Tutorial_AllSolutions_Nov2005 (1) - McMaster University...

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McMaster University Solutions for Tutorial 1 Feedback Concepts 1.1. Drawing symbols : Determine all letters that would be used to designate each of the following instruments on process and instrumentation (P&I) drawings. For example , for a level controller, the designation would be LC. i) Liquid level alarm high, LAH Set value for the alarm is NOT shown on the drawing ii) Pressure indicator, PI Not used for control iii) Temperature indicator in a packed bed, TI “in a packed bed” is not relevant; the symbol is independent of the process application iv) Volume flow rate of butane in a pipe, FI Flow == F The units of the flow are not indicated in the symbol. v) Mass flow rate of hydrogen, FI vi) Weight of a solid in a vessel, vii) Speed of rotation of a shaft, and SI viii) Mole % of propane in a gas stream AI “Analyzer” is A 08/10/16 1 The approach for assigning symbol letters is explained in Appendix A in Marlin, 2000. Much more detail is provided in ISA 5.1-1984. You might wonder, “Where are the details?” A detailed instrument specification sheet is completed for every sensor. This indicates the stream conditions, physical principle, range of operation and other information. You will be able to purchase the instrument and design installation based on the information in the data sheet. Conclusion: We must use a standard set of symbols so that all engineers and plant operators understand the design.
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McMaster University 1.2. Common examples of automation: Discuss whether each of the common systems below uses automatic feedback to achieve its desired performance. a. Boiling water on a burner in a home stove. b. Maintaining a temperature in an oven in a home stove. c. An alarm clock used to wake you for class. 08/10/16 2 Note: The question asks if automatic feedback is applied. “Automatic” implies the use of a computing device, such as a digital computer. Feedback could be applied by a person, which is generally not as reliable. We’re smart but we get tired. The burner is set to a constant gas flow or electrical power, and no automatic adjustment is applied to achieve a desired rate of boiling. Note that the temperature is constant when the water is boiling, regardless of the heating applied. This is NOT due to control, but is a result of the process principles. The typical home oven has a temperature controller. The automatic approach is not complex; it applies and on/off feedback algorithm. If the temperature is below a set point, the furnace is turned on; if the temperature is above a set point, the furnace is turned off. Usually, a “dead band” is applied to prevent the heater from switching on and off too frequently. No automatic mechanism is applied to the alarm clock. If the power fails, the clock cannot recognize this and correct. Also, if you do not awake, the clock stops sounding the alarm after a specified time.
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