Thermo Scientific Apex Service Manual page 109

Thermo Fisher Scientific
REC 4258 Rev C
If we examined the background noise by lowering the amplitude even
more we would see something like this: -
It can be a little tricky to see but the low-pass trace is largely
unaffected by noise – for the most part it runs steady across the
centerline of the scope. Note that the amplitude has been dropped to
just 6 making the screen very sensitive indeed. The high-pass R signal
is very noisy and it is the effect of the low pass filtering that removes
this noise as well as making the signal symmetrical and delaying the
signal slightly.
You should also examine the effect of the QNR filter and the PNR
filter – these both help to reduce the presence of random noise on the
signal and in turn allow smaller detect levels to be attained.
The next scope trace is shown to help you understand the vertical
dotted line crossing the screen. You should note that the time-base
setting on the scope has been reduced to 500ms to emphasize what is
happening:
Using the APEX Oscilloscope
Using the APEX Oscilloscope 8-7