ACS714 Current Sensor - Measuring 120V A/C

I’m working on an undergrad senior project that requires measuring the current draw on a 120V A/C line. I have the sensor circuit built according to the recommended schematic in the data sheet, and it seems to be working pretty well. I have the following question:

The data sheet claims the output response of the sensor is more or less proportional to the current - a higher current will yield a higher voltage, where 2.5V output is 0 A, anything less is negative, anything more is positive. However, the output from my sensor oscillates. It gives me a sine wave that increases in amplitude with higher measured current. Is this because I’m measuring A/C current? Is there any way to get the linear response?



First off, please make sure you are very careful with the 120V.

The sensor works from DC to many kHz, and if your current is fluctuating, the sensor will show that. I don’t think there is a “the linear response”, and when working with AC, there are various properties you might care about, such as peak, mean, and RMS. Depending on what your goal is, there are various ways of getting at those numbers. There must be circuits that can do it, but providing them is beyond the scope of what we can help you with (we can comment if you do most of the design and have specific questions). A more flexible approach would be to use a microcontroller with an analog to digital converter, and then you can do whatever math you want with the acquired data points. The quickest option, if you just need the results, is to connect an oscilloscope to the output and have it do the math for you.

- Jan


Thank you. I’m hooking it up to an Arduino and doing RMS math with that - haven’t quite got the math right yet, I’m still working on doing that for a good calibration. I’ll continue working and ask questions once I educate myself a bit more with this.