Slide 1 Slide 2 Slide 3 Slide 4 Slide 5 Slide 6 Slide 7 Slide 8 Slide 9 Slide 10 Slide 11 Slide 12 Slide 13 Slide 14 Slide 15 Slide 16 Slide 17 Slide 18 Slide 19 Product List
Weigh Scale Introduction Slide 10

One important specification for weigh scales is the number of counts. Counts denote the total resolution over which the scale is accurate. If the customer needs to measure 2 Kg and must have accuracy to 0.1 grams, then 20,000 counts (2 Kg divided by 0.1 g ) are needed. Analog Devices’ full scale voltage is 6 mV. So each 0.1g will be equal to 300 nanoVolts. If the noise is more than 300 nanoVolts, the system will not be accurate enough. So the maximum peak-to-peak noise that can be allowed is 300 nanoVolts. To convert the peak-to-peak noise into RMS noise, divide the peak-to-peak noise by 6.6. This gives users an RMS noise target of 45 nanoVolts. The RMS noise must be translated into bits of resolution. If the equation shown here is used [log (full scale voltage/noise)/log2] customers can calculate the resolution. If the user is looking for peak-to-peak resolution, 14.3 bits will be needed. However, if they are looking for RMS resolution, 17.1 bits will be needed.

PTM Published on: 2010-09-14