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Thermal Sensors Lab
1. In a processing plant, a chemical tower has a liquid which is vaporized.
However, if the vapor in the tower reaches 150°C, an alarm needs to be
generated so that safe shutdown of that system of the plant may be
initiated. An RTD will be used to measure the temperature of the vapor.
The RTD will generally operate between 80° to 175°C and has a resistance
of 220Ω at 20°C. The fractional change in resistance per 1°C is 0.0040.
The dissipation constant is 25mW/°C. Design a circuit to activate an LED
alarm when the temperature reaches 150 °C. The error should not exceed
+/-1°C. Use a single supply voltage.
a. Draw a block diagram for your design. Explain the function of each
block and why it is needed.
b. Design the circuit showing all calculations. Choose standard resistor
values, and specify the tolerances. Provide a drawing of your circuit
with all resistor values and tolerances and parts. You may do this by
creating it in Multisim and then drawing the values on as
appropriate.
c. Construct the circuit in Multisim using the resistor values you chose
and tolerances. Do a screenshot showing how you have set up the
tolerances for the resistors. For the RTD, you may use a
potentiometer or variable resistor for which you can change the
resistance for different temperatures. If you have a bridge circuit
with a potentiometer for nulling, explain how you decide what
resistance to use for the null.
d. Create a table of temperature, RTD resistance, RTD resistance
adjusted for self-heating, LED Status. Test your circuit, and use the
table to display your results. Find the precise resistance and
temperature at which the LED turns on. Provide several screenshots
showing the resistance which reflects the RTD resistance value
used in the circuit and the LED alarm. Which RTD resistance do you
use in the circuit for testing?
e. Put together all of the above in a well-written report including
introduction, requirements, block diagram, design calculations, final
design (including any potentiometer settings), testing (including
which RTD resistance is used in the circuit for testing), and analysis of results. Be sure to provide a summary at the end, noting at which
temperature the alarm was activated, if this was as designed, and
what accounts for differences. Please note any problems you
encountered. “Week 4 Assignment”
1. A temperature sensor is exposed to a sudden change of 20oC to 80oC. The
sensor outputs 0.02 volts for every oC of temperature and has a 2.3 second
time constant. a. What is the sensor output voltage at 1.5 seconds?
b. At what time, t, does the sensor output become 1.0 volt? 2. A sensor, R, that changes resistance is used in a bridge circuit as shown
below.
a. What sensor resistance, R, will null the bridge?
b. What is the off-null voltage if R changes by 0.5 Ω? 3. A measurement system has noise above 20 kHz and the data signal
frequency is between 100 and 500 Hz. Design an RC filter that reduces the
noise by 95%, i.e., only 5% is left. Show the schematic and the component
values.
4. Given a Type J TC with a 25oC reference.
a. What is the temperature if the TC voltage is 22.87 mV?
b. What voltage would result from a temperature of 225oC?
5. A 10-bit ADC has a 5.00-volt reference.
a. What binary output is produced by an input of 3.04 volts?
b. Suppose the output is found to be 1F4h. What is the possible input
voltage?
6. A 12 bit bipolar DAC has a 10-volt reference.
a. If the hex input is 5D7h what is the DAC output voltage?
b. What input is required to get a zero volt output? Mechanical Sensors Lab
1. A capacitive displacement sensor is used to measure rotating shaft wobble
shown in the figure below. The capacity is 520 pF with no wobble. Find the
change in capacity for a +0.035 to -0.035 mm shaft wobble. Show your
calculations. 2. To measure the displacement, assume that the capacitive pickoff in problem 1 is
used in an AC bridge constructed of only capacitors. Using 520pF for the bridge
capacitors, find the offset bridge voltage for the two extremes of shaft wobble.
Assume a sine wave voltage input having an amplitude of 5 V rms and a frequency
of 5 kHz. Rather than using an equation from the book, you are required to
derive the offset bridge voltage using circuit analysis principles. Show all your
calculations.
3. Using Multisim, construct and simulate the AC bridge of problem 2 for the two
extreme conditions. Be sure to provide screenshots. Also, write a brief
summary, noting if the results matched expected results.
