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

SVT protection

SVT must not be cooled without dry air: SVT chiller trips and does not start setpoint is reset at 20 C unless dry air dewpoint is below setpoint.

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.

Monitoring

Over Twitter: Report system status (every 10 minutes) to twitter.com/hpsbot, and failures (as they happen.) to twitter.com/heavyphoton. People can subscribe to text messages from either Twitter feed.

Logging: all system variables, to ~/interlock/log on hpstracker at 1-second intervals.

Remote control

(not implemented yet) Can relay RS-232 commands to either chiller. 

Inputs:

• HTM2500LF temperature+humidity sensor inside SVT box
• Flow switch in FEB chiller return line: relay switch closes if flow is above setpoint
• 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
• RS-232 to PC: commands to relay to chillers

Thresholds:

• Ambient T dewpoint inside SVT box < 25 -10 C (set in Arduino script)
• Ambient RH inside SVT box < 5 10 % (set in Arduino script)
• Cooling system flow > 20 GPH (adjustment screw on flow switch)

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Outputs:

• RS-232 to FEB chiller: if tripped, send "stop" command every 1 sstart/stop, setpoint
• RS-232 to SVT chiller: start/stop, setpoint, watchdog
• 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 immediatelyPrints status to USB serial connection every second (if plugged in)
• RS-232 to PC: print all variables and status

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.

Start EPICS controls. Verify that MPOD channels cannot be turned on with the interlock board off.

Set SVT chiller setpoints setpoint using its touchscreen. When done, switch to remote RS-232 control (Menu->Connect Unit->Remote control). Verify watchdog is enabled (Menu->Connect Unit->Digital Interfaces).

Start FEB chiller and adjust setpoint, then stop the chiller.

Turn on the interlock board. Green LED should turn on immediately; MPOD trip LED (third from top) should clear as chillers start. The other LEDs should stay off.

Turn on MPOD channels through EPICS.

Start In a screen session, start the Arduino monitor script on hpstracker ("~/interlock/arduino_monitor.py /dev/ttyS0 9600"). It should send an initial status tweet.

Special startup (interlock disabled, no unattended running allowed)

Flip Open the interlock board's enclosure and flip the switch on the interlock board to the "BYP" position to bypass the MPOD interlock.

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Turn on MPOD channels through EPICS.

Shutdown

Take the SVT chiller off of remote control (Menu->Connect unit->Remote control). Check the setpoint and make sure it's what you want.

Turn off the interlock board and chillers, in any order. This should trip the MPOD.

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

SVT chiller will go to a noncondensing temperature (20 C) after 30 seconds, protecting the SVT from dry air failure.

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

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

Interlock board failure/power loss

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Chiller status will indicate a trip, or chiller will not respond to RS-232. In either case, the MPOD will trip.

Coolant leak

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

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#3 (red): MPOD trip signal (OR of flow switch trip and Arduino output) - this trips the MPOD unless the interlock is bypassed

#4 (red): chiller trip dewpoint not OK (this is an Arduino output)

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