Here, I will demonstrate how to perform a differential measurement in Proteus using the oscilloscope math function (Add and Invert). This process mirrors actual physical circuit measurements, and I'll use an inverter's output as an example to show you how to capture and display the correct signal waveform.
But first, what is Differential Measurement?
In electronics and simulation environments like Proteus, differential measurement is a technique used to determine the voltage difference between two specific points when neither of those points is connected to ground. It is essentially measuring the floating potential across a component, such as a 220V AC load or a transformer secondary.
Below is the CD4047 based inverter circuit where I will be measuring the differential signal across the load (the bulb).
Now I will show how it works on an Oscilloscope. When using a standard oscilloscope (which is typically ground-referenced), you perform a pseudo-differential measurement by using the Oscilloscope Math Function Add and Invert:
But first you have to place two probes for two oscilloscope channel like Channel A and Channel B. For Channel A: Place a voltage probe Va at the first AC output terminal. Then For Channel B: Place another voltage probe Vb at the second AC output terminal.
Now on oscilloscope you need to perform Invert & Add: On channel B, click on the invert button to invert the signal waveform Vb. Then on channel A, click on the A+B add channel button to add channel A and channel B signal waveforms.
The oscilloscope then performs the mathematical operation Va - Vb. The result is that the final waveform displayed on the screen represents the true voltage difference (Va - Vb) across the load.
1. Avoiding Short Circuits: Standard oscilloscope probe ground clips are connected to the building's earth ground. Clipping a ground lead directly to one side of a live inverter output in a real-world scenario would cause a short circuit.
2. Accurate Waveforms: This method allows you to see the full voltage swing without the interference of ground loops, providing a cleaner and more accurate representation of the floating AC signal.
See the video below which shows how to do differential measurement in proteus which also applies to actual physical circuit.
That's it. Now you have learned what differential signal measurement is and how to take differential signal measurement in proteus.
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