The Wave Inspector is used to closely examine waveforms in a bench-type oscilloscope.
Hi and welcome to our 51th Test and Measurement video. Today’s topic is something we hear a lot about: the sine wave. It has a very characteristic, beautiful appearance.
Here’s what the sine wave looks like in the amazing Tektronix MDO3104 oscilloscope. It is created in the internal arbitrary frequency generator, which is accessed on the back panel. Just run a BNC cable from the port marked AFC to whatever analog channel input is desired. Then you can push the soft key that is associated with Waveforms, and using Multipurpose Knob a, scroll through the available waveforms.
We’ll continue looking at the sine wave. The first thing to emphasize is that even when the horizontal or vertical scale is altered, despite the fact that its appearance changes radically, a sine wave is still a sine wave.
Secondly, we are not actually looking at an electromagnetic or electrical wave. What we are seeing in the time domain is a graph of amplitude that is expressed in volts plotted against the passage of time denominated in seconds or either fractions or multiples thereof. The waveform really consists of oscillations in density of whatever medium if any is applicable.
That being said, we can look at the sine waveform and draw some conclusions. As it is usually configured, the sine wave is centered vertically on the X-axis, which is a horizontal line that crosses at a 90-degree angle the vertical Y-axis. A defining characteristic is that at zero amplitude, the rate of change is greatest, and at the high positive and negative peaks the line becomes horizontal, illustrating that at greatest amplitude the rate of change is least.
Where this is important is in the fact that current flow in a reactive circuit is dependent upon rate of change, not the amount, of the applied voltage. For this reason, in a circuit that has an inductive component, the current through the circuit lags the voltage across the circuit. In a circuit that has a capacitive component, the current leads the voltage. If the impedance is purely reactive, with no resistive component, this phase shift is 90 degrees. In a purely resistive circuit, the phase shift is 0 degrees or to put it another way, there is no phase shift, so current and voltage are in phase.
A very good way to show precisely the same relationship is by means of a polar diagram. The phase relation information is similarly conveyed, but the graph is set up differently. Amplitude is represented by distance from the center of the circle and the phase angle is graphically represented.
We are regularly putting up new Test and Measurement videos regularly, so please check back.
Leave a Reply
You must be logged in to post a comment.