[Dsg-rich] RICH fiber disconnection info

[Tyler Lemon]

Hello, 

DSG has noted that occasionally, the data readout fibers for RICH disconnect. The attached picture "2018-10-05 fiber disconnect.jpg" shows how the scaler readout map looks during a period when a fiber is disconnected. 

For RICH, there are a total of 391 PMTs on 138 tiles (115 tiles have three PMTs, 23 tiles have only two PMTs). All 391 PMTs can be seen in "2018-10-05 fiber disconnect.jpg". Each of these tiles are connected to SSP boards using fiber optic cables. 

When a fiber is "disconnected", it means that the data connection to the tile the fiber is used to read has been lost. When this happens, we lose the FPGA temperature, internal 5 V and 3.3 V monitoring for the tile's FPGA, and scalar counts for the PMTs read by that tile. This can be seen in the attached "plot - tile 81 PMT scalers during fiber disconnect 2018-10-05.JPG" and "plot - tile 81 FPGA info during fiber disconnect 2018-10-05.JPG". 

>From the archiver, we can see that HV is unaffected by during a fiber disconnect (attached "plot - tile 81 HV during fiber disconnect 2018-10-05.JPG". 

To be able to study the conditions present when a fiber disconnects, we have added all RICH HV voltages and currents and have requested the addition of all RICH LV voltages and currents to Mya Archiver. We have also requested that the number of fibers connected be added to the archiver to have a record of how often the fiber disconnect issue occurs. 

Our present understanding is that the fiber disconnects occur randomly in respect to which tiles disconnect and how often a fiber disconnect occurs. It is not always the same fiber that disconnects and the disconnects can happen at any time (we've seen them happen with time period between disconnects ranging from minutes to weeks). 

DSG is looking into the fiber disconnects in detail to determine how often they occur and whether they tend to happen in certain regions of the electronic panel. We will also look into if the tile's HV or LV supply could play into whether it disconnects. 

Best regards, 
Tyler 
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