Experimental Physics and
Industrial Control System

Valentyn Stadnytskyi via Tech-talk <tech-talk at aps.anl.gov> · Fri, 17 Jul 2020 11:13:08 -0400

Hello All,

I hope you all are doing well.

I am a user at BioCars. I have a few questions about data acquisition strategies. But before I ask them let me briefly describe a situation which might be very familiar to all of you.

I am collecting X-ray images (of whatever sample/ technique). I want to know and save other data associated with the image. For example, I want to save temperature, humidity, motor1 position, motor2 position, laser intensity and the pressure(and list can go on and on) at which the image was collected. Let us assume that all of these devices and DAQs are on the network and have PVs associated with the values I am seeking. I can imagine two different peripheral data collection strategies. 

- First, my image collecting software subscribes to the PVs, and whenever I get the new image I save it and all last known values of PVs with it. 
- Second, I sent a request to an archiver(a place where all PV values are saved with according timestamps) that returns values at the requested time. The second one requires additional infrastructure, some kind of server(a middle man) that will collect all PV values and process request from clients. 

How do you collect data from all additional devices\motors etc. Do you use strategy 1 or 2 or else? If you use strategy 1, how do you ensure that you don’t get very old PV value or you don’t get NAN. If subscription to PVs works well my main program should always have the most recent value. Is it correct? 

Can someone recommend something to read on how a beamline handles data collection?

Valentyn

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System