Vped Scan 2018 - Setting Nominal Values

Updated on Tue, 2018-02-27 22:25. Originally created by rjreed on 2018-02-25 12:43.

Executive Summary

New vped settings are uploaded so that the pedestal for a given channel is within an ADC of the pedestal with the CAMAC crate off. This is done in 763 out of 768 FEE channels. A second look will be needed for the 5 channels that differ, however this is not a concern.

Details

For the initial tests of the EPD, we set the vped to 20 in each channel (vped can go from -128 to 127), which is slightly higher than last year's nominal setting of 11 or so.

On 2/24/2018 we scanned through different vped settings, taking a pedestal rhic clock clean each time. The crates had been on and running up until that point, so they were quite warm. The Vbias settings were left at our default of 56V.

These runs were:
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030 - vped = -20
31 - vped = 10
32 - vped = 0
33 - vped = -10
34 - vped = 20

Note that they are not in order, operator error. Next Joey turned off the CAMAC and took another pedestal rhic clock clean, this is
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We then turned the CAMAC's back on and took another pedestal run at vped = 20 to leave the system in the default state.

First, we can compare the average pedestal from the CAMAC off to our nominal vped: drupal.star.bnl.gov/STAR/system/files/Vped2files_FirstDefault.pdf

A typical board is:

Figure 1: Average pedestal channel by channel for the first board (0x10) in crate 1 for vped = 20, which was our starting default and CAMAC off.

We looked at the pedestal distributions channel by channel (Note, physical mapping is on top of each plot, this mapping came from the db and was not hard coded in):

One Page format: drupal.star.bnl.gov/STAR/system/files/Compare_big_02252018.pdf
Small format: drupal.star.bnl.gov/STAR/system/files/Compare_small_02252018.pdf

A typical example:

Figure 2: Pedestal distribution for 5 different vped settings and the CAMAC crate off.

Using these pedestal means and assuming a linear relationship (which seemed to be quite good), we determined the vped settings channel by channel.

One Page format: drupal.star.bnl.gov/STAR/system/files/VpedScan_big_02252018.pdf
Small format: drupal.star.bnl.gov/STAR/system/files/VpedScan_small_02252018.pdf

A typical example:

Figure 3: Pedestal mean versus vped setting for one channel. The CAMAC off setting is plotted at vped = 0 simply for display purposes.

This also created a text file of the nominal value versus EW,PP and TT: drupal.star.bnl.gov/STAR/system/files/VpedOut_02252018.txt

This was combined with the EPD Mapping file from 2/24/2018 to get a new mapping file: drupal.star.bnl.gov/STAR/system/files/EPD_TUFF_MAP_02252018_vpednom.txt

This was then used today and another rhic clock clean run was taken for comparison, that run is:
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The results for all 768 FEE channels can be found at: drupal.star.bnl.gov/STAR/system/files/Vped2files_NewDefault.pdf

With a typical result of:

Figure 4: Average pedestal channel by channel for the first board (0x10) in crate 1 for new nominal pedestal values and CAMAC off.