PLCs and Barcode Readers

Hi All,

Can anybody suggest a PLC solution to me for my following problem:-
My customer has two barcode readers on a production line. He requires a comparasion of both barcodes (in a PLC or something similar..not a PC). If both barcodes are different then I/he must stop the line.

I have ruled out the Allen Bradley SLC 500 with a BASIC module based on cost and the CompactLogix has being ruled out because both RS232 ports cannot be connected to barcode readers.

Any suggestions would be very much appreciated.

I AM NOT SURE OF WHAT KIND OF BARCODE READER YOU ARE USING, BUT IN A SIMILAR SITUATION WITH A VISION SYSTEM I WAS WORKING WITH, I CONNECTED THE 2 CAMERAS TO A MANUFACTURERS "SMART MODULE" AND LET IT DO THE COMPARISION( OF COURSE THAT HAD TO PROGRAMMED WITH THEIR SOFTWARE). THEN I JUST USED THE RELAY CONTACTS FROM THE VISION SYSTEM I/O BOARD TO THE INPUT OF THE PLC.

Yeah me too. What kind of bar code reader?

I tell you what I've used before on conveyor systems that work well. An Allen Bradley Adaptascan. I think now called something else...

But you can use DH-485 or DeviceNet. Works like a champ. I've seen RS-232 to Device Net modules you can purchase. Is that what you are looking for? Some other protocal? Purchase a device net module for your PLC and the converter and you should be good to go for any bar code reader that is RS-232. Kinda of an expensive road to take, but I guess if you truely can't use RS-232 that might be worth a look.

Good Luck.

Adaptascan is now sold and supported by Accu-Sort. I was never an Adaptascan wizard, but I think it did have a way to have two peer Adaptascans compare barcodes and trip a relay based on matching or not-matching them.

Adaptascan is a pretty high-powered reader, though; lots of range, speed, features, and a price to match. If the querent is using a simple barcode-to-ASCII reader (especially if they're already installed) then of course a different model reader isn't indicated.

This device might help you use even a tiny MicroLogix 1000 to do the job:

http://www.tomantron.com/

From what I've read on this guy's website, you can hook up the device to a MicroLogix and have two incoming ASCII strings written to Integer files in the Micro via DF1 protocol. Since you're only comparing, not interpreting, the strings, you can use a low-cost MicroLogix 1000 which has neither ASCII instructions nor STring data types.

I don't know how this device would handle two simultaneous incoming strings.

You might also look at the MicroLogix 1500 LRP controller and a 2-port buffered code-operated ASCII switch like those offered by B&B Electronics.

Those are the two cheapest and simplest ways to do what you've described with an A-B controller. I can think of plenty of others, in increasing levels of complexity and cost.

Our product, the MuxiPort, offers a perfect solution to your problem.
You can take the low cost Micrologix and MuxiPort (369.00 USD)
and hook up two Bar code readers sending out ASCII strings.
MuxiPort will deposit these strings in predefined, separate
Integer files. MuxiPort has double incoming data buffers and
so simultaneous strings will not be lost! Each time a string is sent in to the Integer file in the Micrologix, a number (integer) representing the count of characters in the string is put in
a predefined N file location. Your ladder program would always look at this N file and when it is bigger than 0 you would compare the strings ( actually in your case you would always look at two separate
N files). Once you are done with the comparison you would reset this
N file to 0.
Please visit our web site at www.tomantron.com

I hope that you will use MuxiPort to solve this problem!

Jiri Toman
TomanTron, Inc.

Jiri in alot of cases a person promoting their companies product within this forum is done inappropriately. I am not sure if Ken had you post or you have been lingering in the background..either way I think your post was timely and appropriate in this situation. The question was about a specific plc and a device to use with it, yours seems to fit that application.

Thank you for the information, I have needs for bar code readers at my plant so I will be looking at your website and products.

He's cool, it's alright...

No lurking on Jiri's part... I e-mailed him directly and asked him to post.

I'd still be a little bit concerned that if the strings came in at the same time that it would be hard to tell for sure if you'd just zeroed the register or if you stepped on the second string's toes.... I'm the sort who never recommends anything I haven't seen work with my own eyes.

If the TomanTron unit had separate Nxx:yy files that it could write to for each channel, this would be absolutely ideal.

Folks,

Thanks for all your help. It looks like I might be able to formulate a solution to my little problem now. I knew I came to the right place!

I have to retract my aspersions on the TomanTron device above... I downloaded the configuration software and read more carefully the e-mail Jiri sent me.

If you configure both user ports as ASCII mode, they do have separate target files and offsets, which are configured in separate windows in the configuration utility.

This means the smallest MicroLogix 1000 will work for this application. If you want to manipulate strings with the STring datatype, get a MicroLogix 1200 or 1500.