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Voltage limit of this probe?

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ZakWolf

Sat Oct 31 2015, 10:01AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
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Posts: 608

So I bought the Rigol DS1054z

and this hv probe just in case

Probe specs:

* 100:1 attenuation
* Input resistance of 100 megohms
* Input capacitance of 6 pF
* Compensation range : 10 pF - 35 pF
* Bandwidth: 100 MHz
* Rise Time: 3.5ns
* Maximum operating voltage : 1000V DC + ACPP
* Cable length : 1.1 m

The Scope came with 10x1 and 1x1 modes on the probes via switch. The packaging says 300v av at 10x so what woud the DC be if i were to use them for DC?

Things I want to measure

* Output of my ZVS driver (no flyback of course)
* SSTC bridge output and gate driver waveform

Is is safe to hook up to the output of a SSTC bridge? Do I need a different probe?

I am unsure of what is ok to scope at this point and would greatly appreciate some advice on material to read up on.

Thanks

DerAlbi

Sat Oct 31 2015, 11:33AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Oscilloscope voltages should be obtained by the maximum voltage at the x1-mode. Means: The maximum voltage settings you have is 5V/div, and 4..5 divisions to every side, then you should not apply much more than 30V. The 300Vrms is surely not what you want. DaveJones (eevblog) analysed the input stage of that oscilloscope and its all 45V transistors or whatever. So excessive voltage is clamped behind some series resistance which will burn sooner or later. It also means that you can apply 300Vrms and not get shocked by touching the knobs.. CAT-I. Thats the safety in case of >failure< like probing the mains by accident.
With that 30V beeing said you can use a x10-Probe to x10 the Voltage and a x100 probe to x100 times the voltage. (thats neglecting the probes capability)
Just be carefull: the probe can withstand less voltage the higher the frequency becomes. So there is a difference between DC-High-Voltage and AC-High-Voltage.

ZakWolf

Sat Oct 31 2015, 07:59PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

Thanks DerAlbi Im still a little confused though.

The pic I attached is the interrupter im using for my SSTC (testing ) Its two 555 ics and the output of first is going into pin 2 on the second chip. This gives me varying pulse lengths at different currents to make the arc thicker or thinner.

I was wondering, the voltage per/division is set at 50v I think ( the lower left comer of the scope). With that being said the signal looks to be in the order of 100v ! I doubt the timers are generating such voltages while operating from a 12v battery. What am I reading wrong here ?

Lastly, If i want to measure anything over ~30v I need to use the 10x peobe and anything above that the 100x probe... correct?

I heard scoping the bridge of a sstc will short one of the legs of the mosfets to ground and it will go boom, anyway around this ?

Blue: Output from the first timer square wave
Yellow Output of the second timer *varying

DerAlbi

Sun Nov 01 2015, 10:33AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

The oscilloscope will show you whatever you want it to show you.
If you change the division switch on your probes or even connect a whole different probe for the 1:100 then you also need to adjust the oscilloscope to the division factor. (its not auto detecting in this price range

)
In the probe menu (press the channel-button once) you will see that you can configure the division ratio.
This has nothing to do with hardware at all. Its pure aesthetics.

Let me put it this way: Probe a real 5V signal.
Do it with a x1 probe and set you oscilloscope to x10, it assumes the input voltage was divided by 10, so it will display 50V to you instead of the 5V.

I think the same is happening here: you have your oscilloscope configured to x10 and fliped the switch on your probe to x1. Thus reading ten times the votlage. I mean.. issnt it weird that you get 120V where 12V was suposed to be?

You actually want to use the x10-Mode as often as possible. The x1 mode is only made for really small signals. Keep in mind that in the x1-Mode the probe has extremely limited bandwidth (like 7 to 20MHz at most.) The right way do get the full bandwidth is to use a x10 or x100 probe.
So dont bother with the x1 mode at all..

And dont forget to compensate your probes. While the original probes have the trimmer at the tip, you HV-Probe should have the trimmer at the base (for safety reasons). If its not compensated correctly your voltages will be way off for everything higher than 5kHz.

Mads Barnkob

Sun Nov 01 2015, 12:05PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

ZakWolf wrote ...

I heard scoping the bridge of a sstc will short one of the legs of the mosfets to ground and it will go boom, anyway around this ?

It is called a differential probe, and it will also substitute your 1:100 probe, try to find a good priced Tektronix P5200/P5205 on ebay, it goes up to 1300V.

ZakWolf

Sun Nov 01 2015, 09:18PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

Mads Barnkob wrote ...

ZakWolf wrote ...

I heard scoping the bridge of a sstc will short one of the legs of the mosfets to ground and it will go boom, anyway around this ?

It is called a differential probe, and it will also substitute your 1:100 probe, try to find a good priced Tektronix P5200/P5205 on ebay, it goes up to 1300V.

That 100:1 probe I bought was only 25$ so could I save myself a couple hundred dollars and buy another one and just mess with the settings and invert the other and let them float?

Running from 170v DC what kind of switching spikes am I looking at ? I dont have a variac but I do have a lower voltage AC transformer. If it will possible to run it that way.

Really since the coil is self tuning I dont really need to look at the output of the bridge. What I need to check is the gate driver and signal coming from my CT.

DerAlbi

Sun Nov 01 2015, 10:44PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

if you are ok with just probin one signal at a time you can just cut the ground connection of your oscilloscope. (thats the bad version)
i personally run my one from a isolation transformer but that has its drawbacks.

ZakWolf

Mon Nov 02 2015, 04:12AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

DerAlbi wrote ...

if you are ok with just probin one signal at a time you can just cut the ground connection of your oscilloscope. (thats the bad version)
i personally run my one from a isolation transformer but that has its drawbacks.

One signal at a time ?? Hows that if im running two separate probes? Dont get me wrong I know little to nothing about scopes just what I have read in the last day or so but floating two separate probes each going to their own channels seems like it work fine. I also read on a review of those probes that have been used to test 1300v supplies and they worked fine.

Mads Barnkob

Mon Nov 02 2015, 07:34AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

ZakWolf wrote ...

You should watch this

ZakWolf

Tue Nov 03 2015, 03:25AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

Mads Barnkob wrote ...

ZakWolf wrote ...

You should watch this

Will do man, Thanks !!!

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