302Alvium USB Cameras User Guide V4.6.1
Performance and troubleshooting
Impact by other features
Exposure times and frame rates with Sony IMX rolling
shutter cameras
Alvium 1800 U-1240 m/c, and U-2050m/c
Generally, long exposure times result in low frame rates because one is roughly the
inverse of the other. With Alvium IMX RS cameras
• The range of available frame rates depends on the exposure time.
• The exposure time must be increased when low frame rates are used.
• The available range for frame rate values depends on the exposure time. If by
changing the exposure time, the previous frame rate is moved out of the
available range, the frame rate is adjusted automatically.
Dark current compensation
All sensors accumulate dark current in the pixels. Dark current increases the signal
level and black level. Most sensors in Alvium USB cameras compensate for this.
For Alvium 1800 U-050m/c with the ON Semi PYTHON 480 sensor, see Black level
compensation for 1800 U-050m/c on page 304.
If cameras are operated at high temperatures or long exposure times,
compensation reaches its limits. The typical compensation mechanism uses a
margin to compensate for dark current. This works only until dark current reaches
the size of the margin. The following table shows the relation of the margin and
accumulated dark current for a pixel in 8-bit mode with a maximum value of 255.
Input
Output
Exposure time values Frame rate
AcquisitionFrameRate
Not affected Affected
ExposureTime
Affected as expected Affected
DeviceLinkThroughputLimit
Affected Affected
Height
Not affected Affected
Width
May be affected May be affected
Table 153: Impact by other features
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