<p dir="ltr">This is very low current, so it's not dangerous. I am not sure about safety rule however.</p>
<div class="gmail_quote">On Dec 3, 2014 8:23 AM, "Gabriel CHARLES" <<a href="mailto:charlesg@ipno.in2p3.fr">charlesg@ipno.in2p3.fr</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Am I allowed to measure high voltage with a standard voltmeter if they<br>
can measure up to 400V?<br>
<br>
Le 2014-12-03 06:35, Stepan Stepanyan a écrit :<br>
> OR, we could first measure voltage right at the output of the<br>
> distribution<br>
> module and see if it is different from the set value.<br>
><br>
> Stepan<br>
> On 12/3/14, 6:16 AM, Nathan Baltzell wrote:<br>
>> Yes, we cannot rule out the distribution modules yet.<br>
>> One option to test that is to move a "bad" HV module to a different<br>
>> distribution module.<br>
>> -Nathan<br>
>><br>
>><br>
>><br>
>><br>
>> On Dec 3, 2014, at 12:18 AM, Stepan Stepanyan <<a href="mailto:stepanya@jlab.org">stepanya@jlab.org</a>><br>
>> wrote:<br>
>><br>
>>> Nathan,<br>
>>><br>
>>> Are you sure this is the problem of the slot/channel on the<br>
>>> mainframe/board or the distribution<br>
>>> module. We should find a way of measuring voltages. perhaps before<br>
>>> and<br>
>>> after the distribution<br>
>>> modules in the racks (may be tricky, we can ask electronics group for<br>
>>> help).<br>
>>><br>
>>> Regards, Stepan<br>
>>><br>
>>> On 12/2/14, 9:00 PM, Nathan Baltzell wrote:<br>
>>>> Dear Everyone,<br>
>>>><br>
>>>> This evening we realized another problem probably due to the ECal HV<br>
>>>> supply.<br>
>>>><br>
>>>> First, we see gains from cosmics that are 30/40% higher on all<br>
>>>> channels in<br>
>>>> certain HV groups, while all channels outside those groups are<br>
>>>> within few-%.<br>
>>>> Those high-gain groups are isolated to the left half of the<br>
>>>> calorimeter, on both<br>
>>>> top and bottom, and occur every other HV group.<br>
>>>><br>
>>>> One hypothesis is that it is due to motherboards, since left-top and<br>
>>>> left-bottom are<br>
>>>> from one manufacturer, while right-top and right-bottom are from<br>
>>>> another. But I<br>
>>>> think we ruled that out as the primary cause out by using LEDs:<br>
>>>><br>
>>>> Swapping calorimeter channels from one HV mainframe channel to<br>
>>>> another,<br>
>>>> while keeping everything else constant (including, of course, the<br>
>>>> voltage demand<br>
>>>> and readback settings), resulted in large changes in measured LED<br>
>>>> signal amplitude<br>
>>>> consistent with cosmic gains for these low/high-gain groups.<br>
>>>><br>
>>>> It may also be worth noting that these high-gain HV groups are on<br>
>>>> mainframe<br>
>>>> channels 3,5,7,9,11 for the modules in both slots 0 and 8. When<br>
>>>> plotting for ECal<br>
>>>> geometry the correspondence with mainframe channel is not obvious,<br>
>>>> due to<br>
>>>> mappings and relocation of one dead channel to another slot.<br>
>>>><br>
>>>> So it seems the large variations in cosmic gains for certain HV<br>
>>>> groups must be due<br>
>>>> to the HV supply and nothing to do with the calorimeter. One<br>
>>>> question is what to do in<br>
>>>> the short term for 2014 running. We can try moving the modules to<br>
>>>> open slots, or<br>
>>>> just reseating them, both possible tomorrow. Or measure voltages<br>
>>>> directly at the<br>
>>>> calorimeter and adjust accordingly, ignoring mainframe's readback.<br>
>>>> Or just correct<br>
>>>> with gains, which could require some channel-dependent thresholds<br>
>>>> for data<br>
>>>> acquisition.<br>
>>>><br>
>>>> - Nathan<br>
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<br>
--<br>
Gabriel CHARLES<br>
Institut de Physique Nucléaire d'Orsay<br>
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