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NOTE: When the following methods #2 and #3 are used, the case/chassis of the scope
will be floating above ground at what ever the voltage level the drive is at with respect to
earth ground. This could be as high as 250vac for a Focus drive. Care must be taken as
not to touch the case and earth ground, a severe electrical shock can occur which could
be life threatening. It is also important to set the scope on something non-conductive,
like a rubber mat. Care must be taken so that the scope case does not come into contact
with earth ground when using these methods.
Isolation Transformer Method
2. The next preferred method #2 uses a small isolation transformer to power the
scope, this will effectively eliminate the earth ground connection.
Least Preferred Method
3. The least preferred method ( yet most widely used ) involves cutting off the Earth
ground pin on the power plug, or use of a “cheater “ adapter which has no ground
pin. Use of the adapter is probably the better approach since cutting off the
ground pin may void the warranty on the oscilloscope.
When using a dual channel oscilloscope make sure that you use only 1 scope
ground lead – remove the scope ground lead on the other probe.
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