[Halld-cal] [New Logentry] BCAL gains monitored overnight

[dalton at jlab.org]

Logentry Text:
--
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.

Method:
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 chan
 ge in signal size appears to about 2% for these approximately 2 degree Celcius changes in temperature.

Future work:
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.


---

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/3285987
-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://mailman.jlab.org/pipermail/halld-cal/attachments/20140509/799642ec/attachment-0001.html 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: dump_tree_waveform_11_04_c1.png
Type: image/png
Size: 33800 bytes
Desc: not available
Url : https://mailman.jlab.org/pipermail/halld-cal/attachments/20140509/799642ec/attachment-0007.png 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: ped_gainzoom_roc31slot4_ch1.png
Type: image/png
Size: 23562 bytes
Desc: not available
Url : https://mailman.jlab.org/pipermail/halld-cal/attachments/20140509/799642ec/attachment-0008.png 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: int_gainzoom_roc31slot4_ch1.png
Type: image/png
Size: 23320 bytes
Desc: not available
Url : https://mailman.jlab.org/pipermail/halld-cal/attachments/20140509/799642ec/attachment-0009.png 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: temp_modbcal_gainzoom.png
Type: image/png
Size: 279820 bytes
Desc: not available
Url : https://mailman.jlab.org/pipermail/halld-cal/attachments/20140509/799642ec/attachment-0010.png 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: int_gain_roc31slot6.png
Type: image/png
Size: 533501 bytes
Desc: not available
Url : https://mailman.jlab.org/pipermail/halld-cal/attachments/20140509/799642ec/attachment-0011.png 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: ped_gain_roc31slot6.png
Type: image/png
Size: 424450 bytes
Desc: not available
Url : https://mailman.jlab.org/pipermail/halld-cal/attachments/20140509/799642ec/attachment-0012.png 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: deltas_gainzoom.png
Type: image/png
Size: 15578 bytes
Desc: not available
Url : https://mailman.jlab.org/pipermail/halld-cal/attachments/20140509/799642ec/attachment-0013.png