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iXon 3

Features & Functionality

3.5.2.2 - External & Fast External (NFT)

In External Trigger modes once an acquisition has been started, the camera is placed into the special clearing cycle

called“External Trigger Keep Clean’ which was discussed previously. As can be seen from the gure below the

external keep clean cycle runs continuously until the rst external trigger event is detected at which point the current

cycle series will complete before the exposure phase starts. During the exposure there are no vertical clocks running,

however,therewillbehorizontalclockstoensurethattheshiftregistercontinuestobekeptclean.Oncetheexposure

time has elapsed the charge built up in the Image area is quickly transferred into the Storage area. From the Storage area

the charge is read out as normal. At the completion of the readout the camera restarts the external keep clean cycle.

If the camera is in Fast External Trigger mode it will accept a trigger event immediately and start the next exposure.

If, however, the camera is in normal external trigger the camera will perform sufcient External keep clean cycles to

ensuretheImageareaisfullycleanedbeforeitwillacceptanexternaltrigger.Oncethisperiodhaspassed,Normal and

Fast External Trigger operate the same.

Fast External Trigger is useful in those cases where there is very little background light and the user is looking for the

fastest frame rate. With Fast External Trigger, you may see variation in the background contribution to the signal from

light that may have been allowed to fall on the sensor during the readout of the previous image. Fast external trigger

does not mean that when a trigger is accepted that the system will respond quicker than in normal external trigger

mode.

NOTE: There is no need to worry if the trigger occurs at the early phase of the keep clean cycle as the light signal

will not be lost during the completion of the cycle, since only one vertical shift will have occurred. For pulsed light

of very short duration (of the order of one vertical shift), the resultant image may appear to have shifted one row.

Figure 33: External Trigger in non-Frame Transfer mode

Andor Technology iXon3 Series User Manual

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