Comparing Micro PLCs to Programmable Relays

Hi everyone, welcome to this edition of this newsletter, where we look at Micro PLCs and Programmable Relays.

When we compare the functions of Micro PLCs to those of Programmable Relays, we may say they are almost the same to some extend however they are some subtle application differences that we shall look at herein.

Before we can compare the two, let’s first understand what each system means.

Programmable Relay

A programmable relay is basically a small device that incorporates several inputs and outputs providing relay, timer and counter functions in a single unit. They are typically used as small controllers that can automate operations such as simple sequences based on time or events, time-delays, counters and relay logic.

Micro PLC

This a very compact, inexpensive PLC developed with modern technology to ensure better price/performance ratio. In other words, micro PLCs are compact logic controllers for small-scale to medium scale machine control applications

Micro PLCs vs. Programmable Relays

While both are small controllers that can automate functions such simple sequences based on time or events, time-delays, counters and relay logic or replacement, each system may be an appropriate choice for a particular application depending on the requirements.

Programmable relays work well in simple and fixed applications that require little or no changes and where limited operator interface is needed. In these situations a programmable relay will cost less than a micro PLC and a separate operator interface.

A micro PLC has enhanced features than a programmable relay such as: more communication options, enables easier addition of full-featured operator interface and creation of advanced programs.

A micro PLC is a better solution than a programmable relay for simple to moderate machine control applications. Thus a programmable relay should be selected when the application is very simple and no changes are needed and when the local operators interface display is sufficient and needed.

You may also read:

• Input and Output Modules of a PLC
• Programmable Automation Controllers (PACs)
• Basic Features of Programmable Logic Controllers
• Features of a Programmable Relay