LiveLife
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Time for another myth busting thread.
In previous digital scale myth busting threads we determined that some digital scales (even cheaper models) could be sensitive/repeatable to 0.1 gr for reloading (Actually, few were determined to be more sensitive than 0.1 gr resolution beam scales but this thread is about zero drift of digital scales so no comments about beam scales).
With more sensitive higher resolution digital scales verified by check weights down to 0.03, 0.06, 0.08, 0.1+ gr, there persists the issue of zero drift of digital scales. And that's what this thread is about.
So what causes zero drift and can it be resolved?
In the "Myth Busting Digital Scales - 1 mg Analytical Lab Scale" and "Fine tuning an 'analytical/lab' digital scale" threads and other digital scale threads, we learned that strain gauge or load cell are used for digital scales.
VEVOR Analytical Lab scale with FA DS-750, Gemini-20, WAOAW and Ohaus check weight set along with Dawn container for perspective comparison.
Load cell of VEVOR digital scale
Cause of zero drift - What I found during my resolution of Varget down to single kernel testing is that digital scale zero is influenced by internal/external factors that affect the sensitive load cell:
Solution options to reduce/eliminate zero drift:
I highly recommend use of check weights:
$15 Aluminum (Down to 10 mg/.15 gr) - https://www.amazon.com/American-Wei...rds=scale+check+weights&qid=1629058966&sr=8-2
$82 Ohaus ASTM Class 6 stainless steel - https://www.zoro.com/ohaus-calibrat...edirectid=16290592283668228270010070301008005
$158 NIST Class F stainless steel - https://www.amazon.com/Rice-Lake-Stainless-Calibration-Weight/dp/B006MWG13U/ref=sr_1_2?keywords=CERTIFIED+calibration+weights&qid=1552671682&s=industrial&sr=1-2&th=1
This is where I took member jmorris' practice to heart and disassembled the scale.
If you look at the above picture, you will notice that load cell is attached to the mounting plate with four screws which was crucial key to fine tuning this scale to reduce/eliminate zero drift -
https://www.thehighroad.org/index.php?threads/fine-tuning-an-analytical-lab-digital-scale.876547/
What I found was any touch or slightest pressure on the four mounting screws changed the reading along with any pressure above four corner adjustable feet of the scale. Then the light bulb went on and I realized as temperature of the scale increased in relation to the ambient temperature, there could be unequal expansion of plastic parts/base to exert uneven pressure on the load cell mounting plate.
So when I loosened the screws and tightened again until touch/pressure on the four screws/adjustable feet did not produce change in reading, my zero drift essentially disappeared.
So then I eagerly disassembled my other digital scales only to find that strain gauge/load cell were not readily accessible. So, if you have digital scale with load cell mounting plate that is accessible, you can check to see if mount screws can be adjusted to reduce/eliminate zero drift. If not, apply all the other listed solution options to reduce or eliminate zero drift.
So is this myth confirmed or busted? Do digital scales' zero drift?
Confirmed, but not necessarily due to the scale and there are many internal/external causes which can be resolved.
Only as the last resort, is the digital scale to blame and needs replacement.
In previous digital scale myth busting threads we determined that some digital scales (even cheaper models) could be sensitive/repeatable to 0.1 gr for reloading (Actually, few were determined to be more sensitive than 0.1 gr resolution beam scales but this thread is about zero drift of digital scales so no comments about beam scales).
With more sensitive higher resolution digital scales verified by check weights down to 0.03, 0.06, 0.08, 0.1+ gr, there persists the issue of zero drift of digital scales. And that's what this thread is about.
So what causes zero drift and can it be resolved?
In the "Myth Busting Digital Scales - 1 mg Analytical Lab Scale" and "Fine tuning an 'analytical/lab' digital scale" threads and other digital scale threads, we learned that strain gauge or load cell are used for digital scales.
VEVOR Analytical Lab scale with FA DS-750, Gemini-20, WAOAW and Ohaus check weight set along with Dawn container for perspective comparison.
Load cell of VEVOR digital scale
Cause of zero drift - What I found during my resolution of Varget down to single kernel testing is that digital scale zero is influenced by internal/external factors that affect the sensitive load cell:
- Counter/bench top surface not level or stable
- Operating scale outside of manufacturer specified temperature range (typical 59F-95F but check your manual)
- Warm up of scale as electronic components/IC board temperature increase
- Scale housing construction the load cell/base is attached to
- Movement of air around the scale
- Any source of magnetic field
- Some claim fluorescent light fixture ballasts (I only use LED lighting in the house with no noticeable effect on zero)
- If battery powered, low battery
- Defective digital scale
Solution options to reduce/eliminate zero drift:
I highly recommend use of check weights:
$15 Aluminum (Down to 10 mg/.15 gr) - https://www.amazon.com/American-Wei...rds=scale+check+weights&qid=1629058966&sr=8-2
$82 Ohaus ASTM Class 6 stainless steel - https://www.zoro.com/ohaus-calibrat...edirectid=16290592283668228270010070301008005
$158 NIST Class F stainless steel - https://www.amazon.com/Rice-Lake-Stainless-Calibration-Weight/dp/B006MWG13U/ref=sr_1_2?keywords=CERTIFIED+calibration+weights&qid=1552671682&s=industrial&sr=1-2&th=1
- Stabilize and level counter/bench top surface
- Use digital scale within manufacturer specified temperature range
- Allow sufficient warm up of scale until zero drift is minimized
- Verify accuracy/repeatability of scale with check weights (NOT HEAVY CALIBRATION WEIGHTS)
- Check to see if zero drifts when four corner of more sensitive scale feet/mounting screws are pressed down - If so, adjust screw tension until zero drift is reduced or not affected.
- Close door/window/vents to reduce air movement. Use dome/cover over scale if air movement cannot be eliminated.
- Remove sources of magnetic field (In my case magnetic tip screw driver but also cell phones, speakers, etc.)
- Turn off fluorescent light fixture ballasts or use LED light source
- If battery powered, replace with fresh batteries
- If all else fails, replace digital scale (Contact customer service for replacement or get a different scale)
This is where I took member jmorris' practice to heart and disassembled the scale.
If you look at the above picture, you will notice that load cell is attached to the mounting plate with four screws which was crucial key to fine tuning this scale to reduce/eliminate zero drift -
https://www.thehighroad.org/index.php?threads/fine-tuning-an-analytical-lab-digital-scale.876547/
What I found was any touch or slightest pressure on the four mounting screws changed the reading along with any pressure above four corner adjustable feet of the scale. Then the light bulb went on and I realized as temperature of the scale increased in relation to the ambient temperature, there could be unequal expansion of plastic parts/base to exert uneven pressure on the load cell mounting plate.
So when I loosened the screws and tightened again until touch/pressure on the four screws/adjustable feet did not produce change in reading, my zero drift essentially disappeared.
So then I eagerly disassembled my other digital scales only to find that strain gauge/load cell were not readily accessible. So, if you have digital scale with load cell mounting plate that is accessible, you can check to see if mount screws can be adjusted to reduce/eliminate zero drift. If not, apply all the other listed solution options to reduce or eliminate zero drift.
So is this myth confirmed or busted? Do digital scales' zero drift?
Confirmed, but not necessarily due to the scale and there are many internal/external causes which can be resolved.
Only as the last resort, is the digital scale to blame and needs replacement.
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