Ultra-precise milliOhm meter - Calibration and full assembly
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- Опубліковано 1 лют 2022
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This is probably my final video with this device because now I completed everything I wanted. In this video I show you the assembly process using a microscope camera, so you will see the soldering from a closer perspective. I decided to order more components and finish all four PCBs I had left after building the first device. I also did a "calibration" using a very precise 1 Ohm resistor. So now, as the instrument is "calibrated", it can be used with a higher confidence and credibility.
The circuit is based on the designs published by
@scullcomhobbyelectronics1702: a milliOhm meter and for a 6½-digit voltmeter. I "alloyed" these two project into one, designed my own PCB, then built the circuit.
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Resources: curiousscientist.tech/blog/ul...
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I think it is always a good idea to add area for one or two buttons into a project like this, even if you don't end up using them.
Using a button, you could tell the MCU that you have shorted the kelvin leads. That way it can read an offset resistance that the leads provide and subtract that from further resistance values, which might be helpful when you are reading down to milliohms. Then its also useful for providing a null offset if you want to measure a pure voltage with the ADC.
Thanks! Due to the x10 differential amplifier in front of the ADC, it is not really useful for voltage measurement, except you want to measure below 500 mV. Also, when I do the final calibration and adjustments I do it using the leads shorted. So they are also considered in the measurement.
Классная реализация знакомого проекта со знакомым акцентом )
Молодец!
Thanks!
scullcom electronics is a really wonderful creator. I hope he is doing alright, he made a lot of very useful and cleaver designs.
I agree, his videos are fantastic! I learned a lot from them.
Great build! x4 :)
That soldering third hand are awesome, I looked on your website for it but no luck, then just googled the name, a little bit on the expensive side but seems very well built
Thanks! Yes, they are called Omnifixo and it is a Swedish product. I really like them, they're very helpful. Not only for soldering but also for holding cables, displays, modules...etc.
Great Video's and very well explained , If you look at Louis Scully design he used 25 turn horizontal preset resistors for calibration where I see your using single turn horizontal preset resistors This could be the reason why you can't calibrate the zero and 100Ma current correctly ?, The PCB'S look great and nicely laid out
Thank you very much!
Yes, you are correct, the too coarse potentiometer might cause the issues. In fact I don't really know why I picked this type of potentiometer, probably because of its flat design. Obviously it was not my best decision. Luckily, if I am not wrong Vishay's T93YB, or Bourn's 3266W potentiometers can be used as an alternative and they should have the same footprint as the 3386P potentiometers I used. I will order a few 3266W and try it.
Where did you source LTC2400 from?
mouser.com