TiePie Handyscope HS6 DIFF Series User Manual page 11

Therefore the voltage that is measured with an oscilloscope with standard, single
ended inputs is always measured between that specific point and ground.
When the voltage is not referenced to ground, connecting a standard single ended
oscilloscope input to the two points would create a short circuit between one of
the points and ground, possibly damaging the circuit and the oscilloscope.
A safe way would be to measure the voltage at one of the two points, in reference
to ground and at the other point, in reference to ground and then calculate the
voltage difference between the two points. On most oscilloscopes this can be done
by connecting one of the channels to one point and another channel to the other
point and then use the math function CH1 - CH2 in the oscilloscope to display the
actual voltage difference.
There are some disadvantages to this method:
•
a short circuit to ground can be created when an input is wrongly connected
•
to measure one signal, two channels are occupied
•
by using two channels, the measurement error is increased, the errors made
on each channel will be combined, resulting in a larger total measurement
error
•
The Common Mode Rejection Ratio (CMRR) of this method is relatively low. If
both points have a relative high voltage, but the voltage difference between
the two points is small, the voltage difference can only be measured in a
high input range, resulting in a low resolution
A much better way is to use an oscilloscope with a differential input.
Figure 3.1: Single ended input
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Introduction