Common mode performance.

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22 May 2008
Posts: 1

Some mains powered gear can be difficult to work on if it cannot be isolated from ground.
What sort of common mode performance does the cleverscope give when using the input probes in a differential mode?
Can the input amp. operate in differential mode/

30 May 2008
Posts: 396

Hello Paul,
The Cleverscope BNC inputs are not isolated from each other, or from ground. This decision we made based on the number of people needing this ability, and the cost of implementing it. The BNC grounds are connected to Mains earth for safety reasons. If the scope probe ground clip is connected to mains, the fault current is conducted to the mains earth, and either causes the Ground Fault Interrupter to fire, or the mains fuse to blow. There is also a small sacrificial track between the BNC ground lead and the main Cleverscope ground plane. In addition the ground to the USB is inductively and resistor connected, to increase the impedance to the PC ground. These safety features mean that the PC user is protected should such an event happen.

Cleverscope strongly recommends the use of a GFI wherever the user is probing mains voltages.

Now we do offer differential probes, which offer safe use to 1kV. Details are on our web site at http://www.cleverscope.com/products/accessories.php .

The CMRR at 50/60 Hz is 10,000:1, reducing at higher frequencies.

I hope this helps.
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