PLC Alternative for Dry Contact

[poplar598]

Hi,

I'm wondering if a Rasberry Pi could replace a PLC (Programmable Logic Controller) for machine control. I need three inputs, each sensing 14v AC. If either of the inputs sees 14 v, I need an output of dry contact pulses (like you would get from a water meter). Further, I need to be able to vary the frequency of the dry contact pulses (number of pulses per minute) because the pulses are going to a chemical pump and I want to be able to vary the output of the pump. From what I have read, I may need a GERT board and maybe Arduino? The alternative is to get an inexpensive PLC and use ladder logic.

[boyoh]

Hi,

I'm wondering if a Rasberry Pi could replace a PLC (Programmable Logic Controller) for machine control. I need three inputs, each sensing 14v AC. If either of the inputs sees 14 v, I need an output of dry contact pulses (like you would get from a water meter). Further, I need to be able to vary the frequency of the dry contact pulses (number of pulses per minute) because the pulses are going to a chemical pump and I want to be able to vary the output of the pump. From what I have read, I may need a GERT board and maybe Arduino? The alternative is to get an inexpensive PLC and use ladder logic.

MY advice is us a PLC , easy to program and more reliable, in a industrial environment
Off the shelf spares, and easy to modify the ladder program, Industrial technicians are
Farmiliar with PLC's and ladder programs. Shut down time costs money and
Production lost.

Regards BoyOh, Retired Electrical / Electronic / Technician

[BMS Doug]

using opto isolators you should be able to achieve this with a Pi or Arduino without any issues.

An Arduino may be more suitable as it is more resilient to power failure.

[boyoh]

using opto isolators you should be able to achieve this with a Pi or Arduino without any issues.

An Arduino may be more suitable as it is more resilient to power failure.

Yes Doug, I agree ,he could use a Pi to in place of a PLC. But I made my assumption on that
If he had a problem with the Pi controlled system , he would NOT have some one, with your
Experience of the Pi, looking over his shoulder telling how to correct It

Regards BoyOh

[BMS Doug]

using opto isolators you should be able to achieve this with a Pi or Arduino without any issues.

An Arduino may be more suitable as it is more resilient to power failure.

Yes Doug,
I agree ,he could use a Pi to in place of a PLC.
But I made my assumption on that If he had a problem with the Pi controlled system , he would NOT have some one, with your Experience of the Pi, looking over his shoulder telling how to correct It.
Regards BoyOh

If someone can learn enough about arduino or Pi to set this up in the first place (and this is a good starting project, not too complicated) and keeps notes of how he did it he should also be able to repair it if it fails.

If this is for a business critical system then something that can be easily maintained by a broad base of service engineers (Such as a PLC) is probably best, if its a hobby project for personal use then Pi or Arduino are more than good enough.

[boyoh]

using opto isolators you should be able to achieve this with a Pi or Arduino without any issues.

An Arduino may be more suitable as it is more resilient to power failure.

Yes Doug,
I agree ,he could use a Pi to in place of a PLC.
But I made my assumption on that If he had a problem with the Pi controlled system , he would NOT have some one, with your Experience of the Pi, looking over his shoulder telling how to correct It.
Regards BoyOh

If someone can learn enough about arduino or Pi to set this up in the first place (and this is a good starting project, not too complicated) and keeps notes of how he did it he should also be able to repair it if it fails.

If this is for a business critical system then something that can be easily maintained by a broad base of service engineers (Such as a PLC) is probably best, if its a hobby project for personal use then Pi or Arduino are more than good enough.

Agreed

Regards BoyOh

[poplar598]

Thank you Doug and boyoh for your thoughts. It is an industrial application, so maybe the PLC does make sense. I would be setting up the Pi, but if I were hit by a bus, my replacement would probably fare better repairing a PLC, unless I left adequate documentation. A low cost PLC would work out similar cost-wise.

I have worked with PLC's, but not the one I am considering for this application. It is a Lovato Electric LRDKIT 12RD024 micro PLC starter kit with expansion and communication modules as well as software for $CAD200. All I need is a box, wires, and a clue as to how to set it up! I have not been able to confirm the software can actually produce a dry contact of variable frequency for any 14v input on three contacts. I'm going to dig deeper in this direction though.

This would have been my first Pi. Maybe I'll get a Pi to replace my WD media player that seems to hang too often

Regards,
poplar598

[BMS Doug]

This would have been my first Pi. Maybe I'll get a Pi to replace my WD media player that seems to hang too often

Regards,
poplar598

I'm playing with a string of LED lights at the moment, plenty of fun to be had with Pi in the home environment.

[poplar598]

I am looking for a good excuse to buy my first Pi. I'm sure there are a million things I can try with it.

[BMS Doug]

I am looking for a good excuse to buy my first Pi. I'm sure there are a million things I can try with it.

There are too many projects to count, how about:

A magic Mirror
Internet Radio
Beetbox (I made a clone of this for my kids school, re-skinned as a dinosaur).
Remote control car / robot
Media center / Retrogames console
Wildlife camera

[poplar598]

Thanks Doug!
Too cool. A Beet Box? Good thing it wasn't a Boom Box! I'm thinking about maybe making an HTPC.