LBXXXA Series USB Powe
™
Product Manual PMA (Power Meter Application)
Revision: 08/02/11
- 35 -
Triggering
The
Triggering
menu (standard and option 003) allows for a number of triggering capabilities as shown below. The
single input trigger is controlled by the
Single Meas
button on the display. Trigger In and Recorder Out share a bi-
directional connector labeled TI/RO on the sensor body and their operation is mutually exclusive. Refer to the trigger
specifications on the data sheet for electrical parameters.
The trigger-in features are available on sensors with the option present. The trigger is assumed to be a TTL level and
positive edge triggered. The trigger-in can be enabled, disabled or inverted.
The trigger-in defines or controls the start of a measurement cycle. After the trigger is detected the measurement will
commence and will continue for the specified number of averages. Once a measurement is requested the system will
monitor the trigger-in port. If a trigger is not detected in the allotted time, the system will time out and return an invalid
measurement.
The trigger may be inverted: When the trigger-in is inverted the system will look for a negative edge (instead of a
positive edge) and begin the measurement when a negative edge is detected. There is provision for setting a timeout
period for an external trigger input (up to 30 seconds) as shown.
The trigger-out is compatable with TTL levels. It can be enabled, disabled and inverted (or normal). The trigger-out
occurs at the beginning of a measurement. This means that if the measurement is untriggered (i.e. trigger-in is
disabled) and trigger-out is enabled, a trigger will be produced each time a measurement is made. If the trigger-in is
enabled then the trigger will be passed through when it is received.
A trigger output is normally low. When a trigger is produced it begins with a positive-going edge and stays at a TTL
level for a few microseconds then returns to ground potential. If the trigger-out is inverted it will transition from a high
to a low TTL level. When a trigger is produced a negative edge will be produced going to a TTL low. Then after a few
microseconds it will return to a TTL high.
NOTE:
The application software handles the trigger condition for each sensor in serial fashion. When multiple sensors
are running, the absence of a trigger in one instance will force a wait state and cause the other sensors to update at a
slower rate. This would occur if a sensor lost its external trigger source for example.
