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FEBs must not be powered without cooling: MPOD trips and does not start if FEB flow switch is below setpoint (bypass switch)

SVT protection

SVT must not be cooled without dry air: SVT chiller trips and does not start unless dry air dewpoint is below setpoint (unplug serial cable/disable remote control to bypass)

SVT must not be powered without cooling: MPOD trips and does not start if SVT chiller doesn't respond to RS-232 or is not running (bypass switch)

Monitoring

Report system status every 10 minutes, and failures as they happen.

Inputs:

• HTM2500LF temperature+humidity sensor inside SVT box
• Flow switch in FEB chiller return line
• RS-232 connection to FEB chiller - status, set T, measured pressure/flow/T
• RS-232 connection to SVT chiller - status, set T, measured pressure/flow/T

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• RS-232 to FEB chiller: if tripped, send "stop" command every 1 s
• RS-232 to SVT chiller:
• Enable to MPOD crate (5V) - always on if interlock board is powered
• Interlock to MPOD crate (0V normal, 5V tripped) - trip turns off all outputs immediately
• Prints status to USB serial connection every second (if plugged in)

Procedures

Normal startup

Check dry air is flowing, and all interlock inputs are plugged in. Both chillers and MPOD should be powered but not running. Interlock board should be off.

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Stop the Arduino monitor script on hpstracker.

Failure analysis

FEB chiller shutdown (overtemp, power loss)

Flow switch trips -> interlock trips MPOD. This interlock is independent of the Arduino, and the MPOD will trip if the interlock board loses power or the flow switch is unplugged.

Arduino lockup

Arduino monitor script will tweet a "no status received" error after a timeout (10 sec).

FEB will still be protected: FEB flow interlock is independent of Arduino, so FEB chiller shutdown will still trip the MPOD.

SVT may not be protected from a dry air failure or SVT chiller trip. Neither is likely.

Interlock board failure/power loss

Power loss on the interlock board will remove the "MPOD enable" signal, shutting down the MPOD.

Arduino is powered from the interlock board, so Arduino monitor script will tweet a "no status received" error after a timeout (10 sec).

SVT will not be protected from a dry air failure. Not likely.

SVT chiller shutdown

Coolant leak

 Both chillers have low level protection; a leak in either loop will stop that chiller, and the interlock will stop the MPOD.

Flow switch failure

Unplugging the flow switch, or a break in any line of the flow switch cable, will trip the MPOD.

Interlock board description

LED indicators

Top (green): power on/MPOD enable - should always be on

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