Isolation between PC ground and Cleverscope

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4 Mar 2007
Posts:

Is the Cleverscope isolated from the PC ground ? In other words, can I do floating measurements, and/or avoid ground loops between the hardware and the PC ?

6 Mar 2007
Posts: 73

The acquirer is grounded in two ways - a hard, low impedance ground through the negative lead of the power supply, and a higher impedance connection through the USB port. To provide protection for the USB port should the scope ground be made live, or be elevated in potential we needed a hard ground for routing fault current. We supply grounded power leads for use in the US.

You would need to purchase a USB isolation unit if you want to break the ground connection between the oscilloscope and the PC. http://www.icron.com/products/usb/usb_rover_200.php has one possibility.

If you want to look at a balanced line you have two options. Connect a channel to each leg and use maths to show you the difference signal. Go to View, Maths Equation Builder and make the first equation a-b -> a. You can also use filtering to remove 50/60 Hz mains signals.

Alternatively purchase a CS1030 differential probe - http://www.cleverscope.com/products/accessories.php . That is a lot safer than having the oscilloscope floating!

7 Mar 2007
Posts:

Ok, thanks. It wasnt so much the need to make differential measurements, just the need to avoid ground loops when connected to other mains connected gear. I will consider the options.

10 Oct 2012
Posts: 19

Stupid question: I have an ethernet isolated CS. If I put an isolation transformer between mains and the power adapter, is my scope then isolated/floating from earth ground?

So far I have not needed to do this, but I need as many troubleshooting methods as possible.


Most of my test equipment is "floating" in that the power is transformer isolated.

11 Oct 2012
Posts: 396

The Ethernet interface is isolated from the PC, so there is no ground loop to the PC (which is good, because the PC can be noisy). If you use an isolation transformer, the scope will be floating for DC, but most isolation transformers are rather large, and have high interwinding capacitance which will provide a ground loop. It would be better to use the Cleverscope power supply and just disconnect the earth terminal. I measure the side to side capacitance as 28.5 pF at 10 kHz. That is sure to be quite a bit lower than an isolation transformer. If you buy an IEC to 2-prong cable, that will do it for you.

19 Nov 2012
Posts: 13

I'm utilizing the inherent isolation between the Cleverscope and PC in the Ethernet version, which breaks one tentative ground loop. Then I power the Cleverscope from the same (linear) supply which also powers my SQUID electronics. That way the Cleverscope and my electronics share the ground. The unit eats anything between 6 - 16 V after all, it does not have to be powered by its own (noisy) supply.

21 Nov 2012
Posts: 19

Isolation solves trigger gltich problem.


The CS would cause a big glitch in my signal, until I isolated it, using a 3 wire to 2 wire adapter at the AC plub. The Rigol scope manages to trigger without causing a big glitch in the signal.

I am not sure what is causing it, but it can really drive you up a wall.

This is so important I am going to start a separate topic on this

File glitch setup.doc

The rigol funciton generator is plugged into AC, but turned off. (same thing happens with other
signal sources). All amplifier inputs are with BNC cables.

The rigol scope is connected to the 90X amp output, not the 400X as shown in the picture.

Second picture: Glitch coincident with clever scope trigger.

third picture: clever scope not triggered, or earth ground not connected to power adapter.

Attached Files

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