(a) Suppose that the unknown resistance Ru in Fig. 6.2 is a resistance thermometer
whose resistance at 100C is 500 U and whose resistance varies with temperature at
the rate of 0.5 U/
C for small temperature changes around 100C. Calculate the
sensitivity of the total measurement system for small changes in temperature around
100C, given the following resistance and voltage values measured at 15C by instruments calibrated at 15C: R1 ¼ 500 U ; R2 ¼ R3 ¼ 5000 U ; and Vi ¼ 10V.
(b) If the resistance thermometer is measuring a fluid whose true temperature is
104C, calculate the error in the indicated temperature if the ambient temperature around the bridge circuit is 20C instead of the calibration temperature of
15C, given the following additional information:
Voltage-measuring instrument zero drift coefficient ¼ þ1.3 mV/C.
Voltage-measuring instrument sensitivity drift coefficient ¼ 0.
Resistances R1, R2, and R3 have a positive temperature coefficient of þ0.2% of
nominal value/C.
Voltage source Vi is unaffected by temperature changes.