Model 871A User’s Manual MAKING MEASUREMENTS
Bristol Instruments, Inc. 32
External Trigger
Trigger Logistics
The 871 system can be triggered through the monitor port for coordinating
measurements with external equipment. Either a rising or falling edge TTL trigger can be
specified. Figure 5.1 illustrates the timing of the trigger signal for a falling edge trigger
(T
RATE
). The dotted lines for 2.5v and 1v represent the necessary voltage for rising and
falling TLL triggers, respectively. After being triggered, the instrument will measure for a
period defined by the Frame Rate (T
MEAS
). Once the measurement is finished, the
wavelength computation will take place (T
DATA
). Once the computation is complete the
result will be written out the RS-422 port. To facilitate instrument handshaking, the
CALC signal TTL output is available to show when a measurement cycle is complete.
On the rising edge of the CALC signal the instrument is ready to receive a trigger for the
next measurement.
Figure 5.1: Connection Settings Screen
NOTE: If the instrument is triggered faster than the set Frame Rate, not all trigger signals
will initiate measurements.
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