[Primexd] [Halld-cal] [Revised Logentry] FCAL HV scan

[Colin Gleason]

Hi Ashot,

I do not think you will need to run at 1800V. Most of the FCAL is
calibrated properly (we know the inner and outer layers need to be
calibrated) and when new HV set points are determined it's unlikely that a
lot of new channels will need to be set to 1800V. The bases that are
exhibiting this behavior all have high currents being drawn from them. The
max value we can see on EPICS is 15mA, but it's likely the current being
drawn is higher than this. We have been aware of this for some time now and
are taking steps to address it. If for some reason a base can not hold the
HV at which you want, it can be replaced with a spare. Since we've seen the
failure rate of bases dying decrease this run period, we plan on removing
more bases with large current draw in the future.

-Colin

On Mon, Nov 19, 2018 at 12:23 PM <gasparan at jlab.org> wrote:

>
>   Hi Sasha,
>
>  a very good test. It looks like we may have serious problems if we need
>  to set 1800 V range.
>  We will need to have more information (gains, electronic noise, ...)
>  before making some decision.
>
>  Thanks,
>  Ashot
>
>
> >
> > Logentry Text:
> > --
> > FCAL readout: RAW mode (mode 10)
> >
> > Use violet LED, 500 Hz
> >
> > 1500 V
> > ----------
> >
> > Run  51604,  130 K events,  17 V
> > Run  51605,  122 K events,  22 V
> >
> > 1550 V
> > ---------
> >
> > Run 51606,  120 K events, 17 V
> > Run 51607,  120 K events,  22 V
> >
> > 1600 V
> > ----------
> >
> > Run 51608, 17 V
> > Run 51609,  22 V
> >
> > 1650 V
> > ----------
> >
> > Run 51610, 17 V
> > Run 51611, 22 V
> >
> > 1700 V
> > ----------
> >
> > Problems with setting HV on channel (22,22 ;  -8,-8)
> >
> > Run 51612,  17 V
> > Run 51613,  22 V
> >
> >
> > 1750 V
> > ----------
> >
> > Not able to set this voltage on the following channels:
> > Channel, Read back voltage
> >
> > (1, 31) 1610 V
> > (7, 46) 1601
> > (13, 23) 1618
> > (13, 47) 1651
> > (20, 26) 1600
> > (22, 22) 1607
> > (25, 26) 1620
> > (29,7) 1640
> > (33,47) 1609
> > (35, 37) 1630
> > (44, 30) 1590
> > (41, 39) 1660
> > (44, 30) 1590
> > (47, 38) 1625
> > (49, 31) 1612
> >
> > Run 51614,  17 V
> > Run 51615,  22 V
> >
> > 1800 V
> > ---------
> >
> > Cannot set HVs on 41 channels
> >
> > Run 51616,  17 V
> > Run 51617,  22 V
> >
> >
> >
> >
> >
> >
> > ---
> >
> > This is a plain text email for clients that cannot display HTML.  The
> full
> > logentry can be found online at
> >
> https://logbooks.jlab.org/entry/3628470_______________________________________________
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> > Halld-cal at jlab.org
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>
>
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-- 
Colin Gleason
Postdoctoral Fellow
Indiana University
Department of Physics
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