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Brad's comments on scalers » History » Version 1

Richard Trotta, 12/03/2020 10:47 AM

1 1 Richard Trotta
h1. Brad  Sawatzky's comments on scalers
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In general the scaler trees for each arm expose the scaler data for
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modules associated with that arm (likely stating the obvious).  However,
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a number of signals are fanned out to two scaler modules, one in each
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arm.  If you're running in 'COIN mode' (single DAQ for both arms), then
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the counts for those duplicated signals should be (basically) identical.
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Strictly speaking the content of the two scaler trees is entirely
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controlled by the analyzer software configuration (THcScaler* configs).
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Known reasons for discrepancies between the two scalers viewing the same
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signal could include:
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- There appears to be a problem with some of the "G0 scalers".
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  Apparently they have a bit-flip issue.  Steve documented this here:
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    https://hallcweb.jlab.org/DocDB/0010/001058/001/Scaler_Problem.pdf
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  - If the scaler channels you're seeing issues with are in the same
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    physical modules, then that is almost certainly your problem.
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    - Mitigations are discussed in that file as well.  (Carlos should
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      be familiar with this.)
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- Electronic artifacts and low-level timing differences in the gating
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  between the two scalers
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  - Should only be a difference of a few counts at most on high-rate
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    channels
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You do need to be mindful that the HMS 'trigger scalers' may be
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different than the 'SHMS trigger scalers'.  Each arm has a scaler that
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counts the 'T1, T2,...' trigger signals plugged into each arm's Trigger
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Master module.  Those are not necessarily the same triggers, but the
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names can be confusing because each arm can have its own set of T1, T2,
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....   The trigger assignments are documented in HCLog entries, and
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should also be reflected in the hcana scaler configuration git commits.
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If you're looking at Coincidence-mode runs, and you think you're looking
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at the same hardware signals in two different modules, then try plotting
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the /difference/ between the two duplicate scaler channels for each
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scaler read (note scalers are read out periodically, not on every
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trigger).  It would be interesting to see one duplicate is always
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reading X% more than the other, or if they are generally identical
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except form some occasional outliers.
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the scaler dbase/param files should shed a lot of insight into
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the hardware configuration (without having to get eyes on the physical
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setup).  For direct duplications, we typically jumper an entire 16
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channel ribbon cable across 2 scaler modules, so you'll see two 16
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channel groups in the dbase files that have identical names in the same
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order.
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If you see a situation where an HMS scaler channel and an SHMS scaler
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channel have the same 'name' but they are not embedded in a block of 16
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other identical channels, then you'll want to look a little more closely
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at the details to see if they are really individually fanned out copies
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of the same channel, or if it is a 'similar name' issue. For example,
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one channel is the SHMS arm 'T3', and the other is the HMS arm 'T3'.
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(In that case it is possible they are looking at different input
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signals.)