Deck 17: Developing a Program for a Plc

Question 1

How are the overload contacts connected in the logic circuit described in this chapter?

Answer 1

The normally closed overload contacts for starters 1M and 2M are connected in series with the appropriate starter. It is common practice by many industries to leave the overload contacts hard wired to the starter coil to ensure that the starter will de-energize in the event of an overload. Some manufacturers of motor control equipment provide a second overload contact that is normally open. This contact can be used as an input to the PLC and placed in the logic of the circuit. In this example, however, it is assumed that the overload relay contains a single normally closed contact that will remain hard wired to the coil. The common output terminal is connected to the hot or ungrounded power conductor and the other side of each coil is connected to the neutral or grounded power conductor.

Question 2

How is the operation of motor start coil 1M controlled in the example presented in this chapter?

Answer 2

The first step will be to draw a logic diagram that will control the operation of motor starter coil 1M. Because coil 1M is connected to output 17, coil number 17 will be used for coil 1M. Note that the on-off switch is connected to input 1. Therefore, contact 1 will be controlled by the on-off switch. When the switch is turned on, power will be provided to input terminal 1 and the normally open contact labeled 1 will close. The pressure switch is connected to input 2 and the auto terminal of the selector switch is connected to input 4. Since the control relay is to be assigned coil number 100, the CR1 contact is labeled 100. The normally closed 2M3 contact is labeled 18 because 2M motor starter coil is connected to output terminal 18. The normally closed overload contact (OL1) is not shown in the logic diagram because it is hard wired to the starter coil. The 1M2 contact connected in parallel with the normally closed CR1 contact is labeled 17 because output 17 controls the operation of 1M starter coil.

Question 3

When power is applied to an input, it will cause the contact assigned to that input to ____.

A) activate a push-button
B) close
C) open
D) change state

Answer 3

D

Question 4

A PLC assumes inputs to be ____ when a program is loaded into memory.

A) set
B) high
C) low
D) off

Question 5

The ____ input terminal is connected to the neutral or grounded power conductor.

A) common
B) L1
C) L2
D) tenth

Question 6

Describe the circuit considered in this chapter.

Question 7

In a logic diagram, each line of logic must end with a ____.

A) circuit
B) coil
C) pump
D) switch

Question 8

Given that the internal clock that controls the operation of timers operates in 0.1-second intervals, what value do you have to program in order to get a one-second delay from the timer?

A) 0.1
B) 1.0
C) 10
D) 100

Question 9

A selector switch can be set to any of ____ operating modes.

A) one
B) two
C) three
D) four

Question 10

A(n) ____ occurs when it is possible for one contact to open before another closes or for one contact to close before another opens.

A) bypass
B) contact race
C) off-delay
D) on-delay

Question 11

Referring to the information in Table 17-1 (above), what is the maximum number of internal relays for this particular PLC?

A) 8
B) 16
C) 25
D) 75

Question 12

Control circuits are generally drawn as standard ____.

A) logic diagrams
B) lines of code
C) truth tables
D) schematic or ladder diagrams

Question 13

In a circuit designed to operate two well pumps, what is the protection mechanism?

A) fuse
B) circuit breaker
C) ground-fault protector
D) branch-circuit protector

Question 14

The simplest way to convert a ladder diagram into a ____ is to make the changes in stages.

A) logic circuit
B) terminal diagram
C) schematic
D) coil diagram

Question 15

What rules should be followed when converting a schematic?

Question 16

The water pump circuit will cause the pumps to alternate running each time the ____ switch closes.

A) limit
B) pressure
C) float
D) temperature

Question 17

How are the inputs assigned in the PLC described in this chapter?

Question 18

One advantage of PLCs is that any input can be assigned ____ contact(s).

A) one
B) 10
C) 1000
D) any number of

Question 19

The second step in actualizing a ladder diagram is to add the logic that ____.

A) controls the pump one bypass circuit
B) controls motor starter coil 2M
C) controls motor starter coil 1M
D) controls the pump two bypass circuit

Question 20

Before a program can be developed from a ladder diagram, it is first necessary to determine the number of ____.

A) differential amplifiers
B) protection schemes
C) input and output devices
D) CPUs