In DC coupling mode, the capacitor is bypassed and the bandwidth
is DC up to 75MHz.
2.4.1 Offset Nulling
The input stages of the USBscope50 will naturally tend to cause a
small DC offset error in any readings, and this will change from
range to range and from scope to scope. In order to null this offset
out, the software is able to subtract a DC level from all its readings
and its plots, that will help to remove this error.
Select Settings → Offset Nulling and follow the instructions shown
to null each voltage range and each channel. You will be asked to
ground the probe tip. Note that grounding the probe tip as instructed
is NOT the same as selecting GND coupling
USBscope50 adjustments values are then stored in
OffsetNulling.config file in the same location where the software is
installed.
Note that there is no difference from a hardware perspective whether
you do this with the channel tab set to x1 or x10 coupling; they use
the same ranges in the hardware. There may be a very small change
in offset in the most sensitive scope input range as you change your
probe itself between x1 and x10 mode, but the software assumes this
change is negligible and only stores one null value regardless of the
coupling selected.
2.5 Probe Compensation
Before taking measurements with the USBscope50, the attached x10
scope probe must be compensated to ensure that it is matched to the
scope input stage
This ensures that the probe+scope act together to keep the input
frequency response as flat as possible. Using a scope probe that has
not been adjusted to match the USBscope50 can lead to inaccurate
readings for higher frequency signals.
8
This does not apply to x1 scope probes
Elan Digital Systems Ltd.
16
USBscope50 USER’S GUIDE Iss8
