OT: oscilloscope probes

[Paul Andrews]

I need to get a 10x probe for my Tektronix TDS430A. Any recommendations?

If it helps, I want to be able to observe the ringing on the HV side of a nixie power supply I am trying to design/build. Ringing is at about 20MHz.

[gregebert]

As long as there is a standard BNC connector on your scope, just about any probe should work.

I bought some cheap ones on ebay for about $10-$15 a few years ago, and they work fine. You wont need an expensive probe for 20Mhz; you do need to compensate the probe with a decent square-wave. Most, and perhaps all, Tek scopes will have a test-point on the front to compensate the probe for optimum performance (sharpest-edge on a square wave).

Your scope may want to see a specific type of probe attached so it can automatically set 1X, 10X, etc but that wont affect the actual measurement.

Using AC-coupling will allow you to zoom-in to the ringing. Be aware that the 430A has 100Msa/sec sampling. 20Mhz is well-below Nyquist-limit for a sinusoidal waveform, but not an outright glitch. Most ringing I've looked at is a damped-sinusoid so you should be able to do some good debug for your circuit.

[Paul Andrews]

Yes, my scope can calibrate probes. I was actually reading the manual this morning! I should probably set aside some time to go over it!

[gregebert]

The probes themselves cause few problems, especially when in 10X/100X mode, because they generally present a high-impedance load on the circuit.

Ground-clips/leads are what cause you nightmares and can lead you in the wrong direction when debugging noise issues, including ringing. Be aware that the ground-clip on a scope-probe can cause ground-loops thru the power-line GND and back to your circuit if your power supply or anything else connected to your circuit is also grounded to the power-line. There are quite a few good articles on the web about probing in a noisy environment.

[Tomasz Kowalczyk]

There is a very informative channel on youtube, which teaches about various problems in electronics. This video mentions the earth-to-clip connection and shows the result of forgetting about it. I highly recommend watching his videos, you can learn much about safety while having a good laugh and bad examples.

https://www.youtube.com/watch?v=sI5Ftm1-jik

The earth-to-clip moment is at 2:25.

I learned about it from this video and it seems it is a common knowledge that nobody teaches.