[Hps-ecal] ecal hv

[Stepan Stepanyan]

OR, we could first measure voltage right at the output of the distribution
module and see if it is different from the set value.

Stepan
On 12/3/14, 6:16 AM, Nathan Baltzell wrote:
> 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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