Down counter instruction using example.

Application:-Understand the concept of down counter instruction in the PLC. Explain down counter concept using PLC program.

Components:-Programmable logic controller.

Explanation:-

Generally counter is used to count events in the application. Generally down counter is used to count down sequence (for example it will count from 5 to 1 like 5 4 3 2 1).Down counter will generate output when current count value is equal to 0 or less than 0. And if load input is changed from 0 to 1, it will load PV value.

 

PLC program:-

Write the ladder program for above application using ladder diagram language. Here for ladder logic we can use any supported PLC system like S7-1200, S7-300, S7-1500 or any other PLC which can support this instruction. For PLC logic we need digital inputs and outputs.

For our application on/off button is digital input and lamp is the digital output. So define digital input address and output address as per below explanation,

Digital inputs:-

ON/OFF button=I0.0

Load=I0.1

Digital Output:-

Lamp=Q0.0

PLC program Explanation:-

In above network 1, we have used down counter (CTD). So lamp will be on immediately when 5 in PV. When ON/OFF button is pressed 5 times then counter will become zero.

Press load button to load value into PV.