How to select PLC?

Things to consider while Choosing PLC

Programmable Logic Controller, shortly called PLC, is a general-purpose control system that accepts input from various sources like push buttons, temperature, flow sensors, pressure sensors, limit switches, etc. It can send signals to devices like load relays, motor starters, stepping motors, solenoid valves, and even servo drives.

They are mostly used in industrial plants, factories to control pumps, motors, lights and other machinery.

When operating in harsh conditions, a PLC’s durability, control, and ease of programming make it a feasible solution for numerous applications. However, before you begin to consider the factors for choosing an effective PLC, it is a good idea to have a general understanding of the architecture and basic functionality of a PLC.

System Requirements

The tasks that your system must perform will determine the type of PLC you require. You have to consider the factor whether your machine will be built new or if present products will be used. These considerations are crucial because the functionality of a PLC must be matched to the task at hand as well as any existing products that are installed.

Application requirements

After determining the use of the system, the next step is to determine what input and output device we need to use to meet our requirements.

Electrical Requirements

The electrical requirements for system power, inputs, and outputs; consider these three factors while determining a system’s electrical requirements.

Incoming power (power for the control system);

Input device voltage; and

Output voltage and current.

Speed of Operation

Speed of operation means How fast the control system must operate?.

When determining the speed of operation, study these points:

– How fast does the process occur or system/machine operate?

– Is it necessary to detect “time-critical” operations or events?

– In what time frame must the quickest action take place?

– Is it necessary for the control system to count encoder or flow-meter pulses and respond quickly?


If data sharing is needed outside of the application process, i.e. communication. Communication includes the allocation of application data or status with another electronic device, such as a computer or monitor at a worker station. Communication can take place through twisted-pair wires or remotely via telephone or radio modem.

Operator Interface

Many applications require operator interfaces to convey information about machine or process status, or to allow an operator to input data. Traditional operator interfaces contain pushbuttons, pilot lights and LED numeric display,s etc.

Electronic operator interface tools display machine status messages in descriptive text, display part numbers, and track alarms. It can be used for data input purposes too.

Physical Environment

The physical atmosphere in which the control system is located. Consider the environment in which the control system is located. Place the control system in an IP-rated enclosure in harsh conditions. Keep in mind that accessibility is important for maintenance, troubleshooting, or reprogramming.