The PicoScope XY display mode plots one channel against another on the screen. This plot could be the I–V curve of a component such as a capacitor, inductor or diode, or a Lissajous figure showing the phase difference between two or more periodic waveforms.
Electronic components can be characterized by applying a current-limited AC sine wave voltage, and plotting the resulting current flow (I) and voltage drop (V) on the oscilloscope in X-Y display mode.
The current flow causes a vertical trace deflection on the display, while the voltage across the component causes a horizontal trace deflection. The resulting trace on the display gives an analog signature for the component.
In the case of a resistive component, the analog signature can be thought of as a visual representation of Ohm's Law: V = IR where V = voltage, I = current and R = resistance.
All analog component signatures are a composite of one or more of four basic component signatures: resistance, capacitance, inductance and semiconductor. Each one of those components responds differently to the applied AC test signal, so recognizing the four basic signatures on the oscilloscope display is key to understanding analog signature analysis.
The signature of a resistor is a straight line at an angle from 0 to 90 degrees.
The signature of a capacitor is a circle or ellipse.
The signature of a diode is made of two or more roughly linear segments that usually form an approximate right angle.