often with a magnetic filter in the suction line, via main suction filters, fitted with a differential pressure alarm.

22. These filters may both be automatically cleaned or one hand-cleaned and one automatically.These filters may both be automatically cleaned or one hand-cleaned and one automatically.

23. In some cases, when the differential pressure exceeds a pre-set value, the filter is automatically back flushed with air,In some cases, when the differential pressure exceeds a pre-set value, the filter is automatically back flushed with air,

24. the displaced oil going to an auxiliary drains tank where it is subsequently filtered and pumped back into the system.the displaced oil going to an auxiliary drains tank where it is subsequently filtered and pumped back into the system.

25. Cooling is carried out by a three way by- pass valve in the oil line controlled from a sensor at the inlet to the engine.Cooling is carried out by a three way by- pass valve in the oil line controlled from a sensor at the inlet to the engine.

26. This valve should be fail-safe( 有故障保护 的 ) with all the oil going through the cooler.This valve should be fail-safe( 有故障保护 的 ) with all the oil going through the cooler.

27. In some arrangements the filters are placed after the coolers.In some arrangements the filters are placed after the coolers.

28. Temperature monitoring would be carried out on the common inlet temperature, thrust inlet temperature, and blower outlet temperatures, all having alarms for high temperature.Temperature monitoring would be carried out on the common inlet temperature, thrust inlet temperature, and blower outlet temperatures, all having alarms for high temperature.

29. Low pressure is monitored at the common inlet to the engine with alarm and slowdown or shut down of the main engine.Low pressure is monitored at the common inlet to the engine with alarm and slowdown or shut down of the main engine.

30. In some cases there may be an alarm only for low pressure on all supplies other than to the main bearings, with alarm and shut down only on these.In some cases there may be an alarm only for low pressure on all supplies other than to the main bearings, with alarm and shut down only on these.

31. Low level is monitored on the drain tank and header tank by magnetic switches with a 20 second delay to prevent false alarms due to surging( 起伏、波动 ).Low level is monitored on the drain tank and header tank by magnetic switches with a 20 second delay to prevent false alarms due to surging( 起伏、波动 ).

32. Failure of the circulating pumps is alarmed, as is high differential pressure across the filters.Failure of the circulating pumps is alarmed, as is high differential pressure across the filters.

33. Crankcase oil moist detection( 油雾探测 器 ) alarms on high density with engine shut down.Crankcase oil moist detection( 油雾探测 器 ) alarms on high density with engine shut down.

34. The lubricating oil purifier may take oil from the drain tank and discharge the clean oil into the supply line.The lubricating oil purifier may take oil from the drain tank and discharge the clean oil into the supply line. clarifier

35. The purifier is provided with a level alarm. If the water seal falls below a pre- set level an audible alarm is given and the purifier stopped.The purifier is provided with a level alarm. If the water seal falls below a pre- set level an audible alarm is given and the purifier stopped.

36. In some cases, if the sea water pressure falls, this also operates an alarm.In some cases, if the sea water pressure falls, this also operates an alarm.

37. B. COOLING WATER TEMPERATURE CONTROLB. COOLING WATER TEMPERATURE CONTROL

38. Accurate control of diesel engine cooling water temperature is a requirement for efficient operation.Accurate control of diesel engine cooling water temperature is a requirement for efficient operation.

39. This can be achieved by a single controller under steady load conditions,This can be achieved by a single controller under steady load conditions,

40. but because of the fluctuating( 波动、起 伏、不定 ) situation during manoeuvring a more complex system is required.but because of the fluctuating( 波动、起 伏、不定 ) situation during manoeuvring a more complex system is required.

41. The control system shown in Fig.7 uses a combination of cascade( 级联控制、主从 控制 ) and split( 分区控制 ) range control.The control system shown in Fig.7 uses a combination of cascade( 级联控制、主从 控制 ) and split( 分区控制 ) range control.

42. Main engine cooler Exhaust steam Steam control valve Seawater control valve Seawater inlet Seawater outlet Pump Slave controller Master controller Header tank Desired value Temperature transmitter Fig.7

43. Cascade control is where the output from a master controller is used to automatically adjust the desired value of a slave controller.Cascade control is where the output from a master controller is used to automatically adjust the desired value of a slave controller.

44. The master controller obtains an outlet temperature reading from the engine which is compared with a desired value.The master controller obtains an outlet temperature reading from the engine which is compared with a desired value.

45. Any deviation acts to adjust the desired value of the slave controller.Any deviation acts to adjust the desired value of the slave controller.

46. The slave controller also receives a signal from the water inlet temperature sensor which it compares with its latest desired value.The slave controller also receives a signal from the water inlet temperature sensor which it compares with its latest desired value.

47. Any deviation results in a signal to two control valves arranged for split range control.Any deviation results in a signal to two control valves arranged for split range control.

48. If the cooling water temperature is high, the sea water valve is opened to admit more cooling water to the cooler.If the cooling water temperature is high, the sea water valve is opened to admit more cooling water to the cooler.

49. If the cooling water temperature is low, then the sea water valve will be closed in.If the cooling water temperature is low, then the sea water valve will be closed in.

50. If the sea water valve is fully closed, then the steam inlet valve to heater will be opened to heat the water.If the sea water valve is fully closed, then the steam inlet valve to heater will be opened to heat the water.

51. Both master and slave controllers will be identical instruments and will be two term (P+I) in action.Both master and slave controllers will be identical instruments and will be two term (P+I) in action.

52. Another method of temperature control involves the use of only a single measuring element.Another method of temperature control involves the use of only a single measuring element.

53. A three way valve is provided in the cooling water line to enable bypassing of the cooler.A three way valve is provided in the cooling water line to enable bypassing of the cooler.

