Feb 2, 2010: Patton, Golubieski, Maclean on site at 10:30 MST
TasksPlanned 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
...
This stack is now in box #8, which means it has a new Viasala barometer. rserial shows this is unit 9: B9 752.08 5.2\r\n
Barometer . The barometer in box#1 was unit B7.
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, as it was before this visit.
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 .when sampling at 20 Hz.
Around mid-day Ned and Chris measured the guy tensions and those values have been added to the matrix in the blog entry.
Conclusions
The Conclusion: the problem with sampling Licors at 20Hz seems to be a data system issue, in that it cannot keep up with the total serial interrupt load from the sensors on the tower. Based on what we saw on the scope, it is not an issue with the quality of RS232 signals. Since it didn't change when we swapped system enclosures and the PC104 stacks, it is not related to interface panels, the CPU or the serial cards. The power to the Licor's looks good.
Our simulation of this configuration in the lab did not include 5 TRHs (1 sample/sec), the barometer (1/sec) or the GPS (2 samples/sec). Around mid-day Ned and Chris measured the guy tensions and those values have been added to the matrix in the blog entryThe addition of these inputs seems to break the camel's back.