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EE372 Test 2
Solution:
Problem 4.7. The resistance of RTD at 21 degrees is:
1. The voltage measured at 20 degrees is:
The resistance of RTD at 21 degrees is:
The voltage measured at 21 degrees is:
The resolution is the difference of the 2 voltage measurements:
2. The resistance of the RTD at 100 degrees Celsius without considering self-
heating is:
The power dissipation on the RTD is:
Due to self-heating of the RTD, the temperature will increase by:
The actual temperature measured is:
The actual resistance becomes:
3. If we need to keep the self-heating at 0.01 degrees, then we must modify
the power through the thermistor:
The current through the thermistor must be:
The thermistor voltage is equal to:
If we want to keep the voltage output at 5V at 20 degrees Celsius, then we
need to add a series resistor to the output for additional voltage drop. We
have:
The new upper resistance becomes:
The new circuit becomes:
With this circuit, the voltage drop across the thermistor is reduced, thus
reducing its power dissipation and its self-heating. At 20 degrees, we have a
thermistor resistance of 3.5k ohms, and as we computed previously, we will
arrive at 0.1 degrees self-heating. The new thermistor resistance is:

2. The voltage output at 20 degrees is equal to:
At 19 degrees, the resistance is:
The voltage across the thermistor is equal to:
The power dissipation across the thermistor is:
The self-heating temperature of the thermistor is:
The new thermistor resistance is:
The voltage output at 19 degrees is equal to:
At 21 degrees, the resistance is:
The voltage across the thermistor is equal to:
The power dissipation across the thermistor is:
The self-heating temperature of the thermistor is:
The new thermistor resistance is:
The voltage output at 21 degrees is equal to:
4. The voltage of the thermocouple at 500 degrees Celsius using J-Type TC
is:
The voltage of the thermocouple at -10 degrees Celsius using J-Type TC is:
Since we reference the measurement at -10 degrees, there will be a
correction voltage of -0.995V. So the produced voltage will become: