| Electronics > Projects, Designs, and Technical Stuff |
| mg scale - interesting effect |
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| JBeale:
Hah, likely "no fire" was indeed the extent of their EMC testing. I had a peek inside this ebay thing and sure enough just a load cell and the top cover is entirely plastic so no surprise there is some pickup. Since it's working OK now with the foil, I'd still say it's a reasonable value for the price, though they should maybe include some foil in the box :-) |
| coppercone2:
higher quality ones have equally shitty construction in terms of EMI (200+ $ range) Not china at fault (at least they pretty much visually copied what you can get from America with lower quality plastics). "real' ones will have a common mode torroid around the input DC though. The good ones will also have a much thicker stiffer 'webbed' glass reinforced nylon base (like a cast iron saw table) that connects to the load cell. That one looks very anemic for 1 miligram. The good ones kinda look like the mothership from Independence Day. http://vignette3.wikia.nocookie.net/id4/images/6/6f/Escape_saucer_and_the_colony_mothership.png/revision/latest?cb=20160821201325 The plastic bit in the higher price ones internally is very abrasive and glassy (enough to make it uncleanable with a towel if you spill something on it, you need to use a brush). They make it with a high glass content. It feels similar to fibrous wraught iron if you ever disassembled REALLY old tools before. If the bed flexes you get error. They give you a metal cover plate that you set on top and it rests on the nylon. It's not adhered or fastened in any way. |
| SenseofScale:
Decided to search microgram scales and came across this. The guy should have rehearsed his lines a few times, but I can only guess how awkward I would sound. Interesting nonetheless. |
| ChristofferB:
Transplanting the electronics and load cell+steel plate into a largeish low-profile hammond box, tapping holes for the adjustable feet, adding a much needed round bubble level (a balance like this needs to be level!) might actually be worth wile. There'd be room for PSU filtering too. I'm almost tempted to give that a go now. |
| JBeale:
not visible in the photo as it is in the rear, there actually is a bubble level on this one and it has 4 screw-in adjustable feet. Maybe I was helped by using only very small loads, while it was sitting on a granite countertop but after the foil fix I really did observe +/- 2 mg repeatability (vendor claims +/- 3 mg). I'm not equipped to speak to accuracy but it did read my cheap 10 mg - 100 g test weight series within 1% of marked value. btw I was kind of just using the chemistry experiment as an excuse to Buy More Tools but I also did not have much of the salt to start with, it's a little pricey, so it was going to be a small total weight anyway. The video showing an old panel meter as a magnetic force balance for micrograms is a neat trick! |
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