Why should cameras not have fans for accurate measurements?

Posted by Benny Koene on Thu, May 4, 2017

Cameras produce a significant amount of heat, especially the latest large resolution image sensors running at high frame rates such as the On Semi Vita25k, the Python 25k and the CMV50000. This heat is mainly originating from the image sensor (image read-out) and the FPGA (image processing) and it needs to be removed from the camera efficiently. Too much heat can damage the image sensor or FPGA. Furthermore the image noise will increase with increasing temperature.

For camera manufacturers there are a few options for heat management.

• The best option for heat management is to design the image sensor control and image processing architecture in a way that maximizes the computations per miliwatt and therefore minimizing heat generation in the first place.

• They can design the mechanics to have efficient heat conduction properties such that heat from the sensor and FPGA are directed to the camera housing efficiently. After reaching the camera housing the heat is transferred to the environment which could be by transferring the heat to the air around the camera or by a metal heat sink which is connected to the camera on system level.

• Another option is to implement a fan in the camera to cool the camera by airflow.

The second option is challenging but well worth the effort as using a fan has significant disadvantages on design and measurement accuracy:

• Fans increase power consumption, and more power consumption causes additional heat. For example a fanless camera could have a power consumption of 8 W compared to about 18 W with a fan.

• Fans could cause vibrations that could influence your measurements. This is especially a problem with measurements using multiple images.

• Fans decrease system reliability - the moving mechanical parts require maintenance.

• As fans move air, they also move around dust that could contaminate the optical path.

• Last but not least fans could influence form factor (more than double the width and weight). In general fans are relatively large compared to the camera. Smaller fans are less efficient as well.

Because of the above disadvantages of fans, Adimec designs their cameras without fans and optimizes the mechanical construction to both evenly distribute and efficiently transfer heat away from the sensor and FPGA to the camera housing. This keeps the camera compact (see image below) and if additional cooling is necessary the system integrator could connect the camera to a heat sink, i.e. a large metal surface.

Cameras that use fans are generally poorly designed mechanically but more importantly they are poorly designed in their image sensor control and image processing architectures, using too much computational brute force and unnecessary memory operations.