[Hps-ecal] ecal hv

[Stepan Stepanyan]

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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