Out of curiosity, what are you using that scale for? Are you doing some chemistry or pharmacy? Anyway, bit of hijacking the topic, but recently I was thinking of buying some digital scale of precision of 0.01g for my airplane modelling hobby but those scales are not in the same level as a 0.15mg precise ones :-) Also I would like to use that scale for my other hobby which is numismatics so I could weight my coins. Any suggestion of a scale which is good enough for these but moderate in price? Thanks Tamas On Wed, Sep 30, 2009 at 4:56 AM, Sean Breheny wrote: > We all agree that lots of factors can affect it, but it does puzzle me > why you "don't trust it below a gram." To me, that sounds like saying > "I don't trust my car for trips longer than 1 mile" > > With my SA410, even though it is in questionable condition at this > point, I was able to weigh one nylon 4-40 screw (about 200mg if I > remember correctly), then weigh a bag's worth of them (100), and when > I divided the total by the individual weight, I obtained the screw > count to within +/- 1 out of 100. To me that says that it is clearly > usable well below 1 gram. My experience so far would be trust all but > the last digit (100s of micrograms). > > Sean > > > On Tue, Sep 29, 2009 at 2:00 PM, William Wilson wrote: > > We keep our balances and other sensitive equipment on lab tables. > > They are not granite, but they are some kind of thick burn proof, acid > > proof, scratch proof, shock proof, minimal vibration carrying, hard black > > plastic material. (I can't remember what it is called). > > > > We do keep it plugged in all of the time to a surge protecting power > strip; > > although, the power strip is more for convenience to turn on/off several > > things. > > > > It is sensitive to wind, temperature, and humidity. We had to move it > > away from an air duct because of the air flow and local temperature > change > > when the AC would come on. For the humidity problem (I'm in the south > east US) > > we have just decided not to trust the last digit of resolution - not that > I trust it > > below a gram anyway. > > > > > _______________________________________________________________________________ > > Cris Wilson > > Information Resource Consultant > > College of Architecture, Arts, & Humanities > > Clemson University > > Report computer problems to aah_computers@clemson.edu > > > > -----Original Message----- > > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf > Of Sean Breheny > > Sent: Tuesday, September 29, 2009 1:32 AM > > To: Microcontroller discussion list - Public. > > Subject: Re: [OT] Analytical balance question > > > > OK, thanks for the input. Do you have your SA410 on a very solid > > table? I found that moving it from an ordinary table to a granite-top > > measuring table made a big difference in repeatability and stability. > > I think the vibration really affects it. This thing is so sensitive > > that if you leave one of the doors open and blow into it from across > > the room, you see several digits of the display move when the "wave" > > of air reaches it. Also, do you keep it plugged in all the time? > > > > Sean > > > > > > On Mon, Sep 28, 2009 at 9:04 PM, William Wilson > wrote: > >> The 0.15 mg is the repeatability. You are correct. I didn't move > >> the decimal correctly. > >> I still don't trust the sa410s below a gram though. The 5 of them that > >> I routinely work with swing all over the place with milligrams. > >> > >> > >> > >> ________________________________________ > >> From: piclist-bounces@mit.edu [piclist-bounces@mit.edu] On Behalf Of > Sean Breheny [shb7@cornell.edu] > >> Sent: Monday, September 28, 2009 4:27 PM > >> To: Microcontroller discussion list - Public. > >> Subject: Re: [OT] Analytical balance question > >> > >> Are you sure you are reading that spec correctly? I just checked my > >> manual again and it definitely says 0.00015g for the repeatability. > >> That's 0.15mg (I had said 0.1mg before so I was a little off but not > >> by much). > >> > >> Sean > >> > >> On Mon, Sep 28, 2009 at 2:38 PM, William Wilson > wrote: > >>> The manual I have with my SA410 says that the repeatability is 15mg, > >>> so your measurements seem about right to me. > >>> > >>> As for the flat plate, mine does have a concave plate on it, and a > stainless > >>> steel flat plate that fits on top of that to help with whatever you > want the > >>> mass of (rezeroing required obviously). The plate should lift up > easily, > >>> but it