Omega Engineering OMB-1108-0901 用户手册
1-6 Overview & Theory of Operation
09-06-02
DaqTemp User’s Manual
Triggering
Triggering can be the most critical aspect of acquiring data. The DaqTemp PCI Board supports a full
complement of trigger modes to accommodate a wide variety of applications.
complement of trigger modes to accommodate a wide variety of applications.
Hardware Analog Triggering. Many data acquisition products claim analog triggering, but rely on the
PC to take readings and make a decision, which leads to uncertain and potentially long latencies. The
DaqTemp PCI Board uses true analog triggering, whereby the trigger level programmed by the user, sets an
analog DAC, which is then compared in hardware to the analog input level on the selected channel. The
result is analog trigger latency that is guaranteed to be less than 5 µs, significantly shorter than most data
acquisition devices. Any analog channel can be selected as the trigger channel. The user can program both
the trigger level, as well as the edge (rising or falling).
PC to take readings and make a decision, which leads to uncertain and potentially long latencies. The
DaqTemp PCI Board uses true analog triggering, whereby the trigger level programmed by the user, sets an
analog DAC, which is then compared in hardware to the analog input level on the selected channel. The
result is analog trigger latency that is guaranteed to be less than 5 µs, significantly shorter than most data
acquisition devices. Any analog channel can be selected as the trigger channel. The user can program both
the trigger level, as well as the edge (rising or falling).
Digital Triggering (P1). A separate digital trigger input line is provided, allowing TTL-level triggering,
again with latencies guaranteed to be less than 5 µs. Both the logic levels (1 or 0), as well as the edge (rising
or falling), can be programmed for the discrete digital trigger input. The digital trigger input is labeled
TTLTRG on the Digital and Analog I/O Board.
again with latencies guaranteed to be less than 5 µs. Both the logic levels (1 or 0), as well as the edge (rising
or falling), can be programmed for the discrete digital trigger input. The digital trigger input is labeled
TTLTRG on the Digital and Analog I/O Board.
Digital Pattern Triggering (P2). The DaqTemp PCI Board also supports digital pattern triggering,
whereby the user can designate any of the digital input ports as the trigger port. The programmed digital
pattern, including the ability to mask or ignore specific bits, is then compared to the actual input until a
match is detected, after which the sequencer begins the scan sequence.
whereby the user can designate any of the digital input ports as the trigger port. The programmed digital
pattern, including the ability to mask or ignore specific bits, is then compared to the actual input until a
match is detected, after which the sequencer begins the scan sequence.
Counter Triggering. Triggering can also be programmed to occur when one of the counters reaches,
exceeds, or is within a programmed level. Any of the built-in counter/totalizer channels can be programmed
as a trigger source.
exceeds, or is within a programmed level. Any of the built-in counter/totalizer channels can be programmed
as a trigger source.
Software-Based Triggering. Software-based triggering differs from the modes described above because
the readings, analog, digital, or counter, are interrogated by the PC to detect the trigger event, not in the
hardware as described above. The advantage of this mode is to permit triggering based on more complex -
situations, such as on a specific temperature, which was derived from the acquisition of at least two analog
measurements, plus the calculation of the measured temperature using linearization algorithms.
the readings, analog, digital, or counter, are interrogated by the PC to detect the trigger event, not in the
hardware as described above. The advantage of this mode is to permit triggering based on more complex -
situations, such as on a specific temperature, which was derived from the acquisition of at least two analog
measurements, plus the calculation of the measured temperature using linearization algorithms.
Normally software-based triggering results in long latencies from the time that a trigger condition is
detected, until the actual capturing of data commences. However, the DaqTemp PCI Board circumvents this
undesirable phenomenon 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
later than the actual occurrence of the signal), the DaqTemp PCI Board driver automatically looks back to
the location in memory where the actual trigger-causing measurement occurred. The acquired data that is
presented to the user actually begins at the point where the trigger-causing measurement occurs. The latency
in this mode is equal to one scan cycle.
detected, until the actual capturing of data commences. However, the DaqTemp PCI Board circumvents this
undesirable phenomenon 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
later than the actual occurrence of the signal), the DaqTemp PCI Board driver automatically looks back to
the location in memory where the actual trigger-causing measurement occurred. The acquired data that is
presented to the user actually begins at the point where the trigger-causing measurement occurs. The latency
in this mode is equal to one scan cycle.
Pre- and Post-Triggering Modes. Six modes of pre- 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.
variety of options to accommodate any measurement requirement. When using pre-trigger, the user must use
software-based triggering to initiate an acquisition.
•
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.
trigger, and stops acquiring upon receipt of the stop-trigger event.
•
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.
trigger readings to be acquired, after which, acquisition continues until a stop-trigger event occurs.
•
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.
acquired beginning with the trigger event, and is terminated when the operator issues a command to
halt the acquisition.
•
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.
acquire, after which the system continues to acquire data until the program issues a command to halt
acquisition.