Ahhhh! So basically the same kind, just with way higher precision and the swiss-cheesy mechanism, as those homemade scales made from a speaker!
These usually had an op-amp driven feedback loop, where the op-amp input was from the optical gate that had to be half-shielded by a structure on the transducer, and its output was fed to the voice coil. This worked automatically. The weight was measured as the output voltage (or was it current?) for the coil.
This was from a magazine from 70’s or 80’s. All analog back then. Today a 24-bit ADC would be likely used.
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If you want to use it as a scale, and not merely a balance, the reference weights (masses) need to be calibrated.
Want some dry, esoteric reading? Look up the NIST cleaning standard for calibration masses.
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Exactly.
I have held a few jobs as a design engineer for various old-line New England metrology companies in different fields. After a while I realized that extreme precision and trustworthiness in measurements comes down to doing high-school physics types of experiments with very good controls.
(You might be right about measuring current and not voltage, though I guess they’d be pretty linear given a DC signal and a coil that didn’t have a non-linear resistance curve for anything that might change in the system.)
The coil heats up. Then you get issues with resistance-temperature dependence. That’s probably the reason for current measurements.
True re high-school physics. Few things are more complex.
That’s neither esoteric nor dry. I read it cover-to-cover as a snack. Nom! (And thanks.)
Here’s an interesting mathematical problem, then- given that the internal counterweights are 80, 40, 20, 10, 5, 2, 1 (twice), 0.5, 0.2, and 0.1g (twice), what reference weights would I have to weigh to verify that they’re all correct?
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