·.•.
AI-Mansoura University
Time! 3 Hours.
Faculty of Engineering
First Year Students.
Comm. & Electronics Dept.
June 2013
Electronic MeasurementsfI)
COM 9123
. Attempt in all questions and .assume any-missing data.
Ql: (a)-Define the measuring instruments, and list the advantages of an
electronic measurement.
'100 x n
(b)- For the network shown in Figure
(1),. find the voltage reading·' on
voltmeter, if voltmeter sensitivity is 1
so s o
k Q/volt. If the voltmeter is 'replaced
by
another
voltmeter
having
sensitivity 25 k a/volt, find the new
B
reading. Comment on the answer.
Figure (1)
(10 Marks)
Q2:(a)-Define and explain the following static characteristics: 1- Accuracy, 2Precision, 3- Static error, 4- Resolution 5- Sensitivity, .and 6- Threshold.
(b)- It is desired. to measure the
1000'0.·"
Soon-'
value ..of current in the 500 a
.
resistor shown in the Figure (2), ) -;'
by connecting 100 a Ammeter. 10 V +
.
10000
Find the following: 1- Actual
.
value of curjent. 2- Measured
value of current, and ,3- % Error
Figure (2)
and accuracy.
(10 Marks)
r".....
Q3: (a)-Define the following terms: 1- Speed ofresponse, 2- Lag, 3- Fidelity, 4Dynamic error.
.'
...,
(b)-What are the different standard inputs for studying the dynamic response
of a system? Defineandsketch them.
(c)-A voltmeter reads 40 V on its 50 V range while an ammeter reads 50 mA
on its 125 mA range, while used in a circuit. Both the instruments are
guaranteed to be accurate within ± 2 % at full scale deflection. Determine the
limiting error of the power calculated.
(15 Marks)
Q4:(a)- List the precautions to be taken while using an ammeter.
(b)-Design a multirange DC milliammeter with ~ basic meter having a
resistance 75 a and full scale deflection for the current" of 2 mA. The required
ranges are 0-10 mA, 0-50 mA and 0-100 mA.
(c)- Design an Aryton shunt to provide an ammeter with the current ranges
lA, 5A and 10 A. A basic meter resistance is 50 Q and full scale deflection
current is 1 mA.
.'
(15 Marks)
'r.'_._.
Q5: (aj-Explain with drawing both the true current and true voltage circuits.
Derive an expression for the unknown resistance for each one.
(b)-A basic D'Arsonoval movement with an internal resistance of 50 Q and a
full scale deflection current of 2 mA is to be used as a multirange voltmeter.
Design the series string of multipliers to obtain the voltage ranges of 0..10 V, 050V, 0-100 V, 0-500 V.
(c)-A 50 n basic movement requiring a full scale current of ImA is to be used
as an ohmmeter. The internal battery voltage is 3V. A half scale deflection
marking desired is 1000 Q. Calculate: 1- Values of RI and R2 2- Maximum
value of R2 to compensate for a 5 % drop in battery voltage.
(15 Marks)
Q6-(a)-List the advantages of the Wheatstone bridge.
(b)- The
four
arms
of
the
Wheatstone
bridge,
shown in
Figure (3). The galvanometer has
sensitivity
of 1 mm/J.1A with
internal
resistance
of 200 n.
Determine the deflection of the
galvanometer if arm DA increases
~.~;;..'
. .;;;.'. ~~--"~-to 121 Q and arm CD decrease to;~~
_,
.
119 n
Figure (3)
(c)- The temperature dependent resistor is used in one arm of a Wheatstone
bridge. The other resistances are: RI = 10M2, R2 = 10M2, R3 = 10M2 and
V = 10V. The variation of resistance in k.Q against temperature is given by:
R = 6 + t! 20 kn .. Calculate the temperature at which the bridge is balanced.
Also calculate the error voltage at 60° C and 90° C.
(18 Marks)
Q7: (a)-Define the following: R.M.S value, Average value, Peak value, Form
factor, and Peak-factor,
(b)-The Schering bridge shown in Figure
(4),
has
the
following
constants:
RI = 1.2M2, Cl = Ij.lF,. R2 = 4.7M2,
andC3 = Ij.lF. The frequency of supply
is 0.5 kHz. Calculate the unknown
impedance Zx.
A.C.
supply "V
f H%
Figure (4)
(c)-An AC Voltmeter uses a full wave bridge rectifier and the basic meter with
full scale deflection current of 2 mA and the meter resistance of 500 Q.
Calculate the multiplier resistance for a 10 V r.m.s. range on the voltmeter.
(18 Marks)