Sunday, November 21, 2010

Line scan screamer

A note came across my desk the other day informing me that Dalsa have introduced a pair of Piranha 3 line scan cameras. (For all I know they’ve been on sale for a while, but I’ve only just learnt about them.) There are three features of these cameras that I find interesting: the resolution, the speed and the pixel size.

Resolutions are 8k and 12k, which for the user means either higher resolution or fewer cameras for a web. Of course, a wider field of view can also mean more optical distortion, and more pixels means more bits to process, so speed can become an issue.

And talking of speed, these babies are fast! The 8k has a line rate of 33.7kHz while the 12k manages 23.5kHz. That’s a whole bunch of pixels to process every second. (The 8k
Basler Sprint delivers a line rate of 70kHz, but they don’t offer a 12k line scan camera, to the best of my knowledge anyway.)

Now what about pixel size? Well if you download the Piranha 3 datasheet, (registration is required,) you’ll see that the 8k sensor features 7µm pixels while the 12k has pixels 5µm in size. This keeps the two sensors approximately the same length, but what does it mean for imaging?

To answer this, in part anyway, Dalsa have provided a graph on the datasheet showing the responsivity of each sensor. This tells us that the 8k sensor with the larger pixels is about 30% more sensitive to light than the 2k with the smaller pixels.

Surprising? Well it shouldn’t be. A 7µm pixel has almost twice the area of one measuring 5µm, so naturally, it catches more photons. And that should raise a flag for those of you drawn to a 12k line scan sensor: it’s going to need an awful lot of light if you want to run it at its max speed.

1 comment:

Anonymous said...

e2v AViiva UM8 (ex-Atmel) goes up to 24.7kHz with 12k pixels and some smaller resolution cameras goes up to 98kHz.