EEVblog #778 - Oscilloscope Vertical Confusion

[EEVblog]

Dave answers a beginner forum question on why the Rigol DS1054Z oscilloscope does not show the intended vertical Volts/Div setting he expects.
A trap for young and old players alike.
1X and 10X probes, and auto probe interfaces.

The forum question:
https://www.eevblog.com/forum/testgear/how-do-i-get-1mvdiv-on-the-1054z-i'm-only-getting-10mvdiv/

[TheSteve]

I was thinking of popping a clear piece of heat shrink over the 1x/10x button on the Rigol probes so they stay at 10x at all times. The slide moves much too easily.

[DanielS]

I was thinking of popping a clear piece of heat shrink over the 1x/10x button on the Rigol probes so they stay at 10x at all times. The slide moves much too easily.

It depends on the probe. I have 13 of Rigol's 100MHz probes and out of the lot, there are 3-4 that have extremely soft 1X/10X switches that can change position by simply dragging the probe across my antistatic mat, which is indeed very annoying. Most of the others require more direct force.

The reason I have so many probes is because out of my original 8, I had 5 which had very glitchy 1X contact and two of those were hopeless. Last week, I was testing an adjustable load I was putting together and after half an hour of chasing the cause of unstable current and large errors, it turned out that one of my "good" probes was acting up on the 1X position.

Rigol appears to have major QA issues with those switches. They seem outrageously unreliable.

[guido]

Tek 1:10 probes have an ~11k resistor between pin and gnd. A no-name with ~9k also works fine.
Works also with my Iwatsu scope (SS-7810).

I have a 500MHz HP 1:10 probe and it is a dead short between pin and gnd.
Put it on a tek scope and it thinks it's a 1:1000 probe. The Iwatsu thinks it's 1:100...

I don't own a HP scope to test it the other way around. All old tek stuff, except for the Iwatsu.
Looks a bit like vendor lock-in 

[Tek_TDS220]

Dave's right about the 10x switch on cheap probes.  I've done that accidentally and had some head-scratching moments before I figured out what had happened.

[EEVblog]

Dave's right about the 10x switch on cheap probes.  I've done that accidentally and had some head-scratching moments before I figured out what had happened.

Must have happened to everyone I'm sure. Happened to me countless times.

[Stephan_T]

Hi Dave,

i just read this in the Rigol Manual:

Chapter 18 Specifications

Maximum Input Voltage (1M?)

Analog Channel: CAT I 300 Vrms, CAT II 100 Vrms, Transient Overvoltage 1000 Vpk With RP2200 10:1 probe: CAT II 300 Vrms

As far as I understand this, accidentally switching from 10:1 to 1:1 is not only a nuisance, it may also become a safety issue, switching from green to orange or red.

A little mechanical (twist lock) solution should be really simple and cost only a few cents.

BTW. The issue of how to do oscilloscope measurements on the hot side (mains voltages) of an SMPS in a safe way would be an interesting topic for a video. This includes questions like

• is a switchable 10:1 enough, or should we use fixed 100:1 probes
• how not to invalidate the effect of a an isolation transformer with the oscilloscope ground (most people probably don't  have a 300V differential probe, but maybe two 100:1 probes will do the trick at an affordable price).
  
• Is the secondary side of an isolation transformer (230V:230V) still CAT II or does it become (or can be brought down to) CAT I.