# Noob question about my new oscilloscope

#### wayneh

Joined Sep 9, 2010
17,152
Never owned an oscilloscope before today, so it’s a great day! My new toy shows right on the front panel that the max voltage is 400V. Siglent 1202E-X

So I think that means there’s nothing in my house or in any of my projects that I can’t probe directly. Does that sound right? What, where and when should I be afraid to stick the probe?

#### nsaspook

Joined Aug 27, 2009
8,394
Never owned an oscilloscope before today, so it’s a great day! My new toy shows right on the front panel that the max voltage is 400V. Siglent 1202E-X

So I think that means there’s nothing in my house or in any of my projects that I can’t probe directly. Does that sound right? What, where and when should I be afraid to stick the probe?
It depends on the scope probe. I have a few that can measure up to 40,000V.

https://www.tek.com/high-voltage-probe-single-ended

I have a few other probes that can be used with a scope for up to 200,000V.
https://www.rossengineeringcorp.com/hv-measurement/hv-probes-multimeters/hv-probes.html

#### MrChips

Joined Oct 2, 2009
23,565
So I think that means there’s nothing in my house or in any of my projects that I can’t probe directly. Does that sound right? What, where and when should I be afraid to stick the probe?
Ooh! I can think of a few places but I think I'm not allowed to mention them here on AAC!

#### wayneh

Joined Sep 9, 2010
17,152
It depends on the scope probe. I have a few that can measure up to 40,000V.

https://www.tek.com/high-voltage-probe-single-ended

I have a few other probes that can be used with a scope for up to 200,000V.
https://www.rossengineeringcorp.com/hv-measurement/hv-probes-multimeters/hv-probes.html
Good point. I believe mine is the PB-215 and therefore limited to my line voltage if set to 1X. That’s still a no-worry except for the occasional 240V project, when I can switch it to 10X.

#### upand_at_them

Joined May 15, 2010
766
Be sure to watch EEVblog #279: "How NOT To Blow Up Your Oscilloscope!"

And congrats. You're gonna wonder why you waited so long to get one.

#### MrChips

Joined Oct 2, 2009
23,565
I would be scared touching anything over 100V.
If you have to go there call me first.

#### sparky 1

Joined Nov 3, 2018
544
Inside a siglent, How much signal does it take to damage it ? I think that's a $400 dollar question. Before I was comfortable with attenuation I had different resistors, I only wanted just enough signal to do a standard procedure and probing all kinds of things was a no no. I have had my share of mistakes. Carrying a dead scope can ruin your whole day and I noticed the Austrailian guy has really improved over the years. Last edited: #### Delta Prime Joined Nov 15, 2019 1,028 Hello there Sir. What, where and when should I be afraid to stick the probe Whatever you do try not to take floating measurements with your O-Scope in which neither point of the measurement is at ground potential. The signal common can be elevated to hundreds of volts from earth and at the very least... it will ring your bell. #### tautech Joined Oct 8, 2019 205 Inside a siglent, How much signal does it take to damage it ? I think that's a$400 dollar question.
Before I was comfortable with attenuation I had different resistors, I only wanted just enough signal
to do a standard procedure and probing all kinds of things was a no no. I have had my share of mistakes.
Carrying a dead scope can ruin your whole day and I noticed the Austrailian guy has really improved over the years.
View attachment 228741
Inputs are rated to 400V however a 1x probe is not. Even a 10X probe is typically rated to 600V although this is a DC rating only so like for any probe consultation of the probe booklet is necessary for higher frequency derating where detailed study of the booklet can be very revealing !

Not one SDS1202X-E of the many dozens I've sold has been damaged by improper usage to my knowledge.

#### wayneh

Joined Sep 9, 2010
17,152
Not one SDS1202X-E of the many dozens I've sold has been damaged by improper usage to my knowledge.
Excellent news. I’ll try to not be first.

#### wayneh

Joined Sep 9, 2010
17,152
Hello there Sir.

Whatever you do try not to take floating measurements with your O-Scope in which neither point of the measurement is at ground potential. The signal common can be elevated to hundreds of volts from earth and at the very least... it will ring your bell.
Not following. Do you mean failing to connect the ground clip before probing?

