Turbo Freeze Drier (Sample Prep) - EMS 775

EMS775 SOP

Overview

1. Make sure the unit is powered up. 2. Determine what drying protocol is appropriate for your specimen, and make sure it is reflected in the profile configuration you intend to use. 3. Finally, make sure the "stage cool trip point" is set to a resonable temperature.

Startup

1. With no samples placed as yet, close the chamber lid, and press start. This will pump down the chamber.

  a. When proper vacuum has been reached, the display will read "Start Cooling Now"

2. Fill liquid nitrogen and press start. The system is now cooling down.

  a. Once the target "stage cool trip point" has been reached, the display will read "Press ENTER when ready to load sample".

3. From the moment ENTER is pressed, the pumps are shut down and the chamber is vented. Once you are able to open the chamber, you now have 1 minute to load your sample and press start again. 4. The drying protocol is now being followed by the unit from step to step. 5. When the unit is powered off, please keep in mind that the heater is no longer in operation. If the unit still has liquid nitrogen in the dewar and has been vented to atmosphere, the samples will be exposed to moisture.

Running

During the system operation, you will see the following: "End Tmp" "Target" "Stage"

• It is worth defining what these mean, as it can be confusing:
  • End Tmp represents the temperature that will be reached at the end of the current segment (When the time left approaches zero for that segment).
  • Target Temp represent what the internal PID controller is trying to hit in the given moment. THIS HAS NOTHING TO DO WITH WHAT WAS PROGRAMMED! It represents what the computer is trying to hit in a given moment
  • Stage Temp represents the temperature of the stage in real time.

General Notes

• mbar and torr are roughly equivalent (within an order of magnitude). 5E-04 vacuum is vaguely acceptable. 5E-05 is pretty good. If there are problems with the vacuum, make sure that no debris has acculumated between the seals and mating

surfaces.

Ending a session

It is critical that a session be ended properly. If this is not done correctly, the specimen may continue to be cold while venting to atmosphere. If this happens, condensation will form, which will ruin the sample.

• There are two purge inlets on the machine. One simply vents to atmosphere, while the other vents to a restrictor valve which limits the flow. Having the restricted valve hooked up to a dry nitrogen purge can be very beneficial.
• Restricted purge will take a very long time (which keeps samples from blowing around inside), however, it may cause the sample to cool down if the heater is turned off. This can ruin the sample.

Things to test

When not using an absurdly long "hold cycle", is it possible to vent the chamber while not removing heater power?