plc lab report

8/10/2019 PLC Lab Report

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3.0 Theory

The instructions from a ladder diagram, mnemonic, or SFC are translated to machine

code that can be stored in the PLC memory. The logic in a ladder diagram typically flows

from left to right. The diagram can be divided into sections called rungs, which are

roughly analogous to the rungs on a ladder. Each rung typically consists of a combination

of input instructions. These instructions lead to a single output instruction; however,

rungs containing function block instructions may be more complicated. There are three

basic symbols used in ladder logic.

The first one is NO - NC contacts. NO contact is an instruction that tells the processor to

look at a specific bit in its RAM memory. If the bit is 1, the instruction is true. and if it is

0, the instruction is false.

Normally Open Contact

NC contact plays the same role as the previous one, except that if the bit addressed is 1,

the instruction is false and if it is 0, the instruction is true.

Normally Closed Contact

The second symbol is output. It is use for outputting to output module. If the instructionsto the left on its rung have a true path, then the PLC will set the bit to which it is

referenced via the address to 1. If no complete true path is available, the bit is set to 0.

Device Output

The third symbol is special instruction boxes: Along with the basic logic instructions

addressed in the previous part, PLCs are microprocessor-based and they facilitate a wide

area of useful built in functions like timers, counters, comparators.

Counter

IN TON


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3.1 Procedure

1. Three PLC instructions are given hereunder. Each of them is run using the

available S7-200 CPU and Input Simulator.

2. For Exercise 1a: Controlling lamps by toggle switcher is created using simulation

interface. Figure 3.1 shows the circuit for exercise 1a.3. After the circuit simulation is downloaded and played, switch 1 is activated and

the result is observed and recorded.

4. Switch 1 & switch 2 are both activated and the result is recorded.

5. The difference between rung 1 and rung 2 is discussed and recorded.

6. The input I0.3 is replace by Q0.0, the condition for the second lamp to light up is

observed and the result is recorded.

7.

For Exercise 1b: Controlling an electrical motor by push buttons and overloadrelay is created using simulation interface. Figure 3.2 shows the circuit for

exercise 1b.

8. After the circuit simulation is downloaded and played, Start Pushbutton is

activated and the result is recorded.

9. Stop Pushbutton is activated and the result is discussed and recorded.

10.The input elements I0.0 and I0.1 are interchanged, the result is recorded and

discussed.

11.The effect of having an overload relay is discussed and recorded.


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12.For Exercise 1c:Controlling a pilot light by Timers is created using simulation

interface. Figure 3.3 shows the circuit for exercise 1c.

13.

After the circuit simulation is downloaded and played, Start Pushbutton is

activated and the result is recorded.

14.Stop Pushbutton is activated and the result is discussed and recorded.

15.The input elements I0.0 and I0.1 are inter-changed, the result is recorded and

discussed.

16.For Exercise 2:Traffic Light Simulation is created using simulation interface.

17.The sequence of traffic light is set up as the condition given: Red

5 seconds later

Red and Amber

5 seconds later

Green

5 seconds delay


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18.A ladder diagram is developed based on the conditions given.

19.The results is observed and discussed.

4.0 Observation and Data Collection

Exercise 1(a) Controlling lamp by toggle switches

Element Address Remarks

Toggle switch 1 I0.0 Input of rung 1




Indicator light 1 Q0.0 Output of rung 1

Indicator light 2 Q0.1 Output of rung 2

In rung 1, when the switch 1 is activated, the output lamp has no response. There is no

output when the switch 1 is activated. However when both the switch 1 and switch 2 are

both activated, the lamp (Q0.0) is lighted up.

In rung 2, either the switch 3 (I0.3) or switch 4 (I0.4) is activated, the output lamp Q0.1 is

lighted up. In another word, only one switch is needed to give the output.

After the input I0.3 is replaced by the rung 1 output Q0.0, the output lamp Q0.1 is only

lighted up when both the I0.0 and I0.1 is activated or when I0.4 is activated.


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Exercise 1(b) Controlling an electrical motor by push buttons and overload relay


Start Pushbutton (NO) I0.0 Input

Stop Pushbutton (NC) I0.1 Reverse of input

Overload Relay I0.2 Reverse of input

Motor starter Q0.0 Output

When Start Pushbutton (I0.0) is activated, the lamp (Q0.0) lighted up. The lamp Q0.0

continued to light up although the input I0.0 is deactivated sooner. When either the Stop

Pushbutton (NC) I0.1 or I0.2 is activated, the lamp is turn off.

After the input I0.0 and I0.1 are interchanged, the output results changed. The output

lamp (Q0.0) is lighted up when input I0.0 is activated, however when it is released, the

lamp turn off. It cannot sustain continuous output as before interchange the input I0.0 and

I0.1.


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Exercise 1(c) Controlling a pilot light by Timers


Start Pushbutton (NO) I0.0 Input

Stop Pushbutton (NC) I0.1 Reverse of input

On-Delay Timer (TON) T37 Delay of input

When the Start Pushbutton I0.0 is activated, the pre-set timer 150ms started to run. When

the timer reached 150ms, the on-delay timer (T37) is activated and the lamp lighted up.

When the Stop Pushbutton I0.1 is activated, the timer stop running and the lamp turn off.

When the input elements I0.0 and I0.1 are interchanged, the lamp sustain the continuous

output. The lamp lighted up as long as the input I0.0 is activated and the lamp turn off

when the Stop Pushbutton I0.1 is activated. It can sustain continuous output as beforeinterchange the input I0.0 and I0.1.


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5.0 Discussion

Exercise 1(a) Controlling lamp by toggle switches

The obvious difference between the rung 1 and rung 2 is the connection of the switches.

