Page 351 - Programmable Logic Controllers, Fifth Edition - Mobile version

40. Explain how redundant media works.
41. Define the term bandwidth as it applies to a 44. What is Fieldbus used for?
45. Summarize the two main functions of a SCADA
network. system.
42. What is Ethernet/IP used for? 46. In what way does distributive control differ from
43. What type of protocol does Modbus use? the supervisory control of a SCADA system?

CHAPTER 14 PROBLEMS

1. Distributive control systems have to be network b. Calculate the upper and lower limits beyond
based. Why? which the controller functions as an on/off
2. Assume an alarm is sounded in a control system unit.
with an electronic HMI interface. How would you 6. Explain the advantage of using a 4 –20 mA current
proceed to identify and solve the problem? loop as an input signal compared to a 0–5 V input
3. How would an on/off controller respond if the dead- signal.
band were too narrow? 7. What does the term deterministic mean, and why is
4. In a home heating system with on/off control, what it important in industrial communications?
will be the effect of widening the deadband? 8. How might a SCADA system be applied to deter-
5. a. Calculate the proportional band of a temperature mine the production rate of a bottled product over
controller with a 5% bandwidth and a set-point a two-week period?
of 500°F.

332 Chapter 14 Process Control, Network Systems, and SCADA

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