Any PLC guys here? Looking for a super basic PLC

[fastline]

I work with automation equipment, but never had to program a PLC from scratch. However, the current need is SUPER basic and because I want to employ these little critters on each machine, I am looking for an inexpensive solution.

Basically we are installing PCs on every machine to provide some other functionality, but with that, I want to also be able to remotely control certain things in a machine. These machines are already VERY loaded up with PLC goodies, but messing with the current systems would mean having to edit ladders in every machine, and will be a huge hassle.

Basically want to remotely tell PC to flip a couple switches, and I want the PLC through a few small relays, to do just that. So spotting a small PLC with onboard relays would be nice, but we can also just fab up some boards if it comes to that. Probably already solutions for all this, so figured I would ask here.

 

[petersonra]

I don't know what your role in this whole idea is but my opinion is that you're better off just modifying the existing program in the PLC already being supplied. Otherwise you're going to end up with two different PLC programs to keep track of, and potentially two different pieces of software that you're going to have to have available. The end users that have to maintain these machines will curse your name.

If you are determined to do something that will probably turn out to be a bad idea, the click series from automation direct is pretty cheap.

If you truly hate your customers, you could supply a micrologics 800 from Allen Bradley.

Best bet is to find the guy that came up with this horrible idea and drive a stake through his heart.

This is an idea that is bad enough that it had to have come from a vice president or a salesman.

 

[fastline]

I don't know what your role in this whole idea is but my opinion is that you're better off just modifying the existing program in the PLC already being supplied. Otherwise you're going to end up with two different PLC programs to keep track of, and potentially two different pieces of software that you're going to have to have available. The end users that have to maintain these machines will curse your name.

If you are determined to do something that will probably turn out to be a bad idea, the click series from automation direct is pretty cheap.

If you truly hate your customers, you could supply a micrologics 800 from Allen Bradley.

Best bet is to find the guy that came up with this horrible idea and drive a stake through his heart.

This is an idea that is bad enough that it had to have come from a vice president or a salesman.

Thank you but I think once you understood the goal, you would be more accepting. The current PLC is in a CNC machine and already taxed to the moon. On top of that, the type of functionality we need to add is totally stand alone from the machine, and that functionality was simply not offered back then.

 

[petersonra]

Besides the automation direct click series mentioned above, Siemens makes an S7 1200. There are a bunch of lesser known PLCs you could use too, but I don't have any experience with cheap PLCs beyond those, and the micro 800 that I would only recommend to someone I actively disliked.

In the end you may have to select what is actually available. Right now the pickings are pretty slim.

.

 

[ptonsparky]

The CLICKs are pretty decent little PLCs. They have WiFi, Bluetooth, and ethernet capabilities depending on your needs.
I tried the 800 and never could get it. Learning it wasn't worth the time when the CLICKs were so easy. I may still have it in a box somewhere.
My projects were comparatively very limited in scope.

 

[petersonra]

It occurred to me that we use some small omron PLCs for one of our customers. I'm not involved in it so I hadn't thought of it but we must build a couple of hundred control panels a year with these little omrons in them. Customer seems happy with them.

Emerson bought the GE PLC line. I think there is a low end PLC in that line now too. Not sure what it's called because I've never used their low end PLC.

 

[fastline]

I did stumble into Velocio? Curious if you guys are familiar? They get high marks for their free and simple software. They were supposed to be a 'budget' product but looks like their prices climb quickly. However, I cannot expect a quality product to cost pennies. I am probably more frustrated that someone has not kicked out something with a few onboard relays.

 

[petersonra]

I did stumble into Velocio? Curious if you guys are familiar? They get high marks for their free and simple software. They were supposed to be a 'budget' product but looks like their prices climb quickly. However, I cannot expect a quality product to cost pennies. I am probably more frustrated that someone has not kicked out something with a few onboard relays.

There are several models of an micrologic 1400 that have onboard relays but given they seem to be on the verge of obsoleting them and you can't get them anyway, it would seem to be a bad choice.

Had not heard of velecio PLCs before.

 

[Electromatic]

You might search around for programmable relays. They're kind of a "light" version of PLCs. If you just needs some INs and OUTs and a simple program, they should get the job done. You might have to get an ethernet or other comm module to go with them.

 

[MasonF]

Id look into a Schneider Modicon M221 series.

 

[drktmplr12]

Emerson bought the GE PLC line. I think there is a low end PLC in that line now too. Not sure what it's called because I've never used their low end PLC.

did they?

oh no.

 

[Jraef]

If it's just a couple of relays and inputs, I would think along the lines of a "nano PLC" like a Siemens LOGO! or an A-B Micro810. Under $150 for something with 8 inputs and 4 relay outputs, free software or program it from a built-in HMI.

 

[petersonra]

did they?

oh no.

I think it's a major step up. Emerson is a better managed company and dealing with the GE bureaucracy just to get quotes was painful to say the least. Other parts of Emerson that I have dealt with have been a whole lot easier to deal with than the GE PLC people.

 

[paulengr]

So what you are asking for is PC controlled IO.

If you use a PLC chances are you will be communicating to it over Modbus/TCP.

So why bother with the PLC at all? Just buy some field IO and use Modbus/TCP directly. Lots of options here.

For example consider say Acromag. Look at the NT2130 for instance but they have tons of options from huge IO densities to very small. Configuration is done from a web page so no need for “programming”. Programming Modbus is super simple and plenty of libraries exist. The protocol is 100% public domain. Go to Modbus.org and you can download it for free. Every major PLC brand supports it.

I’d suggest similar stuff from Automatikn Direct but they’re having stock issues. But this approach is very, very common.

