Cheetah Python Cameras User Manual | CoaXPress (CXP) Interface
August 27, 2019
Page
60
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86
Rev 1.0
Frame Time Control
Internal Line and Frame Time Control
The camera speed (frame rate) depends on the CMOS read-out time (frame time). Frame
time is the time it takes to read out all of the pixels on the CMOS imager. The following
formula (1.1) calculates the frame rate:
Frame rate [fps] = 1 / read-out time [sec]
(1.1)
4.2.1.1
Pixel Clock Rate Control
The camera read-out speed exceeds the CoaXPress (CXP) interface output rate. You can use
the Pixel Clock Rate function to program the camera’s speed to match the CXP image
capture rate. Decreasing the pixel clock rate decreases a camera output rate.
You should never use Pixel Clock to control camera frame rate; for best image quality, you
should always set the Pixel Clock to the maximum rate possible without the CXP interface
missing or skipping data. This minimizes the dark current generated within the pixel and
the dark current noise.
Changing Pixel Clock for the C5190, C4191, and C4190 cameras is not recommended.
4.2.1.2
Programmable Frame Time Control
After adjusting the Pixel Clock Rate to minimize the line read-out time, you can increase the
frame time using the programmable Frame Time function. When enabled, the sensor reads
out the frame, then idles and inserts a vertical blanking period at the end of the frame
readout to provide the desired frame rate.
In this way, you can match the camera’s frame rate to application requirements. You can
reduce the frame time to about one second with a precision of one microsecond. Using
Frame Time control, you can achieve exposure times longer than the time needed to read
out the image sensor.
Zero Row-Overhead Time (ROT) Control
A Row-Overhead time (ROT) control is provided and the control is called: “Zero-Row
Overhead Time” (Zero-ROT). Disabling Zero-ROT adds one microsecond of blanking time at
the end of each row to further reduce the line rate. Zero-ROT should only be used as a last
resort and only when decreasing Pixel Clock line rate control to the minimum value still
results in frame grabber overruns. Zero-ROT must always be disabled and is not supported
when pixel averaging is used.
If the exposure time is greater than 50 ms, keep camera vibration to a minimum to keep a
motion induced smear from appearing on the image.
