Problem Description

The production line may be powered off accidentally or turned off for noon break. The
program is to control the counter to retain the counted number and resume counting after
the power is turned ON again. When the daily production reaches 500, the target
completed indicator will be ON to remind the operator for keeping a record. Press the
Clear button to clear the history records. The counter will start counting from 0 again.
PLC Ladder Programming Practice Problem 5
 Topics Covered in this example is 
Latched 16 bit UP counter.
Number of PLC Inputs Required
 
 
X0 – Product Detecting Sensor.
X1 – Production Counter RESET/Clear

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Number of PLC Outputs Required
 
Y0 – Production Counter Target Completed.
Number of PLC Counter Required
C120 – 16 Bit Latched Counter. (Max Count =32,768)
PLC Ladder Programming:
 
PLC Ladder Programming Practice Problem 5
PLC Ladder Programming Description:
·
The latching counter is demanded for the situation of retaining data when power-off. 
·
When a product is completed, C120 will count for one time. When the number reaches 500, target
completed indicator Y0 will be ON. 
·
For different series of PLC, the setup range of 16-bit latching counter is different.
BASIC PLC LADDER PROGRAMMING
Description of language ladder
There are different types of programming languages for PLCs. Perhaps the most common is the ladder programming. The ladder 
diagrams are commonly used schemes to represent the control logic of industrial systems. Is called "ladder" diagram because they 
resemble a ladder, with two vertical rails (supply) and "rungs" (horizontal lines), in which there are control circuits that define the logic 
through functions. In this way the main ladder language features are:

Input instructions are entered on the left.

Output Instructions are located on the right.

Power rails are the power supply lines L1 and L2 for alternating current circuits, and 24 V - earth for DC circuits.

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
Most PLC allow more than one output for each row (Rung).

The Processor (or "Controller") explores rungs of the ladder from top to bottom and from left to right.
The input instructions are the conditions that the circuit has to let or not let to pass current from one line to another. These conditions 
are commonly handled with normally-open or normall-closed contacts which interpret the high and low signals of sensors or switches. If
conditions are true the current reaches the output instructions, which generate actions such as energizing a motor coil or power on a 
lamp. In this way the flow of current to the output coils is conditioned by the logic managed by the input instructions.
A PLC has many input and output terminals, through which "high" or "low signals are produced " to be transmitted to power lights, 
solenoids, contactors, small motors and other devices provided to on / off control. In an effort to make PLCs easy to program, ladder 
programming language was designed to resemble ladder logic diagrams. Therefore, an industrial electrician or electrical engineer 
accustomed to read ladder logic diagrams will be more comfortable programming a PLC if the ladder language is handled.