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6 - 40 THE CPL PROTOCOL
Time base In case of a sampled signal the horizontal scale is called the time
base. The time base setting is usually expressed in
seconds/division. Without magnification or compression the
oscilloscope always displays 50 samples per horizontal division.
Note: The horizontal scale as well as the FFT scale can differ. In
that case it is expressed in X-units per division.
Time base = 50
*
Xr
*
Xu/div
Delay Delay is the time delay between the trigger moment and the
moment that the first sample is taken. If the delay is negative, the
first sample is taken before the trigger moment. This is called pre-
trigger view. In case of pre-trigger view the trigger point (horizontal
position of which T[n]=0) is indicated on the screen. The delay or
the position of the trigger point can be adjusted by means of the
TRIGGER POSITION control.
Delay is usually expressed in X-units (seconds).
Note: Traces can also be positioned in horizontal direction with
the X- POS control, but this does not affect the delay. The
reason is that X-POS is a pure display function and
therefore does not affect the signal sampling.
Delay = -(Xz + (dT-corr
*
Xr))
*
Xu
Trigger pos = (Xz + (dT-corr
*
Xr))
*
Xu
These values can also be expressed in divisions :
Delay = ( -(Xz + (dT-corr
*
Xr)) / Xr )
*
1/50
*
div
Trigger pos = ( (Xz +(dT-corr
*
Xr)) / Xr )
*
1/50
*
div
Notes:
•
The mathematic functions only give useful results, if there is no conflict
between the units. For example, it makes no sense to add amperes to volts.
•
The trigger delay and the time base setting of the two traces must be equal.
This is always guaranteed, if the traces were acquired at the same time,
because the trace elements are from the same register.
•
Consider the following useful example of a mathematics function:
- Perform the multiplication of two traces with different units, i.e. a trace
representing volts over time and a trace with amperes over time.
- The resulting trace is expressed in watts and gives the power over time.
- After integration this gives the Pulse Power in joules.