PLC's

Question 1

Three applications for PLC’s?

Answer 1

Chemical and petrochemical
Auto manufacturing
Metal smelting and mining 
Lumber, Pulp and Paper 
Food and beverage production

Question 2

The three basic components of a control system are:

Answer 2

• input
• output
• controller

Question 3

PLC’s are selected based on?

Answer 3

Number of I/O points

Question 4

Smart relays are considered to be

Answer 4

Smaller PLC’s and may have fewer than 10 I/O points

Question 5

List (4) advantages of a PLC over relay control

Answer 5

• lower cost
• programmability
• reliability
• expandability

Question 6

PLC programs can be changed while running.

True or False?

Answer 6

True

Question 7

List the major hardware components of a modular PLC system?

Answer 7

• power supply / clean power
• backplane / provides communication
• processor; CPU
• input/output (I/O) modules

Question 8

Does the power supply for a PLC supply the field devices?

Answer 8

No; only the processor and I/O modules

Question 9

What part of the PLC does the CPU form part of?

Answer 9

The brain

Question 10

What is the purpose of the backplane?

Answer 10

Power and communication bus for the PLC components

Question 11

Name three (3) types of memory used by a PLC

Answer 11

• RAM; random access memory
• ROM; read only memory
• EEPROM; electrically erasable programable memory

Question 12

An input module _________ signals from _________ devices.

Answer 12

Receives signals from sensing devices

Question 13

The processor is also called the ________ and is the _________.

Answer 13

CPU; Brains

Question 14

A data highway is a type of:

Answer 14

LAN

Question 15

A remote I/O is used to:

Answer 15

Reduce the amount of cabling between the PLC and I/O devices

Question 16

The three (3) primary functions of a PLC processor are to:

Answer 16

• read and store status of all input devices
• execute user program by solving the program logic
• update the status of all the outputs

Question 17

The processor carries out its functions in a sequence called a ____________ ________.

Answer 17

Processor scan

Question 18

Is the signal voltage to an input module from a field device the same as the processor power supply?

Answer 18

No, field I/O devices require their own supply.

Question 19

How is the processor input isolated from the field input signal?

Answer 19

By optoisolators or small relays and filter circuitry

Question 20

What other problems are the processor isolated from?

Answer 20

• Voltage transients

- Magnetic interference that may develop in the signal circuits

Question 21

What are some functions that require special I/O modules?

Answer 21

• position control
• high speed counters
• temp controls
• PID controls
• fuzzy logic
• ID sensors
• cam positioners
• analog I/O

Question 22

Sensing devices are designed to sense what two kinds of signals?

Answer 22

Analog (levels of voltage or current)

Discreet (simple switches; ON or OFF)

Question 23

What kind of devices can be used to program a PLC?

Answer 23

• small keypad
• hand held plug in keypad
• personal computer

Question 24

PID

Answer 24

Personal Integral Derivative