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Tech Papers

The Camera's Too Hot!?

by Robert Miskelly, Technical Marketing Manager - Basler AG

 

Today's machine vision cameras are getting smaller and smaller. The reason for this trend is that camera manufacturers are listening to their customers and to the demands of the market. Most OEMs and SIs are building vision systems that are a component of larger process systems, for example, tablet filling and inspection machines. Process system manufacturers want the vision system to be a small part of their overall system, literally.

Today, many high-performance camera vendors such as Basler Vision Technologies (Machine Vision Components, Basler-MVC), DVC, and Teli offer smaller cameras to meet the demands of the market. But some other camera vendors and users are critical of this new smaller camera trend. Critics say that a camera's small size allows for little heat dissipation and is a detriment to the camera's performance.

The electronic devices used in digital cameras are typically specified to run at up to 70¼ C (158¼ F). If the temperature inside of the camera rises above that point, the devices may be damaged or destroyed. An electronic camera usually contains a CCD sensor and several types of analog and digital devices. As the temperature increases in an analog device, electrical noise in that device usually increases noticeably. Digital devices react in the same manner, but with digital signal interpretation, the noise is not usually an important factor. The performance of the CCD sensor is also influenced by increase in temperature, such that the image produced by the sensor gets noisier.

As you can see, with the potential for component damage and poor performance caused by heat, it makes great sense to keep the components inside of the camera as cool as possible. What can be done to keep the devices inside of a camera cool?

Good heat flow
Design the camera so that there is good heat flow from the internal electronic devices to the exterior camera housing. Good heat flow between the components and the housing allows the heat to be dissipated to the atmosphere around the camera rather than being held inside of the camera.

Optimal power consumption
Design the camera for optimal power consumption. Power input to the camera must equal power output from the camera, this is known as energy balance. Cameras usually have two ways for power to exit, the first is through the data connection to the frame grabber and the second is as heat. Therefore, any power that is not used by the digital drivers for LVDS communication will be converted to heat. Camera engineers carefully select the electronic devices used in cameras so that power consumption is at a minimum.

External cooling
Use external cooling. If the camera has proper heat flow between the internal components and the external housing, external cooling devices such as heat sinks, fans and Peltier coolers are very efficient.

We spoke to Basler-MVC on this topic and they said that the heat created by their camera's electronics has no effect on performance. To prove their point, Basler-MVC put their camera to the test.

The goal of the test was to see the effect of temperature on black level, bright level, fixed pattern noise (FPN), and photo response nonuniformity (PRNU) over a 24-hour period. Basler-MVC's camera was mounted and plates were affixed which could be heated by an external heating coil. Heat was applied and increased from 25¼ C to 65¼ C (77 - 149¼ F) in 5¼ C increments.

Basler-MVC is happy to report that the results showed no significant changes in performance or noise as the temperature was increased.

  • Black Level: Increased from DN2 to DN4
  • Bright Level: Fell from DN201 to DN197
  • Fixed Pattern Noise: Remains constant at +/- 1
  • Photo Response Nonuniformity: Remains constant at +/- 3 DN

The design of the camera is critical to the dissipation of heat. Basler-MVC remarks that their favorable temperature test results are a direct effect of the design of the camera and sensor housing.

Picture of camera housing
Basler-MVC's camera housings are designed for maximum passive heat dissipation. The heat of the CCD sensor is dissipated by ‘‘sandwiching’‘ the sensor between aluminum plates. The rear plate is in direct contact with the rear of the sensor package and dissipates the majority of the heat created. The front plate surrounds the sensor's photosensitive areas as though the sensor was an island surrounded by water. This ‘‘sandwiching’‘ design efficiently moves the heat created by the sensor to the exterior of the camera housing where it can be dissipated or transferred to the mechanical devices holding the camera to the vision system. In effect, the camera uses its exterior housing and other mechanical devices attached as elaborate heat sinks.

Clever housing designs are currently capable of removing excess heat from sensitive components, but as speeds continue to increase, other alternatives must be created. Basler-MVC engineers believe that new technologies, such as CMOS image sensors, will help them design higher performance cameras (over 500fps @ 1k x 1k) without the worry of heat and excess noise. An advantage of CMOS image sensors is that they use much less power and thus will create less heat, so Basler-MVC will be able to increase clock rates without any effect on heat.

The next time you touch a cool camera remember to ask yourself where is the heat going.

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