Galvanic Isolation and accuracy of 3000 series

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Galvanic Isolation and accuracy of 3000 series

Post by measureMan » Wed Mar 21, 2007 2:42 pm

I'm thinking of buying a 3204 scope and I got two questions :

1. is the ground/shield of the probes connected to the ground of the USB, or is there a galvanic isolation?

2. Is it right that in the highest accuracy of the scope (100mV/screen with 8-bit resolution) the smallest horizontal step corresponds to approx. 0.4 mV?

As an explanation : I want to use the scope for current measurement, by measuring the voltage drop over a shunt (0,2 Ohm). Therefore I need to make a differential measurement over the shunt (by connecting the shield of the probe to one side of the shunt).

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Post by ziko » Mon Mar 26, 2007 2:40 pm

Hi and thank you for your post.

1) Yes they are connected and not there is no isolation
2)No, the smallest resolution would be 0.8mV , you forgot the sign bit.

Hope this helps.

Kind regards

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Re: Galvanic Isolation and accuracy of 3000 series

Post by andisho » Sat Dec 26, 2015 7:57 pm


Do you offer some USB3 cable that would do the galvanic isolation ?

I once mistreaded the whole line of scope, microcontroller, programmer, mac book pro because I introduced a ground loop.

I would like to avoid that for the future.

Since my power supply from my MBP 2013 is very noisy (you feel it with the back of your hand, very much stray capacitive current flowing), I would like to have it isolated from my scope anyways.

Since nowadays you can get small DC-DC isolated power supply circuitry with efficiencies well over 90%, even the transfer of power for the picoscope is no problem.

USB3 offers the advantage of up to 900mA current sourcing here.

I would wish it would be implemented in every picoscope, for more demanding models perhaps one additional USB isolated plug for additional power.

Thank you!


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Re: Galvanic Isolation and accuracy of 3000 series

Post by AndrewA » Wed Dec 30, 2015 12:27 pm


None of our scope have isolated USB ports, we have tested a USB wifi printer hub (IOGEAR GUWIP204), let me know if need more information about this.
Most USB isolators and IC's only supports low and full speed data rates. (Low and full speed data rate: 1.5 Mbps and 12 Mbps)
And not the High Speed (480 Mbit/s, with USB 2), which normally runs at on a PC.
The scope will work at full speed -12 Mbps, with a USB isolator, when streaming (slow timebases -100ms/div or slower) maybe issue, but otherwise ok for block captures.
In block mode you may notice the waveform refresh rate to slower due to this lower transfer rate, but scope is still usable.

USB Power- You could use a powered USB hub with a isolated DC supply. The AC adaptor that comes with hub may already be isolated. You would need to check with a multimeter. This would still not be safe if you measuring mains referenced circuits. Only for working on CATI circuits.
It may pay to check what isolation ratings/standards the USB isolator has.

There are now some expensive fiber optic USB 3 isolators, but we have had reports from customers that they do not work with our PicoScope.
If do buy a USB isolator, it would be better to buy it from a supplier that you easily return if does not work with your PicoScope.
Regards Andrew
Technical Specialist

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