How do I measure Newton with an accuracy of 0.02mN? - Page 1
Forum section: electronics / beginners

author: seyedsaeed
author_rank: Regular Contributor
timestamp: June 02, 2020, 09:23:29 am
content: HiHow do I measure Newton with an accuracy of 0.02mN?I use load cell 200 gram and ADS1232But I only reached accuracy 0.1 mNhttps://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwik9_6k5-LpAhWEqHEKHXaGCiMQFjAAegQIAxAB&url=http%3A%2F%2Fwww.phywe.fr%2Findex.php%2Ffuseaction%2Fdownload%2Flrn_file%2Fbedanl.pdf%2F12110.00%2Fe%2F1211000e.pdf&usg=AOvVaw14vHXR9apCCFXpjXvnCWXE

author: Domagoj T
author_rank: Frequent Contributor
timestamp: June 02, 2020, 09:53:21 am
content: The device you linked has 0.035 mN resolution, so it's not suitable for your application.I would also be concerned with Drift < 0.5 mN/min spec.

author: seyedsaeed
author_rank: Regular Contributor
timestamp: June 02, 2020, 10:27:22 am
content: Quote from: Domagoj T on June 02, 2020, 09:53:21 amI want to design it myself with 0.02mN accuracy

author: Domagoj T
author_rank: Frequent Contributor
timestamp: June 02, 2020, 05:29:15 pm
content: Maybe this could be a start for your project:

author: splin
author_rank: Frequent Contributor
timestamp: June 02, 2020, 06:53:25 pm
content: Quote from: seyedsaeed on June 02, 2020, 09:23:29 amLevers. Make a 1m long beam pivoted at one end; fix a nail into the bottom of the beam at 1 CM from the pivot point and use the nail to apply force to your load cell. Any force applied at the end of the beam end is therefore multiplied by 100cm/1cm = 100x at the load cell. If the force you are measuring is in a vertical direction, extend the beam on the other side of the pivot and apply a counterweight as required to ensure the resting force on the load cell is within its limits. If the force is horizontal then let the beam hang vertically.Scale up or down according to the desired accuracy and sensitivity, allowing for how accurately you can measure the distances (in particular the centre of the area of the object applying the force being measured) and how low you can make the pivot friction. It is important that the force is applied to the load cell at exactly 90 degrees; similarly the force to be measured must be applied to the end of the beam at 90 degrees to the beam otherwise part of that force will be applied to the pivot rather than the load cell.Also be sure to calculate or estimate the magnitude of all the error terms. For example, I suggested a 100x force multiplication using distances of 10mm and 1000mm from the pivot. That effectively increases the sensitivity of the load cell by 100x but the downside is the increased accuracy of those distance measurements. A 1mm error in the 10mm measurement creates a 10% error in the force multiplication ratio.

author: Rick Law
author_rank: Super Contributor
timestamp: June 03, 2020, 02:22:43 am
content: What happened to your other project "measuring temp with 0.01C resolution ?"Quote from: seyedsaeed on April 11, 2020, 10:41:31 amThe sets of problems you will likely run into with either project are going to overlap a lot. Both are sensor and electronics, and both require a good design set up designed to measure with high accuracy; and both are ambitious.It may serve you well to stick with one before you start the other:- work out the problems,- solve those that can be solve- identify those that you must accept and understand why that is the limitation of your system/design.Whether you choose the temperature project or the mN project as first of the two, the design of the second will greatly benefit from the experience of the first project.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: June 03, 2020, 04:08:24 am
content: You'll learn very quickly that an electronic balance is not just a load cell, an A/D converter and a display. Drift and temperature correction must be done in software with hints from real temperature sensors. If you take an inexpensive balance and very slowly add weight to it, you'll find you can trick it into thinking it is drifting rather than sensing a weight change. Some balances have a "stable weight" and zero indicator; when they're in this mode the balance is most likely assuming it is drifting when the data coming from the A/D converter changes.

author: seyedsaeed
author_rank: Regular Contributor
timestamp: June 04, 2020, 08:28:17 am
content: Quote from: Rick Law on June 03, 2020, 02:22:43 am