There is some excellent advice in this thread, but also some conflicting information. Here’s a go at a summary on my part.
Attached is a spreadsheet that models the DSO Nano input stage. This is to the best of my knowledge an accurate model and is also how V3 firmware calculates voltage. Note that input resistance depends on selected gain range (choice of V/Div).
When using a 10x probe, 800V is within safe range for the Nano input stage (only 43V seen on connector input) as long as we operate on battery power. The issue is not the voltage itself, but potentially high ground loop currents when operating the Nano from USB power (see explanation from lygra). The second issue is with limited isolation against absolute voltage levels as pointed out by dnordenberg.
Lessons learned may be as follows:
- Never use the Nano for measurements (disconnect test leads) when operating from USB unless the measurement target and Nano/USB port shares a common ground.
- Avoid touching the Nano when test leads are exposed to a high ground level offset and keep the Nano at a safe distance from other conductive material.
Nano Input Stage.zip (8.03 KB)