HOW to Use USB-DSO on 230v AC Mains to workout on AC Dimmer

[dattlara76]

Hi,
My USB DSO model 6022BE and probe used 10X.
To comply the subject work, I have googled and understood that, need isolation trasformer(1:1, ie, 230v/230v) to protect the PC/DSO/DUT. And it also correct if use 230/12v for 2 nos in cascading connection, ie, Mains-230-12 --12-230v.
So, my questions are:
1) Why cant use the dso on the mains without isolation trf ?
2) is 10x probe sufficient, here dso will take 23v with 10x probe. or shuld i use 100x?

TNX

 

[betwixt]

You can either use a single 1:1 transformer or two back-to-back 230V/12V transformers but bear in mind there are some losses in each transformer so you probably won't see the full 230V if you use two.

1. possibly you can but there is a serious risk of the ground pin on the DSO being connected to the mains ground (Earth). That means when you connect it to your device it could short out the other AC lines to ground either directly or through the circuit. The laws of physics say something will go bang and the laws of economics say it will be the most expensive thing in line that does it.

2. use 100x. The reason is that even if there are no spikes on the mains, 230V is the RMS value. The peaks of the waveform will typically be 1.414 times the RMS values so they will exceed 300V. Make sure the probe is rated to withstand at least 350V for safety. If it isn't you should consider using an external voltage divider to bring the voltage down to safe levels.

Brian.