Solutions for PLC Test 1

Solutions for PLC Test 1

N F I I n d u s t r i a l A u t o m a t i o n &

C A D T r a i n i n g A c a d e m y

S C O 2 3 , S e c t o r 1 8 - D ,

C h a n d i g a r h

0 1 7 2 - 5 0 7 8 7 6 7

w w w . n f i a u t o m a t i o n . o r g

w w w . n f i i n n o v a t i o n . o r g

NFI

This document is created for NFIers to review the answers

for PLC Test 1.

Note:

Kindly download the Automation Studio file & Code

(present in the directory) where you can find the Schematic

Diagram & Programming Code of the control circuit made

in this document. You can run & simulate that schematic

diagram in respective software for better understanding.

Copyright@NFI

NFI Industrial Automation & CAD Training Academy | Chandigarh | Panchkula|

| www.nfiautomation.org | www.nfiinnovation.org | Page 1

PLC TEST 1 WITH SOLUTIONS

(Questions 1 ~ 35 2 marks Each)

Theoretical Questions & Answers:

1) What is Industrial Automation??

Using Automation Technology in Industries to make the process flexible, fast & easy to

troubleshoot is Industrial Automation. In other words, its inculcating intelligence in the

machines to make production faster, more accurate & safe.

Equipments such as Industrial Controllers, Sensors, Actuators & network Protocols can be used

to accomplish the task.

2) What are the benefits of Industrial Automation?

Industrial Automation makes the process:

Flexible using controllers & Computer Operator Screen

Good Quality Products

Lesser Cost/Unit by reducing waste & idle time

More Profit By overproduction

Safety in circuits by using safety sensors

Easy to troubleshoot using Flexible Controllers like PLC & PAC

Easy to monitor & control using HMIs

3) Explain the working of NO/NC terminal in Electromagnetic relay with diagram

An electromechanical relay is an electrical switch actuated by an electromagnet coil. As switching

Devices, they exhibit simple on and off behavior with no intermediate states. The electronic schematic symbol for a simple single-pole, single-throw (SPST) relay is shown here:

A coil of wire wrapped around a laminated iron core provides the magnetic field necessary to actuate the switch mechanism. This particular relay is equipped with normally open (NO) switch contacts, which means the switch will be in the open (off) state when the relay coil is de-energized. A relay switch contact will be in its normal status when its coil is not energized. A single-pole, single-throw relay with a normally-closed (NC) switch contact would be represented in an electronic schematic like this:



Relay Symbols:

In the below figures, a relay coil is connected to a Toggle switch with 24 VDC supply & auxiliary terminals are connected to a lamp. In figure 1, when relay is de-energized, its common terminal is connected to the NC terminal. So the 24 VDC is connected to the NC terminal.

Now, when the toggle switch is closed, relay is energized & due to its magnetic force, it attracts common terminal towards NO terminal , & hence 24 VDC travels from common to NO terminal which is connected to the lamp. It causes the lamp to Glow as potential difference across the lamp terminal is maintained.

In this way, we can use relays as a switching devices to isolate the heavy load circuits with controlling

circuits. Thats how relays provide isolation & safety to the circuits



4) Name different types of Sensors & Actuators with applications

5) Draw the symbol for :

a. NO Push Button

b. NC Push Button

c. Toggle Button

d. Indicator light

e. 3 Phase Motor

f. Solenoid

g. Relay



Symbols

a. NO Push Button

b. NC Push Button

c. Toggle Button

d. Indicator light

e. 3 Phase Motor

f. Solenoid

g. Relay



6) What is the difference between PNP & NPN Sensor?

PNP sensors are those which gives HIGH signal (typically 24 VDC, 5 VDC or 12 VDC) from its output terminal on sensing whereas NPN sensors given LOW signal (0 VDC) from its output terminal on sensing.

7) What is Sink/Source in PLC? Explain with the help of diagram.

Sink/Source is very fundamental principle in PLC Wiring. We know that we have two typical kind of sensors NPN & PNP. And our PLC Cards have a Common or Sink/Source terminal in Input Terminals.

Now, If we are using NPN Sensors we must apply 24 VDC to the common terminal of PLC to fetch the state of sensor. This is to maintain the potential difference of 24 VDC across Common & PLC Input terminal where sensor is connected. As show below:

Now, in case If we are using PNP Sensors we must apply 0 VDC to the common terminal of PLC to fetch the state of sensor. This is to maintain the potential difference of 24 VDC across Common & PLC Input terminal where sensor is connected. As shown below:

1-1IC2

IN0

IN1

IN2

IN3

IN4

IN5

IN6

IN7

COM

A

1-1IC1

IN0

IN1

IN2

IN3

IN4

IN5

IN6

IN7

COM

A



So, if we use NPN sensor & apply 0 VDC to common terminal, then PLC cant sense the input from sensor, even if the sensor is working perfectly.

8) How a relay helps in isolation? Explain with diagram

Relay Isolation: Consider the following circuit, in which a controller is used to run a heavy current motor. Now, we know that the controller critical current value is 0.5 amps & the load (Motor) operated at 4 amps. So we cannot directly connect the controller to drive the motor, as it will burn the controller immediately. So we added a relay as an Isolation & switching device between them.

