T1: Grinding Time. This value determines how long the mill will grind during each cycle. It is
programmed in tenths of a minute, e.g. 1.5 minutes = 90 seconds. The maximum grinding time
per cycle is 10 minutes; a typical grinding time is 2 minutes per cycle.
4.12 PROGRAMMING
(Cont’d)
To program the grinding time, press the T1 key; the TIME display will flash as will the T1 LED.
Enter a value using the numeric or INCREASE/DECREASE keys (↑↓). Then press the ENT
key to load the number in temporary memory. (If you immediately want to enter this setting in
permanent memory, press the ENT and 0 keys simultaneously.)
T2: Cooling Time. This is the length of time between individual grinding periods, and is
programmed in tenths of a minute. The maximum cooling time setting is 10 minutes. Typical
cooling time is 1 or 2 minutes or 1/3 to ½ of grinding time T1, depending on the length of the
grinding period and the sensitivity of the sample to slight temperature increases.
To program cooling time press the T2 key; the TIME display will flash as will the T2 LED.
Enter a value by pressing the numeric or INCREASE/DECREASE keys (↑↓). Now press the
ENT key to load the setting in temporary memory. (If you want to store this setting in
permanent memory immediately, press the ENT and 0 keys simultaneously.
T3: Pre-Cooling Time. This is the length of time before grinding starts, programmed in tenths
of a minute. Maximum pre-cooling time is 30 minutes. Typical pre-cooling time for biological
samples is 10 minutes, and for polymers is 15 minutes. Certain silicones and very flexible
polymers may require more pre-cooling time.
To program pre-cooling time press the T3 key; the TIME display will flash as will the T3 bar
LED. Enter a value by pressing the numeric or the INCREASE/DECREASE (↑↓) keys. Now
press the ENT key to enter the value in temporary memory. If you want to store this setting in
permanent memory, press the ENT and 0 keys simultaneously.
Obviously the grinding vial and its enclosed sample must be thoroughly chilled before effective
cryogenic grinding can take place. However, the pre-cooling step is needed as a regular part of
a grinding program only if the vial has not been pre-cooled in some other way. Grinding of a
succession of samples can be speeded up by pre-cooling vials in the pre-cooling slot in the coil
housing, or even outside the mill in a plastic or metal container filled with liquid nitrogen. If you
don’t need the pre-cooling step, enter T3 as zero.
RATE: Impact Frequency. The number displayed in the LED over RATE is the number of
back-and-forth movements of the impactor per second. The factory setting is 10, which is 20
actual impacts per second (one to each side). To change the impact frequency, either in Program
Mode or while the mill is running in Automatic Mode, press the INCREASE key (↑) to speed it
up, or the DECREASE key (↓) to slow it down. The maximum setting is 15. The impact
frequency rate is not stored in permanent memory, but always reverts to the factory setting of 10.
(Whenever the 6750 Freezer/Mill is switched off and then on, the program in permanent memory
will include the set values for cycles, grinding time, cooling time, and pre-cooling time, but the
impact frequency will always come up as 10.)
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