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-webkit-text-stroke-width: 0px; background-color: rgb(255, 255,
255); "><span style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; ">Hi Everyone,</span>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; "><br>
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<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; ">I received some feedback
from IU on some of the issues that were brought up in
yesterday's control meeting.</div>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; "><br>
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<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; ">The first issue was the
instability of the ADC Cathode reading, how base responses
could vary in the hundreds of volts some percentage of the
time. Paul tells me that this instability is due to the
switching noise of the capacitors in the Cockcroft Walton
chain, and is not a physical effect on the PMT Cathode. So
this is something that I will just need to work around. I
have seen this noise on the scope when monitoring the test
pulser, but the capacitors can apparently affect ADC
measurements as well.</div>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; "><br>
</div>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; ">The other issue was setting
a Trip Current on the firmware. The ADC Current only monitors
Base current, while the PMT will only pull in the microAmp
range. I had shown a distribution of ADC currents over a long
period of time for many bases, and there was a large peak from
2 to 4 mA, and a long tail extending out to 15mA, which the
last 15mA bin peaking due to the ADC maxing out. Paul says
that this tail is likely caused by extra current drawn by the
ADC to take the actual ADC Current measurement, and is also
unavoidable.</div>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; "><br>
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<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; ">I'll try to focus on
solutions to both of these issues on the Firmware side. One
possibility for ADC Cathode would be to take several
measurements on the firmware during an ADC Cathode request,
and if the RMS is over a certain amount, throw that
measurement out and re-measure. The switching noise is in the
nanosecond range, so multiple measurements would be much
slower than that scale. This would only allow real effects on
the ADC Cathode to show up back in Epics, but you would risk a
base not responding indefinitely if the base had an error
which caused every set of ADC Cathode measurements to produce
an RMS which was not below that threshold I just mentioned. </div>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; "><br>
</div>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; ">For ADC Current, this same
solution would not be as ideal, since the effect is a
consistent high-side tail in the distribution. I will still
look into averaging these Firmware side, but Paul had
suggested that using the Power Supply current monitor, which
will average the current drawn by 100 bases, would be a better
indicator for Base current draw. Either way, the Bases are
individually fused, and the entire PSU is fused, so I do not
know how critical a fast threshold current would be.</div>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; "><br>
</div>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; ">I'll keep working on all of
this, and keep everyone updated.</div>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; "><br>
</div>
<div style="color: rgb(34, 34, 34); font-size: 13px;
font-family: arial, sans-serif; ">-Dan</div>
</div>
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