Test Stand - A/D Conversion Rate/Bits?

mrmonteith

Anyone had any experience with using a motor test stand with a load cell? I'm trying to find out what would be needed in the way of an A/D converter such as how many bits and what rate I would need? I'm thinking at least 10-bit for sure. Speed I'm not so sure. Since so much happens within a second or two I would think 1Khz or better. But wondering if anyone has been there already?

Michael

troj · Fleet Captain Joined: Jun 30, 2007 Posts: 1506

Take at a look at what Aerocon Systems offers. Their stuff, and similar, is used by lots of folks.

-Kevin

mrmonteith · Posted: Mon Feb 04, 2008 8:46 pm Post subject:

Kevin,
Thanks. I've looked at their systems and it's a possibility. The only issue I take with it is the 240Hz sampling rate. Seems a bit weak seeing so much is changing in such a short time it would be next to impossible to see burn rate instabilities. I could be wrong. But I guess I'd like to hear with someone that did try higher sampling rates to see if it did help.

That and I'll more than likely use it for other projects.

Thanks
Michael

troj · Fleet Captain Joined: Jun 30, 2007 Posts: 1506

There's no doubt a higher sampling rate will provide you more information. I think most folks (me included) are out to control cost a bit.

That said, I've done some poking around in the past, and an outfit called Measurement Computing has some really nice A/D converters, if you want higher rates.

I know I've found some others, but I cannot remember company names off the top of my head.

-Kevin

mrmonteith · Posted: Tue Feb 05, 2008 7:56 am Post subject:

Actually I'm excited. I found something better:
http://www.coridiumcorp.com/ARMmite.php?gclid=CNnr9IyerZECFQmgGgodySiqew

It's a microncontroller with 8 channels of 10-bit A/D with 100Khz sampling rate. No software to unlock and I get a microcontroller to boot. Instead of paying for a dumb A/D only type system. PLus with the breadboarding area I can put an instrumentation amp chip and support circuits right on board. I found some great ideas for that. I like the fact I get something I can use on this project and others as well. For $49 it's worth it alone.
That kind of cost is very reasonable.

Michael

troj · Fleet Captain Joined: Jun 30, 2007 Posts: 1506

Looks pretty cool.

The one thing I would do with a setup like that is make sure you have a good, solid enclosure for it -- you don't want it too close to the stand, and have a motor failure destroy your board.

What we did was place the amp near the stand, then run leads from that to the A/D converter, which sits over 100 feet away.

-Kevin

mrmonteith · Posted: Tue Feb 05, 2008 12:20 pm Post subject:

Kevin,
Thanks. That's a great idea. Since I'll have tons of room at the new place I'll probably have some sort of setup to protect it physically like putting the test stand down in a pit or something.

Keep the ideas coming though. I'm sure there's things I haven't thought of. I've got plenty of time seeing I don't have money yet. lol

Michael

scottm · Trainee Joined: Jul 02, 2007 Posts: 8

I like MCC's stuff, check out the USB 1208 FS, it's what we use at the Embry-Riddle Propulsion Labs to take thrust, pressure and mass readings when firing liquid and hybrid motors.

We use 2 because we have so many things being recorded, 5 pressure transducers, 2 load cells and 2 mass reading loadcells. They have 4 differential or 8 single ended channels and interface with Labview, which allows us to have a graph of whats happening as its happening, as well as calculate impulse, averages and such on the fly, then dump it all to an excel sheet.

If you have any questions, feel free to email me at mcnee229 at erau.edu. I helped build our test stand, and designed the data aq and flow systems for our set up...

Scott