In rung 1 the toggle switches are connected in series whereas rung 2 toggle switches arearranged in parallel. In the series connection (rung 1), both the two switches I0.0 and I0.1

are needed to activate to give output on the lamp. This is because both the switches are

needed to activate to form a closed connection. However, in the parallel connection (rung

2), only one of the switches, either I0.3 or I0.4 are required to activate to form a closed

connection and give output.

After replacing the input I0.3 with Q0.0, the output lamp (Q0.1) become dependent on

I0.0, I0.1 and I0.4. This is because Q0.0 is depend on both the I0.0 and I0.1. Q0.0 is

activated when both the I0.0 and I0.1 are activated. In order to give output lamp Q0.1,

either the Q0.0 or I0.4 are required to activate.

Exercise 1(b) Controlling an electrical motor by push buttons and overload relay

The output lamp (Q0.0) continued lighting up although the input I0.0 is deactivate

afterward. This is because of the input I0.0 is connected parallel with the energized

output Q0.0. Even if the normally open input I0.0 is released, the energized output Q0.0

will complete the circuit connection, hence the lamp continuing on.

The Stop Pushbutton is a normally closed switch, which mean that no activation is

needed to complete the connection. It gives reverse effect of Start Pushbutton. The

function of the Stop Pushbutton I0.1 and I0.2 in this connection are functioned to cut off

the circuit if necessary.

When the input I0.0 and I0.1 are interchanged, the output lamp (Q0.0) only light up when

the Start Pushbutton I0.0 is activated, but it failed to light up after the I0.0 is released.

This is due to the termination of the circuit at I0.0 when I0.0 is released. The normally

open switch I0.0 is now connected in series manner with the normally closed switch I0.2.

I0.0 must be activated in order to make a closed connection. Without activate I0.0, theconnection is open, the circuit is cut off and hence no output light.

For the overload relay, the application in the real system circuit will be a huge

contribution in order to increase the safety measurement and prolong the component

lifespan. This is because the overload relay acts as a cutter to the circuit whenever there is

excessive current flow maybe in the real world, the current from the lightning during a


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storm or in some cases the overshoot amount of current after recovering from blackouts.

The overload relay will prevent the overflow current and thus, it will prevent a bad

accident and also save the important component from severe damage.

Exercise 1(c) Controlling a pilot light by Timers

When the input I0.0 is activated, the circuit is complete, therefore the timer started

running. The on-delay timer (T37) is activated only when it reached the pre-set time.

Since in this setup, the pre-set time is 150ms, therefore the lamp is lighted up after

150ms.

The Stop Pushbutton is a normally closed switch, which mean that no activation is

needed to complete the connection. The function of the Stop Pushbutton I0.1 in this

circuit used to cut off the circuit if necessary.

There is no significant change when the input elements I0.0 and I0.1 are interchanged, it

function as before. This is due to both the input I0.0 and I0.1 remain connected in series

manner.


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Exercise 2: Traffic Light Simulation

Figure above shows the ladder diagram for traffic light. Initially all the switches

are turned off. All the lights are off. When input I0.4 is activated on the first line, the

circuit is energized and current passes through Q0.2. Q0.2 is in off condition since Q0.2

has no output at that time. Q0.2 acts as a normally closed switch, which mean that no

activation is needed to complete the connection, thus current can pass through Q0.2 and

flow to Q0.0. Output Q0.0 represents Red light and it is on in the simulator. In second

line, Q0.0 then activate timer T37 of 50 ticks. After 5 seconds, output Q0.1 which

represents Amber light is energized and on in the simulator. Both of the Red light and

Amber light are lighted up in this state. In the fourth line, Q0.1 then activate T38 which is

set to 50.


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After 5 seconds, on fifth line, signal passes through T39 which is off at that time.

Since T39 acts as a normally closed switch, signal can flow through T39 at offstate and

flow to output Q0.2. Q0.2 which represent Green light is now energized and light up on

the simulator. Since Q0.2 is also an input which act as reverse switch in the first line of

programme, when Q0.2 is activated, input for reverse switch Q0.2 in the first line is

turned on, resulting the current being cut off at input Q0.2 since the connection is cut off

and signal could not pass through it. This causes output Q0.0 is turned off since current

cannot flow to Q0.0, resulting Red light being turned off on the simulator. Since Amber

light depends on the signal from Red light, when Red light is turned off, Amber light is

also off. Thus, both Red light and Amber light are turned off when Green light is turned

on.

On the fifth line, Q0.2 is added parallel to the circuit as an input. It ensure

continuous flow of current to light up Green light even when T38 is turned off. In the

sixth line, Q0.2 then acts as the input and activates timer T39 which is set to 50. After 5seconds, T39 sends signal to input T39 in fifth line which is then turned on. Since input

T39 acts as normally closed switch, when the input receive signal, it is turned on,

resulting in cut-off of current at input T39. Connection is cut off and current stop flowing

at T39 and cannot flow to Q0.2. Hence, Green light (Q0.2) is turned off. Since Q0.2 is off

now, the normally closed switch Q0.2 at the first line is turned off. Current can flow

through input Q0.2 in the first line, resulting light up of the Red light (Q0.0). The whole

cycle will keep on repeating itself.


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6.0 Conclusion

From this lab session we had learnt the basics of Programmable Logic Controller. Many

different types of simulations can be made using various configurations by PLC

programming. The combination of simple switches of different types can produce various

complex outputs and commands that fulfill the users needs. PLC programming is indeed

a useful invention and it has high potential to be a user-friendly problem solver

application.

In conclusion, PLC is a system designed to multiple inputs and output arrangements. The

combination of some simple switch can produce various complex outputs and commands.

PLCs are used in many industries and machines. No doubt, the PLC system is one of the

greatest inventions in the engineering field.

plc lab report

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