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EE372 Test 2

EE372 Test 2
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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:

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: