Aluminum Interlock

After melting aluminum, precious little will make us want to freeze it (Melting and Freezing). In order to ensure that this does not happen by accident, we built an interlock box that monitors the output (an analog signal proportional to the current of the Sorenson) of the Al power supply. In the event that the current drops below a threshold value, the interlock box will switch to the backup power supply at a level that is set by the interlock box.

Before melting Al make sure that the backup power supply is hooked up to the UPS and the UPS in turn is connected to the emergency power outlet.

Needs to be updated with next melting. Nate has paper notes to accord with this and a new melting.

Set points

There are two main parameters for the interlock box:

The threshold current at which the interlock box will switch from main to backup power supply.
The setpoint for the backup power supply.

The procedure to setting up these two parameters is as follows.

After melting Al, take the cell to 765 C (~100 °C above the melting point).
Let it sit at this temperature for about 30 min. to let power requirements of the cell stabilize.
Once stable note down the current reading on the Al main power supply and the output percentage on the Al Eurotherm.
Change the minimum output percentage on the Al Eurotherm to this value.
Next slowly increase the threshold dial on the interlock box until it switches from main power supply to the backup. Now adjust the backup power supply setpoint potentiometer on the interlock box until the output current is the same as that noted in step 3. Do this quickly to avoid rapid cooling of the Al cell.
Next switch the Al Eurotherm to manual mode and set the output percentage to 0.5% above the current value.
Turn the key on the interlock box to off position, wait for a second and then turn the key back to on position. The interlock box should have switched from backup power supply to main power supply.
Switch the Al Eurotherm back to auto and ramp to 800 C. This should be the idle temperature of the Al cell.
Finally, the Al Eurotherm settings must be changed in order to insure the proper functionality. In particular, a minimum output must be set that is sufficiently high to prevent the interlock box from switching to the backup power supply when ramping down from growth temperature.
- For System Bravo this minimum output is currently 13%.

Resetting the interlock box after a trip

After insuring that the system is in good working order and that the issue that caused the trip has been resolved, the interlock box can be reset to put the Al cell back onto the primary Sorenson supply. To insure low thermal stressing on the Al cell, follow the checklist below to reset the interlock box.

Set the Al eurotherm to manual mode and lower the output power level on the Eurotherm to the minimum output. Typically this is about 13%.
- This will prevent the Eurotherm from rapidly ramping up the cell heater when the interlock is reset, as the Eurotherm will have pegged the output power at the maximum allowable power after the interlock has been tripped.
Disable the interlock box by switching the key to "off." This will return control of the cell temperature back to the primary Sorenson supply.
Verify that cell power has switched back to the primary
Switch the interlock box key back to "on" to set the interlock.