PLC vs. PCB

Hello all,

One of the machines that we build uses a PCB for the controls. I know very little about PCB. This machine is VERY simple and if we go the route of a PLC it would be a AB Micrologix 1000 with 6 inputs and 4 outputs. From inital research about the machine it looks like the program will only be 10 lines. The main reason for this post is for opions on which would be better, the PLC or PCB. The issue with the PCB, as I have been informed, is that some of the components are now obsolete. As I stated I know nothing about PCB desgin or componets. As far as I know we have negatives of the PCB and a list of all parts used. I have also been told the cost for the setup a new PCB is rather high and most have high cost unless ordered in quanity. Also, lead time would be an issue. Any and all information would be great. At this point I am looking at $130 for thr PLC and a ship date around the end of the year. We have not produced these machine for almost a year and may or may not build them agin after these four units. Thanks in advanced.

Micheal

I think it really depends on the application. I have worked with both PLCs and embedded circuit design and in my mind there are advantages to both.

You didn't provide many details about your machine, but if it is a typical piece of production equipment with an electrical cabinet, then I'd say a PLC is definitely the way to go. The program will be easier to modify by the end user, if necessary. (I'd say we end up having to make PLC program changes to at least 50% of the equipment we purchase.)

Designing your own circuitry usually has a lower component cost and a much smaller footprint, but there is much more time involved in design. Not only do you have to write a MCU program and spec all the components, you also have to design the PCB and get it manufactured (which can be expensive as you noted), then populate the board. There are some companies like www.expresspcb.com that can do small runs fairly inexpensively, however.

Just my two cents.

-John

Thanks for the input John. Our end users ARE NOT and DO NOT change the PLC program. Our machines are FDA medical devices. Any changes could cause serious illness or death. I was looking at expresspcb, one of their adds it what got me started on this. I have been able to track down most of the parts, but one I am having trouble finding info on is a white cube about 3/4 x 1/4 x 1/4 inch. Number on top is 149ES-2C-12VDC any clue, anyone?

Micheal

Michael,

If you wanted to stay with the PCB look there are companies, including ourself that offer a PLC that is a bare circuit board.

Based on what you talked about, our Smart-PAK would be sufficient for your application. www.entertron.com/smart-pak.htm

There is no additional charge for the programming software.

From a manufacturing perspective, if you are not going to be making that many machines with your design, it may make better sense to go with an off the shelf solution.

If you have any questions, feel free to contact us.

Hope this helps.

God Bless,

If it is in a safety sensitive like this I would think twice about a programmable controller that can be changed by the end user. A PCB cannot be modified.

I've never had a user defeat my dual-layer strategy of the OEM Lock bit and epoxy putty in the serial port ! I can buy a lot of $140 controllers for a day's worth of lawyer's time.

For a production run of four units, the buy v. build (or resume building) equation is, in my opinion, heavily weighted in favor of an off-the-shelf controller. Even the labor involved in purchasing the components for a PC board run is going to be greater than the full cost of a logic controller of this size.

Use the controller that you think you'll learn most easily, whether that's Entertron, Automation Direct, or Allen-Bradley.

A white cube is pretty vague for an electrical component. Anything from a relay to a resistor could fit that description.
The 12VDC sounds like a relay coil voltage, the 2C maybe 2 contacts?
Is there a mfg name on it? How many pins and what configuration? Can you post a photo of the top side and the pins side?

I'm with Ken and Stephen on this one. If you were going to build 400 of these machines it may make sense to re-do the PCB with up-to-date components. But for four machines I would go with the PLC. I know next to nothing about the requirements of the medical industry but my guess is that anything you do will need to be re-certified anyway. Go with the PLC of your choise, get something that works then break the comm ports so the program can't be changed.

Keith

I have used Device Logix on Compact Block IO for this type of thing. It is far less likely that someone will tamper with the code and you get built in DeviceNet connectivity. The programming tools are basic but perfectly usable.

Andybr

As always, PLCs.net user come through. I have never been let down by you guys. At this point I think we are going to go with a PLc do to time requirements. But, I would like to continue witht the PCB if for nothing else but the knowledge.

Ken, there would be little learning curve, I program AD pretty much every day and learned PLCs on a AB.

Rotatech, yes I know white cube is not very descriptive...sorry. Since yesterday I have figured out that it is a Gurdian Relay. It has six pins on the bottom. As for pictures, yes, I will get some on here this afternoon. I also have some diagrams that I will try to include.

kamenges, since we are FDA regulated we have a ton of paper work to fill out ofr this simple change. We do all of the Verification and Validation on our machines and keep records.

As far as breaking/filling the com ports this is not something we do. All of out machines have PLCs in them and we have never hadf an issue. I will get some more info toghter on this and get back with everyone. Once again thanks for the insight and help.

Micheal

lets see if this works........

If its just a relay you have to replace their are many man. out their that make them couldn't you just choose one of them? Also check out a AB pico controller, I have never used one but I think they are less money than a micro for the I/O that you have and you don't have to buy any software to program it. Just a thought!

The component is a common 12v dc pcb relay - one leg turns on a buzzer or sounder.

measure it and look in electronic catalouge - you will be able to match the No of pins and physical size

At this point I am still looking around for parts and information. Everyones input has been great.

hipoint2, thanks for the suggestion on the Pico, I have never used one and did not know about them. I called our local rep and the cost of the Pico is a bit higher even without the display. We have RSLogix 500 (kinda, the hard drive crashed on the computer it was loaded on) plus I also have the free 10pt Micro version. At this point the Micro is a better fit.

Goody, I was told that this relay was different because it loops to ground or something..... I do not know. When I was told this I was told to look at the first pic, bottom row on the right hand side of the drawing where the relay is. If you look at J1-2 it goes to the Coil of the relay and ground.....but like I said I do not know.........

Micheal

You mentioned that this was an FDA medical device. If you change the controller do you have to go through the FDA approval process all over again? Something to consider. (edit, nevermind, I should have read the whole thread)

The disadvantage to the PICO is that it's program can be changed without the software just by using the front keypad. Big disadvantage there.