Now, when button is pressed, the controller gives 24 VDC signal to relay & energize it, which will run the motor as shown below:

Now, in case if some short circuit occurs in motor terminals, it will cause heavy current to flow in relay auxiliary contacts, which will burn out the contacts, but controller, will be safe, because the coil is at some distance to the auxiliary contact. In other words, they are not intact; they are having very high resistance between them. So our controller is safe. We just have to troubleshoot the circuit & replace the relay.

A

RELAY

COMMONNC

NO

220_VAC_4_Amp

Controller Circuit

24_VDC_0.5_Amp

LOW CURRENT

HIGH CURRENT



9) Write the codes/syntax/Symbol for the following commands

a. Rising edge

b. Falling edge

c. Set coil

d. Reset coil

e. Timer

f. Counter

g. Compare command in timer

h. Move command

Syntax a. Rising edge LDP X0

b. Falling edge LDF X0

c. Set coil SET Y0

d. Reset coil RST Y0 or RST T0 or RST C0 or RST M0



e. Timer TMR T0 K50

f. Counter CNT C0 k5

g. Compare command in timer LD= T0 k50

LD> T0 K50

LD< T0 K50

LD= T0 K50

LD T0 K50

h. Move command MOV K50 D0



MOV D1 D4

MOV T0 D5

MOV C0 D6

10) What does this model name means DVP 14 SS?

DVP 14 SS DVP is manufacturers (Delta Electronics) standard code for PLC. 14 is its number of terminal. In this PLC we have 8 Inputs & 6 Outputs terminals. SS is the series of Delta PLC which is having only Digital Inputs & outputs

11) Draw the Electrical & Ladder diagram to latch an output using Push Button.

1. Ladder Diagram for Latching:



ELECTRICAL DIAGRAM FOR LATCHING: When Circuit is not energized:

The moment when button is pressed:

The moment when button is released:



12) What is the significance of current rating in any device/instrument?

Significance of Current rating: Every instrument is made up of some electronic component which when operated possess some

resistance & having some current limitations. In other words, they are having some critical value

of current passing through them. If current increases beyond that value, excessive heat will

cause burning of the component. Hence, while making electronic circuit, we should always

check out the current rating of all the components even wires used in making that circuit. And

compare that value with the LOAD current requirement. The ampere or current rating of the

electronics components should always be higher than the load requirement attached to it to

avoid excessive heat & burning of circuit under optimum conditions

13) What is potential difference?

Potential difference is the difference in potential at two points. For example, if a point is at + 24 VDC & another point is at +48 VDC. The potential difference between the two points would be +24 VDC. Similarly potential difference between + 6 VDC & 0 VDC is 6 VDC.

14) Define redundancy in a circuit

In engineering, redundancy is the duplication of critical components or functions of a system

with the intention of increasing reliability of the system, usually in the case of a backup or fail-

safe.

In Controller circuits we usually apply two power sources in parallel to it. So in case, one power

supply got failed, other will provide fail safe or back up without interrupting the system.

Function of Redundancy:

The two functions of redundancy are passive redundancy and active redundancy. Both

functions prevent performance decline from exceeding specification limits without human

intervention using extra capacity.

Passive redundancy uses excess capacity to reduce the impact of component failures. One

common form of passive redundancy is the extra strength of cabling and struts used in bridges.

This extra strength allows some structural components to fail without bridge collapse. The

extra strength used in the design is called the margin of safety.

Eyes and ears provide working examples of passive redundancy. Vision loss in one eye does not

cause blindness but depth perception is impaired. Hearing loss in one ear does not cause



deafness but directionality is impaired. Performance decline is commonly associated with

passive redundancy when a limited number of failures occur.

Active redundancy eliminates performance decline by monitoring performance of individual

device, and this monitoring is used in voting logic. The voting logic is linked to switching that

automatically reconfigures components. Error detection and correction and the Global

Positioning System (GPS) are two examples of active redundancy.

Electrical power distribution provides an example of active redundancy. Several power lines

connect each generation facility with customers. Each power line includes monitors that detect

overload. Each power line also includes circuit breakers. The combination of power lines

provides excess capacity. Circuit breakers disconnect a power line when monitors detect an

overload. Power is redistributed across the remaining lines.

Practical Questions:

15) Practical Experiment

a. Device a circuit to actuate 3 DC motor (12 VDC) timely alternatively after interval of 5 seconds in a

continuous loop.

b. Use PUSH BUTTON ON to start the process & PUSH BUTTON OFF to stop the process

c. Count the number of times each motor turned ON

Note: Make the list of components used with neat circuit diagram before performing

Practical Experiment.

1. Wiring Diagram: 2.



List of Components: 1 Power Supply: 24 VDC 1 PLC Delta DVP 14 SS 1 Push Button (NO) 1 Push Button (NC) 3 DC Motors Wires Ladder Diagram: as per Delta DVP 14 SS

Documents

Solutions for PLC Test 1