System Solutions

Fractional Encoder Division

It is often the case that the external encoder signal's frequency is too high to be handled by a camera.
grabber supports fractional division factor for the encoder (line trigger) signal to the camera. It is a rarely met grabber's feature in the market, as most of smart cameras and/or grabbers allows only using  an integer division.

The importance of having ability to divide the encoder signal with real (fractional) factors can be explained in the following example:

Let's take a typical linescan camera with a maximum line rate of 18K lines/second. And let's assume that for engineering reasons the 5000-pulse encoder had to be mounted on cylinder size of 120 mm and the material is running under the camera at speed of 280 m/min.  As a result, the encoder cylinder rotates at angular speed of 12.379 rev/second. This transforms into encoder frequency of 61.894 KHz, which is 61.894K / 18K = 3.439 times higher than the allowed camera clocking. Therefore, to avoid camera overclocking the encoder frequency has to be divided by a factor equal or larger than 3.439. 

Some grabber, that would have only integer division, will allow using the factor of 4, resulting in 61.894K/ 4 = 15.474K lines/sec. It is OK from clocking speed point of view but let's see what is happening to the image resolution in this case.  If the maximum resolution for a given camera was 377 mm over 5000 pulses multiplied by division factor of 3.439 = 249 micron/ pixels, after we chosen integer division factor of 4 we reduced the resolution linearly to 290 microns. 
Therefore, by rounding up the exact required division factor to  an integer value, we, in most of cases, lose the maximum achievable resolution proportionally to the ratio of actual division factor to the required one. Depending on exact numbers, the losses could be quite high, especially with small division factors. If the required divisor is 1.1, and we have to use 2 instead, we are losing in this case more than 80% of otherwise achievable resolution.

The Crontium grabbers allow you choosing a
fractional division factor, as accurate as 0.1%. Hence, for our example, the exact division factor of 3.439 (instead of 4) can be supplied to the grabber, maintaining this way a maximum camera line rate and scanning resolution.

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Crontium stocks only very limited number of the devices. Usually only evaluation samples are available out of shelf.

Please contact Crontium for further information on quotes and lead time for a higher volumes.

Usual lead time is about 4 to 8  weeks, depending on order quantity and level of required  customizations.


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