So I need to build some type of scale where one can place four 600mL beakers on it and measure out its weight down to a milligram level of accuracy. I'm doing this so I can dose a very small amount of liquid (2 microliters) into the beakers at a time. The problem is that load cells and essentially all resistance based force sensors are only accurate down to ~.03 - .05% of their fullscale load (at best). I've looked into piezoelectric sensor solutions but it seems that they are ill suited for detecting static loads.
I'm completely open to having 4 seperate scales but the problem of having an accurate enough load cell will still exist.
Is there any way to detect changes in weight to this level of accuracy? Any suggestions?