The same 61 msec glitch pair was also reported in klog#13237 and klog#13240. ~ 0.06sec in these klogs were checked to be precisely 61 msec.

[Ushiba, Yamamoto, Aso, Miyoki, Yokozawa]

Abstract

The source of pair glitches in GR PDH was identified to be thermo-hydrometers called "Ondotori" cordless handsets. Also, a set of glitch "parade" rows was also identified to be the base unit of "Ondotori".

What we checked and found

1. Before starting the investigation, a proper termination in DGS systems was done, including the related dolphin system by Yamamoto-kun and Ushiba-kun (Please somebody writes in detail, if necessary).
2. Firstly, the power supply for the units in the ALS rack was turned off, except for the Gr PDH Ver.2 unit where the pair glitches were observed. We monitored the signal of "OUT2" in photo.1 at Ch.1 of an oscilloscope. The pair glitches were still there even if we disconnected all cables to the Gr PDH Ver.2 unit including 24V/18V power supply cables!
3. The single glitch in this pair consisted of a 430MHz sinusoidal wave as shown in photo.2. (According to Oshino-kun, the frequency of EMWs of the ondotori for communication was just 430MHz!)
4. Judging from 2 and 3, So we suspected that the source could be Electro Magnetic Waves from somewhere. So, I made a simple loop with a probe as in photo.3, then we monitored the waveforms from this loop probe at Ch.2 of the same OSC. Then, the pair glitches were observed.
5. We noticed that a thermo-hydrometers called "Ondotori" cordless handsets was put just below the Gr PDH Ver.2 unit. I took this ondotori cordless handset from the rack and check the EMWs with the loop probe as shown in photo.4 (the probe was set just around the bar antenna of the ondotori), then larger pair glitches were detected. When I set the probe by 30cm away from the ondotori, the amplitude got smaller(no photo, sorry). I also tried the change the position of the probe from near to far from the ondotori before and after the first glitch was observed. The second glitch amplitude got smaller! So, we concluded the source of pair glitches came from Ondotoris.
6. After we reproduced the cabling and power supply conditions of the Gr PDH Ver.2 unit, we verified that pair glitches were observed if we put the ondotori just below the unit, and that the amplitude depends on the distance between the unit and ondotori, and the inclination of the ondotori antenna. So we removed this ondotori in the ALS rack. However, other ondotoris were set in each rack beside this ALS rack (totally 3 racks in addition to ALS rack). So much weaker pair glitches were still observed. After removing all ondotoris around the ALS rack, there were no more pair glitches.
7. After this success, we also noticed that a very slight glitch parade row appeared in some time as in photo.5. We suspected the source could be the EMWs from the ondotori "base units" that had a role to collect data from each ondotori cordless handset. We monitored the waveforms of a ondotori base unit near the ALS rack with a loop probe as in photo.6. Then remarkable glitch parade row was detected as in photo.7. We did not remove this base unit because it is necessary to collect data from ondotori around each vacuum tanks in clean rooms.

What we did for the temporal measures

• We removed all ondotoris around the ALS rack and IOO/LSC rack(?). Please inform more in detail by other members.

What should we do for the future

• It is better to remove ondotori cordless handsets near the DGS racks and optical tables. we don't know how much glitches can be generated in LSC/ALS/ASC signals from ondotoris around vacuum tanks in clean rooms.
• It is better to prepare a new temperature monitoring system using cryo-con.
• Do you have any idea?

We removed 10 ondotori in total from the following DGS racks.
IOO0, IOO1, ALS0, ALS1, PRM, PR3, PR2, BS, LSC0, and ASC0.