PLCs: For Residential or Commercial Control?

Jan. 1, 2000

Send us your comments, suggestions or solutions to this problem.

We received a question today about programmable logic controllers (PLCs) and their use from one of our LinkedIn group members.

Syed Mustafa Hussain, lighting control engineer for Technolight, asks: Can PLCs be used for residential or commercial control systems? What if the PLC replaces relays or actuators in lighting control systems?

Stephen Luft, technical sales, marketing and consulting for Eternity Sales, responded: The PLC was originally designed to replace relays. Today, it can do so much more than replace relays. We offer a product from Triangle Research.

Syed: You are absolutely right Stephen, but I don't think that a PLC can be a solution for cost-effective home automation. It's better suited for industrial purposes.

Don Fitchett, industrial automation training -  software to maintenance, engineering, manufacturing: Cost is definitely an issue. Where using a PLC will be an exception to the rule, it is a good choice if you want custom and more control than current available inexpensive consumer home automation control devices offer. And there are inexpensive PLCs models with each PLC vendor. Like AB's Micrologix 1000, or PLC direct's low end models. Price would definitely be a barrier with PLC vendor's PAC models (advanced PLCs). But with the basic PLC, you could easily learn and write ladder logic to customize actions to take place based on sensor inputs.

Stephen: Cost effectiveness is entirely dependent upon desired results. Replacing two or three relays with a PLC will likely cost more. However, if there is repeatability and savings in other areas, it could be advantageous. One must take into account all costs associated with the project. Where the PLCs of today shine is being able to process the results from any different device. Adding into the mix the idea of the connected home and the incorporation of Ethernet at the PLC level, and you can now deploy connectivity throughout the home. The same can be done wirelessly as well.

Jibran Mohiuddin, lighting control engineer at TECHNOLIGHT: Definition: A Programmable Logic Controller (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program to control the state of output devices. Take the example of Clipsal system. Input devices are your sensors. These give a signal to the relays. As you program in a class for elevators, the same way you program the entire system and dump the output on the system via a USB port. The program on which you do the programming is basically a refined (user-friendly) version of the 1/0 logic controller you used in a basic course of PLC. So basically it's the same thing as internally the programming you performs just 1/0 logic.

Syed is looking for more answers to his question. So send us your comments, suggestion or solutions to this problem below! You can also follow the thread on our LinkedIn page and submit your answers there.