[Hps-ecal] ecal hv

[Nathan Baltzell]

Yes, we cannot rule out the distribution modules yet.
One option to test that is to move a "bad" HV module to a different distribution module.
-Nathan




On Dec 3, 2014, at 12:18 AM, Stepan Stepanyan <stepanya at jlab.org> wrote:

> Nathan,
> 
> Are you sure this is the problem of the slot/channel on the 
> mainframe/board or the distribution
> module. We should find a way of measuring voltages. perhaps before and 
> after the distribution
> modules in the racks (may be tricky, we can ask electronics group for help).
> 
> Regards, Stepan
> 
> On 12/2/14, 9:00 PM, Nathan Baltzell wrote:
>> Dear Everyone,
>> 
>> This evening we realized another problem probably due to the ECal HV supply.
>> 
>> First, we see gains from cosmics that are 30/40% higher on all channels in
>> certain HV groups, while all channels outside those groups are within few-%.
>> Those high-gain groups are isolated to the left half of the calorimeter, on both
>> top and bottom, and occur every other HV group.
>> 
>> One hypothesis is that it is due to motherboards, since left-top and left-bottom are
>> from one manufacturer, while right-top and right-bottom are from another.  But I
>> think we ruled that out as the primary cause out by using LEDs:
>> 
>> Swapping calorimeter channels from one HV mainframe channel to another,
>> while keeping everything else constant (including, of course, the voltage demand
>> and readback settings), resulted in large changes in measured LED signal amplitude
>> consistent with cosmic gains for these low/high-gain groups.
>> 
>> It may also be worth noting that these high-gain HV groups are on mainframe
>> channels 3,5,7,9,11 for the modules in both slots 0 and 8.  When plotting for ECal
>> geometry the correspondence with mainframe channel is not obvious, due to
>> mappings and relocation of one dead channel to another slot.
>> 
>> So it seems the large variations in cosmic gains for certain HV groups must be due
>> to the HV supply and nothing to do with the calorimeter.  One question is what to do in
>> the short term for 2014 running.  We can try moving the modules to open slots, or
>> just reseating them, both possible tomorrow.  Or measure voltages directly at the
>> calorimeter and adjust accordingly, ignoring mainframe's readback.   Or just correct
>> with gains, which could require some channel-dependent thresholds for data
>> acquisition.
>> 
>> - Nathan
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