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USING THE COMBISCOPE INSTRUMENTS 3 - 43
PROGRAM EXAMPLE:
CALL Send(0, 8, "SENSe:SWEep:TIME?, 1) ’
Requests sweep time
CALL Receive(0, 8, STIME$, 256) ’
Reads sweep time
CALL Send(0, 8, "TRACe:POINts? CH1, 1) ’
Requests number of trace points
CALL Receive(0, 8, TPOINTS$, 256) ’
Reads number of trace points
SWETIM = VAL(STIME$) ’
Converts string to variable
TRAPOI = VAL(TPOINTS$) ’
Converts string to variable
MTB = 50
*
SWETIM / (TRAPOI-1) ’
Calculates the MTB
PRINT "Main Time Base ="; MTB ’
Prints the MTB
In a similar way, the time value Ts that is associated with a trace sample point can
be calculated from the following expression:
Ts = <sample_index>
*
SENSe:SWEep:TIME / (TRACe:POINts - 1)
where <sample_index> is the point number of the sample in the trace.
3.8.3 Real time acquisition
Since there is a physical limit to the maximum sample rate of the ADC, traces with
a duration which is less than 200 ns cannot be sampled within one real-time
acquisition. To allow you to go below the 200 ns limit, the CombiScope instrument
uses particular random sampling techniques, where points in the requested trace
are collected from a number of successive acquisitions. The result returned is a
reconstruction of the original signal out of several acquisitions, which is not real
time.
When real time acquisition needs to be guaranteed, the command
SENSe:SWEep:REALtime[:STATe] must be set to ON. This disables the random
sampling techniques. The trade-off is that the SENSe:SWEep:TIME range is
limited to 200 ns. After
*
RST the :REALtime command is set to OFF.
The "peak detection" function allows the Analog-to-Digital Converters (ADC) to
operate at their highest speed, even when a lower time base speed is selected.
The result is that maximum and minimum peaks of the signal are detected, even
at lower time base speeds. This is called oversampling. The
SENSe:SWEep:PDETection[:STATe] command allows you to switch peak
detection on or off.
PROGRAM EXAMPLE:
CALL Send(0, 8, "
*
RST", 1) ’
Real time mode off
CALL Send(0, 8, "SENSe:SWEep:REALtime ON", 1) ’
Real time mode on
CALL Send(0, 8, "SENSe:SWEep:PDETection ON", 1) ’
Sets peak detection on.