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 Post subject: Carat scale drift - normal ?
PostPosted: Thu Oct 24, 2019 3:35 am 
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Joined: Wed Jul 22, 2015 6:39 am
Posts: 166
Hello

I recently upgraded from a cheap 4 year old carat scale to a more costly Ohaus TAJ carat scale.

Ive never really owned a large "proper" carat scale before and this one has some drift at zero, usually flickering between -0.005ct/0.005ct & 0.010ct & -0.010ct.

Is this normal on larger carat scales (or any scales?)
Previous one didn't have this but it was extremely basic.

On my travels and when I buy from brokers their commercial scales all seem to have some flickering drift.

Id be grateful for some advise please


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 Post subject: Re: Carat scale drift - normal ?
PostPosted: Thu Oct 24, 2019 2:05 pm 
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Joined: Thu May 12, 2016 2:18 am
Posts: 1542
The problem with scales with three digits of precision is that air movement in the environment will show up. That is why most high end scales have a glass enclosure.


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 Post subject: Re: Carat scale drift - normal ?
PostPosted: Thu Oct 24, 2019 6:37 pm 
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Joined: Wed Jul 22, 2015 6:39 am
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Thankyou
This does have a draft shield. I left the scale on for 20 mins today and the drift went slowly up to -0.120cts.
It would not stopincreasing.

Am i right in thinking this is faulty?
I paid alot for the scale and did not think id have this much drift


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 Post subject: Re: Carat scale drift - normal ?
PostPosted: Fri Oct 25, 2019 3:34 am 
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That is too big an error for me to operate with. You should probably look for a scale that is "Legal For Tender". Some of the Ohaus scales are.


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 Post subject: Re: Carat scale drift - normal ?
PostPosted: Fri Oct 25, 2019 7:22 am 
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Thank you 1bwana1
It was proving a headache, so returned this morning.
Will look for legal tender scales next


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 Post subject: Re: Carat scale drift - normal ?
PostPosted: Fri Oct 25, 2019 11:13 am 
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Raj_uk wrote:
Thankyou
This does have a draft shield. I left the scale on for 20 mins today and the drift went slowly up to -0.120cts.
It would not stopincreasing.

Am i right in thinking this is faulty?
I paid alot for the scale and did not think id have this much drift


I had a look at my scale yesterday and today. It is always on, and only drifts +/-0.001 g. No way a scale should drift that much. You made the right move.


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 Post subject: Re: Carat scale drift - normal ?
PostPosted: Fri Oct 25, 2019 1:41 pm 
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Raj_uk wrote:
Thank you 1bwana1
It was proving a headache, so returned this morning.
Will look for legal tender scales next


Last time I bought a quality desktop "Legal Tender" scale I also had to send the first one back because the calibration was inconsistent. The second one has been rock solid so far. If you have ever learned the GIA requirement for weighing stones, and rounding to two digits, you know how important that third digit is. Also, very important in calculating SG in the lab. You did the right thing.


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 Post subject: Re: Carat scale drift - normal ?
PostPosted: Sat Oct 26, 2019 3:45 am 
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1bwana1 & Brian - thank you both for confirming this.
It was bought primarily for SG measurements.


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 Post subject: Re: Carat scale drift - normal ?
PostPosted: Mon Nov 11, 2019 10:12 pm 
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Joined: Fri Jun 25, 2010 12:04 am
Posts: 257
Location: Idaho
We have a nice set of precision scales, +/- 0.001 ct. VERY sensitive to light air flow, temperature changes, and vibration from the nearby 5 lane highway - we are next to the busiest intersection in the state. I know - that doesn't mean a whole lot, since it is only Idaho...

It was OK until we moved it from a heavy desk to a lighter counter in our vault, probably twice the swing now. I thought the concrete walls of the vault would dampen things. Maybe there is a jack hammer banging through the wall from next door? :shock:

0.0002 grams (.001 ct) is a very very small amount of change.

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