Instrument Trade Theory N3 — Document
August 2018 — N3 — Instrument Trade Theory
N3
2018
Nated Engineering
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Q1— Section header —
1.1Various options are given as possible answers to the following questions. Choose the answer and write only the letter (A D\ next to the question number ( 1.
1.11.
1.5\n the ANSWER BOOK
1.1.1The presen ce of the stuffing box or gland through which the shaft travels may cause a dynamic friction load, particularly if a viscous fluid is present
1.1.2If moving parts are in contact, static friction forces are set up tending to oppose any travel Static f riction
1.1.3nstru ment which measures resistance but is calibrated in temperature units
1.1.4ade from metal oxides and has a negative temperature coefficient Pyrometer
1.1.5Method to compensate for supply voltage variations A regulator called a barretter lamp is used
1.2Indicate whether the following statements are TRUE or FALSE. Choose the nswer and write only 'T rue' or 'F al se' next to the question number (1.2.1
1.2.5the ANSWER BOOK
1.2.1The value of the load resistance does not affect the operation of an electrical telemetering system.
1.2.2The lead wires between the receiver and the tra nsmitter have an effect on the total resistance of the system.
1.2.3A ratiometer instrument can be used to compensate for supply voltage variations.
1.2.4Process lag concerns the capacity (tank of liquid\and the resistance (valves\ of a proces s.
1.2.5Proportional control is used to counteract the deviation or change in a process. (5 1\ (5\ [10] 1104046310
Q2— Section header —
2.10\the ANSWER BOOK COLUMN A COLUMN B
2.10ction of a controller where the magnitude (size\of the output signal is dependent on the rate ( speed\at which the measured deviation changes ction of a controller where the output signal
Q3— Section header —
3.1strain gauge is a device used to measure strain on an object.
3.1.1Explain the principle upon which all strain gauges operate and give a basic formula that illustrate this principle
3.1.2Explain the construction of non bonded and bonded strain gauge (4\
3.1.3Explain the term gauge factor as applicable to strain gauge. (1\
3.2how ith the aid of sketches, how one or more s train gauges can be used to do the following:
3.2.1Measuring low pressures (5\
3.2.2Measur ing small differential pressures (5\ 20
Q4— Section header —
4.1A resistance thermometer is an instrument which measures resistance but is calibrated in t emperature units
4.1.1A platinum coil has a resistance of 38 at 0 = 3, 92 10
4.1.2The resistance of thermo ohm is 150 at 25 = 0, 00392 /
4.2Give a definition for each of the following:
4.2.1Seebeck effect (2\
4.2.2Peltier effect (2\
4.3In a pot entiometer circuit used for temperature measurement, all resistances are manufactured from material of which resistance changes very little with temperatur e change, except for one
4.3.1Name this resistor and explain why its value must change (4\
4.3.2One of the resistors has a variable resistance. Explain what is adjusted with the aid of this resistance (2\ 11040463
4.3.3Another c omponent in the circuit supplies a constant voltage. Explain why this constant voltage is required (3\
4.3.4Another resistance is connected parallel with the slider wire. Explain the reason for this arrangement (2\ 20
Q5— Section header —
5.1neumatic systems are characteris ed by the simplicity of the technology on which they are based and the relative ease with which they can be installed, operated and maintained. They ar e based on the use of a flapper
5.1.1Make a neat label ed sketch of a flapper and
5.1.2Discuss the prin ciple of operation of the system in QUE STION
5.1.1Clearly indicate the function of the feedback bellows and the relay valve (5\
5.1.3Name FOUR disadvantages of a flapper and nozzle system. (4\
5.2State THREE factors which can adversely affect the operation of electrical telemet ering systems, and explain how the effects of these factors can be counteracted (6\
Q6— Section header —
6.1Give the names of the control actions and curves in the diagram below by writing the answer next to the letter (A F\ in t he ANSWER BOOK. (6\
6.2An operator must control the temperature of water which is flowing at a constant rate through a tank as shown below. The water is heated by passing steam through a heating co il at the
6.2.1What is the name of the con trol system he uses ? Justify your answer (2\
6.2.2Suppose the steam flow control valve has two positions only. Position 1 is such that the valve is closed and no steam flows Position 2 s such that the supply of steam is sufficient to maintain the temperature of the outgoing water at 80
6.2.3Define the control action you have named in Q UESTION
6.2.2(2\
6.2.4Make neat label ed sketches showing how the temperature of water varies around the set point and also how the valve positions must be changed by the operator to control th e water temperature
6.3Make a neat label ed diagram for the proportional position balance controller. (4\ [20] TOTAL SECTION B: 8020
Multiple Choice Options
3A)Write only
D)C.
D)C. =
Mark Allocation
Total100 marks
Sections10 + 20 = 30 marks
Paper information
TitleDocument
SubjectInstrument Trade Theory
LevelN3
Document typeQuestion paper
Year2018
MonthAugust
Pages10
Downloads3
Examination context
Decade2010s
Years ago8y
SeasonWinter (SH)
Start dayWednesday
Exam periodAugust 2018
Days since exam2,992
About Instrument Trade Theory examination preparation
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