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→Data Acquisition
=== Data Acquisition ===
=== Data Acquisition ===
==== Acquisition Method and Efficiency ====
A Tektronix TDS 2024 (2Gsmp/s, 200MHz) is used to acquire the SiPM signal from its [[SiPM_Amplifier|preamplifier]], the response of which is well understood based on detailed [[MATLAB amplifier in detail|analysis and simulation]]. Since tens of thousands of waveforms are necessary to construct a clean histogram of collected charge, a fast PC based data collection system was necessary. The data export module installed on this oscilloscope allows RS-232 interface over which commands can be issued and data transfer requested. Unfortunately going above the baud rate of 9600 always resulted in lost bytes. At 9600 the 2500-sample waveform collected by the oscilloscope takes about 2-3 seconds to transfer. Since we are dealing with time windows of 1μs in which the unit is too slow to collect all 2500 samples (it was found to copy or interpolate between actual samples) it was resolved to just collect the first 1000 samples, corresponding to the first 4 divisions on the screen. The waveforms now trickled at one per second.
A Tektronix TDS 2024 (2Gsmp/s, 200MHz) is used to acquire the SiPM signal from its [[SiPM_Amplifier|preamplifier]], the response of which is well understood based on detailed [[MATLAB amplifier in detail|analysis and simulation]]. Since tens of thousands of waveforms are necessary to construct a clean histogram of collected charge, a fast PC based data collection system was necessary. The data export module installed on this oscilloscope allows RS-232 interface over which commands can be issued and data transfer requested. Unfortunately going above the baud rate of 9600 always resulted in lost bytes. At 9600 the 2500-sample waveform collected by the oscilloscope takes about 2-3 seconds to transfer. Since we are dealing with time windows of 1μs in which the unit is too slow to collect all 2500 samples (it was found to copy or interpolate between actual samples) it was resolved to just collect the first 1000 samples, corresponding to the first 4 divisions on the screen. The waveforms now trickled at one per second.
For the purposes of collecting integrals of waveforms (proportional to total charge collected per received flash) it was later found that the averages of the functions can be requested much faster, about 3 per second. This value times the window duration equals the desired integral!
For the purposes of collecting integrals of waveforms (proportional to total charge collected per received flash) it was later found that the averages of the functions can be requested much faster, about 3 per second. This value times the window duration equals the desired integral!
Aside from the convenience of usable results within hours instead of a day, is the issue of avoiding systematic drifts. It was found that while higher statistics smooth out the histogram of integrals, there are also drifts, whether due to environmental variations over the course of a day or electronic effects. These drifts smeared the histograms, most of which already had a very faint sign of photon peaks. So, faster data acquisition also meant avoiding these drifts.
== SiPM Measurements ==
== SiPM Measurements ==