Measurement Computing WaveBook rev.3.0 - Manual (Page 142)

8-8 Theory of Operation, 6-24-99 WaveBook User’s Manual
Acquisition Operation
Acquisition Modes
The acquisition mode determines the make-up of the acquisition—the number of scans and their relation to
the trigger. The 4 acquisition modes are: N-shot, infinite post-trigger, N-shot with re-arm, and pre/post-
trigger.
N-Shot Acquisition Mode
The N-shot mode, shown below, is the simplest. After the trigger, it collects a fixed number of scans,
from 1 to 100,000,000.
Scan 1 Scan 2 Scan 3 Scan N Scan N-1
No acquisitions
before trigger
Scan Period
Samples in Scan
Trigger
Time
N-Shot Acquisition
1 µs/sample
Channel ch1 ch3 ch5 ch2 ch7 ch1
×1 ×5 ×10 ×5 ×1 ×5 Gain
Uni Uni Uni Bi Bi Bi Offset
After the acquisition has started with the daqArm command, the N-shot mode waits until a trigger occurs.
After the trigger, it collects the post-trigger number of scans (as specified by wbkSetAcq) and then stops.
No more data will be collected until another acquisition has been started. As shown above, each scan
consists of one or more samples, taken 1 microsecond apart. The scans are repeated with the post-trigger
scan period that was specified with daqAdcSetRate or daqAdcSetFreq. The number of scans
collected (N) may be set from a minimum of one scan after the trigger to a maximum of 100,000,000 scans.
Infinite Post-Trigger Acquisition Mode
It is possible to collect an unlimited number of scans after the trigger by using the infinite post-trigger
acquisition mode as shown below.
Scan Period
Infinite Post-Trigger Acquisition
Trigger Disarm
Time
This mode is similar to the N-shot mode except the total number of scans is not limited. With infinite post-
trigger, scans are continually taken at the post-trigger scan rate. When the desired number of scans have
been gathered, the daqDisarm command must be used to terminate acquisition.
N-Shot with Re-Arm Acquisition Mode
The N-shot with re-arm acquisition mode is used to collect scans after each trigger, as shown below.
Scan 1 Scan N
No acquisitions
before trigger
No acquisitions
after dis-arm
Scan Period
N-Shot With Re-Arm Acquisition
Trigger
Time
Trigger Trigger
Disarm
****
This mode is similar to the N-shot mode except that after the "N" scans have been acquired, the trigger is
re-armed so another "N" scans will be taken for each subsequent trigger. As in the infinite post-trigger
mode, the daqDisarm command must be invoked to prevent further acquisitions.