Shellab SVAC9-2 - Manual (Page 17)

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OPERATION (CONTINUED)
T HEORY OF O PERATION
The SVAC9-2 is intended for use in closed-cycle, under-vacuum applications such as, drying,
baking out volatiles, and evolutions of molecular clouds. The oven is not built to operate exposed to
free atmosphere or circulate air within the chamber. Running the oven with the door or vent open
risks damaging the vacuum pump and the integrity of the oven.
A cylinder of neutral gas may be connected to the vent inlet in the cabinet in order to purge the
oven chamber during applications and procedures structured to prevent oxidation.
The oven is rated to 10 millitorr. Vacuum levels in the oven are dependent on pump performance
and the nature of the application or process.
Vacuum pumps and door gaskets should be selected on the basis of the application or procedure.
Some gaskets are vulnerable to different chemicals, and vacuum pumps vary in suitability and
safety depending on the exhaust and moisture levels produced in the oven chamber.
The InstruTech 301 VGC301 vacuum gauge on the control panel displays vacuum in absolute
(torrs), rather than relative pressure.
The Watlow EZ-Zone controller stores 40 programmable heating steps in its memory, each with
parameter options. The steps are divided between 4 profiles with ten steps each, though the steps
may be programmed sequentially to run as longer profiles. Extended profiles must divide the 40
steps between them.
The Over Temperature Limit System
The OTL is a backup mechanical heating control system that operates independently of the Watlow
digital controller unit. The OTL system consists of a thermostat, dial control, and independent
hydraulic temperature probe. In the event of a failure of the Watlow controller while in its heating
mode, the OTL system prevents runaway heating by tripping a pair of power relays when the
temperature i
n the oven chamber exceeds the OTL system’s setting.