Posted: March 17th, 2017
Consider a 500-gallon tank that needs to be filled when the level goes below 25 gallons and will stop when the level goes above 475 gallons.
Control systems can be either open-loop or closed-loop; each one of them has its own advantages and problems. For the system described above:
Describe how you would implement it using an open-loop system. Describe how you would implement it using a closed-loop system. What are the type(s) of sensors required in each case? Compare and contrast the potential problems that may arise in implementing the control system as an open-loop vs. a closed-loop system. Assume that one of the pumps uses a ¼ hp DC shunt motor with an input voltage of 115 VDC that pulls 1.6 A running at 1,500 rpm. The field resistance for the motor is 600 Ω and the armature resistance is 8.5 Ω. Find the constants Kemf and KT for this motor. The process to be controlled described earlier is a relatively simple process that can be implemented using straightforward methods. However, more complex processes require different types of control approaches.
Describe Ratio Control and give an example of a situation in which you would use it. Describe Adaptive Control and give an example of a situation in which you would use it. Describe the similarities and differences between Cascade Control and Feedforward Control. In most situations it is also desirable to send information from the process to be controlled–in this case the 500-gallon tank–to a central station for processing and storage. This information can be transmitted and processed in different ways.
Fieldbus is one of the methods used to transmit large amounts of process information. Describe the advantages and disadvantages of using Fieldbus. In the case of a problem in the communication process in general (not just using Fieldbus), describe how you would troubleshoot a communications problem at the physical layer. Describe also the tools that you would use to troubleshoot the communications problem at the data link layer.
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