Yutaro, Kiwamu,
We investigated the glitch issue (4072) today and traced it down to the DACs.
The glitches are actually generated from the DACs --- the output voltages go to zero for a few 100 msec and 1 sec occasionally.
Miyakawa-san and company will be swapping the IO chassis at some point soon to see if it eliminates the glitches.
[The investigations]
- We brought an oscilloscope to the Y end.
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We looked at the coil driver output for the IPs and saw that the requested DC voltage occasionally went to zero for a short period of time (100 msec - 1 sec).
- While looking at the IP drive voltage, we also intentionally applied a DC bias to the BF coil to see if the glitch happens for both IP coil signal and BF coil signals.
- The glitch seems to coincide between the IP and BF coils, according to this test.
- So we determined that this was a global phenomenon rather than an local one which can be in a particular coil channel only.
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We looked at the 18 V power directly with the oscilloscope, but didn't find the glitches at all.
- So we think that the issue is not from the 18 V power supply.
- Then we looked at the DAC raw outputs by hacking an AI chassis which had a SCSI-DB9 converter inside.
- We found that the DAC raw outputs also had the glitches in DAC0 (which is the one controlling the ETMY tower).
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We checked DAC1 while keeping DAC0 connected to the ETMY coils.
- We learned that the glitches happen in both DACs 0 and 1 simultaneously.
- So, again, this is an indication that this is some kind of a global phenomenon.
The attached picture shows an example of the glitches that we saw with the oscilloscope.
This is a glitch from DAC0 with the oscilloscope directly probing the raw DAC output. The rise time is typically very fast and is on the order of 100 usec which smells like a glitch from the digital system.
