Basic Logic Programming on PLC

By
Muhammad Jafar Shiddiq

Tuesday, August 13, 2019

Basic Logic Programming on PLC – This article will discuss about understanding logic
basic PLC programming using the ladder diagram language. Basically there are 5 types of languages
programming in PLC programming namely:

Ladder diagram
Function Block Diagram
Sequential Function Chart
Structure Text
Instruction List

Before starting, apologize in advance to the article
This is me
will not discuss all the programming languages ​​that are on the PLC. If you
wonder what languages ​​are
most often used for PLC programming, everyone will probably
different, but specifically I can answer ladder diagrams. This language which
most commonly used in PLCs and almost always in all types of PLCs. Need
note that some PLCs can be programmed in more than 1 language
programming. "Then why are ladder diagrams a type of programming language
that
most used? "
Make a program with ladder diagrams no
much different from arranging electrical installations and in my opinion installation lessons
electricity is almost the most basic material
owned by everyone
that
plunge in the field of electricity, there are even some
SMK graduate mechanics can program PLC provided they understand the basic material for electrical installations.

Ladder Diagram or commonly called a ladder diagram
is a special scheme commonly used to document systems
logic of control in an industrial environment. Called the "ladder" because of the ladder itself
resembles a ladder, with two vertical rails right – left (power supply) and
many "steps" (horizontal lines) that represent the control circuit. For more details can be seen in the picture
below this.

See the picture above that displays
how a simple electrical circuit is written using ladder diagrams. In the picture (a) the left shows
the circuit is used to ignite or
turn off an electric motor. You
can redraw the circuit in the left image in a different way,
i.e. uses two vertical lines to represent the rail at the input power and add contacts and
relay between the two. Then in the picture
(b) to the right shows the results of the simple electrical circuit being di
confirm in the form of a Ladder Diagram. Both of these circuits have a series switch with a relay
will turn on the motor when the switch
closed down. If there are dozens of such circuits, it will be clearer
illustrate resembling a ladder like a ladder diagram.

1. In the ladder diagram, the vertical line on the left can be analogous to the positive side of the voltage source, while the vertical line on the right is the negative side of the voltage source. Electric current will flow from left to right through a logic circuit on each line.
2. Then in each line represents a set of process control logic.
3. How to read ladder diagrams by reading from left to right and from top to bottom.
4. When the PLC is activated, the scanning process will work on all program lines until it is finished. Starting from the left to right line, then the top row down to the line below it and then continuing from left to right so on until the right end of the bottom row.
5. Furthermore, in each line basically it must start with an input and end with at least 1 output. Whereas the output will give commands or control devices connected by PLC.
6. Output and Input are identified based on the address, each naming of the address depends on the existing PLC manufacturer. This address will be used as a storage condition in its PLC memory.
7. Some contacts may appear more than once on different lines, the contacts will be active simultaneously if they have the same address. But this is not the case with the output or relay on the left. They are only allowed to write one time only.

For
draw a ladder diagram
there is
some things that become the basic reference in making it, include the following:
Image below
is the PLC program reading flow in the program that has been created.

CONTACT AND RELAY ON LADDER DIAGRAM1. Existing contacts on PLC programming are generally used as
connection or circuit breaker. Like the workings of the switch, Contacts have 2 main conditions, namely NO (Normally Open) and NC (Normally) conditions
Closed). At the time of contact in the NO condition this condition has not been activated in an open state,
whereas in the NC condition
closed. In a PLC program with Ladder diagrams, contacts are connected
or program logic breaker to the right side.

2. Coil
or Relay in the Ladder Diagram programming language is generally the same as a relay when viewed with its physical form. In PLC programming languages, relay in general
symbolized by the shape of a circle. Examples of contacts and relays in Ladder Biagram
as follows:

On picture
above is a contact from Input with the address 0.00 used for
controlling the relay on
1.00 and 1.01. The first line uses NO contacts while the second line uses NC Contacts.
In the Input condition has not been activated, the NC contact is connected so that the relay
1.01 on the on condition.
When Input is activated, what happens is:

At the moment Relay 1.00 is inside
active condition due to Contact
0.00 has been activated.
From the picture above it can be seen if the relay with a certain name is activated, then
all contacts with the same name will be active, therefore all contacts are on
relay 1.00 will be active.
BASIC LOGICS IN PROGRAMMING
PLC
Basically there are many control conditions that require some
the conditions that must be met in PLC programming,
so that certain output conditions can be active accordingly
with the expected in accordance with the program created. for example, on an automatic drilling machine, there may be several conditions that state that
The drill motor is only activated if the limit switch is depressed which indicates it is present
workpiece and drill position as on the surface of the workpiece. Situation of some kind
This will involve the programming logic "AND" as a function of logic, which conditions
A and condition B which are the two conditions
fulfilled. So the output can be activated.
1. Basic Logic NOT
In the picture below. Before contact A is pressed, the output is on. But on the contrary when the contact condition A is pressed, the output will die. This logic is called NOT Logic logic. This logic is often used to cut off the flow of electric current or be used as an OFF instruction.

2. Basic Logic AND In the picture below shows the output can not be activated except the second
that contact
in active condition. This contact combination
called logical AND Logic. Thus, if one of the inputs is A or
B is active, the output will not turn on.

One example
the application of the basic logic of PLC programming is the operation of several machines
industry, for example in the product stamping process. When stamping, the operator must press 2 buttons near the right and left hand,
so that work accidents can be avoided.
3. ORP Basic Logic In the picture
below shows the output can be activated only by activating incorrectly
just one contact, contact A or contact B. This contact combination is called
OR Logic logic.

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