Oscilloscope operation differential voltage measurement

[wane13drkboy]

i want an american teacher. my instructor rally sucks

[Xynx]

I was wondering what type of oscilloscope is that you have there?

I have a Tektronix TDS 1002B

Two Channel

Digital Storage Oscilloscope

60MHz

1GS/s

However I can't seem to get the dual mode to happen so that it would use my channel 2 as ground, so I"m guessing my oscilloscope can't do it.

[torchddv]

Thanks. Been trying to figure out a safe way to check the waveform on a DC motor drive -- after I learned about the probe ground the hard way at the cost of one probe, 2 SCRs, 3 diodes and a lot of copper trace. Ooops. I thought about an isolation transformer too, but realized that would leave all the BNC connectors on the panel energized. Your way looks much safer!

[nottinghamnc]

You Sir, as a BTC instructor are excellent! I wish I had teachers like you when I was in college for my EE. Great job with your video explanations! Soothing narrative too!

[BTCInstrumentation]

@nottinghamnc You are very welcome!

[michor10]

@nottinghamnc I second that though. It's nice to see/listen to a knowledgeable person in action! Sadly, most of my college "professors" weren't. :(

[wateraarde]

Yes indeed, a big thank you for this educational and potentially cost, and what is more important, life saving advice!

[SignorZukini]

Thank you for this very informative, well presented and clear video.

Can't believe I have gotten away with using my scope incorrectly for so long!

[ragundo]

Very good tip. What kind of probe is needed for cheking an VFD? 100:1 ?

[BTCInstrumentation]

@ragundo 100:1 should be a good ratio to use. Be sure to check the specifications on the probe for maximum voltage. VFDs can put out very high voltage spikes, especially if there is "ringing" on the motor conductors (voltage pulses echoing back and forth along the cable's length).

[WisdomVendor]

Very informative vid. Thanks

[Daedronus]

How about if you use a isolation transformer on the scope power supply?

You should be able to connect one of the ground clips to a point that is not true ground?

[BTCInstrumentation]

You can use an isolation transformer (and rest the scope on a rubber mat so it won't ground through the metal workbench), but then the entire chasses of the scope rises to the potential that the "ground" clip is connected to. This can be very dangerous. Additionally, if measuring high-frequency signals (e.g. communications, radio), the capacitance between the now-ungrounded scope chassis and surrounding (grounded) objects will cause problems.