a) A potentiometer circuit as shown in adjacent figure is used to
measure emf of a thermocouple. A fixed voltage of 1.215V is
applicd across points A and B. A current of 3mA flows through
resistors R_(1),R_(2) and R_(G). The range of temperature variation is
from 150deg C to 650deg C. Find values of R_(1),R_(2) and R_(G) for an
ambient temperature of 25deg C. Data given for thermocouple at
14.682mV, C) cmf at 650deg C=53.512mV
b) A thermistor with resistance R_(T) at Tdeg C is connected in a
wheatstone bridge as shown in adjacent figure. Derive the
relation between thermistor resistance at any temperature and
R_(T) for the case where, R_(T)=R_(1)=R_(2)=R_(3).
c) A strain gauage with gauage factor 4 is attached to a metal bar that stretches from
0.25m to 0.255m when strained. What is the pereentage change in resistance? If the
unstrained resistance of gauage is 120Omega , calculate resistance of gauage on strained.
d) A full bridge circuit consisting of 4 identical strain gauages
S_(1),S_(2),S_(3),S_(4) is to be designed. On application of load. S_(1) and S_(3)
[2M-
CO4
are stretched. while S_(2) and S_(4) are compressed. The change in
resistance due to stretching and compression is identical.
Compare following ways of connecting strain gauages in bridge
shown in adjacent figure, in terms of sensitivity. A) S_(1) in arm AD,S_(2) in arm AB,S_(3) in
CD,S_(4) in BC B) S_(3) in arm AD,S_(2) in arm AB,S_(4) in CD.S_(1) in BC C) S_(1) in arm AD,S_(3)
in armAB,S_(2) in CD,S_(4) in BC.
owresistances.
ne bridge to avoid contact re
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Q4) a
[3M- 1650 CO4] MME R2
150
R1
14.682mV C) cmf at 650'C = 53.512mV
Thermocouple
[3M- CO4]
b)
A thermistor with resistance Rt at Tc is connected in a wheatstone bridge as shown in adjacent figurc. Derive thc relation between thermistor resistance at any temperature and R for the case where,R=R=R=R3
[2M- CO4]
c)
[3M- C04]
(p
forfollo
