JAI RMC-4200GE User Manual

Contents

JAI RMC-4200GE User Manual Manual pdf 26 page image

RM/TM-4200GE Series26 Operation3.3.5 Pulse Width Control ModeIn Pulse Width Control (PWC) Mode, the exposure time is controlled by the external trigger. When an externaltrigger is applied, one discharge signal (Vsub) is generated right after the active edge of the trigger. Theexposure starts when the discharge signal is in the off state. The exposure ends following the trigger active off.Exposure time is controlled by the pulse width of the external trigger. Because the CCD requires some overheadfrom trigger-active-off to the transfer gate event, the actual exposure time is equal to:Exposure Time = Pulse Width + 20.6 μsSince one discharge signal (Vsub) is generated right after the active edge of the trigger, it is asynchronous withLDV, and the discharge signal may happen during an active video transfer period, causing visible reset noise toshow in the current image. To avoid reset noise, the maximum trigger frequency in PWC mode should be lessthan 1/ (exposure time + one frame transferring time).The minimum active period of the external trigger is 5μs. Theoretically, the maximum active period of theexternal trigger is unlimited. But, due to the usability of images at 25 oC it is recommended the active period ofthe external trigger be no longer than one second.Figure 18. Pulse Width Control Trigger3.3.6 Particle Imaging Velocimetry Fixed Exposure ModeIn Particle Imaging Velocimetry (PIV) Fixed Exposure Mode, when an external trigger is applied, the first timeexposure starts the same as in PWC mode. It lasts a very short period (8μs). The second time exposure startsduring the transferring time of the first image. The second time exposure continues until the first imagetransfers completely. The second image is transferred after the second exposure. There is a short period(500ns) between the first exposure and the second exposure. In order to keep two exposure periods constant,the LDV is reset before the first image is transferred out.The maximum trigger frequency in this mode is equal to 1/ (transfer time of two frames + 4μs). The minimumactive period of the external trigger is 5μs