GolamMostafa:
When the data sheet says that the response of ACS712 is: 66mV - 185V/1A current at the hor circuit, it means that the response varies sensor to sensor due to manufacturing tolerances. Therefore, the equation that is true for ACS712(1) that may not be true for ACS712(2). Do we have any better way of determining its gain and offset of the sensor without adopting the 2-point calibration philosophy?
The 66 to 185 is for the full suite of sensors...the 5A, the 20A, and the 30A. If you read the datasheet more closely, you will see that the 20A has a sense of 100 mV/A +/- 4 mV/A and a total output error of +/- 1.5% over the full range -20A to +20A.