Electronic and Control System of Deck Machinery and Cargo Handling Equipment
1). The Ziegler-Nichols method is used in control engineering when setting up the system. Which of the system components given in the options would this method be applied to during initial set up?
✔️ PID controller for tuning
2). A power card taken from diesel engine cylinder using a mechanical indicator has a flat top. Which of the possible actions given in the options is most likely to correct this irregularity on the power card?
✔️ Change the indicator spring for one with a higher rating
3). A deadweight tester is used to check and calibrate a pressure gauge. The tester consists of a hydraulic pump and a hydraulic chamber and balance weight system. After completing the calibration of the pressure gauge the hydraulic pressure should be relieved before removing the weights. Select from the options given, the main reason for this requirement.
✔️ To protect the piston in the hydraulic system from possible impact damage as it many reach the end of its stroke.
4). During maintenance of a pneumatically operated, diaphragm actuated control valve the diaphragm is found to be split. Select, from the options given, a suitable material to use to make a temporary replacement if there is no spare diaphragm available.
✔️ Natural rubber sheet of approximately the same thickness and elasticity as the original diaphragm material
5). Which of the methods given in the options will give the most accurate test of the accuracy of a bourdon tube type pressure gauge with a range of 0 to 20 bar?
✔️ Check the gauge on a deadweight tester
6). A simple level control for a water tank consists of a horizontal lever with a float at one and a filling valve at the other. The lever is provided with an adjustable pivot positioned between the valve and the float. How will the ‘offset’ in the system be affected under changing demand conditions if the pivot is moved closer to the filling valve?
✔️ It will increase the offset across the demand range
7). With the set point at the actual desired value, a temperature control system is giving an unacceptably large offset (difference between set point and measured value) on high load resulting in a low system temperature. Which of the actions given in the options should be taken to reduce this effect and therefore achieve closer control of the temperature?
✔️ Reduce the width of the proportional band for the controller
8). During maintenance work on a compensated mechanical hydraulic governor air is drawn in to the hydraulic circuit after draining and flushing out the unit. Which of the actions given in the options is most likely to assist in the removal of the air from the system?
✔️ With the governor in operation open the compensation needle valve to introduce instability and disturb the engine load to make the governor hunt.
9). The refrigeration system for the ships provisions consists of a number of cold rooms served by a central refrigeration system. The evaporator coils for the vegetable room are found to be frosting up even though the room is down to temperature and the liquid line valve has closed. Select, from the options given, the automatic control component which is likely to be malfunctioning and so cause this condition.
✔️ Back pressure control valve
10). A pressure gauge of the bourdon tube type is reading incorrectly and shows 2 bar when the pressure in the system is zero. There is no spare available. Which of the options would be the best temporary remedy for this situation?
✔️ Use a deadweight tester to mark a new scale on the gauge throughout the working range.
11). A standard outside micrometer requires regular maintenance, including calibration, in order to ensure accuracy of measurement. How is the accuracy of this type of instrument normally checked? Select the answer from the options given.
✔️ By measuring a standard gauge block or rod at a common temperature.
12). As part of the regular maintenance for a paramagnetic oxygen analyzer used for measuring the oxygen content of exhaust gas it is important to keep the sample line filter as clean as possible. Why is this necessary with this type of instrument?
✔️ Pressure variations in the sample chamber can cause errors so restrictions must be kept to a minimum
13). Compressed air for instrument and control purposes needs to be of high quality in order to condition the air filter modules are usually fitted to remove the contaminants. If there is evidence of oil carry over to the final elements in the instrumentation air system what is the most likely cause?
✔️ The coalescer module is saturated and requires renewal
14). Vibration analysis is often used as a conditioning monitoring tool onboard ship as part of the approved planned maintenance system. Many vibration measuring instruments are fitted with a harmonic filter/analyser. How would these filters normally be used during vibration measurement on a centrifugal pump?
✔️ To isolate a single frequency of vibration associated with one of the pumps components
15). When would gassing-up of cargo tanks on an LNG carrier normally be necessary?
✔️ Pass fresh air through the sample chamber
16). Which of the methods given in the options should be used as part of the check of the accuracy of a liquid filled thermometer used in the cold rooms of the ships provisions stores?
✔️ Immerse the thermometer in a mixture of distilled water and ice made from distilled water to check the zero reading.
17). Following replacement of a diesel alternator governor the machine is test run on load. It is found that as the load is gradually increased the voltage and the frequency gradually fall to an unacceptable level. The governor is a mechanical hydraulic type. Select from the options given the correct adjustment to make to correct the situation.
✔️ The governor droop should be reduced.
18). With reference to the installation of pressure gauges for steam systems. Complete the following statement from the options given. To protect a bourdon tube type pressure gauge which is to be fitted to a steam line it should ….
✔️ ..be fitted with a siphon loop between it and the steam pipe.
19). Which of the methods given in the options should be used to test a remote reading temperature gauge for the auxiliary boiler exhaust gas?
✔️ Check the resistance change in the sensor over a known temperature range against the resistance value in the product sheet
20). What could be the cause of a refrigeration compressor running continuously even though normal temperatures for the cold rooms have been reached?
✔️ Low-pressure cut-out is stuck in closed position.
21). A vapour compression refrigeration system is usually fitted with a number of devices to give protection and control of the system. Which of the methods given in the options should be used to test the high pressure cut out during routine maintenance and checking of the system?
✔️ Gradually shut in the condenser cooling water valve or the condenser refrigerant inlet valve while closely monitoring the compressor discharge pressure.