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Frame Interval Timings - 2

This section describes camera timings when using continuous read mode controlled by the on-board DSP.

  • CCD clear only occurs on the first cycle and is typically on the order of 75 ms. Cycles 2 - n do not have a CCD Clear cycle.
  • Exposure time specifies the time the sensor is exposed to light and is set as part of the 'Set Exposure Time' command
  • Read-out time indicates the time it takes to readout the array. This time depends on array size and and read-out mode selected. For Hamamatsu 7031-1007 type sensor (1024x128) using FVB that time is in the 5 ms range. For the same array using area read-out mode the time is ~ 250 ms.
  • Frame pad is the time added to each cycle to accommodate the data transfer time to a PC or the balance of the frame interval time (see Frame Interval Timings Explained)
  • Communication to the PC using High speed USB link is typically 100 MBits / sec and is overlapped with the previous exposure and read out time

Example:
7031-1007 (1024x128) FVB, 1 sec exposure, 2 sec frame interval will yield the following:

  • Cycle 1:
    o Clear CCD: 75ms
    o Exposure: 1 sec
    o CCD Readout: 5 ms
    o Frame Pad: 995 ms (Balance of the 2 sec frame interval time)
  • Cyc 2
    o Clear CCD: 0 (No Clear CCD takes place)
    o Exposure 1 sec
    o CCD Readout: 5ms
    o Frame Pad: 995 ms
  • Cyc n
    o Clear CCD: 0
    o Exposure 1 sec
    o CCD Readout: 5ms
    o Frame Pad: 995 ms

Note: effective exposure for first cycle is 1 sec, however, effective exposure for cycles 2 - n is ~ 2 sec.
Also, data transfer to the PC (4K bytes) takes less 1 ms and is effectively overlapped with (exposure, read-out, and frame pad). In this scenario it's best to discard the 1st frame.

Example 2

7031-1007 (1024x128) FVB, 1 sec exposure,  0 sec frame interval will yield the following:
  • Cycle 1:
    o Clear CCD: 75ms
    o Exposure: 1 sec
    o CCD Readout: 5 ms
    o Frame Pad: 0 sec
  • Cyc 2
    o Clear CCD: 0
    o Exposure 1 sec
    o CCD Readout: 5ms
    o Frame Pad: 0 sec
  • Cyc n
    o Clear CCD: 0
    o Exposure 1 sec
    o CCD Readout: 5ms
    o Frame Pad: 0 sec

Note: In this case the effective exposure for all the cycles (1, 2, n) is 1 sec

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