Re: Scaler/MCS dark counts?

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

Hi Jesse,

I don't have the solution you are asking about.  But many beamline counting chains have the following components in sequence:

• Detector with current output (e.g. ion chamber or photodiode)
• Current to voltage amplifier (e.g. SRS 570)
• Voltage to frequency converter
• Scaler or MCS

In that case the current to voltage amplifier typically has an offset adjustment that can be used to set the dark counts to very close to 0.

In the interest of data integrity, it may be better to record the dark counts separately in data files and apply the correction later.  That is how we do it with images in tomography, since doing the correction in real time can make it hard to recover if it turns out the dark values applied were incorrect.

Mark

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Jesse Hopkins via Tech-talk <tech-talk at aps.anl.gov>
Sent: Friday, March 13, 2026 11:48 AM
To: EPICS Tech-Talk <tech-talk at aps.anl.gov>
Subject: Scaler/MCS dark counts?

 

Hi folks,

I wanted to check with the community and see if anyone has a clever way of handing dark counts for scaler and MCS records (e.g. those from a Joerger VSC 8/16 and Struck SIS3820 or measurement computing CTR08). For years we’ve essentially just been creating ao records, writing our current values dark to these records as cts/time, and then in our data collection software (python based) we manually apply these corrections as needed. I’m working on setting up and testing a new set of scalers and MCS for our beamline and it seems like there should be a better way.

At least for a scaler, I could imagine setting up a set of calc or scalcout records that take as input the dark cts/time, the counts, and the count time, and does the subtraction. Presumably you could trigger these off the COUT or COUTP links in the scaler (though that triggers each time it starts or stops). I don’t know if there’s a way to make sure that this happens synchronously enough that you could use these dark subtracted calcs in a scan. For an MCS, I don’t know if there’s a way to do this calculation on the fly (as we typically read out values as they come in).

Anyways, I suspect this is something that lots of folks have thought about, and maybe someone already has a nice working solution I could just slot in or adapt for our needs. I’d be interested in hearing what folks have done, there doesn’t seem to be a lot that’s searchable, either on this list or just on the web) about dealing with dark counts for these types of records.

All the best.

- Jesse

 

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Jesse Hopkins, PhD (he/him)
Director, BioCAT

Sector 18, Advanced Photon Source

Research Associate Professor, Illinois Tech