jerry,

for a 7190, 16 bits of resolution is GOOD. since you say that your pcb is good, i will give you the other ways to increase resolution-

the conversion frequency is inversely proportional to noise in the output result. so you should choose a frequency so that the notch filter in the ADC corresponds to the supply freq.

another method is to use averaging. you can for example set the freq to 100Hz and take the average of 100 samples to get one reading /sec. or you could put the freq to the least freq, (say 5Hz ) and use a moving window averaging technique.

the above method can give you a boost in the useful resolution but is recommended only for slow input signals such as from a loadcell or a strain gauge.

kodi