# Motor Starter Control PLC Logic

In most industrial applications we generally find the PLC controlling motor starters. Starters are required for dc motors and induction motors to limit the starting current and protect the armature winging.

A universal motor (ac series motor) is used in this experiment. Although the above motor may be started directly from the rated voltage, it is required to start the motor with a resistor as shown in Figure (b). The starter resistor is to be shorted out after 8 seconds.

## Motor Starter Control

Figure a: Ladder program for the motor starter control

Figure b: Electric circuit for the motor starter control

## PLC Logic Explanation

The ladder program is shown in Figure (a) is designed for the following sequential task:

1. Start pushbutton is pressed. Reference input SP0 (I:1/0) is closed, the output Coil_C0 (O:3/0) is energized. Contactor C0 closed and the motor starts with the resistance in the circuit.

2. Contact (O:3/0) across pushbutton closes sealing in the output Coil C0.

3. Contact (O:3/0) in the second rung closes and the timer is energized.

4. After 8 seconds TMR is enabled closing the timer contact (T4:0.DN) in the third rung. This will energize output Coil_C1 at (O:3/1). The contactor C1 across the resistor is closed, shorting out the resistor.

5. The stop pushbutton SP1 stops the motor releasing the holding contact across the START contact.

Also Read: Star Delta Motor Starter

## Basic PLC Instructions

Symbolic representations of contacts and coils are the basic symbols of any ladder logic instructions set used in the PLC programming.

A complete PLC ladder diagrams program consists of several rungs, each controlling an output interface which is connected to an output field device.

## Warning Signal When Moving Equipment Ladder Logic Program

A ladder logic program, which can be used as a warning signal when moving equipment, such as a conveyor motor, is about to be started.

## Two Floor Elevator PLC Program

PLC program to execute an elevator system in a two-floor apartment using Allen Bradley PLC ladder logic programming.

## Timers and Counters

Timers and counters are PLC internal instructions that provide the same functions as timing relays and counters.