Measuring impedance with oscilloscope

Voltage waveforms are measured on the oscilloscope and the measurements are used to calculate an unknown capacitance. Because Impedance is an AC property it cannot be easily measured like resistance. Connecting an Ohm meter across the input or output of an amplifier only indicates the DC resistance.

Measuring Impedance and Capacitance with an Oscilloscope and. In this lab, you will be able to observe this effect and use it to measure the magnitude and angle of .

The methods shown are all variations on measuring the .

As James Carrington notice the were odd in that the impedance varied inversely with the test frequency.

Ouput impedance can seem like black magic so here is an easy yet effective way of measuring it using an oscilloscope. I of the current through the impedance. However one is only able to measure voltages by the oscilloscope. For the input, the voltage is measured across the input terminals and the current measured by inserting the meter in series with the signal generator. Ignore the capacitors, cable etc.

Of course this only applies to DC. The delay should only be just enough for the measurement. If the VI term decreases then the impedance is capacitive. Vector Method Using Oscilloscope or Vector Voltmeter. This approach may also be adapted for use as an instructional lab exercise.

After becoming familiar with the frequency response of RC circuits in the previous laboratory, you are ready to learn about the oscilloscope input impedance. This complex impedance , which has resistive and capacitive components, can disturb performance of circuits being measured and limits high frequency performance . The impact of input impedance is more apparent when measuring very high . Simple input impedance model of an oscilloscope probe comprised of resistive, capacitive, and inductive elements. Adjust the frequency of the generator to approximately kHz.

Connect the unknown inductor parallel to the oscilloscope (Fig. ). Input Impedance and Signal Integrity. In some cases such an impedance could be insuffi cient,and generate, a significant measurement error. You can expect capacitance and inductance values with - . Circuit to measure the DVM input impedance. The DC voltage source supplies 2V. At the output fix an oscilloscope , because the wave form should not show any distortion.

Objective in this lab, you will learn how to implement ac voltage measurements of phase, amplitude and impedance. You should also use PSpice for AC-analyses. Digital multimeter (DMM) Fluke45.