Subtract scope channels

[doggy]

Hello, I have just received my AD3. Very nice!

I also have on order the BNC module.

I want to do scope measurements using the Scope on a 24V 5kW inverter, specifically the full bridge low voltage output. I am running from a lab power supply so I can ensure the bridge output is +-24V. Here are my questions:

1. I do not (yet) know if there are any spikes, although I cannot see anything on my 100MHz analogue scope. How resilient is the front end differential amp if there is a spike which exceeds 25V? I will be very close to the +-25V with my 24V system.

2. I would prefer to use BNC probes, particularly with 10:1. However I note that the two channels will not be differential. Can I use both channel 1 and channel 2 and display the sum of both channels and force one of them to be negative? I can easily do this simple thing on my analogue scope to produce a single channel differential input. I assume this is possible on the AD3 as it is a very simple and common requirement and I'm just not yet knowledgeable enough on the AD3 to see how to do it. I suspect that I can add a Maths channel and define it to be C1 minus C2?

Advice appreciated....

Edited December 31, 2023 by doggy

[JColvin]

Hi @doggy,

The Analog Input Channels on the Analog Discovery 3 have overvoltage protection to +/- 50 V DC (or +/- 30 V RMS) as per the last row in the Vertical System table here https://digilent.com/reference/test-and-measurement/analog-discovery-3/specifications#analog_input_channels, so you should be fine (relatively speaking) with the +/- 24 V system, particularly if the supply is being inherently limited.

You are correct that when using the BNC probes each of the analog inputs will then be single ended. You can add a Math channel through the "Add Channel" dropdown on the right hand side and set it up to do C1 minus C2 like you asked about. There is some additional information about the Math Channels in Section 3.6 of the Scope section of the Help tab.

Let me know if you have any questions.

Thanks,
JColvin

[doggy]

Thanks very much. All working okay as you described and I am pleased to know the electrical limits.

I'm FFTing the subtracted channels and that is also working very nicely.

 

Thanks again...