I am looking to create a setup of 4 3-wire load cells like shown in this video. However, I'm having trouble finding a reputable brand that makes these; I just see tons of cheap Amazon versions. I know Adafruit makes the 4-wire bar style, but I need this setup of 4 load cells and I'm not sure if I can achieve that efficiently with the 4-wire style.
I'm looking specifically for something in the 3-10 kg range (for each cell) so I can have a better resolution at low weights.
Thank you! I see they have one three-wire load cell and I'm trying to figure out what the error is. The datasheet says the comprehensive error is 0.05 mV/V, but I'm not sure how to convert that into a weight value (e.g. +/- 0.1 kg).
Would you have any insight on this?
Pretending that "comprehensive error" should be translated as "combined error" then 0.05 mV/V = 5 parts in 10,000.
I would take the "repeatability" spec as representative, which for the Sparkfun load cell is 0.03 %FS. Decide what "FS" will mean for your project and take 0.03% of that as the typical error. For 50 kg FS, the repeatability error is .015 kg.
Thanks for the explanation. Repeatability is more along the lines of precision--I'm interested more in the accuracy of the sensor. Even if the measurements over time are consistent, there is still some amount of systematic error, which I'm trying to figure out.
So you're saying the "combined error" of the sensor (according to the datasheet) is 5/10,000 = 0.05% = 0.025 kg (assuming 10 V correlates to 50 kg)?
Accuracy depends on calibration, and nonlinearity. The nonlinearity error is comparable to the repeatability error. 0.05% combined error would be about right to take both effects into account.
Using combination of errors, sqrt(0.03^2 + 0.03^2) = 0.043.
The proof is in the pudding. Build it and then carefully calibrate the device with accurately known loads. In the process, the various errors will manifest themselves.
Yeah I assumed the given error was for perfect calibration. 0.025 kg sounds too good to be true, even with perfect calibration, but I guess I'll believe it after I build it lol
If you want precision you really need to go to 4 wire IMO, for that reason getting a 3 wire precision device is very hard . You can make a 3wire connection to a 4 wire cell by connecting locally to the cell , or ..
You can connect load cells together to give one output , common in weighing devices .