I needed to do some AC current measuring with Arduino, more accurately than with special AC current sensor I tested earlier. To do that measuring I bought Meeeno ACS712 Current Measuring Sensor Brick Module Board for Arduino. This is a picture of that module from dx.com:
This module is pretty easy and safe way to measure AC or DC current with Arduino. This module is based on ACS712 current sensor IC. Can measure current value of +/-30A. The output is analog output: 66mV/A. When there is no current flowing, the output is at half of the power supply (powered from 5V source means output is at 2.5V). The module is as such very suitable to be directly connected to Arduino sensor shield three pin analogue sensor connector.
ACS712 sensor IC used on the module is based on hall technology and it provides good isolation from the measured current to Arduino side. Hall technology means that device consists of a precise, low-offset, linear Hall sensor circuit with a copper conduction path located near the surface of the die. Applied current flowing through this copper conduction path generates a magnetic field which is sensed by the integrated Hall IC and converted into a proportional voltage.The internal resistance of this conductive path is 1.2 mΩ typical, providing low power loss. According to the ACS712 chip data, it provides quite fast operation: 5 µs output rise time in response to step input current and 80 kHz bandwidth (can be reduced with filter pin of needed). The total output error is 1.5% at TA = 25°C
ACS712 provides economical and precise solutions for AC or DC current sensing with 2.1 kVRMS Voltage Isolation. This isolation level allows the ACS712 current sensor IC to be used in applications requiring electrical isolation without the use of opto-isolators or other isolation techniques. This specific module has construction so that there is large insulation distance on the circuit board from measured circuit to output, so that high voltages can be measured safely (some other modules I considered dx.com had input and output sides very near to each other which will most likely not be safe at mains voltages). That 2.1 kVRMS Voltage Isolation and several millimeters distance from measured side to low voltage side means that it could be used for mains current measuring in applications where 2 kV isolation is enough (surge voltages lower than this and no dual-insulation needed). I plan to test this on overcurrent fault protection.
Verdict: Easy to connect to Arduino. Works well. Well constructed module. Reasonable price. If you need current measurement from few amperes to 30A with Arduino, check this sensor module.