Programmable Logic Controller - Program Control Instruction(MCR)

An MCR zone in PLC programming refers to the section of ladder logic that is bracketed by two Master Control Reset (MCR) instructions—one to start the zone and one to end it. This zone allows you to control the execution of all rungs within it as a block, giving you the ability to enable or disable their outputs based on the condition set by the first MCR instruction

Setting up MCR zone

First step is to setup the MC Start zone via MC Control.MC – controls the status of relay coils, timers and counters in the rungs above MCR instruction.

Now to setup the MC end zone for the MC instruction.

So this is what it looks like

Lets solve a problem

A conveyor system receives 50kg and 25 kg cement bags from two delivery gates, which are controlled by a single switch. If the switch is ON, the 50 kg cement bag delivery gate opens and if it is OFF, 25kg delivery gate opens. The conveyor delivers the cement bags to a carrier which can hold a maximum weight of 300kg. Every time a start push button is pressed the conveyor delivers this maximum load according to the mode (50kg / 25 kg) selected.

Input – Output Allocation

<Relay>
<No.> <Label> <Comment1> <Comment2> <Comment3>
0000 :START Start Push Button
0001 :STOP Stop Push Button
0003 :DUMMY1 Dummy for Counter 1
0004 :DUMMY2 Dummy for Counter 2
0005 :SENSOR1 Sensor for 50Kg
0006 :SENSOR2 Sensor for 25Kg
0010 :SWITCH Switch for Weight Determination
0500 :CONVEYOR Conveyor Motor
<Counter>
<No.> <Label> <Comment1> <Comment2> <Comment3>
C200 :COUNTER1 Counter for 50Kg
C201 :COUNTER2 Counter for 25Kg

Ladder Logic