Site visit, move licor, diagnose sampling issue, dead TRH fan

Feb 2, 2010: Patton, Golubieski, Maclean on site at 10:30 MST

Tasks:

• Move Licor 7500 from 30 meters to 2 meters
• Investigate why data system can't sample 4 7500's at 20 Hz
• Measure guy tensions

First noticed a high-pitch sound from a TRH fan. Chris determined it was the 16m TRH. The propeller had come off the shaft, and was not repairable. Swapped the 16m and 2m TRHs, so that now the 2m TRH does not have fan ventilation. And, the ventilation of the 16m TRH has not been working for some period of time. Need to replace the 2m TRH.

Initial licor 7500 serial port configuration:

Looked at RS232 transmit signal from Licors with oscilloscope and a serial breakout box. Ports 17,11 and 7 all showed clean, square signals, ranging from -7V to +7V.

Moved 30m licor to 2m.

Looked at the signal ground of the 2m licor, with the oscilloscope probe ground connected to power ground. Saw hair-like spikes with a range of +- 1V at the bit frequency of the bits. By shorting signal ground to power ground we could get rid of these spikes.

Temporarily switched the cables on the 7m and 2m Licors, so that the 2m was plugged into port 7. Port 7 is on a Diamond Emerald serial card, which are the ports (5-20) that have not been working at 20Hz.

Up'd the sampling frequency of the 2m licor in port 7 to 20Hz, 19200 baud. Saw an increase in "spurious interrupts" which did not diminish when we shorted the signal and power grounds, so those spikes do not seem to be the issue.

Swapped dsm chassis boxes, replacing box #1 with box #8. Also swapped PC104 stacks. This configuration did not work well at all, with data_stats showing bad data rates. Swapped original PC104 stack back, and still saw problem. Eventually noticed that the input from the licor on port 17 had lots of jibberish. Moved this to port 20 and it cleaned up and the data_stats issues went away. So now believe the data_stats issue was due to a bad port 17 on the new box and not an issue with the pc104 stack.

The PC104 stack (which is what has been at the site all along):

Tried increasing the sampling rates of the licors to 20 Hz, 19200 baud. The number of spurious interrupts increased to somewhere around 600+. The system was generally keeping up, as shown by data_stats, but sometimes things looked bad. So reduced the rates back to 10Hz, 9600 baud. The system runs well, with a background level of around 170 spurious interrupts/sec.

The licor message length is between 44 and 49 characters. So at 20Hz this is roughly 10bits * 49 * 20/sec = 9800 bits/sec, so we must use 19200 baud instead of 9600.