- 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.
- Draw a block diagram for your design. Explain the function of each block and why it is needed.
- 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.
- 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.
- 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?
- 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.
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