is possible that someone glued it in place to keep it from > getting > >>> stolen - or they glued a flat plate over an acid hole in the concave > one. > >>> > >>> The SA410s are not very accurate when get down to milligrams. I don't > >>> trust mine below a gram. If I need something below a gram I use a > different > >>> scale. Or as one of my assistants just said, "It's meant for massing > marijuana, > >>> not cocaine" > >>> > >>> > >>> > _______________________________________________________________________________ > >>> Cris Wilson > >>> Information Resource Consultant > >>> College of Architecture, Arts, & Humanities > >>> Clemson University > >>> Report computer problems to aah_computers@clemson.edu > >>> > >>> > >>> -----Original Message----- > >>> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On > Behalf Of Sean Breheny > >>> Sent: Sunday, September 27, 2009 11:43 PM > >>> To: Microcontroller discussion list - Public. > >>> Subject: [OT] Analytical balance question > >>> > >>> Hi all, > >>> > >>> I have a question that I hope someone here can answer - someone who is > >>> familiar with high-accuracy analytical balances. > >>> > >>> I recently bought an as-is Scientech SA410 analytical balance on eBay > >>> for about $60. This is a 410g capacity unit with a repeatability to > >>> 0.1milligram. It has a wind screen with sliding doors. This model is > >>> still sold and goes for about $3500 USD new. > >>> > >>> It did not work when I received it but I discovered that the only > >>> apparent problem was that a TVS device inside was shorted. I replaced > >>> it and it seems to work. > >>> > >>> I don't have the proper weights to calibrate it. However, I do have a > >>> 150g weight which is spec'd to +/- 7.5mg. When I weigh this on the > >>> balance, I get 150g to within about 2mg. However, removing and > >>> replacing the weight causes a variation of about 0.5milligram up to as > >>> much as 1mg. In other words, the overall calibration seems close if > >>> not very close, but the repeatability is off by a factor of 5 or 10 > >>> from the spec. The unit always returns to exactly zero when the weight > >>> is removed, and lower value weights have less variation in repeated > >>> readings. I handle the weight using a piece of sheet plastic to avoid > >>> getting oils from my hand on it, so I don't think that is the reason > >>> for the discrepancy. I also have been operating the unit on a large > >>> granite-slab table we have at work so vibration does not seem to be > >>> affecting it much. > >>> > >>> If I place the weight on different parts of the weighing pan, I can > >>> make the reading vary by 10s of milligrams. I am wondering if perhaps > >>> the repeatability problem I am seeing is due to inexact placement of > >>> the weight. > >>> > >>> Can anyone tell me if it is normal for weight positioning to make such > >>> a difference? It almost seems like the repeatability spec is rather > >>> meaningless if so. I do notice that the weighing pan seems to have > >>> been modified on this unit: instead of being a concave circular pan as > >>> shown in the manual, it looks like someone attached (welded? glued?) a > >>> flat plate to the top of it. > >>> > >>> For my own purposes, its present capabilities are more than enough. I > >>> am toying with the idea, though, of re-selling it, stating that it > >>> does work, hoping to get more money for it. If I were to do this, I > >>> would probably spend the $50 or so to get some more accurate weights > >>> to perform the proper calibration on it. > >>> > >>> Thanks, > >>> > >>> Sean > >>> -- > >>> http://www.piclist.com PIC/SX FAQ & list archive > >>> View/change your membership options at > >>> http://mailman.mit.edu/mailman/listinfo/piclist > >>> > >>> -- > >>> http://www.piclist.com PIC/SX FAQ & list archive > >>> View/change your membership options at > >>> http://mailman.mit.edu/mailman/listinfo/piclist > >>> > >> > >> -- > >> http://www.piclist.com PIC/SX FAQ & list archive > >> View/change your membership options at > >> http://mailman.mit.edu/mailman/listinfo/piclist > >> -- > >> http://www.piclist.com PIC/SX FAQ & list archive > >> View/change your membership options at > >> http://mailman.mit.edu/mailman/listinfo/piclist > >> > > > > -- > > http://www.piclist.com PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > -- > > http://www.piclist.com PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.mcuhobby.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist