[Hps-ecal] ecal hv

[Gabriel CHARLES]

Am I allowed to measure high voltage with a standard voltmeter if they 
can measure up to 400V?

Le 2014-12-03 06:35, Stepan Stepanyan a écrit :
> 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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-- 
Gabriel CHARLES
Institut de Physique Nucléaire d'Orsay