In this article, we are going to see the sequential motor control using PLC. To be exact, we are going to discuss the sequence control of three motors.
In an industry, there are many motors working at a time. For an application, there is a possibility to operate more than one motor. In that case, if all motors are going to start at a time then the power consumption will be more.
If the supply current is low, there is a high chance for the miniature circuit breaker also known as MCB to get tripped. Hence, there is a need to develop a sequential motor control PLC program to avoid this problem.
Take 3 electric motors for their sequential control. At first, start Motor 1, then after some time start Motor 2, and then, in the end, start Motor 3.
Sequentially starting the motors will reduce the sudden use of power during the low current supply. Take a timer of 2 seconds delay for each motor to start. Use the stop push button to stop all the motors at a time.
List of Input and Output tags
In this example, we have used Siemens S7-1200 PLC and Siemens TIA portal for programming a ladder logic diagram. The PLC we selected has a work memory of 100 kb, 24 V DC power supply with 24V DC 14 digital inputs, 10 digital outputs, and 2 analog inputs on board.
|I0.0||Start Push Button||Input|
|I0.1||Stop Push Button||Input|
Sequential Motor Control ladder logic diagram
To draw a ladder logic diagram, we use the Siemens TIA portal. For a better explanation, we have divided the program into 4 networks. The function of each network is discussed below.
It is the cycle Start and Stop network. Push Button (PB) is used for starting and stopping purposes.
A Normally Closed (NC) input is taken for Stopping the cycle. A Normally Open (NO) input is taken to start the cycle. A memory (M0.0) is taken that will be used in further networks. This memory is latched to the Start PB.
The cycle is started by pressing START PB (I0.0) and is stopped by pressing STOP PB(I0.1).
Network 2 shows Motor 1 on.
As soon as the memory M0.0 gets high, Motor 1 will start. As it is the first motor, there is no necessity to give delay for its starting.
Network 3 shows Motor 2 ON. In this diagram, a TON timer is used.
The input from Motor 1 is given to the Timer DB1. This timer counts the time of 2 seconds and then energizes the Motor 2 coil resulting in starting of Motor 2.
Network 4 shows Motor 3 ON. It is similar to network 3.
The input from Motor 2 is given to the Timer DB2. This timer counts the time of 2 seconds and then energizes the Motor 3 coil resulting in starting of Motor 3.
From the above images, we can see that all motors turn ON sequentially according to the time set by the TON timer. When the cycle is turned on using a push-button, memory M0.0 will energize causing Motor1 to start without any delay.
Motor 1 ON signal will activate timer DB1 and Motor 2 will start after the timer’s set value. The timer will not activate until it receives a signal from Motor 1. For Motor 3, the same process occurs.
In this way, all three motors turn ON sequentially within a time span of 4 seconds(as we have set in this example). To stop all motors, just push STOP PB and all the motors will stop.
Networks 2,3, and 4 can be combined to form a single network of sequential motor control. The same is shown in the figure below.
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