How a Wheatstone Bridge Works - DC to Daylight
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- čas přidán 4. 07. 2024
- In this DC to Daylight episode, Derek explains the basics of a Wheatstone bridge, how it works, what happens when it's said to be balanced, and how to use that information to measure an unknown quantity of resistance. In addition, he tries out measuring an "unknown" resistor using a fairly old Wheatstone bridge, so old that it's mounted in a wooden box and made of Bakelite plastic!
Naturally, Derek needs to check out what's going on inside this cool piece of vintage tech, so he does a teardown as well.
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#0:00 Welcome to DC To Daylight
#0:44 Wheatstone Bridge
#6:09 Teardown!
#11:30 Give Your Feedback
#wheatstone_bridge #wheatstonebridge #resistor #resistors #teardown - Věda a technologie
In the 1960’s and early 1970’s, I was a calibration laboratory technician in US Air Force PMELs (Precision Measurement Equipment Laboratory). When I worked in the electrical standards area of the lab, I used Wheatstone Bridges exactly like the one you used in your video. I also calibrated and repaired those used by Flight Line maintenance shops. They are very accurate when not damaged, but lack the precision of current digital standards. Using an external indicating device can increase the sensitivity, and therefore the resolution of the device.
Thanks Harry.. That must have been an exciting place to work! I would usually try to snag a digital piece of equipment to demonstrate some of these things, but I've found that reliability due to complexity takes a nosedive - especially when sourcing from eBay. I love that you used the same unit in industry and shared a bit of your history. Thanks again for your feedback! -Derek
Wheatstone bridge, in a (simplified) nutshell, it's what you use to measure resistance when you don't have a calibrated voltage source. Of course, there's much more it can do as well, but this is an easy one-liner to remember. More or less, it's what you showed in this video when you no longer trusted the batteries.
Great video. Well done.
That's a good point and useful one liner. Thanks! -Derek
A K3 Poteniometer was a similiar device from that era. Since you should not draw current from a standard cell (precision battery) you used the balanced bridge method (K3 POT) to measure precision dc voltage back then... I too, was a PMEL tech, but I "floated" on the big grey ships with numbers on their side. The "modern" rcl bridges ZM-11 and the like used the "green eye" instead of a galvo.... Enjoyed the video...
My father had a multimeter that used what I believe was a Wheatstone bridge to determine the values. There was a large wire wound rheostat that had the pointer knob attached to it. The circuit will connect to a vibrator that will make a buzzing sound into a pair oaf headphones and the value was found when the knob was turned to the null point. This one measured DC volts and resistance. it was made for the visually impaired people.
Dave Jones wouldn't like those 90 degree angles - "All the electrons are gonna fly off!" LOL - but I love it. Clearly whoever assembled that took some pride in his work.
I love this kind of old test gear, but I wonder how well it compares to modern cal equipment or even a basic DMM.
Nothing beats modern equipment, but when it comes to $$$ of precision gear, old fundamental gear is a good close second. There's a video out there, I think it was Bil Herd, that characterized the electrical characteristics of sharp 90 deg corners in traces.. The electrons may not go flying off into space as DJ says, but I think there are parasitics that are actually a real thing! -Derek
@@AmRadPodcast Sure, there may be parasitics that could even become significant at higher frequencies (Bil Herd's niche is digital IIRC, where rise times can have transients approaching daylight), but would it even be measurable at the DC end of the spectrum where a Wheatstone bridge operates?
@@petersage5157 at DC no... I was thinking fast transitioning digital signals.
Oh boy. This takes me back to the school physics lab in the 60s. Except the variable was a meter long resistance wire over a boxwood ruler with a handheld insulated brass 'pointer' and the ratio was determined by where a null reading on the galvanometer was measured on the ruler. No touching anything else but the insulated part of the pointer.
That would have been a fantastic demonstration! However, I just can't "resist" test gear in a wooden box. -Derek
You can definitely see the green corrosion. I can almost smell the grease
from here!!
Then I did my job!
Let me just find that like button first, then I'll watch. 👍🏻
I remember the teacher at school told us not to measure the impedance of the powergrid with the expensive wheatstone bridge. That was already tried by a student in the past.😂
I have similar stories from my high school electronics classes.. including questionable demonstrations by the faculty, but I'll leave those stories for off the record opportunities. -Derek
Love all the old measurement hardware out there. More videos on stuff like this please. Bonus points if it's an electromechanical tool used to measure some kind of values on a circuit. That probably a pretty rarified subset of tools but they do exist.
Yes! I'm going to try to pull in old gear that demonstrates the concepts... especially if it comes in a wooden box and has bakelite knobs! -Derek
@@AmRadPodcast yes, I love those old Bakelite knobs that have been curing for 70 years. They have a texture and weight all their own. It's neat to see how the measurement instruments were used to make the next generation of tech, which was then used to make the next generation of measurement instruments, which is used to make the next gen of tech...and so on, hopefully ad infinitum. I just finished reading "The Chip" by T.R. Reid which documents the history and implementation of "the monolithic idea", which is the concept of putting not just transistors, but capacitors, resistors, inductors, wires, and etc all on the same silicon chip, aka the microchip or integrated circuit. It's an interesting read. But in that book he talks about how prior to the IC the calculations to actually create the first IC were done either with a slide rule or vacuum tube computer. More often the former as it was close at hand, although slide rules only offer approximations. Anyway, after the IC came out, Jack Kirby, one of the co-inventors of the monolithic IC (shared this distinction with Robert Noyce, cofounder of Intel) started to work in the first smash hit device to use an IC, the handheld calculator. So he had to use a slide rule to develop the calculator, and then the calculator can (and was) used by future engineers to create the next generation of progress. People don't really talk about instrumentation used for invention and experiment that much but they are very important. I almost lose my breath when I look at some of the early hand built HP instruments, they are beautiful in their design and optimization! Anyway, thanks for reading my ramble to its destination!
I love your nerd videos. Keep these coming!
I love being a nerd, and I will do my best! -Derek
Why is the Wheatstone Bridge important in sensors and instrumentation?
Funny you ask! The wheatsone bridge leads into the next video where I'll put it to use. -Derek