Oscilloscope isolation

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Hai all,
Could you please explain the need for isolating the oscilloscope. If not isolated what will happen?
 

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  • #2
berkeman
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Hai all,
Could you please explain the need for isolating the oscilloscope. If not isolated what will happen?
A regular oscilloscope will have a 3-prong plug (at least in the US), and all of the external metal on the 'scope, including the ground shield and clip of the probes will be connected to chassis ground. So you cannot connect the ground clip of your 'scope to Neutral or Hot when working with powerline measurements.

To work with powerline voltages, you either need to use an isolation transformer on the mains power, or use a battery-powered (floating) oscilloscope.

Does that address your question? What is the context of your question?
 
  • #3
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A regular oscilloscope will have a 3-prong plug (at least in the US), and all of the external metal on the 'scope, including the ground shield and clip of the probes will be connected to chassis ground. So you cannot connect the ground clip of your 'scope to Neutral or Hot when working with powerline measurements.

To work with powerline voltages, you either need to use an isolation transformer on the mains power, or use a battery-powered (floating) oscilloscope.

Does that address your question? What is the context of your question?

Thanks. I can understand. But still I've some doubts. Is it enough to disconnect earth connection? If isolation transformer is to be used, how it protects the device?
 
  • #4
dlgoff
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If isolation transformer is to be used, how it protects the device?
In electronics testing, troubleshooting and servicing, an isolation transformer is a 1:1 power transformer which is used for safety. Grounded objects (desk, lamp, concrete floor, oscilloscope ground lead, etc.) near a device under test which is not isolated may be at a hazardous potential difference with respect to that device. By using an isolation transformer, the bonding is eliminated, and the shock hazard is entirely contained within the device—there is no danger in touching a live part of the circuit while another part of the body is at earth potential.
http://en.wikipedia.org/wiki/Isolation_transformer" [Broken]
 
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  • #5
vk6kro
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Hopefully you wouldn't need to float the whole oscilloscope.

Dual trace oscilloscopes have two vertical inputs which you can usually invert or add with front panel switches.

So, if you want to measure the voltage drop across a resistor in a mains circuit or anywhere else (and assuming you do this with great care) you put one probe on one side of the resistor and one on the other. Then invert one of the inputs and add the two inputs.

This is the same as subtracting one of the inputs from the other.
 

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