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</style><article id="node-358731" class="node node-logentry article ia-n clearfix" role="article"><header class="node-header"><h1 class="node-title" rel="nofollow">
<a href="https://logbooks.jlab.org/entry/3285987" rel="bookmark">BCAL gains monitored overnight</a>
</h1>
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<p class="author-datetime">
Lognumber <a href="https://logbooks.jlab.org/entry/3285987" class="lognumber" data-lognumber="3285987">3285987</a>. Submitted by <a href="https://logbooks.jlab.org/user/dalton">dalton</a> on <time datetime="2014-05-09T18:31:47-0400" pubdate="pubdate">Fri, 05/09/2014 - 18:31</time>. </p>
<table class="field-vitals"><tr><th>Logbooks: </th><td><a href="https://logbooks.jlab.org/book/hdbcal">HDBCAL</a> <a href="https://logbooks.jlab.org/book/hdlog">HDLOG</a></td></tr><tr><th>Tags: </th><td><a href="https://logbooks.jlab.org/tag/detector">Detector</a></td></tr><tr><th>Entry Makers: </th><td>dalton</td></tr></table></div>
<div class="logentry node-content">
<p>The gains of the BCAL North detectors were monitored overnight using the LED system. A fluctuaton is observed on the 20 minute timescale, strongly correlated with temperature in the BCAL radout modules, which could be attributed either to a changing gain in the MPPCs or to a changing power in the LEDs. A further analysis of this data could show which of these possibilities it is.</p>
<p>Method:<br />
Data was taken overnight with the LEDs flashing at 0.756 Hz. A single event for a single fADC module can be seen in Fig. 1. For each waveform, the first 10 samples are used to measure the size of the pedestal. The pedestal history is shown for the first few hours for a particular channel in Fig. 2. An easy (not necessarily ideal) measure of the signal size is the integral of the full 100 samples, pedestal subtraced and normalized to each sample ( fullintegral/100 - pedstalingetral/10 ). This is shown in Fig. 3 for the same channel for the same timescale. This channel was chosen because the periodic fluctuations are very clearly visible. Comparing to the characteristic temperature fluctuation in the BCAL modules, Fig. 4, shows a strong correlation, the signal size decreases with increasing temperature. Figures 5 and 6 show a more representative sample of the signal and pedestal repectively, for the full dataset overnight. Looking at a just a few of the plots, the change in signal size appears to about 2% for these approximately 2 degree Celcius changes in temperature.</p>
<p>Future work:<br />
Since the upstream and downstream readout modules have different temperature cycle periods, and since we flash LEDs on only one side at a time, we can diambiguate the source of the signal changes. If there are different timescales between US and DS in the data we can blame the MPPCs and if there are not we can blame the LEDs. Since no effort was made to stabilize the signal of the LEDs, while considerable effort was made to stabilize the MPPCs, it seems natural to suspect the LEDs at this stage.</p>
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<div class="image-wrapper"><img class="image-style-plentybig" src="cid:8d65e09c47b446329a00beaa89c7fe55@logbooks.jlab.org" width="696" height="674" alt="" title="Single event LED waveforms" /></div> <div class="image-wrapper"><img class="image-style-plentybig" src="cid:6e2106a0fe13370805d876eaf83726a8@logbooks.jlab.org" width="796" height="574" alt="" title="Pedestal with time from 6 pm" /></div> <div class="image-wrapper"><img class="image-style-plentybig" src="cid:505e3041c96b7f494543950c6b4b25e4@logbooks.jlab.org" width="796" height="574" alt="" title="Signal with time from 6 pm" /></div> <div class="image-wrapper"><img class="image-style-plentybig" src="cid:21220e1acb497b848f690a3a2f87f308@logbooks.jlab.org" width="960" height="463" alt="" title="Temperature in BCAL modules for similar period from 1 am" /></div> <div class="image-wrapper"><img class="image-style-plentybig" src="cid:11106699c37db044bc973baffcb42d5c@logbooks.jlab.org" width="960" height="561" alt="" title="Signal with time overnight from 6 pm" /></div> <div class="image-wrapper"><img class="image-style-plentybig" src="cid:414c547893185cc82f2fd49ca4d95163@logbooks.jlab.org" width="960" height="561" alt="" title="Pedestal with time overnight from 6 pm" /></div> <div class="image-wrapper"><img class="image-style-plentybig" src="cid:9cff82b001d8a93605dac55d7e40ae4f@logbooks.jlab.org" width="636" height="454" alt="" title="Maximum difference in signal size (averaged over 100 samples) per channel" /></div> </div>
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