Date: Tue, 07 Jun 2005 13:47:58 -0400 (EDT)
From: Dan Edmunds <edmunds@pa.msu.edu>
Subject: Using BLS signals in the Sidewalk Cal Trig test stand

Hello,

This note was to let folks know that the BLS signals out on the
sidewalk are working again.  The problem (and the reason why I
had earlier pulled the Splitter out of the BLS signal path)  was
a failed power supply to the Splitter.  That situation would have
caused trouble for the currently running Beam Physics system.

While talking with people at D-Zero last week I heard a number
misconceptions about what the BLS signals are and how they can
be used in sidewalk tests.

1. We do not need the live BLS signal on the sidewalk to record
   pedestal value data from the ADF.

   ADF can send pedestal value data at anytime - with or without live
   BLS input signals.  If it helps debug something then we are happy
   to setup the pedestals from the ADF in any special way that you may
   want.  You could record a few events with the pedestals at some
   value and then change the pedestal of one or more channels to a
   new value and and record a few more events or whatever.

2. Using the BLS signals, we can not see ADF data that includes energy
   deposits in the Calorimeter by making recorded runs between Stores.

3. Using BLS signals, we will not be able to see ADF data that includes
   any substantial number of real Calorimeter energy deposits by
   running during a Store with the current "stand-alone" trigger file
   that you use for reading out just the sidewalk test stand.

   The trigger file that you use to readout the sidewalk test stand at
   a few Hz is based only on a prescale to control when it fires.
   That is, the L1_Acpts are issued for random beam crossings.  Using
   random triggers to readout the sidewalk test stand, even during a
   Store at the highest D-Zero luminosities, you will almost never see
   an energy deposit in a set of 4 or 16 Trigger Towers.

   The only way get get events that have any juice in them is to
   use the current L1 Cal Trig to pick the beam crossings on which
   L1_Acpts are sent to the sidewalk test stand.  That is use the
   current L1 Cal Trig as part of what causes the L1 Trigger to fire
   that reads out the sidewalk test stand.

   The Reference Set used in the current L1 Cal Trig for this can be
   clamped down in eta,phi coverage  so that it requires, not only energy
   in the Calorimeter, but energy in the 4 or 16 Trigger Towers that
   are connected up to the sidewalk test stand.  That is you can set
   things up so that every event that you record will have a Cal energy
   deposit in it.

4. This whole exercise is useless unless for the same beam crossings
   (for the same L1_Acpts) you also record the Precision Cal Readout
   data and the current L1 Cal Trig data.  If you only record test
   stand data then it is just a bunch of random numbers.

   If for the same events you also record the Precision Cal Readout
   and the current L1 Cal Trig data then you can make a correlation
   with the test stand TAB readout data and prove that things are working.
   You can prove that you know where in the TAB data the signal from
   TT x,y is located and that in response to the L1_Acpt you readout
   data from the TAB for the correct BX (and not from an adjacent BX
   with no Cal energy in it).

5. Doing this correlation between the readout of the different systems
   (sidewalk TAB, Precision Cal Readout, and current L1 Cal Trig readout)
   is a good way to get the software people downstream of the hardware
   doing something interesting with the data.  The correlation between
   the Cal Precision readout and the current L1 Cal Trig readout is
   so important that it is checked by an examine for every Physics run
   and plotted in the Log Book.

   The point is that this correlation between  L1Cal2B  and the Cal
   Precision Readout is one of the first things that people will want
   to check once the new Cal Trig is installed.  This data is a way to
   interest software people in working on this now.

6. Doing all of this will require writing a trigger files to
   control the setup of the Trigger DAQ system and it will require making
   a Special Run.  You can prove that it is all working by testing it
   between stores and then it will require just a short 10 minute
   Special Run at the end of a Store to collect all the data that is
   needed.

   When testing this trigger configuration between Stores I can
   put a pulser signal into the BLS Splitter that feeds both the
   current L1 Cal Trig and the new L1 Cal Trig.

     - The pulser output bump will cause the current L1 Cal Trig to
       send And-Or Terms to the TFW that will cause the L1 Trigger,
       defined in your Trigger Configuration file, to fire.

     - The firing of this L1 Trig will send L1_Acpt's to both the
       current L1 Cal Trig and the New Li Cal Trig.  That is it will
       cause both the current L1 Cal Trig and the New L1 Cal Trig to
       readout.

     - The readout data from the current L1 Cal Trig will show the
       bump signal in the TT that the pulser is plugged into.  The
       readout data from the New L1 Cal Trig should also show this
       signal.

     - You can also readout the Precision Cal system but because this
       pulser signal is inserted at the BLS level the Cal Precision
       system will not see it.

     - If you want, the pulser can be set to inject a bump BLS signal
       for a particular BX in a turn around the accelerator  or  to
       fire on random beam crossings.

Thanks,  Dan