load cell project

GS Solutions

I'd like to use the basic stamp to build a project similar to the "Liquid Filler Machine by Mohamed Refky" in the "industrial / commercial" section of the customer applications on this site.·I only need to use AC Excitation on a load cell and want a 4 to 20 ma output for a PLC. The problem is the Schematic is unreadable on the site. Can someone please help me with this?·

PVJohn

This is a link: http://www.parallax.com/html_pages/resources/custapps/app_paint.asp

As far as I know, there's no LC with AC excitation. That must be a typo.The output volage (DC) from LC is very low·so you need a VERY good low noise amplifier. Don't waiste your time on building conditioners, just go and buy one.·I used these before and they worked fine:

http://www.dataforth.com/catalog/doc_generator.asp?doc_id=82

http://www.dataforth.com/catalog/doc_generator.asp?doc_id=106

http://www.dataforth.com/catalog/doc_generator.asp?doc_id=85

http://www.dataforth.com/catalog/doc_generator.asp?doc_id=266

PVJohn

GS Solutions

Thanks PVJohn for the reply.
I am at present already working with both kinds of signal conditioner but have found the AC to give you allot cleaner signal in an EMF noisy environment. The problem is the AC Excitation units are not as available as DC or as industrial as I'd like to see so I though if I had a place to start from like in the http://www.parallax.com/html_pages/resources/custapps/app_paint.asp·customer project I could build my own fairly easy.
Here's a couple of links that have some AC Excitation controllers I've looked at but I'd be interested to know the circuit that was used in the customer project listed here on this site.
http://www.analog.com/en/prod/0,2877,3B20,00.html
http://www.analog.com/UploadedFiles/Application_Notes/59049444287803AN_683_A.pdf

Mohamed Refky

Look at AD7730 data sheet,figure 24.typical connections for AC excited bridge application

Mohamed Refky

GS Solutions

Thanks Mohamed Refky!
Your project looks great and it is probably very stable. Great work!
I'll check out the article you posted.
I'm not looking to steal your invention· just borrow a few sections from it. Anyway, if·you could send me just the load cell to the basic stamp section of your print it would save me allot of time on this project.
Thanks,
John

Mohamed Refky

Dear Jon,
Load Cell is connected directly to the AD7730 that outputs a serial digital word.
BASIC Stamp II controls the AD7730,MAX7219 LED display driver,and EDE1144 keypad encoder.
You should rout the layout on double sided board with ground plane .

What is the GS Solutions.

Regards
Mohamed Refky

GS Solutions

Mohamed,
·
Thanks again for your help!
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I decided to go with the ADI 3B Series modules and backplane for this project as they appear to be an exact match for the project. I also did order the AD7730 for some experimenting on the side for some future projects. Thanks for pointing me in their direction.
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To answer your question about GS Solutions, it’s a small software integration company run by yours truly in my spare time. At present GS Solutions is designing all of the MMI software for a company called Lasercard in Mountain View, Ca, consisting of all the PLC programming, wiring design and documentation in AcadE, user interfaces mostly programmed in VS.NET and SQL database serial number tracking and security. If I tell you any more about this I’ll have to kill ya (haw just kidding). The day job is 20 years at a confections company (candy i.e.: gummy bears etc) in Santa Cruz as the maintenance & engineering manager, doing basically the same as what I described above with a crew of about 20 maintenance employees and a total of about 200 employees. A little off the topic, but you asked.
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This load cell project is to retrofit a CFA (color flavor acid) batching system original designed in the Netherlands with something more reliable.
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I’m all set so thanks to all who replied.···
John