Skip to main content

How to use Master Control Reset (MCR) Instruction in PLC

 A Master Control Reset (MCR) instruction is an output instruction. MCR instructions are always used in pair.

The paired instructions cause the PLC to enable or inhibit a zone of ladder logic program outputs according the application logic. The zone being controlled is known as the MCR zone control. It begins with the rung that has the first MCR instruction. The MCR zone ends with the rung that has the second MCR instruction only.

Using this instruction, we can disable all the outputs at the same when MCR condition goes off.

Two MCR instruction are used to perform the function, One is to start the MCR zone with input condition as must and another one is to end the limit area.

An input condition like Emergency switch is programmed on the rung of the first MCR to control rung logic continuity. When the rung goes “false” all non-retentive outputs within the controlled zone are disabled. When the rung goes “true” all rungs are scanned according to their normal rung conditions.

No need to give any condition for closing MCR zone.

Let’s study the working of MCR using example,

Master Control Reset
Introduce MCR zone in automatic bottle filling system.

Problem Logic
Step Conditions:

Start and Stop PB is used to start and stop the process.
MCR zone need to activated to start the process
Start is pressed Conveyor starts moving until the Proximity Sensor is ON.
Then solenoid valve is open for 5s. After 5s Conveyor should start moving.
The above process should continue unto 3 bottles.
Process should continue still stop push button pressed.
In any emergency case, MCR condition goes off, all output disabled irrespective of its input.
List of Inputs and Outputs



If MCR Goes Off :
see the below same ladder logic when the Master Control Reset (MCR) instructions becomes de-activated.


Program Description
RUNG 0000
Latching rung to operate the system through Master Start and Stop PB.

RUNG 0001
MCR zone is introduced with input condition.

RUNG 0002
To turn ON Conveyor motor, memory bit (B3:0/1 ) is used .

 RUNG 0003
To turn on Conveyor motor using memory bit of start latching PB and B3:0/1, it will automatically turn off when B3:0/2 turns on once Proximity sensor activates. Timer done is connected in parallel to turn conveyor motor ON again.

RUNG 0004
Proximity sensor output saved in memory bit to use in previous rung.

 RUNG 0005 and Rung 0006

To store the status of proximity sensor B3:0/3 is used, Comparator block is used to compare counter accumulator value to stop the process once three bottle process had filled.

Rung 0007
To count the number of bottles, proximity sensor is given to up counter with preset value sets to 3.

RUNG 0008
Stop input is given to reset the counter.

RUNG 0009
MCZ zone is ended here.

Conclusion:
The above example of MCR explanation for simple bottle filling system. It may vary from real time.
Labels:

Comments

Post a Comment

Popular posts from this blog

PLC Program for Mixing Tank

 Create a ladder diagram for controlling a batch mixing process. Implement a PLC program for mixing tank or Mixing Process using PLC Ladder Logic. PLC Program for Mixing Tank Fig : Mixing tank A tank is used to mix two liquids. The required control circuit operates as follows: A. When the START button is pressed, solenoids A and B energize. This permits the two liquids to begin filling the tank. B. When the tank is filled, the float switch trips. This de-energizes solenoids A and B and starts the motor used to mix the liquids together. C. The motor is permitted to run for 1 minute. After 1 minute has elapsed, the motor turns off and solenoid C energizes to drain the tank. D. When the tank is empty, the float switch de- energizes solenoid C. E. A STOP button can be used to stop the process at any point. F. If the motor becomes overloaded, the action of the entire circuit will stop. G. Once the circuit has been energized, it will continue to operate until it is manually stopped. Solution...
2 comments
Read more

Ferrules and Cross Ferruling

 Ferrules are identification labels provided for every wire terminations in an instrument, equipment, or electrical/instrumentation control panels. These tube-shaped sleeves can be inserted easily on each individual wire in a multi-core cable. In earlier days fixed digits/letters are used as ferrules, but now Instrumentation engineers/technicians prints out desired ferrules by using a ferrule printing machine. Typical Ferrule The numbers/ letters on the ferrules will be given as per the approved electrical hook up or loop diagrams. This helps technicians to easily identify a particular loop/wiring from a series of terminal blocks and to troubleshoot the desired terminal connection. Separate numbers on the ferrules distinguish the positive and negative polarities of wires, thus ensure the polarity protection of the instrument. Cross Ferruling  As a wire is connected on its both ends, it is quite useful to use a cross reference method for wire identification. Unlike normal ferru...
1 comment
Read more

What is Relay? How it Works? Types, Applications, Testing

 We use relays for a wide range of applications such as home automation, cars and bikes (automobiles), industrial applications, DIY Projects, test and measurement equipment, and many more. But what is Relay? How a Relay Works? What are the Applications of Relays? Let us explore more about relays in this guide. What is a Relay? A Relay is a simple electromechanical switch. While we use normal switches to close or open a circuit manually, a Relay is also a switch that connects or disconnects two circuits. But instead of a manual operation, a relay uses an electrical signal to control an electromagnet, which in turn connects or disconnects another circuit. Relays can be of different types like electromechanical, solid state. Electromechanical relays are frequently used. Let us see the internal parts of this relay before knowing about it working. Although many different types of relay were present, their working is same. Every electromechanical relay consists of an consists of an Elect...
1 comment
Read more