Other Parts Discussed in Thread: ADS1232, ADS1262, ADS1232REF, , INA163
I'm working on a project similar to a weigh scale. The sensor is a 300 gram load cell with 1mv/v sensitivity. My plan is to use ADS1231 and take advantage of 24-bit measurement with internal gain = 128. AVDD, Vref, and bridge supply will all be from same voltage = 5V.
The most difficult part is that i require very fine resolution, 5mg. Of course this should all be achieved at the lowest cost.
Before each use, the product will be calibrated at 3 points, zero, ref mass 1, ref mass 2.
My original plan is to connect the bridge output directly to the ADS1231 and use the internal 128v/v gain. My calculation shows i get 5mV output per 300 grams (16.67uV per gram before internal gain). At 5mg, load cell output is 83nV! This is very small and i think may not be possible.
Is sensing directly by ADS1231 in a single stage the best option?
As i mentioned, the unit will be frequently calibrated. Is there an advantage to using different voltages for VREFN and VREFP, for example VREFN = 1.5V and VREFP = 3.5V? It seems this would give 24bits over 2V instead of 5V.
Should I add an Inamp with gain and use a different ADC with less internal gain to improve upon the resolution?
I searched through a few app notes. TIDLBU0A seems similar, but my resolution requirements are more difficult. Any advice is appreciated.