TNP #46 - Torbal AD60 Precision Balance (0.001g) Repair, Teardown & Experiments

[@foobarables]

I've read that back in the days mathematicians used precision scales to perform integration by plotting the graph on a piece of "precision" paper then cut it out and place it on a scale. This one would be perfect for something like that. Really wonderful mechanism.

[@KallePihlajasaari]

Yep, an A4 sheet of printer paper weighs 5g nominally. I would use plastic if doing this to achieve high accuracy though because paper absorbs moisture so one would have to weigh a known sample of paper that is in the same state as the cut out shape.

[@madPac34]

Analytical chemists also used it to integrate the peaks on chromatographs when they where still scribed onto paper

[@zebo-the-fat]

many years ago I worked in a lab with a similar balance, I was always amazed that you could weigh a scrap of paper, make a mark on it with a pencil and then see the weight of the extra graphite on the paper!

[@shazam6274]

Fixed it! Now you can take a deep breath for a sigh of relief. No, wait, Acetone! Never mind.

[@wiwingmargahayu6831]

amazing machinery sir

[@wtf028]

What an interesting fix. The broken piece is a flexure, a part to isolate rotational movement in a lever system which amplify the mechanical movement. Any changes to these parts will affect linearity or placement error (large measurement difference when item is place off center on the pan).

[@_droid]

I was under the impression that high precision scales like that require a sealed enclosure because air movement and temperature can change their readings. That one looked really stable out in the open. Neat

[@kanetw_]

They're stable out in the open without anything on it. Not so much when there's stuff on it that can be affected by wind currents.

[@Volcanoelectricity]

Actually I have a similarly high precision scale, (0.0001g) I got as a neat repair attempt. If you put it on a stable bench, have no fans running anywhere in the room, and don't move anywhere near them they're perfectly capable of giving you stable readings. But that usually isn't possible in a lab with active climate control, or other people working. If your alone in your own workshop however, no problem!

[@Thesignalpath]

You can actually buy a dome for this one!

[@jhonbus]

@@kanetw_Even if what you're measuring isn't big enough to be significantly affected by air currents, the measurement can be thrown off a lot just down to the pan size. In tiny jewellers' scales it's not so much of a problem, but a lab balance like this has a much larger pan so tiny pressure differentials can make a big difference. Say this balance has a pan area of about 0.01 m^2, a one Pa pressire difference will exert a force of 0.01 N, equivalent to a mass of 1 gram. Considering that's a pressure difference of 1/100000 atmospheric pressure, it's very significant.

[@kanetw_]

@@jhonbus you're not going to get pressure differential in a room like that. 0.2 m/s airflow (realistic limit for air speed indoors) will cause an error of 25mg in your situation (0.01m2 area) -- if the force is normal to the plate. It's not as airflow is rarely vertical.

[@Darkknight512]

Always really satisfying with any instrument, to be able to put a test input and just see exact values show up for ANY of the test inputs.

[@dogastus]

Nice demo using evaporation.

[@craigs5212]

Eons a a go in college chemistry we used precision balances to weigh samples. You just added on the weights on one side and your sample on the other. You had to shut the draft door, and wait for the thing to settle out then add or remove weights, took for ever to get three readings. In one lab they had a couple of Chainomatic scales that used tiny chain links as the test weights. A mechanical counter kept track of how many links and thus your weight, very high teck for the time.

[@mxskelly]

very funny how just today I had to install multiple precision scales in coating machinery with those bubble levels and had to get them all perfectly level! I didn't know that was a thing before today, very cool stuff!!

[@glasslinger]

Big time luck out! There could have been so many HORRIBLE problems with it that would have made it almost impossible to repair! I would like to see the effect of a slight tilt on the accuracy. (move the bubble just to the edge of its range)

[@zetasyanthis]

That acetone demonstration was really cool! Thanks for the idea! :D

[@davidgustafik7968]

Thanks for another great video! Funny thing, I have a similar 50g scale, also made in Poland, also 0.001g resolution, but made by a different company (AXIS). The electronics inside are old (Intel 8052 processor, ADC with an LM399 and other goodies), but the mechanics of the scale are very similar.

