control element exam 2007

7/31/2019 Control ELEMENT Exam 2007

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Minia University Faculty of Engineering

Dept. of Computers and Systems Eng. Second Year

Control Elements Final Exam.

Attempt the following questions and assume any missing data

QUESTION (I): Identify the letter of the choice that best completes the

statements or answer the question.

(1)A "single-pole/double throw" toggle switch:(a) Has two sets of contacts that move together, each set has two terminals.

(b) Has one set of contacts, the set has two terminals.

(c) Has two sets of contacts that move together, each set has three terminals.

(d) Has one set of contacts, that set has three terminals.

(2) A general purpose relay has the following specifications: Coil: 6 V at 1000,Contacts: 2 A at 125 Vac or 28 Vdc. What is the current required to energize the

relay?(a) 6 mA (b) 2 A (c) 6000 mA (d) 125 mA

(3) Which of the following characteristics do not belong o an op-amp.(a) Very high open loop gain (b) Very high input resistance

(c) Very high output power (d) Low input resistance

(4)An amplifier has a voltage gain of 40 dbs. The straight line gain is:(a) 4 (b) 10 (c) 100 (d) 400

(5)In general, we say that a "high pass filter" :(a) Will reject frequencies above the cutoff frequency.

(b) Will reject frequencies below the cutoff frequency.

(c) Will reject frequencies above and below the cutoff frequency.

(d) Will reject frequencies in the pass band.

(6)A "current loop" is a system where :(a) The information is converted by current to avoid voltage drop problems.

(b) The wire is wound in a coil to increase the inductance.

(c) The signal is modulated on an AC carrier wave.

(d) A loop type antenna is used to receive the signal.

(7) The term "ground loop" refers to:(a) When grounds are connected from unit to unit in a loop.

(b) When the grounds from all the equipment are connected together.

(c) When a safety ground and a signal ground are connected together.

(d) When equipment is ground at different places

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(8)A "single point ground" means:(a) All the shields and equipments are connected to ground at the same place.

(b) Any time the earth ground is connected to the negative side of the dc power.

(c) Refers to an electrical ground made by driving a metal rod into the earth.

(d) When the same ground is used for magnetic and electrostatic interface.

(9) A 350 Potentiometer is being used as a position sensor. If the potentiometer is

supplied with 10 V and it is currently at 90, what would be the approximate

output voltage ?(a) .9 V (b) 5 V (c) 2.5 V (d) 10 V

(10) An Incremental Optical Shaft Encoder:(a) Reports its position as a binary word.

(b) Reports the rpm of the shaft.

(c) Create a DC differential voltage.(d) Create a variable linear voltage.

QUESTION (II):

(1) Draw block diagrams of an open-loop control system and a closed-loop

control system.

(2) Use these diagrams to describe how each system works.

(3) What are advantages of each system?

QUESTION (III):

(1) Draw block diagrams of a microprocessor-based control system.

(2) Describe the possible data format of this system.

(3) What are differences between a microprocessor and a microcontroller?

(4) An 8-bit DAC has Vref= 15 V. The binary input is 1011 0101. Find the

analog output voltage.

QUESTION (IV):(1) The ground-loop problem can be avoided, in some cases, by using isolation

circuits. Explain the use of this technique in digital signal transmission.

(2) Show how to use shielding to avoid magnetic field noise and electric field

noise.

QUESTION (V):

A lever with pivot at one end is used as a hand lever brake on a machine. To

achieve a brake, 12 N force is required at the free end with a stroke of 11 cm. The

total length of the lever is 1.6 m and the distance from a mid point P to the pivot

is 25 cm.

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(1) Find force and stroke result at P.

(2) Make a simple sketch of the system.

QUESTION (VI):(1) Numerate some types of gears used as control components.

(2) Explain the term "backlash". What is the effect on backlash from long gear

trains?

(3) Derive the mathematical formulate related the following parameters: gear

ratio, number of teeth, gear position, angular velocity, and angular acceleration of

gear mesh.

QUESTION (VII):Draw the symbols of the following switches and explain its use:

(a) SPST (b) SPDT

(c) DPDT (d) DIP

With my best wishes, Prof. M.

Moness

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control element exam 2007

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