WaveBook/512 and WaveBook/512H
03-06-02
WaveBook Operation Reference 3-9
Triggers
External signals can be used to start or synchronize the data acquisition process. WaveBook/512 and
WaveBook/512H 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.
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.
•
Without SSH, the trigger threshold is settable from -5.0 to +9.996 volts with 12-bit
(WaveBook/512) resolution, regardless of any channel's gain settings. This gives better than
1% resolution at even the smallest input ranges (such as 0-1 or ±0.5 volts).
•
With SSH, the single-channel (Channel 1 analog) signal is first amplified by the SSH
programmable gain amplifier before being compared with the programmable voltage. This
allows precise trigger-level adjustment, even at high gain. The analog-trigger comparator
threshold-voltage range and resolution (with SSH) are shown in the following table.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
