[Eleonora, Matteo, Enomoto, Yuhang, Yuefan (remotely)]

A fiber system is in place in TAMA to send and receive signals between the central area and end rooms. Since we considered the possibility to use such a system (to avoid a timing system in the digital control system), we report some details about its organization and performances.

"STANDARD" BOARDS

In the central area and in the south end room there are respectively 2 boards, named both A and B. The two A boards (that in the central building and that in the end)  are connected between each others with 2 fibers each (one to send signal in one direction, the other in the other direction).  The same happens for the two B boards.

Each fiber can transmit 4 channels, so that each board has 4 input channel and 4 output channel.

VIDEO BOARDS

There are also 2 video board in the central and in the end room, named respectively video board 1 and video board 2. The two video board 1  (that iin the central building  and that in the end)  are connected between each others with 2 fibers each.  The same happens for the two video board 2.

In the case of the video boards each fiber corresponds to one channel and they are only used to send signals from the end room to the central building.

DELAY

In order to estimate the delay of the trasmission we sent a signal through the fiber to the end room and we sent it back to the central building and measure the TF beetween the two. See attached pic 1.

The phase delay at 500 Hz is 49.15 deg, corresponding to a delay of 0.27 ms (round trip)

The delay due to the finite speed of light (which is 2us)  is a negligible contribution.

SIGNAL QUANTIZATION

By looking at the signal after a round trip it is clear that there is a quantization effect from the board ADC. See attached pic 2, 3.  The sampling frequency is 12 kHz.

Recap of the fibers disposition:

board A (central)                    board A (end)

TX:   1-9                                 TX:   1-10

RX:  1-10                                RX:  1-9

board B  (central)                   board B (end)

TX:   1-11                                 TX: 1-12

RX:  1-12                                 RX: 1-11

Video board 1 (central)          Video board 1 (end )

CH1:  1-15                               CH1: 1-15

CH2:  1-16                               CH1: 1-16

Video board 2 (central)           Video board 2 (end )

CH1: 1-13                                 CH1: 1-13

CH2: 1-14                                 CH1: 1-14

Current channel  use:

video board 1                           video board 2                board  B

CH1 : GREEN  CAMERA          CH1: IR CAMERA          CH2 (from end to central) : FC_IR_TRA_DC

CH2:  SECOND TARGET    

Other infomation:

1) The fibers numbered from 1-9 to 1-16 are arriving from the south end,  close to the east input vacuum chamber (see pic 4, 5). From there, some extensions are used to connect them to the boards. In the past ( see entry #444 and #518) some of these cables have been exchanged because they were too short. I took the time to redo all the labels of the extension cables to make them match the fiber number.

2) The fibers for the west end  are numerd as 3-XX.  Fibers numered 2-XX and 4-XX comes from the 150 m station respectively of the south and west arm. 

3) The fiber from 1-1 to 1-4 arrive in the up-right corner of the storage room.

4) There is another fiber which has a dedicated reciver and sender box, it is currently used to send the signal FC_GREEN_TRA_DC from the end room. See entry #524. Its performances should be better than the other fibers.

I attach also a pictures of the boards. (pic 6)