Kaon_LT Experiment

h1. Brad  Sawatzky's comments on scalers

In 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.)