AC1 Fundamentals Unit 2 – AC Measurements
Exercise 2 – Measuring With an Oscilloscope
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to measure voltage by using an
oscilloscope and determine current and impedance by using Ohm's law. You will verify your
results with information found in this exercise.
DISCUSSION
- A current-sensing resistor (R2) is present on this circuit board. It is placed in series with the
circuit under test and is a small enough value not to affect circuit performance. - When the two-post connector is removed, the voltage drop across R2 is measured and, using
Ohm’s law, the current can be calculated. - Once the circuit current is determined, the circuit impedance can be calculated using Ohm’s
law and the source voltage (VGEN). - The oscilloscope, generator, and power source all have a common ground reference.
- Two scope probes and the ADD-INVERT method are used to measure the voltage of a
component in order to prevent R2 and L2 from being shorted out. - Follow these steps to perform the ADD-INVERT method:
Place both channel vertical input attenuators on the same setting.
Connect the channel 1 input to the side of the component with the greatest potential.
Connect the channel 2 input to the opposite side of the component.
Connect both oscilloscope probe ground clips to the generator common.
Invert channel 2.
Switch the vertical mode to ADD.
Record the voltage. - If the ADD-INVERT method is used, even though one end of a component is connected
directly to ground, the oscilloscope can be safely placed directly across the component.