Measurement Computing WaveBook rev.4.0 - Manual (Page 55)

WaveBook User’s Manual 06-08-01 WaveBook Operation Reference 4-9
Triggers
External signals can be used to start or synchronize the data acquisition process. Both WaveBook/512 and
WaveBook/516 series support the following trigger sources:
•
Software Trigger. This trigger event is generated by a software command from the PC
without waiting for an external event. This feature may be used to begin a data acquisition
immediately or to force an acquisition to occur if the expected trigger did not occur.
•
Digital Trigger. Digital (or TTL-level) triggering (either rising- or falling-edge input) is
performed by digital logic connected to the digital expansion connector.
•
Single-Channel Trigger. Single-Channel (or Channel 1 Analog) triggering (rising or falling
signal level) is performed by comparator-based analog hardware connected directly to
analog input channel 1.
•
Multi-Channel Trigger. Here, the trigger event is a combination of measured channel
values. WaveBook's Digital Signal Processor (DSP) performs multi-channel triggering. The
DSP samples the specified channels; if programmable conditions are met, a trigger is generated.
Multi-channel triggering examines digitized data, and the trigger latencies are much greater.
WaveBook/516 supports the four trigger sources identified above, plus two more:
Digital-Pattern Trigger and Pulse Trigger.
•
Digital-Pattern Trigger: WaveBook/516 supports a digital-pattern trigger. This expanded
digital-trigger capability allows data collection to start when a user-defined 16-bit digital
pattern is matched on the digital I/O connector. This feature is useful when trying to
capture noise, vibrations or some other physical disturbance; such as those that can occur in a
programmed logic controller’s digitally sequenced process.
•
Pulse Trigger: WaveBook/516’s pulse trigger is a high-bandwidth input that enables
triggering and the correlation of lower-speed waveforms with the occurrence of a high-
speed pulse. With pulse trigger, the user defines pulse amplitude between
±5 V and pulse
width from 100 ns to 800 ms.
More detailed information regarding triggers follows.
Digital Trigger & Single-Channel Trigger
The input of the digital (TTL) trigger and the output of the single-channel signal-comparator are each
connected directly to hardware circuits to provide low-latency triggering. WaveBook can respond to a TTL
or analog trigger with a jitter (or uncertainty in latency) of no more than 100 nanoseconds (ns).
•
If not collecting pre-trigger data, WaveBook responds to the trigger with a latency of less than
200 ns for TTL and 300 ns for analog.
•
If collecting pre-trigger data, then triggers are not acted upon until the end of the current pre-
trigger scan. This increases the trigger latency and jitter, but preserves the specified scan rates.
When using the single-channel trigger, the Channel 1 analog input signal is compared with a programmable
voltage level to generate an internal TTL signal that is true if the analog input is greater than the
programmable voltage level (false if less).
When the digital trigger is used, then the TTL trigger signal from the digital I/O connector is used directly.
The resulting TTL signal is examined under program control for either a false-to-true (rising edge) or true-
to-false (falling edge) transition which, when it occurs, is the trigger event.
If the system is ready for a trigger, then the trigger event will be acted upon. If the system is not ready (due
to incomplete configuration or because it is still finishing the previous trigger's action), the trigger will be
ignored. No indication of an ignored trigger is given.
The low-latency analog trigger compares the analog signal with a programmable voltage source. The
effective range of this voltage source depends on whether or not the WBK11 SSH option is installed.