How to build a precision 0-50g balance

[mdamdam]

build a balance piezo

Hi all,
I am looking for infos about building an electronic weighing machine.
I dont know the principle used on small letter balance ?
Is it based on strain gauges, piezo, resonnant device ???
Where can i find sensor for weighing small devices of approx D=3cm and 25g
with a precision of 0.1 g

Thanks

MDamdam

 

[eda4you]

Hi all,
I am looking for infos about building an electronic weighing machine.
I dont know the principle used on small letter balance ?
Is it based on strain gauges, piezo, resonnant device ???
Where can i find sensor for weighing small devices of approx D=3cm and 25g
with a precision of 0.1 g

Thanks

MDamdam

I can remember Analog Device has an app. note designing a weighing machine with prec. of 0.1g. They also demonstrate it in the converter seminar. They are using a bridged transducer (load cell -- cost $200 !!) and a bridge ADC --> AD7730. I'm sure you will find the app.note on their www.

 

[luc2002]

take a look at this **broken link removed** and change the load cell with a lower maximum capacity.(source codes available also) Another personal ideea is a speaker withouth membrane (or 3 speakers in triangle 4 stability)used as a magnetic suspension for the unknown weight . the driving current is directly proportional with the weight .. "0" point is opticaly detectable ... high precision can be achieved ... mechanical construction is the key .... and don't forget to "hide " everything in "aquarium", away from dust and vibrations...good luck

 

[mdamdam]

Thanks all,
those circuits are intersting but my main problem is to find small sensors in the range of 0-50g ...
Most of time I find load cells for a range of min 0-5Kg .... difficult to achieve the 0.1g in this case :?
I have heard about piezo devices principle but cannot find the component.

MDamdam

 

[guysk]

WPI has load cells in the 10g, 100g, 250g, etc. The FORT100 is probably the what you are looking for. Check it out at: **broken link removed** . Combine the AD7730 with the FORT100, along with good board design techniques, and you should get better than 10mg resolution.