ADAndor iKon CCD low saturation point

["Pearson, Matthew R. via Tech-talk" <tech-talk@aps.anl.gov>]

Hi,

We have an Andor iKon CCD that we recently updated to RHEL7 from RHEL6. This involved updating the Andor SDK2 from version 2.98 to 2.102, and the ADAndor module from 2.2 to 2.8. 

We’re seeing that the CCD saturates at a lower point compared to before. Before, we could get >50,000 pixel counts and not see any saturation effects, but now we only get about 35,000 counts and we start to see saturation. That’s with the PreAmpGain set to x1. If I increase the PreAmpGain then I can get reasonable results and use the whole 16-bit ADC range before we see the CCD saturate. 

I’m wondering if anyone else has seen this issue, or can point in the right direction? 

The driver in ADAndor has some extra support, related to setting the frame transfer mode, vertical shift period, EM gain, read out mode. Not sure if they affect the CCD saturation point. I tried varying vertical shift period but it didn’t affect things much. And the iKon doesn’t have an EMCCD so i don’t think EM gain applies.

There was a change related to setting the pre amp gain on Jan 3, 2017, which seems to change which PV is used to set the pre amp gain (ADGain to AndorPreAmpGain)… and, as I’m writing this, I realize this might be the issue:

My current value of ADGain is 1. Setting this in the Andor SDK corresponds to x2 gain. So we were using x2 before. 

My current value of AndorPreAmpGain is 0, which corresponds to x1 in the Andor SDK. 

So I guess that might explain it. It seems like that commit didn’t have to break the existing ADGain function, in order to get the AndorPreAmpGain record working?

Cheers,
Matt

Data Acquisition and Controls Engineer
Spallation Neutron Source
Oak Ridge National Lab