Appendix B
External Triggering
Overview
The USB4000 supports five triggering modes, which are set with the Trigger Mode command. A detail of
each triggering mode follows.
Normal (Free Running)
In this mode, the USB4000 uses the user-defined integration clock and continuously scans the CCD array.
All of the signals described in the previous section are provided by the spectrometer to the CCD
automatically based on the integration time selected in the software by the user.
External Software Trigger
In this mode, the ExtTrigIn signal acts as an enable switch. If ExtTrigIn is kept HIGH, the USB4000 will
acquire spectra as if it was in the normal free running mode. If ExtTrigIn is kept LOW, the USB4000 will
not acquire spectra.
External Hardware Trigger
In this mode, the USB4000 uses the software (user) defined integration clock; however, the integration
period doesn’t begin until the External Trigger Input Signal (ExtTrigIn) goes HIGH. If no External
Trigger Input Signal is applied, the spectrometer will not take any spectra, and the software will appear
“frozen” until an External Trigger Input Signal is detected. With ExtTrigIn going HIGH, the
spectrometer will provide the required signals to the CCD as shown below (note that in the following
diagram, the spectrometer is in non-shutter mode):
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