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| How to use load cells, weighing very small mass |
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| ptricks:
I need to either build or purchase a scale for weighing small amounts 1-50 milligram. The retail scales I see on places like amazon seem to be okay down to about 500 milligrams. I have never used load cells before and am not sure they are the best option or if there is another tech , resistance based, capacitance ? We have a dog that requires medication that is not sold in her weight so we have to cut the pills and the pills shatter no matter how we cut, tried all the pill cutters. The dog is epileptic so if the dosage is off because the fragments we use are not enough she will still have seizures. There is a liquid version of the drug but it is 20 times more costly . The vet is at a loss on how best to do it except if there were a way to reliably measure the dosage of the cut pills, which is why the scale is needed. I know that industry has to have a way but that is probably expensive compared to what I can afford so hoping for alternatives. |
| GeorgeOfTheJungle:
https://www.amazon.com/milligram-scale/s?k=milligram+scale This one is 0.001g accuracy: https://www.amazon.com/Homgeek-Milligram-Calibration-Tweezers-Weighing/dp/B071GYVQF3 |
| Kleinstein:
There are relatively affordable (e.g. $20-50 range) small electronic scales available, made for something like coins. Going down to 1 mg resolution would be tricky though - best chance there would be a used scientific one, maybe an old style mechanical balance the weights. Building a mechanical balance is also possible DIY - so no electronics. Small range weights can be cut from wire reasonable good. For a DIY solution one could consider using the magnetic compensation - so the sample force is compensated by a mechanical force. There are a few instructions around to reuse an old analog meter movement for very tiny masses (e.g. a hair) - so may be 1 mg full scale. For the larger range there are DIY instructions based on a speaker. Another option is using a suitable spring (e.g. a strip if thin metal) and detect the deflection the capacitive way. Measuring with high resolution usually need an draft shield. If the medication can be dissolved in water - this may be an easy way to divide things down to very tiny fractions. |
| ptricks:
--- Quote from: GeorgeOfTheJungle on November 06, 2019, 04:17:19 pm ---https://www.amazon.com/milligram-scale/s?k=milligram+scale This one is 0.001g accuracy: https://www.amazon.com/Homgeek-Milligram-Calibration-Tweezers-Weighing/dp/B071GYVQF3 --- End quote --- Not accurate at small doses. If you read the reviews the lower the mass the less accurate it gets. The majority seem to be that way, probably all using the same internals. |
| ptricks:
--- Quote from: Kleinstein on November 06, 2019, 04:21:40 pm --- For a DIY solution one could consider using the magnetic compensation - so the sample force is compensated by a mechanical force. There are a few instructions around to reuse an old analog meter movement for very tiny masses (e.g. a hair) - so may be 1 mg full scale. For the larger range there are DIY instructions based on a speaker. Another option is using a suitable spring (e.g. a strip if thin metal) and detect the deflection the capacitive way. Measuring with high resolution usually need an draft shield. --- End quote --- Not sure how I would use the analog meter as they are so delicate in the movement but I can also see the benefit to using something that easy to move. The speaker is an idea if I could find one that has the right characteristics. Metal and the deflection is another idea. Thanks |
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