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Brad's comments on scalers » History » Revision 2

Revision 1 (Richard Trotta, 12/03/2020 10:47 AM) → Revision 2/3 (Richard Trotta, 12/03/2020 10:51 AM)

h1. Brad    Sawatzky's comments on scalers 

 In general, general the scaler trees for each arm expose the scaler data for 
 modules associated with that arm (likely stating the obvious).    However, 
 a number of signals are fanned out to two scaler modules, one in each 
 arm.    If you're running in 'COIN mode' (single DAQ for both arms), then 
 the counts for those duplicated signals should be (basically) identical. 

 Strictly speaking the content of the two scaler trees is entirely 
 controlled by the analyzer software configuration (THcScaler* configs). 

 Known reasons for discrepancies between the two scalers viewing the same 
 signal could include: 
 - There appears to be a problem with some of the "G0 scalers". 
   Apparently they have a bit-flip issue.    Steve documented this here: 
     https://hallcweb.jlab.org/DocDB/0010/001058/001/Scaler_Problem.pdf 
   - If the scaler channels you're seeing issues with are in the same 
     physical modules, then that is almost certainly your problem. 
     - Mitigations are discussed in that file as well.    (Carlos should 
       be familiar with this.) 

 - Electronic artifacts and low-level timing differences in the gating 
   between the two scalers 
   - Should only be a difference of a few counts at most on high-rate 
     channels 


 You do need to be mindful that the HMS 'trigger scalers' may be 
 different than the 'SHMS trigger scalers'.    Each arm has a scaler that 
 counts the 'T1, T2,...' trigger signals plugged into each arm's Trigger 
 Master module.    Those are not necessarily the same triggers, but the 
 names can be confusing because each arm can have its own set of T1, T2, 
 ....     The trigger assignments are documented in HCLog entries, and 
 should also be reflected in the hcana scaler configuration git commits. 

 If you're looking at Coincidence-mode runs, and you think you're looking 
 at the same hardware signals in two different modules, then try plotting 
 the /difference/ between the two duplicate scaler channels for each 
 scaler read (note scalers are read out periodically, not on every 
 trigger).    It would be interesting to see one duplicate is always 
 reading X% more than the other, or if they are generally identical 
 except form some occasional outliers. 

 the scaler dbase/param files should shed a lot of insight into 
 the hardware configuration (without having to get eyes on the physical 
 setup).    For direct duplications, we typically jumper an entire 16 
 channel ribbon cable across 2 scaler modules, so you'll see two 16 
 channel groups in the dbase files that have identical names in the same 
 order. 

 If you see a situation where an HMS scaler channel and an SHMS scaler 
 channel have the same 'name' but they are not embedded in a block of 16 
 other identical channels, then you'll want to look a little more closely 
 at the details to see if they are really individually fanned out copies 
 of the same channel, or if it is a 'similar name' issue. For example, 
 one channel is the SHMS arm 'T3', and the other is the HMS arm 'T3'. 
 (In that case it is possible they are looking at different input 
 signals.)