44 CBLé System Guidebook
About CMD3—Sample and Trigger Setup
(Continued)
External Clock Source
This parameter lets you select one of two physical sources to be used as
a clock or trigger signal. It is used only when an external clock is
specified when you set the Sample Time parameter to zero (see page 39),
or when you set the Trigger Channel to 21 (see page 41). (Default:
0
)
0
Selects the signal on the External Clock-In line of Channel 21
(
DIG IN
). This input is a 0–5 Volt logic input with a threshold near
one-half battery voltage. The polarity of the clock edge or trigger
transition is established by the Trigger Type parameter that you
select.
1 Selects the signal on the Vin line of
CH1
. This input is a ±10 Volt
analog input. The threshold can be set to one of seven levels in
this range by the value of the Trigger Threshold parameter (see
page 71). The polarity of the clock edge or trigger transition is
established by the Trigger Type parameter that you select.
Note: To ensure that samples are only taken at external clock events,
Trigger Channel 21 (
CH21
) should normally be selected when using an
external clock source.
Record Time
This parameter lets you specify whether CBL records absolute or
relative time during data collection. (Default:
0
)
0
1
2
None. No time value is recorded.
Absolute. Records the actual time in seconds from the start of
data collection.
Relative. Records the time in seconds between samples.
If any derivatives are requested (Post-processing set to 1 or 2 in
CMD1
),
relative record time is automatically turned on.
Note: Record Time will not operate when the Number of Samples
parameter in Sample and Trigger Setup (
CMD3
) is L1 (for real-time
display of collected data).
When the Sample Time parameter specified in
CMD3
is greater than or
equal to 0.25 seconds, the absolute record time for the first sample will
be about 0.013 seconds longer than the Sample Time that you specify for
points stored after the trigger point.
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