You can't use an oscilloscope to directly measure electrical current. For that, you'd need what's called a multimeter. However, you can indirectly measure electrical current with an oscilloscope by attaching resistors of known value to the oscilloscope's probes, measuring the voltage across the resistor, and then using Ohm’s Law to calculate the electrical current.
Plug in the oscilloscope. Press the AUTOSET or PRESET button, if there is one. If not, then set the oscilloscope's controls to their standard positions: 1) set the display to channel 1, set the volts to the mid-range; 3) turn the variable volts/division off; 4) turn the magnification settings off; 5) set channel 1 to DC, if the input is direct current, or AC if the input is alternating current; 6) ensure the trigger mode is auto and the trigger source is channel 1; 7) turn off the trigger holdoff; and 8) set the intensity control to nominal.
Attach measuring probes with resistors of known value to your electrical system or circuit. If you know the power output of the electrical system or electrical circuit you’re measuring, be sure to use a resistor with a power rating equal to or greater than the power output of the system. For example, if your electrical system or electrical circuit has a power output of 9V or less, use at least 1/8-watt rated resistors.
Ground yourself by wearing a grounding strap, a simple conducting strap that wraps around your wrist at one end and is attached to your floor at the other end, if the system you're working with is an integrated circuit.
Set the trigger mode to auto, as this is the simplest way to start measuring a signal. This means getting the oscilloscope to start to measure the time-varying nature of the voltage signal by identifying the peak voltage point or the zero voltage point. Identifying one of these two points “triggers” the oscilloscope. In this way, the oscilloscope can capture and measure the range of the voltage signal, both its strength and time-varying parameters.
Adjust the horizontal and vertical controls until you get a stable sine wave, and then take measurements along the center vertical line that has the smallest divisions. The vertical control will give you the voltage of the signal.
Take a voltage measurement and then plug that value along with the value of the resistor into Ohm’s Law to calculate the current. The formula is current = voltage divided by resistance.
Sometimes the automatic trigger mode will fail to synchronize the oscilloscope with the time varying nature of the voltage output of the electrical system or electrical circuit that you’re trying to measure, and the oscilloscope will not show a signal at all. At this point, you’ll have to manually set the trigger. How exactly you do this depends on the specific component makeup of the electrical system or electrical circuit and the specific model of the oscilloscope you're using. Consult your oscilloscope’s owners manual for specific troubleshooting steps.