[@mogoreanu]

Cool repair, thank you

[@SzymekCRX]

Wow, that was amazing to watch and learn :) That kind of videos would definitely bring even more audience to this channel ;)

[@lasersbee]

That was VERY interesting... Thanks for the additional info..

[@t1d100]

Yes, more repairs, please.

[@megejaslt]

About 10 years ago I repaired some similar precision scales and there was my first meeting with LTZ1000. Firs of all I thought it was bad because it was hot :)

[@autolancegega599]

Nice video, I worked on loadcells, carrying several hundred tons to a few hundred Kgs, never seen a electronic weighing scale for so small weights with such high precision . Nicely explained loved it .

[@prbmax]

I remember where I worked they had a lab of which I didn't work in but the scale they used had a glass cage with a door to eliminate air currents effecting the measurements.

[@NiHaoMike64]

Reminds me of college chemistry class where I actually asked what to write down for the mass of a liquid since it was constantly "counting down".

[@SeanBZA]

Have a similar mass reference set, and a cal cert for all of them. Error as you get smaller is larger, along with uncertainty, but the milligram pieces are all given to 2 decimal points, and the larger ones to 3 decimals, except the 1g mass, which is 4 decimal points. Yes I do have a very old Oetinger massmeter that is capable of showing the mass of those, down to the 0.1mg mark. Been repaired, the mains schaffner filter let out the magic smoke, and was replaced with 2 small chokes, as this unit has a mains transformer anyway, and is nearly a half century old, with a VFD readout.

[@jimturpin]

Thank you for the video. I found one of these scales in the garbage of a company that had moved out, after getting it home and researching it, found it was supposed to have a bell jar over the top to shield it from air drafts. It was really sensitive too, it could sense and measure the weight of an eyelash dropped on it and I was wondering how it achieved such sensitivity.

[@bossecarlberg]

very nice

[@stazeII]

Used to use scales like this in chemistry. Generally they had a box over the top to prevent air disturbance from impacting the balance. Pretty cool to see the interior. And yeah, guess someone overloaded it or just dropped/set it down too hard. Pretty cool.

[@thomasw6169]

Had to get one of those right away after seeing the video. Very inspiring.

[@graealex]

Oh, that's why the label on the device is "balance" and not "scale". Technically that would be a "servo balance"?

[@kanetw_]

I tore apart a microgram balance from a broken TGA (thermogravimetric analyzer) a while ago. Unfortunately multiple critical parts failed (it's been a while so I forgot which) so I scrapped the entire module as it's not worth attempting to repair.

[@JohnGotts]

It's amazing that you can now buy 1 mg resolution scales for ten to twenty bucks. I have one and it works great.

[@snik2pl]

I have a scale from 1992 that has same electromagnetic type of sensor. It was broken the same way. One of links snaped. Mine is d1g and I thought this electromagnet was used because it's old and resistive gauges were not good for resolution or expensive but 0.001g is nice

[@VictorSilva-rq4kz]

Shahriar, I wish you would post the price that you paid for your items. You say a good deal, but what is that? I have always wanted a high precision scale in a glass enclosure (0.0001grams). They are so easy to damage, I wonder if the scales in the glass enclosure use similar technology to this.

[@Thesignalpath]

I paid $116 for this one including shipping.

[@SeanBZA]

Yes the more precise all use force balancing, because it is the only thing that is sensitive enough, and repeatable enough. A 16 bit DAC to operate the current source, along with another 8 bit one to set the range of the current source, with the optical sensor running into a very stable ADC to read the light level. The LED is driven with AC normally, so as to allow a synchronous rectifier to sample the amplitude, so as to reduce temperature drift in both the LED and photodiode down to a much smaller level, as you are now looking at deltas rather than absolute values. That is the reason they also have temperature sensors on the head, and on the sensor, so as to allow only valid readings within a certain temperature range. They do really like a constant temperature, preferably managed within 0.1C by the instrument, and normally are mounted on a plinth, or heavy concrete foundation, isolated from the rest of the floor.

[@GTechno13]

Did anyone else notice the interference in the microphone when his hand>tweezers>weight>plate were all connected? Something to do with the electromagnet?

