Measuring femto Newtons - Page 1
Forum section: electronics / general

author: WattsThat
author_rank: Frequent Contributor
timestamp: December 13, 2022, 04:56:34 am
content: Wow, is this guy passionate about mass measurement

author: mendip_discovery
author_rank: Super Contributor
timestamp: December 13, 2022, 05:08:41 pm
content: I always enjoy these little insights into the national labs and the levels they go to.With the efforts they do it gradually makes the high end stuff become cheaper and then we end up with better accuracy all around.Sadly I just don't have the pocket money to buy any of this kit. A kibble balance even one made with lego would do.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 13, 2022, 06:45:21 pm
content: No, can't build that easily. OTOH, you can go far with some quartz rod and a good torch- build a microbalance based on very fine quartz fiber and it's almost perfect spring constant. You can also get way down with a quartz crystal scale- tiny things on the quartz crystal will change the frequency, and we can measure that with a fair bit of resolution.

author: mawyatt
author_rank: Super Contributor
timestamp: December 13, 2022, 09:13:06 pm
content: Quote from: Conrad Hoffman on December 13, 2022, 06:45:21 pmThat's the way some early contaminate aerosol mass detection devices worked. Filter airflow, pass over quartz crystal with highly selective holding film, measure frequency drop of crystal in oscillator compared to identical crystal not exposed to contaminate. This is basis for some older battlefield experimental chemical agent detectors.Best,

author: iMo
author_rank: Super Contributor
timestamp: December 13, 2022, 09:37:16 pm
content: We used to use crystals (oscillators basically) in the vacuum chamber for measuring the amounts of deposited materials (like atomic layers of something sprayed on the wafer).

author: TimFox
author_rank: Super Contributor
timestamp: December 13, 2022, 09:52:56 pm
content: Quote from: imo on December 13, 2022, 09:37:16 pmYes, that was amassmeasurement, as opposed to the video that seems to be aforcemeasurement (mis-named a mass measurement by the OP).

author: WattsThat
author_rank: Frequent Contributor
timestamp: December 14, 2022, 05:20:49 am
content: Quote from: TimFox on December 13, 2022, 09:52:56 pmThe video was both. I was quite interested at the beginning with the dead weight sets down to 10 ug and the sub-division concepts so, yup, I was thinking mass but they indeed ended up discussing force measurement which if I understood the kibble balance, it was measuring mass by using force.

author: guenthert
author_rank: Frequent Contributor
timestamp: December 14, 2022, 06:16:45 pm
content: Quote from: TimFox on December 13, 2022, 09:52:56 pmIt was mentioned in the video (in the same brief hand-wavey manner as in the documentation of the kibble balance I've seen) that they measured the local gravity (once) very precisely. Isn't that kicking the can down the road? How do you measure gravityaccurately?

author: TimFox
author_rank: Super Contributor
timestamp: December 14, 2022, 06:41:20 pm
content: Quote from: guenthert on December 14, 2022, 06:16:45 pmWith a Kater pendulum.http://www.hep.vanderbilt.edu/~velkovja/VUteach/PHY225a/writeups/kpend/katerpend.pdfI did this as a lab experiment back in 1969. The original textbooks showed measuring the periods by counting beats against a grandfather clock, but the physics department was proud of their new Hewlett-Packard counter (vacuum tubes and nixie display), so I used a photocell instead.

author: DavidKo
author_rank: Frequent Contributor
timestamp: December 15, 2022, 06:41:38 am
content: Quote from: mendip_discovery on December 13, 2022, 05:08:41 pmYou can use optical fiber for a home experiments. To measure its deflection you put another fixed fiber against it and measure the how much light is going through the system. Longer the free end of the fiber will be, more sensitive system you will have. You can also play with distance between the fibers.It is not hard to create the sensitive balance. It is hard to achieve the repeatability and calibrate such a device. That is also the main reason why weighting was long time based on comparisons with known objects. The reason why they use electrostatic force for measurements - you can create the system where you know the exact force that you have.Hardest thing is to achieve high resolution. It is still relative "easy" to weight 1ug, but hard to measure such a change in 1.2 kg object. Even the buoyant force need to be neglected by placement in vacuum.I recommend to look also to another video from another end of the mass measurement.

author: mendip_discovery
author_rank: Super Contributor
timestamp: December 15, 2022, 08:18:05 pm
content: Am I not the only person here who could watch a full on documentary series with the nutters at NIST and other NML. I always enjoyed the more informational heavy videos shown in science lessons. I soak up that info much easier than reading a book.On a the subject of those big weights I wonder if they could get that on a kibble balance.