[dsg-hallb_ltcc] LTCC Pressure Setpoints

[Brian Eng]

There was some confusion on exactly what the LTCC controls were doing in regards to S2 that is being leak checked so I'll try to clear things up a bit with this email after going to the hall to verify that there were no software/hardware issues.

There are 3 levels of protection for the LTCC sectors:
1. The LabVIEW code that runs on the cRIO - what people normally interact with for setting values
2. The Omega process controllers - hardware fail-safe of valve control
3. The bubblers - 100% independent limit for pressure

#3 is completely separate from the control system, meaning there is no associated logic and the pressure can never go above/below the oil level of the bubblers. However, #1 and #2 are in series with each other: they both must be within their respective ranges in order for a valve to operate.

What happened earlier today with S2 was that while the setpoints for #1 were changed but the ones for #2 were left the same. As the Omega for S2 is currently set to be active below 2.7 and with a dead-band of 0.2 this means that it will only allow flow below 2.7 and up to 2.9 before it opens its relay to prevent the supply valve from opening.

The confusion comes in due to the fact that the screen will indicate that the solenoid valve is open, however it is only indicating the cRIO is trying to open the valve not that the valve is in fact actually open as their is no remote functionality to monitor the valve itself.



For any operations that involve changing setpoints (especially large changes) make sure that both the software and hardware values are changed appropriately. Both a LED on the cRIO module as well as the setpoint indicator on the Omega must be active in order for the solenoid valves to open.



Hopefully that clears things up a bit, if not let me know.
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