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Re: Analytical balance question
by Sean Breheny
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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 <CRIS@...> 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@... [piclist-bounces@...] On Behalf Of Sean Breheny [shb7@...]
> 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 <CRIS@...> 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@...
>>
>>
>> -----Original Message-----
>> From: piclist-bounces@... [mailto:piclist-bounces@...] 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
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 <CRIS@...> 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@... [piclist-bounces@...] On Behalf Of Sean Breheny [shb7@...]
> 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 <CRIS@...> 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@...
>>
>>
>> -----Original Message-----
>> From: piclist-bounces@... [mailto:piclist-bounces@...] 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
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