[@danmenes3143]

Interesting that it is literally a "balance." I was expecting it to work more like my (reasonably good quality) kitchen scale, which measures the distortion in a support beam by observing the change in capacitance between two parallel plates.

[@filipozimek8281]

So actually what is being measured in this device? An output signal from a PID controller that is driving a magnet?

[@Thesignalpath]

Yes - the control signal from the PID controller which stabilized the balance.

[@46I37]

It would be great to do a teardown on the mechanics to see what all the hinges do and how the electromagnet for force balancing works. Does the photo diode look for a maxima? Is there mechanical damping? What the DAC resolution for driving the electromagnet?

[@InXLsisDeo]

Then it's impossible to recalibrate if you are even capable of building it again.

[@46I37]

@@InXLsisDeo A sacrifice worth the education though! Recalibration could part of the adventure!

[@der.Schtefan]

I am a bit confused. I thought precision scales like a 0.001g jeweler's scale from Amazon are much simpler to implement and cost 20 USD on Amazon? What is the difference here?

[@Thesignalpath]

This is a balance, not a scale. The cheap scales from Amazon are based on strain gauges. They have poor accuracy, repeatability, linearity and stability particularly for small weights.

[@gacherumburu9958]

👍👍

[@maximanikeev5914]

👍

[@karlbesser1696]

I need a scale that reads accurately to one microgram because I'm currently on a weight loss diet.

[@NiKolyan96]

Если ацетон нагреть немного сильнее, то при испарении он должен создавать реактивную тягу и вжимая - компенсировать утрату веса через испарение.

[@aliemlek]

👌👌👍👍

[@rosskappa5410]

Thank you, very enjoyable video and I'm curious about something. How did you know about the working principle? Is this a common knowledge that can be found with research or did you do some other intricate research or reverse engineering?

[@Thesignalpath]

It is by observation - this general technique is the foundation of many types of measurement techniques.

[@godfreypoon5148]

0.001g? That's torbal!

[@largepimping]

* mass, not weight 😁

[@tommihommi1]

no, weight

[@ionstorm66]

The instrument uses an electromagnet to counter the force of gravity. Thus it measures weight.

[@ikocheratcr]

You can only convert to mass, if calibration is verified and passes at the location the device will operate, but still call it weight.

[@largepimping]

Interesting. The display on the device shows grams. Grams are now a measure of weight - filed under "good to know." By the way, allow me to be really clear here - I'm just trying to start a "controversy" to help engagement...

[@SeanBZA]

@@ionstorm66 Your calibration is going to compensate for the local gravity force, though there is little difference in a relatively large area. However altitude has a larger difference, because the bouyancy of the reference masspieces will vary with altitude. I used to get on site calibration, but, as the test lab is almost the same altitude, and only 10km away, I used to also take them half of the units at a time for certification, and carefully pack them for transit, and then do the other half. Only thing done on site was the Avery personal weigher, which was used as parcel scale, and it only needed to be done every 5 years. Too heavy to move easily, and also had oil dashpots in it.

[@wolpumba4099]

*Summary* *Introduction to the Precision Scale and Initial Problem* - 0:07 Introduction to the episode: repairing a Torbal 860 Precision Scale. - 0:18 Scale specifications: 60g maximum weight, 1mg resolution. - 0:26 Scale condition: purchased without a power adapter, displaying an "Unload" error on startup. *Teardown and Inspection* - 1:31 Description of the internal structure and mechanical design of the precision scale. - 2:00 Observations of sensors, adjustment screws, and the analog board inside the scale. - 2:44 Discovery of a broken mechanical link causing the scale's malfunction. *Repair Process* - 3:49 Attempt to fix the broken link using soldering and a piece of nickel. - 4:22 Reinstallation of the repaired link and discussion of the scale's working principle. *Testing and Calibration* - 6:08 Successful zero reading after repair. - 6:15 Testing with a 50g weight shows accurate measurement. - 6:26 Testing with 1g and smaller weights confirms the scale's precision. - 7:03 Experiment to measure the evaporation of acetone, demonstrating the scale's ability to detect very small weight changes. *Conclusion* - 8:10 Closing remarks and appreciation for support, with plans for future repair videos. Disclaimer: I used chatgpt4 to summarize the video transcript.