The unknown resistance Ru of a resistance thermometer is to be measured by a
bridge circuit of the form shown in Fig. 6.5, but where the bridge components and
the excitation voltage are different from the values shown in Fig. 6.5, having instead
the following values:
Nominal thermometer resistance at temperature of 20C ¼ 100 U; Rm ¼ 10K U
(unchanged):
R1 ¼ 100 U; R2 ¼ 1000 U; R3 ¼ 1000 U; Vi ¼ 10V
(a) Using The´venin’s theorem, derive an expression for the sensitivity of the bridge
in terms of the change in output voltage Vm that occurs when there is a small
change in the resistance of the thermometer.
(b) If the resistance thermometer has a sensitivity of 400 mU/
C, calculate the temperature measurement sensitivity in bridge output volts (Vm) per C.