Measuring current with respect to time

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Measuring current with respect to time

Post by om_tech_support_JT » Thu Nov 07, 2013 12:51 pm

Q: Hello. I am working on a R&D project and I would like to measure the motor output power with respect to time to calculate the torque. We all know that power equals voltage times current. I know how to measure the voltage using my oscilloscope, but can you please suggest me the best way to measure the current drawn by one of your AC motors using an oscilloscope?

A: Current probes allow the user to measure the current flowing through a wire without “breaking” the circuit to insert a different measuring device, such as a digital multi-meter or a “sensing” resistor. The current probe clamps-on the wire, and connects to an oscilloscope.

To measure the current drawn by one of Oriental Motor's 3-wires AC motors, clamp-on the current probe to the BLACK wire. The BLACK wire is the common for both windings, so the total current flows through it.

Remember to balance and to degauss the probe before making measurements. Balancing removes unwanted DC offsets. Degaussing removes residual magnetization from the probe core. Most probes will come with a user manual with balancing and degaussing instructions.

Set a wide time division in the oscilloscope’s x-axis to capture the current drawn for a long time, say 1 or 2 seconds per division.

Most oscilloscopes have the option to capture and save the waveform to a flash drive or a floppy disk to move the data to your PC for further analysis.

If you are considering buying a current probe, please consider compatibility between the current probe and your oscilloscope, as well as the bandwidth and max peak current.

Feel free to call/e-mail/chat with us if you need more assistance.

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