 

[fastline]

So what you are asking for is PC controlled IO.

If you use a PLC chances are you will be communicating to it over Modbus/TCP.

So why bother with the PLC at all? Just buy some field IO and use Modbus/TCP directly. Lots of options here.

For example consider say Acromag. Look at the NT2130 for instance but they have tons of options from huge IO densities to very small. Configuration is done from a web page so no need for “programming”. Programming Modbus is super simple and plenty of libraries exist. The protocol is 100% public domain. Go to Modbus.org and you can download it for free. Every major PLC brand supports it.

I’d suggest similar stuff from Automatikn Direct but they’re having stock issues. But this approach is very, very common.

I am taking notes with all the good ideas for PLCs, and I am sure that will come in handy, but Paul I believe you are correct per an earlier convo with a colleague. I think logic level IO is just fine for this, as there is nothing that really has any power requirement. I will review your recommendations. I will say that there are now two that we have looked at that must have been built by Kmart because they an FTDI 232 chip and state in the specs that "board will have a glitch on first power up"....Uh, not like anything we will do will be crashing a machine, but that seems ridiculous. Some are going I2C. I probably need to figure out the most robust and simple way here.

Just to provide some level of understanding on what is going on. The PC on machines will be used for several things, but among those are process cameras that can be viewed on the network remotely. If something is of concern, we want the ability to remotely stop the equipment. There are tons of ways to do that, but the easiest is simply tie into the Estop circuit. Simple relay trip for 1sec will put machine in a safe mode until help can arrive.

There is likely to otherwise be simple sensors and alarms that can be sent via email/text/etc. Basically some processes are going to be done unmanned.

 

[paulengr]

I am taking notes with all the good ideas for PLCs, and I am sure that will come in handy, but Paul I believe you are correct per an earlier convo with a colleague. I think logic level IO is just fine for this, as there is nothing that really has any power requirement. I will review your recommendations. I will say that there are now two that we have looked at that must have been built by Kmart because they an FTDI 232 chip and state in the specs that "board will have a glitch on first power up"....Uh, not like anything we will do will be crashing a machine, but that seems ridiculous. Some are going I2C. I probably need to figure out the most robust and simple way here.

Just to provide some level of understanding on what is going on. The PC on machines will be used for several things, but among those are process cameras that can be viewed on the network remotely. If something is of concern, we want the ability to remotely stop the equipment. There are tons of ways to do that, but the easiest is simply tie into the Estop circuit. Simple relay trip for 1sec will put machine in a safe mode until help can arrive.

There is likely to otherwise be simple sensors and alarms that can be sent via email/text/etc. Basically some processes are going to be done unmanned.

The specific Acromag card I listed has 6 relay outputs and 6 dry contact inputs, not logic level (3.3 or 5 V). They also make analog cards.

The problem with modern PCs is that short of say PCI cards there simply isn’t any “low level0 hardware IO. Everything is some kind of control mmunication port. Sure you can get embedded PCs Luke Arduino or others but I’ve learned not to buck the trend:. Don’t think about today: think about 5-10 years f I’m now when we are on Windows 13 and your favorite embedded system is gone.

Modbus/TCP relay na a n Ethernet. It is supported by every PC and PLC brand either natively or with some software or hardware adapter. Ethernet is cheap and not going away any time soon. Don’t get me wrong vanilla Modbus is also well supported on the PLC side but PCs have gone to USB or Ethernet for virtually all external devices. So Modbus on RS-485 needs a dongle and it will always be trouble:

For the same reason I would stay away from I2C. The key advantages of I2C is that it only requires a logic gate to work: thus it is ideal for chip or board level comms. So if I needed a way to say send and receive data from an Ethernet chip to an ARM CPU I2C is often helpful: but you hit the same road blocks.

If you are wanting to go full embedded though things look very different. Arduino is a good option, especially Automation Direct’s MKR Productivity which is an Arduino sitting on high end PLC hardware. Or there are Maple Systems HMIs that have embedded IO in them that do what you want. But this is a hard turn away from a “PC” solution.

 

[BrandonMD]

Dont know if theyve been mentioned but we use WAGO pLC’s for some smaller stand alone applications and they work well.

 

[fastline]

I appreciate the feedback on the PLC! I am certain to reference this thread as soon as we actually need one, though I realize the market is ever changing.

However, I think @paulengr really nailed it that we just don't need a true PLC for this, and we really have to have a PC involved in this system for all the other stuff that we need to do.

We were able to find some pretty inexpensive boards we are evaluating that have I think 10, 10A dry contact relays, and board requires a separate power source, and then IO switching from the PC. I have not yet figured out a best method for that just yet. What sucks is boards like this are around for several hundred $!!, then you find something on Amazon for like $30.... Our intention is to source quality components from USA vendors, but I didn't see much difference!

One thing I will say is China relays (most actually are anyway) suck if you are going to try to run close to their ratings, but for this application, they might be just fine. I smoked one last year and was mission critical. Welded the damn contacts closed. Replaced the board mount relay in the field with an Omron and has been fine.

 

[ptonsparky]

...

One thing I will say is China relays (most actually are anyway) suck if you are going to try to run close to their ratings, but for this application, they might be just fine. I smoked one last year and was mission critical. Welded the damn contacts closed. Replaced the board mount relay in the field with an Omron and has been fine.

I found contacts of ice cube relays from my favorite On Line supplier that bounced too much for the application. Installed some CH and no more problems in 10 years. I had to use the scope capabilities of my 43B to find and prove the issue. I was not the original EC but at the time I saw no reason to not use the relays he had.