Measurement Computing DaqBoard 3000USB Series - Manual (Page 38)

1-12 Device Overviews 988093 DaqBoard/3000USB Series User’s Manual
Digital Triggering. A separate digital trigger input line is provided, allowing TTL-level triggering with
latencies guaranteed to be less than 1 µs. Both the logic levels (1 or 0), as well as the rising or falling edge
can be programmed for the discrete digital trigger input.
Pattern Triggering. The user can specify a 16-bit digital pattern to trigger an acquisition, including the
ability to mask or ignore specific bits.
Software-Based Channel Level Triggering. This mode differs from the modes just discussed because the
readings [analog, digital, or counter] are interrogated by the PC in order to detect the trigger event.
Triggering can also be programmed to occur when one of the counters reaches, exceeds, or is within a
programmed window.
Any of the built-in counter/totalizer channels can be programmed as a trigger source. Triggers can be
detected on scanned digital input channel patterns as well. Normally software-based triggering results in
long latencies from the moment a trigger condition is detected until the instant data is acquired. However,
theDaqBoard/3000USB Series circumvents this undesirable situation by use of pre-trigger data.
Specifically, when software-based-triggering is employed, and the PC detects that a trigger condition has
occurred, (which may be thousands of readings after the actual occurrence of the signal), the DaqBoard
driver automatically looks back to the location in memory, to where the actual trigger-causing
measurement occurred. The acquired data presented to the user begins at the point where the trigger-
causing measurement occurs. The maximum latency in this mode is equal to one scan period.
Multi-Channel Triggering. The DaqBoard/3000USB Series board can be configured to trigger on any
combination of analog, digital, and/or counter input; however, not on temperature measurements. In the
multi-channel triggering mode, the maximum latency is one scan period.
Triggering can occur based on a logical “and” or a logical “or” of the multiple trigger conditions. For
example, a trigger condition could be programmed to occur for when the following three conditions are
met:
a) three analog input channels each reach their respective trigger level
b) AND two digital inputs are in the specified logic state
c) AND three counters exceed a specified frequency
Stop Trigger. Any of the software trigger modes previously described, including scan count, can be used
to stop an acquisition. Thus an acquisition can be programmed to begin on one event, such as a voltage
level, and then can stop on another event, such as a digital pattern.
Pre-Triggering and Post-Triggering Modes. Six modes of pre-triggering and post-triggering are
supported, providing a wide variety of options to accommodate any measurement requirement. When
using pre-trigger, the user must use software-based triggering to initiate an acquisition. The six modes are:
o No pre-trigger, post-trigger stop event. This, the simplest of modes, acquires data upon receipt of
the trigger, and stops acquiring upon receipt of the stop-trigger event.
o Fixed pre-trigger with post-trigger stop event. In this mode, the user specifies the number of pre-
trigger readings to be acquired, after which, acquisition continues until a stop-trigger event occurs.
o No pre-trigger, infinite post-trigger. No pre-trigger data is acquired in this mode. Instead, data is
acquired beginning with the trigger event, and is terminated when the operator issues a command
to halt the acquisition.
o Fixed pre-trigger with infinite post-trigger. The user specifies the amount of pre-trigger data to
acquire, after which the system continues to acquire data until the program issues a command to
halt acquisition.
o Variable pre-trigger with post trigger stop event. Unlike the previous pre-trigger modes, this
mode does not have to satisfy the pre-trigger number of readings before recognizing the trigger
event. Thus the number of pre-trigger readings acquired is variable and dependent on the time of
the trigger event relative to the start. In this mode, data continues to be acquired until the stop
trigger event is detected. Driver support only.