NI 1772 camera exposure time adjustment resolution

[Rob518]

What is the exposure time adjustment resolution capability for the NI 1772 camera?  I'm getting only 10ms.  Can I get 5 or even 1ms resolution?

[Rob518]

My bad.  Units are in us, not ms. 

[BlueCheese]

Hi Rob,

The 1772's exposure time adjustment goes from 33.125us to about 1.2 seconds I believe. I can't recall the granularity off-hand, but it is certainly sub-microsecond.

What software are you using with the camera? Have you tried adjusting the exposure time inside of Measurement and Automation Explorer (MAX)?

Eric

[Rob518]

Hi Eric, 

Thanks for the help.  I'm using Vision Builder AI 2011.  I would think that adjustment changes of 10us of exp time would be enough granularity, but I'm getting large changes of intensity readings from the camera (157; 197; 215) for each 10us change in exp time.  My image brightness changes more than I would like.  I do not know what MAX is. 

[Rob518]

Also, there are some adjustments to the exposure time that don't change the intensity at all.  For instance, a change from 70 to 80us gives the same intensity of 215.  A change from 80 to 90us changes the intensity to 231. 

Thanks, Rob

[BlueCheese]

Hi Rob,

I am unclear what the problem you are seeing is. Vision Builder AI does not appear to impose any restrictions on the granularity of the exposure time. You can put any value with precision down to sub-microsecond levels (no need to go by units of 10 microseconds).

As for the changes in intensity vs exposure time, keep in mind that image sensors and the hardware that reads them don't necessarilly behave linearly and so you may not see such a linear relationship in the data. While you said that you saw no change in intensity from 70us to 80us, were you looking at a single pixel or an average of the entire sensor? If you average it over the whole sensor I think you'll see the difference (although it might be small and less than a single count).

Eric

[AnalogKid2DigitalMan]

Are you using a DC powered source and are there any AC powered lights that may be reflecting off of the object you are imaging?

I wonder that if your exposure are so short that you may be picking up AC powered light sources that actully turn on/off 100-120 times per second. But that may lead to totally random intensities. No direct 'exposure' to this, just postulating an idea.

-AK2DM

[AnalogKid2DigitalMan]

Eric:

Did you give me the kudo for the bad pun or my hypothesis?

Thanks

-AK2DM