63868-Ch09 - PLCs-3e-S 11-28/06, 06/04/07 Chapter 9...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
PLCs-3e-S 11-28/06, 06/04/07 Chapter 9 DISCRETE CONTROL USING PROGRAMMABLE LOGIC CONTROLLERS AND PERSONAL COMPUTERS REVIEW QUESTIONS 9.1 Briefly define the two categories of discrete process control? Answer : Discrete process control can be divided into two categories: (1) logic control, which is concerned with event-driven changes in the system; and (2) sequencing, which is concerned with time-driven changes in the system. 9.2 What is an AND gate? How does it operate on two binary inputs? Answer : An AND gate outputs a value of 1 if all of the inputs are 1, and 0 otherwise. 9.3 What is an OR gate? How does it operate on two binary inputs? Answer : An OR gate outputs a value of 1 if either of the inputs has a value of 1, and 0 otherwise. 9.4 What is Boolean algebra? What was its original purpose? Answer : Boolean algebra is a special form of algebra based on the logic elements (AND, OR, and NOT) that was developed around 1847 by George Boole. Its original purpose was to provide a symbolic means of testing whether complex statements of logic were TRUE or FALSE. 9.5 What is the difference between a delay-off timer and a delay-on timer? Answer : A delay-off timer switches power on immediately in response to a start signal, and then switches power off after a specified time delay, whereas a delay-on timer waits a specified length of time before switching power on when it receives a start signal. 9.6 What is the difference between an up counter and a down counter? Answer : An up counter starts at zero and increments its contents (the count total) by one in response to each pulse. When a preset value has been reached, the up counter can be reset to zero. A down counter starts with a preset value and decrements the total by one for each pulse received. 9.7 What is a ladder logic diagram? Answer : A ladder logic diagram shows the various logic elements and other components along horizontal lines or rungs connected on either end to two vertical rails. The diagram has the general configuration of a ladder, hence its name. The elements and components are contacts (representing logical inputs) and loads, also known as coils (representing outputs). 9.8 The two types of components in a ladder logic diagram are contacts and coils. Give two examples of each type. Answer : Contacts include switches and relay contacts, and coils include motors, lamps, and alarms. 9.9 What is a programmable logic controller? Answer : A programmable logic controller is a microcomputer-based controller that uses stored instructions in programmable memory to implement logic, sequencing, timing, counting, and arithmetic functions through digital or analog input/output (I/O) modules, for controlling machines and processes. 9.10
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 10

63868-Ch09 - PLCs-3e-S 11-28/06, 06/04/07 Chapter 9...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online