Dec 17, 2010

How to Choose your PLC or PLC Choosing Criteria

Choosing a PLC or Controller for your Process is very important as it help in Cost optimization.If you choose a wrong PLC it may happen that you are out of I/O's while programming or may be you have excess of I/O's left which are of no use. So it become very important that you choose a right PLC for your Automation Process.There are several criteria that help in choosing a PLC. Before knowing the Criteria of choosing a PLC you should know basics of PLC. Subscribe to Automation-Talk by Email. Below are some points which will help in choosing a PLC but keep in mind that you should know exactly the need of the Customer,s and should know how many Input,output he wants for present and for future.
PLC are chosen generally on the basis of some requirement of the company or individual person. We should keep in mind the following below point while choosing a PLC.

Some of the PLC choosing criteria are:

1. Number of I/O's :
It is very important that you know the exact number of input and output that are going to be used in the process for best and economical use.

2.Type of I/O's:
The Automation Engineer should also know the type of I/O's whether he needs a digital input like Sensor, Push Buttons etc. or a analog input like RTD, thermocouple etc. The requirement for Output should be also known as what type of Output is required whether you required a digital Output like Relay, Contactor, Lamp etc. or you need a Analog output like Drive and control Valves.

3.Memory size of PLC:
Choosing PLC memory size is also important as you may be out of space in PLC while writing a PLC program if you choose less memory size PLC.

4.Compact or Modular PLC :
Compact Type PLC are those which has Power supply and controller in a same housing while Modular type PLC has Power supply and controller in different housing. So it is good to choose compact or Modular type PLC according to your requirement.

5.AC or DC PLC:
AC PLC are those which are operated on 220 V i.e they require 220 v for running. Whereas DC PLC require only 24V for Running. So you should know which type of PLC will be good for you according to the Power Supply available in your Control Panel.

6.Sinking & Sourcing PLC:
Making a PLC in source at Input or making a PLC sink at input depends upon the requirement of user so PLC should be chosen in that way. Some PLC may support both Sink and Source at Input and Output Both.

7.PLC Scan Time :
PLC scan time is a time needed for PLC to completely Scan one cycle of PLC. It may consist of reading PLC input status , clearing PLC memory, Executing the PLC program and updating the Output. The PLC with less Scan time are found to be more Costly.

8.Number and type of Communication port in PLC:
Number of Communication Port or type of Communication port is also very important in choosing a PLC. Suppose you want to communicate your PLC in MODBUS but you don't have a MODBUS port so your PLC is of no use.Also take a example where you want to communicate a HMI with RS232 port but you don't have one. So communication Port should also be in mind while choosing a PLC.

So these were some of the Criteria of Choosing a PLC which should be kept in mind while you buy a PLC.PLC choosing criteria of Allen Bradley, ABB, Siemens, Omron, Mitsubishi, GE Fanuc, Delta, Fuji, GE or any other PLC are same in all cases.
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