Measurement Computing StrainBook/616 - Manual (Page 99)

TTL Trigger
The TTL digital trigger signal connects via pin 13 on the DB25 digital I/O connector, and is used directly.
An optional CA-178 cable (following figure) can be connected to the front panel DB25 connector to
provide convenient Trigger and/or External Clock connection via BNC connector.
The TTL trigger signal is examined under program control for either a false-to-true (rising edge) or true-to-
false (falling edge) transition. When the transition occurs we have a 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.
Chapter 7 contains additional information regarding triggers.
StrainBook with Optional Clock and External Trigger Cable (CA-178)
StrainBook/616 977794 Digital I/O, TTL Trigger, and External Clock 8-3
External Clock
The External Clock Input connects to pin 20 on the front panel DB25 connector. An optional CA-178
cable (preceding figure) can be used to provide convenient Trigger and/or External Clock connection via
BNC connector. The External Clock feature enables data scanning to be correlated with an external pulse
train
.
To enable the external clock, select the button for the Scanning Rate in the Acquisition
Configuration
Dialog Box (see following screen shot). When the external clock is enabled the StrainBook
begins a scan
only after a rising edge on the TTL level occurs. Optionally, the external clock may be
divided [by a factor of 1 to 255]. This “pre-scaling” allows the user to select a reduced scan rate.
The external clock is useful when data collection depends on rotational speed or axial position. By
synchronizing the system with an external event for correlation of data, you can collect event-dependent
data instead of time-dependent data.
Make sure to adhere to the minimum slew rate requirement of 20 v/µs.
Note: The Clock Divider
can be set to a value
from 1 to 255.
Acquisition Configuration Dialog Box with External Clock Enabled