Sheets
1) Briefly discuss the different physical principles that are used in temperature
measuring instruments and give examples of instruments that use each of these
principles.
2) What is a strain gauge and how does it work? What are the problems in making and
using a traditional metal-wire strain gauge and how have these problems been
overcome in new types of strain gauge?
3) Discuss some applications of strain gauges
4) Discuss the mode of operation and characteristics of a linear motion potentiometer.
5) What is an LVDT? How does it work?
6) What is a coded-disk shaft encoder? How does its output differ from that of an
incremental shaft encoder? Explain the mode of operation of the three main types of
coded-disk shaft encoder?
7) The temperature of a fluid is measured by immersing an iron constantan
thermocouple in it. The reference junction of the thermocouple is maintained at
0 C in an ice bath and an output emf of 5.812 mV is measured. What is the indicated
fluid temperature?
8) The temperature of a fluid is measured by immersing a type K thermocouple in it.
The reference junction of the thermocouple is maintained at 0 C in an ice bath and
an output emf of 6.435 mV is measured. What is the indicated fluid temperature?
9) The output emf from a Chromel-constantan thermocouple whose hot junction is
immersed in a fluid is measured as 18.25 mV. The reference junction of the
thermocouple is maintained at 0 C. What is the temperature of the fluid?
10) A copper-constantan thermocouple is connected to copper-constantan extension
wires and the reference junction exposed to a room temperature of 20 C. If the
output voltage measured is 6.537 mV, what is the indicated temperature at the hot
junction of the thermocouple?
11) If a J-type thermocouple is used in a standard two-junction thermocouple
configuration (see Figure) with a 100 C reference temperature, what measurement
temperature would correspond to a measured voltage of 30 mV?
12) If a J-type thermocouple is used in a standard two-junction thermocouple
configuration (see Figure) with a 0 C reference temperature, what voltage would
result for an input temperature of 200 C?
13) A copper-constantan thermocouple measuring the temperature of a hot fluid is
connected by mistake with iron-constantan extension wires (such that the two
constantan wires are connected together, and the iron extension wire is connected
to the copper thermocouple wire). If the actual fluid temperature was 200 C, the
junction between the thermocouple and extension wires was at 160 C and the
reference junction was at 0 C, calculate the emf measured at the open ends of the
extension wires. What fluid temperature would be deduced from this measured emf
(assuming that the error of using the wrong extension wires was not known about)?
14) An Iron-constantan thermocouple measuring the temperature of a fluid is connected
by mistake with copper-constantan extension leads (such that the two constantan
wires are connected together, and the copper extension wire is connected to the
iron thermocouple wire). If the fluid temperature was actually 200 C, and the
junction between the thermocouple and extension wires was at 50 C, what emf
would be measured at the open ends of the extension wires if the reference junction
is maintained at 0 C? What fluid temperature would be deduced from this (assuming
that the connection mistake was not known about)?
15) If a 120 Ω strain gage with gage factor 2.0 is used to measure a strain of 100μ ε (100
10-6 ),
how much does the resistance of the gage change from the unloaded state to the
loaded state?
16) A new experimental strain gage is mounted on a 0.25 inch diameter steel bar in the
axial direction. The gage has a measured resistance of 120 Ω, and when the bar is
loaded with 500 lb in tension, the gage resistance increases by 0.01 Ω. What is the
gage factor of the gage?
17) A steel bar with modulus of elasticity 200 GPa and diameter 10 mm is loaded in
tension with an axial load of 50 kN. If a strain gage of gage factor 2.115 and
resistance 120 Ω is mounted on the bar in the axial direction, what is the change in
resistance of the gage from the unloaded state to the strained state? If the strain
gage is placed in one branch of a Wheatstone bridge (R1 ) with the other three legs
having the same base resistance (R2=R3=R4= 120 Ω), what is the output voltage of
the bridge (Vout ) in the strained state, as a function of the excitation voltage? What
is the stress in the bar?
18) A bridge circuit is used to measure a strain-gage output. Under zero-strain
conditions the gage resistance is 120 . R2 = R3 = 110 and the galvanometer
resistance is 70 . The gage factor is 1.8. Calculate the galvanometer current when =
350 μm/m for a power supply voltage of 4.0 V. Also, calculate the voltage output for
the bridge when used with a high-impedance detector. If the gage is installed on
steel, what stress does this measurement represent?
19) A 2880 pulse per revolution incremental encoder is connected to a shaft. Its phase A
outputs 934 pulses when the shaft is moved to a new position. What is the change in
angle in degrees?
20) A 1440 pulse per revolution incremental encoder outputs an 1152 Hz square wave
from phase A. How fast is the encoder shaft turning in RPMs?
21) A 12 bit binary absolute encoder is outputting the number 101100010111. a) What
is the resolution of the encoder, and b) what is the range of angles indicated by its
output.