Thermal Sensors Lab
1. In a processing plant, a chemical tower has a liquid which is vaporized.
However, if the vapor in the tower reaches 150°C, an alarm needs to be
generated so that safe shutdown of that system of the plant may be
initiated. An RTD will be used to measure the temperature of the vapor.
The RTD will generally operate between 80° to 175°C and has a resistance
of 220Ω at 20°C. The fractional change in resistance per 1°C is 0.0040.
The dissipation constant is 25mW/°C. Design a circuit to activate an LED
alarm when the temperature reaches 150 °C. The error should not exceed
+/-1°C. Use a single supply voltage.
a. Draw a block diagram for your design. Explain the function of each
block and why it is needed.
b. Design the circuit showing all calculations. Choose standard resistor
values, and specify the tolerances. Provide a drawing of your circuit
with all resistor values and tolerances and parts. You may do this by
creating it in Multisim and then drawing the values on as
appropriate.
c. Construct the circuit in Multisim using the resistor values you chose
and tolerances. Do a screenshot showing how you have set up the
tolerances for the resistors. For the RTD, you may use a
potentiometer or variable resistor for which you can change the
resistance for different temperatures. If you have a bridge circuit
with a potentiometer for nulling, explain how you decide what
resistance to use for the null.
d. Create a table of temperature, RTD resistance, RTD resistance
adjusted for self-heating, LED Status. Test your circuit, and use the
table to display your results. Find the precise resistance and
temperature at which the LED turns on. Provide several screenshots
showing the resistance which reflects the RTD resistance value
used in the circuit and the LED alarm. Which RTD resistance do you
use in the circuit for testing?
e. Put together all of the above in a well-written report including
introduction, requirements, block diagram, design calculations, final
design (including any potentiometer settings), testing (including
which RTD resistance is used in the circuit for testing), and analysis of results. Be sure to provide a summary at the end, noting at which
temperature the alarm was activated, if this was as designed, and
what accounts for differences. Please note any problems you
encountered. “Week 4 Assignment”
1. A temperature sensor is exposed to a sudden change of 20oC to 80oC. The
sensor outputs 0.02 volts for every oC of temperature and has a 2.3 second
time constant. a. What is the sensor output voltage at 1.5 seconds?
b. At what time, t, does the sensor output become 1.0 volt? 2. A sensor, R, that changes resistance is used in a bridge circuit as shown
below.
a. What sensor resistance, R, will null the bridge?
b. What is the off-null voltage if R changes by 0.5 Ω? 3. A measurement system has noise above 20 kHz and the data signal
frequency is between 100 and 500 Hz. Design an RC filter that reduces the
noise by 95%, i.e., only 5% is left. Show the schematic and the component
values.
4. Given a Type J TC with a 25oC reference.
a. What is the temperature if the TC voltage is 22.87 mV?
b. What voltage would result from a temperature of 225oC?
5. A 10-bit ADC has a 5.00-volt reference.
a. What binary output is produced by an input of 3.04 volts?
b. Suppose the output is found to be 1F4h. What is the possible input
voltage?
6. A 12 bit bipolar DAC has a 10-volt reference.
a. If the hex input is 5D7h what is the DAC output voltage?
b. What input is required to get a zero volt output? Mechanical Sensors Lab
1. A capacitive displacement sensor is used to measure rotating shaft wobble
shown in the figure below. The capacity is 520 pF with no wobble. Find the
change in capacity for a +0.035 to -0.035 mm shaft wobble. Show your
calculations. 2. To measure the displacement, assume that the capacitive pickoff in problem 1 is
used in an AC bridge constructed of only capacitors. Using 520pF for the bridge
capacitors, find the offset bridge voltage for the two extremes of shaft wobble.
Assume a sine wave voltage input having an amplitude of 5 V rms and a frequency
of 5 kHz. Rather than using an equation from the book, you are required to
derive the offset bridge voltage using circuit analysis principles. Show all your
calculations.
3. Using Multisim, construct and simulate the AC bridge of problem 2 for the two
extreme conditions. Be sure to provide screenshots. Also, write a brief
summary, noting if the results matched expected results.
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