54. The cooler is provided with a full flow of sea water which is not controlled by the system.The cooler is provided with a full flow of sea water which is not controlled by the system.

55. A temperature sensing element on the water outlet provides a signal to a two term controller (P+I).A temperature sensing element on the water outlet provides a signal to a two term controller (P+I).

56. The controller is provided with a desired value and any deviation between it and the signal will result in an output to the three way control valve.The controller is provided with a desired value and any deviation between it and the signal will result in an output to the three way control valve.

57. If the measured temperature is low, more water will be bypassed and its temperature will therefore increase.If the measured temperature is low, more water will be bypassed and its temperature will therefore increase.

58. If the measured temperature is high, then less water will be by-passed, more will be cooled and the temperature will fall.If the measured temperature is high, then less water will be by-passed, more will be cooled and the temperature will fall.

59. A simple system such as this can be used only after careful analysis of the plant conditions and the correct sizing of equipment fitted.A simple system such as this can be used only after careful analysis of the plant conditions and the correct sizing of equipment fitted.

60. C. BOILER WATER LEVEL CONTROLC. BOILER WATER LEVEL CONTROL

61. A modern high pressure, high temperature watertube boiler holds a small quantity of water and produces large quantities of steam.A modern high pressure, high temperature watertube boiler holds a small quantity of water and produces large quantities of steam.

62. Very careful control of the drum water level is therefore necessary.Very careful control of the drum water level is therefore necessary.

63. The reactions of steam and water in the drum are complicated and require a control system based on a number of measured elements.The reactions of steam and water in the drum are complicated and require a control system based on a number of measured elements.

64. When a boiler is operating, the water level in the gauge glass reads higher than when the boiler is shut down.When a boiler is operating, the water level in the gauge glass reads higher than when the boiler is shut down.

65. This is because of the presence of steam bubbles in the water, a situation which is accepted in normal practice, 。This is because of the presence of steam bubbles in the water, a situation which is accepted in normal practice, 。

66. If, however, there occurs a sudden increase in steam demand from the boiler, the water in the drum at the higher pressure will now ‘flash off’ and become steam.If, however, there occurs a sudden increase in steam demand from the boiler, the water in the drum at the higher pressure will now ‘flash off’ and become steam.

67. These bubbles of steam will cause the drum level to rise.These bubbles of steam will cause the drum level to rise.

68. The reduced mass of water in the drum will also result in more steam being produced, which will further raise the water level.The reduced mass of water in the drum will also result in more steam being produced, which will further raise the water level.

69. This effect is known as ‘swell 膨胀、隆起 ’.This effect is known as ‘swell 膨胀、隆起 ’.

70. A level control system which used only as a level measuring element would close in the feed control valve when it should be opening it.A level control system which used only as a level measuring element would close in the feed control valve when it should be opening it.

71. When the boiler load returns to normal the drum pressure will rise and steam bubble formation will reduce, causing a fall in water level.When the boiler load returns to normal the drum pressure will rise and steam bubble formation will reduce, causing a fall in water level.

72. Incoming colder feed water will further reduce steam bubble formation and what is known as ‘ shrinkage( 收缩 ) ’ of the drum level will occur.Incoming colder feed water will further reduce steam bubble formation and what is known as ‘ shrinkage( 收缩 ) ’ of the drum level will occur.

73. The problems associated with swell and shrinkage are removed by the use of a second measuring element, ‘steam flow’.The problems associated with swell and shrinkage are removed by the use of a second measuring element, ‘steam flow’.

74. A third element, ‘feed water flow’ is added to avoid problems that would occur if the feed water pressure were to vary.A third element, ‘feed water flow’ is added to avoid problems that would occur if the feed water pressure were to vary.

75. A three element control system is shown in Fig. 8.A three element control system is shown in Fig. 8.

76. P+I controller Water level Feed water control valve Feed water Auto/manual selector Steam flow transmitter Steam from boiler Level transmitter Desire value Differential relay Feed water flow transmitter

77. The measured variables or elements are ‘steam flow’, ‘drum level’ and ‘feed water flow’.The measured variables or elements are ‘steam flow’, ‘drum level’ and ‘feed water flow’.

78. Since in a balanced situation steam flow must equal feed flow, these two signals are compared in a differential relay( 差动 继电器 ).Since in a balanced situation steam flow must equal feed flow, these two signals are compared in a differential relay( 差动 继电器 ).

79. The relay output is fed to a two term controller and comparator into which the measured drum level signal is also fed.The relay output is fed to a two term controller and comparator into which the measured drum level signal is also fed.

80. Any deviation between the desired and actual drum level and any deviation between feed and steam flow will result in controller action to adjust the feed water control valve.Any deviation between the desired and actual drum level and any deviation between feed and steam flow will result in controller action to adjust the feed water control valve.

81. The drum level will then be returned to its correct position.The drum level will then be returned to its correct position.

82. A sudden increase in steam demand would result in a deviation signal from the differential relay and an output signal to open the feed water control valve.A sudden increase in steam demand would result in a deviation signal from the differential relay and an output signal to open the feed water control valve.

83. The swell effect would therefore not influence the correct operation of the control system.The swell effect would therefore not influence the correct operation of the control system.

84. For a reduction in steam demand, an output signal to close the feed water control valve would result, thus avoiding shrinkage effects.For a reduction in steam demand, an output signal to close the feed water control valve would result, thus avoiding shrinkage effects.

85. Any change in feed water pressure would result in feed water control valve movement to correct the change before the drum level was affected.Any change in feed water pressure would result in feed water control valve movement to correct the change before the drum level was affected.