Actual Resolution of ACS712: How small can we measure

The ACS712 is very popular ic used to measure alternating current (ac). It comes in three variants which can measure ±5, ±20 and ±30 peak to peak current. Following specifications are important for calculation of minimum current that can be measured by ACS712.

Part Number	Optimized Range, Ip (A)	Sensitivity (Typ) (mV/A)
ACS712ELCTR-05B-T	±5	185
ACS712ELCTR-20A-T	±20	100
ACS712ELCTR-30A-T	±30	66

Here, consider ADC resolution of an Arduino 10-bit, which is 1024 in decimal.

Mostly, ADC reference voltage for Arduino is set to 5V.

So, minimum voltage can be measured by Arduino is,

5/1024 = 4.88mV

Therefore, actual minimum current can be measured by Arduino (considering ACS712ELCTR-20A-T) is,

(4.88) / (100) = 0.0488 A peak-peak = 48.8 mA peak-peak

The RMS value of minimum current can be measured by Arduino (considering ACS712ELCTR-20A-T) is,

(48.8 mA peak-peak) / (√2) = 34.5 mA

Results: 

Table: minimum peak-peak current can be measured using ACS712 for different ADC resolutions.

Sensitivity (mV/A)	For 12-bit ADC (mA)	For 10-bit ADC (mA)	For 8-bit ADC (mA)
185	6.6	26.4	105.6
100	12.2	48.8	195.3
66	18.5	73.9	295.9

The maximum RMS value for optimized range can be calculated from following equation:

RMS = optimized peak value / √2