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(FREQUENTLY ASKED QUESTIONS)
Q: How can one determine of the direction of the current for AC current using a Hall Effect Transducer?
A: There are a few methods to determine the direction of AC current flow
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(1) Acquire the waveform of the AC Voltage and AC current to see if the current is leading or lagging the Voltage. This is also called “determining the phase angle” between the two waveforms. One simple device that can acquire this data is LabJACK U12 USB data acquisition box. It can measure 4 channels in differential mode (Differential means that two channels are used to get one high quality measurement). This LabJACK device comes with free data logging software and O-scope software with a sampling rate of over 6,000 samples per second. Plenty of speed when looking at 60 Hz AC. The LabJACK also comes with free LabVIEW drivers so you can customize the software to your liking using LabVIEW.
Measuring the current is easy with this method using one of the Hall Effect current sensors sold on this website. They have a -8V to + 8V output range that the LabJACK U12 can easily monitor. The challenge is condition the AC Voltage signal so that it is scaled down to within a -10V to + 10V Range for the LabJACK . One most also have a way to provide electrical isolation between the AC voltage source and the LabJACK / Computer you are using. To do this one can use a simple AC to AC doorbell transformer thac converts 120VAC down to 16V AC. Like this one: [amazon text=Transofmer&template=my favourites&asin=B001G0MB46] Then use a simple voltage divider to divide the Voltage down in half so that it can be monitored by the LabJACK USB data acquisition box.
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(2) Another method is to use a cheap arduino microprocessor that monitors the zero cross over points for Voltage and Current, subtract the time between the two events which will allow you to determine if the current is leading or lagging the Voltage. For this you will also need to provide AC voltage isolation through a transformer and divide it down to a 5V level so the Arduino can monitor the signal without being damaged. You will also need to use an AC Current sensor to input into the Arduino. You will have to divide the voltage down from the current sensor so it falls within a 0 to 5 Volts range. The current sensors on this website such as the H2A-ACDC-72-MK can do this. (See owners manual here)
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(3) One can use a specialized chip and circuit board that is designed to analyze AC power like the Maxim 78M6613 Single Phase AC Power Measurement IC. This chip is mounted to an evaluation board here: http://pdfserv.maximintegrated.com/en/an/UG5297.pdf This board can measure up to 20 Amps and provides some electrical isolation from your computer so it does not damage your computer when you hook AC power to it. To use this board you will need to use a simple terminal emulator like hyper terminal.
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