Hey guys! So I have this ACS714 board made by Pololu: http://www.pololu.com/catalog/product/1187 After spending some time with it, there are a couple of things I don't quite understand....
First of all, the output fluctuates. For example, when I apply a constant 2A of current across the terminals, here is what happen: Then I hook up an oscilloscope to the output, and here is what happen: Note that the Delta_V is 248mV. I figured this might be the problem as the ADC on the Arduino has a sensitivity of 5V/1024=.0048V=4.8mV... But this doesn't add up either because the Delta_V on the oscilloscope is 248mV, which represents 248mV/4.8mV=52 digits of fluctuation. I am only getting 4 digits of fluctuation at most (from 175 to 179). So what exactly cause the fluctuation?
I tried a software approach by using a for-loop and take 100 samples and then the average. The final value still fluctuates by around 2-3 digits. So I decided to look for a way to reduce the noise from the output pin. According to the website, there is already a RC low pass filter implemented on the board, but as you can see, I still get a lot of noise to a point that it affect the ACD reading. I am wondering if it is possible to build another filtering circuit at the output pin to further reduce the noise? If it is possible, what kind of circuit can be use to filter the noise?
Last, I am intended to use this sensor for sensing a 100V DC source. If I am understanding it correctly, this hall effect IC can achieve isolation for up to 2.1kV at its current path (pin1+2 to pin3+4). But, basically the Pololu website states that if the voltage is higher than 30V I will get killed: "Warning: This product is intended for use below 30 V. Working with higher voltages can be extremely dangerous and should only be attempted by qualified individuals with appropriate equipment and protective gear." Now I am confuse. What exactly is restricting the voltage from go over 30V? Is that an issue with the board or the IC? Cause I can't find this limitation on the data-sheet of the ACS714 IC. http://www.pololu.com/file/0J196/ACS714-Datasheet.pdf If it is an issue with the Pololu board, what area should I pay more attention if I am to make on own PCB using the same IC that can enable me to sense a 100V DC source safely?
Any input would be appreciated!