It is not a modern tech but still mystery for beginners. After I bought my test gears such oscilloscopes, I noticed that I should have an isolation transformer in my bench. Then, I forgot again with the other projects. One day, after seeing Dave and Todd videos blog about isolation transformer, I started the construction of DIY isolation transformer.
For those interests, here is Dave and Todd explained videos. Thanks both. http://www.eevblog.com/2012/05/18/eevblog-279-how-not-to-blow-up-your-oscilloscope/http://www.toddfun.com/2011/04/30/isolation_transformers/
And later, I recently found a post at Keith’s Electronics Blog. There is also original schematic from manufacturer. It isolates even ground pins of each output. Yes, system ground (Chassis ground) is purposely isolated.http://www.neufeld.newton.ks.us/electronics/?p=500
And here is an AN from APC concerning about isolation in UPS system but worth to read.http://www.apcmedia.com/salestools/NRAN-7NB2FG_R0_EN.pdf
I agree with Todd suggestion. This is the schematic from commercial isolation transformer. The output winding NEUTRAL is CONNECTED to main GROUND!!!http://www.carebase.com/Isolation-trans ... -1000B.htm
This is the edited diagram as per suggestion. Disconnected secondary winding (NEUTRAL) from main GROUND.
All blogs and AN have their point of view in isolation but questions still exit.
- DUT (device under test) should be isolated with transformer rather than oscilloscope.
- BUT, Dave scenario-3… if DUT power supply is grounded to chassis (main ground), the problem is still existed. Disconnect DUT ground ?? or use with floating power supply?! or with battery?
- Test device such as oscilloscope should not be floated (must be grounded) without special reason.
- Most forum and articles talked about isolating oscilloscope not DUT. If someone know the best practice and pros, cons, let me know.
- Differential probe, usb isolator are also good but I cannot still effort.
- I need GFCI outlet at my bench.
- My thought is that isolating system ground has some pro and cons. Sometime we need to isolate for full safety or purposely. In most case, test equipment should be grounded for safety.
My construction is here.http://okelectronic.wordpress.com/2012/12/04/diy-isolation-transformer/
Pls share your thought, experience and best practices.