#### wayneh

Joined Sep 9, 2010
17,152
I would be scared touching anything over 100V.
If you have to go there call me first.
I can only think of 2 places I might encounter >100V. One is line voltage, which I would only probe to demonstrate a sine wave. The other is the EL tape power supply I built, which may hit 200V or more. I have 240V lines in the house but I can’t imagine ever needing to see it on an o’scope.

#### MrChips

Joined Oct 2, 2009
23,565
Not to side track your investigation at this point, the number 1 error with newcomers to using an oscilloscope is connecting the GROUND clip of the probe to any place in a circuit willy-nilly.

Before you connect the ground clip, ask and answer yourself two questions:
1) is the ground clip necessary?
2) is this the right place to connect the ground clip?

#### MrChips

Joined Oct 2, 2009
23,565
I can only think of 2 places I might encounter >100V. One is line voltage, which I would only probe to demonstrate a sine wave. The other is the EL tape power supply I built, which may hit 200V or more. I have 240V lines in the house but I can’t imagine ever needing to see it on an o’scope.
Also high voltages in tube equipment and CRT TVs and monitors.

#### MrChips

Joined Oct 2, 2009
23,565
Some folks may choose to disagree with this but anyhow, here goes.

1) You don't always have to connect the ground clip of the probe to the DUT (device under test). The oscilloscope is already grounded.

2) Having a ground clip dangling from the probe can cause a short circuit if you are not careful. Sometimes, depending on the work you are doing, it would be best to remove the ground clip. If you are testing 50/60Hz AC mains, remove the ground clip.

3) Know if the DUT is grounded or not. Generally, if you touch the probe tip to any part of the DUT circuit and you see 50/60Hz then that likely indicates that the DUT is floating.

4) If the DUT is bonded to EARTH ground and you are only interested in DC voltages or low frequency signals (under 1kHz) then it is alright to use the probe without the ground clip.

5) If you are viewing high frequency signals or digital signals with sharp edges then you want to connect the ground clip to a place on the DUT that you have ascertained is EARTH ground. Never connect the ground clip anywhere you please without knowing that it is an EARTH node. If you see ringing at the rising and falling edges of digital signals then you need to connect the ground clip.

6) If the DUT is not grounded then that deserves another discussion.

#### wayneh

Joined Sep 9, 2010
17,152
6) If the DUT is not grounded then that deserves another discussion.
That seems like my most likely scenario, probing a breadboard circuit I’m working on, or maybe some small failed appliance.

#### tautech

Joined Oct 8, 2019
205
That seems like my most likely scenario, probing a breadboard circuit I’m working on, or maybe some small failed appliance.
Some battery powered circuits you can pull a node to mains earth and not affect it and some not.
This is where your DMM is handy to check with before connecting the probes earthed reference lead.

#### wayneh

Joined Sep 9, 2010
17,152
Never connect the ground clip anywhere you please without knowing that it is an EARTH node.
That makes sense. It's NOT like the black lead on a multimeter. It's earth ground and a potential current path.

#### MrChips

Joined Oct 2, 2009
23,565
That makes sense. It's NOT like the black lead on a multimeter. It's earth ground and a potential current path.
Yes, you have that right. An oscilloscope is not the same as a voltmeter or DVM/DMM even thought they can both measure voltage. A handheld DMM is "floating".

As you correctly state, (6) occurs more often than not, if you are testing battery operated devices, hobby circuits plugged into a laptop computer power from an AC charger, or powered by a floating PSU.

If you know that the DUT is not grounded, choose a reference node in the circuit that you want to call COMMON and connect the ground clip to that node.

When I wrote (6) above I was thinking of making a "high side" voltage measurement. I'll leave that for another discussion.

#### BobaMosfet

Joined Jul 1, 2009
1,780
Never owned an oscilloscope before today, so it’s a great day! My new toy shows right on the front panel that the max voltage is 400V. Siglent 1202E-X

So I think that means there’s nothing in my house or in any of my projects that I can’t probe directly. Does that sound right? What, where and when should I be afraid to stick the probe?
@wayneh - slow down, danger wil robinson!