Monitor Mains on Oscilloscope

[bryan]

Hello:

Would like to monitor the AC mains for potential noise that is affecting some X10 controls. Any suggestions on the best way to do this. Obviously it's very dangerous to do so, but i will take proper precautions so as not to electrocute myself, but I don't want to damage the scope.

Should I best use a trasformer to drop the voltage down to 24 volts or go ahead and use a voltage divider such as found in this link.

**broken link removed**

My goal is to monitor the noise on the scope and unplug appliance's etc to pinpoint the culprit(s).

Thanks

 

[Nigel Goodwin]

I wouldn't like to suggest how I would do it - a few people would only complain

I would suggest you use your 24V transformer, presuming the noise travels through it OK?.

 

[felis]

My goal is to monitor the noise on the scope and unplug appliance's etc to pinpoint the culprit(s).

Why do you want to use a oscilloscope for this? Short transients riding on top of the mains are pretty hard to observe. And you already have much better detector - your suffering X10. I would rather loop an X10 transmission and (dis)connect appliances watching the error rate.

 

[Hero999]

The voltage divider is a bad idea as the neutral is bonded to the earth (usually where it enters your house) and connecting it to the oscilloscope's case will cause a huge ground loop and will also trip and earth leakage breakers. The 24V transformer is a good idea but it might not have enough bandwidth to measure the transients.

Another thing is how do can you trust your scope's reading if the noise is interfering with it?

You can eliminate as much noise as possible by installing an EMI filter on the mains line to it which might help but I don't see the point in trying to measure the noise which is causing the problem.

 

[bryan]

Thanks all. turns out the problem was a defective cord connecting the controller to the X10 interface. Guess it was picking up signal noise and messing things up.