Ulvac CRYO-U Series, Instruction Manual

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Operation
5-4 ULVAC CRYOGENICS INCORPORATED
２． When the pressure of vacuum chamber has reached 40Pa, close the roughing valve
（
RV2
）
and then turn off the roughing pump.
mended to add a fore-line trap in the
３．
V1
）
for fine pumping the chamber by the cryopump.
４．
required value, proceed with
reach the
If the abnormal rise of the pressure in the cham ks out during operation, the
cryopump case may dew. It may cause short- trical device is put under the
If you use an oil-sealed rotary pump as a roughing pump, and rough pumped for a long
time at the pressure of 40Pa or less, it is recom
rough pumping line.
To determine the crossover pressure, refer to Section 5.6.
Open the main valve
（
When the pressure of the vacuum chamber has reached the
vacuum process such as deposition or sputtering. The time required to
intended pressure depends on the volume, contents, and the wall conditions of the
chamber, etc.
ber brea
circuit if an elec
cryopump. Be careful about the operating condition of equipment, and surrounding safety.
5.6 Crossover
“Crossover pressure” refers to the roug ssure of a vacuum chamber immediately before
opening the main valve to switch to cryopump after roughing the vacuum chamber. The
e roughing pressure in this case is called the maximum allowable crossover
pressure. The moment the main valve is opened, gases in the vacuum chamber flow into the
value
e pum ally, a value which keeps the
The maximum gas quantity varies with the heat load to the cryopump and the quantity of gas
CAUTION
hing pre
maximum allowabl
cryopump and be pumped, but when the flow rate of gas exceeds the limit, cryopump cannot
restore its pumping performance, warms up and release gases captured so far.
The maximum allowable crossover pressure is calculated as follows;
Maximum quantity of gas that can be processed
instantaneously (Pa
•
L)
Volume of vacuum chamber (L)
Maximum allowable crossover
pressure (Pa)
≦
The maximum quantity of gas that can be processed instantaneously is given by the limit
ping performance. Norm at which the cryopump can restor
cryopanel temperature lower than 20K is used ressure. as the maximum allowable crossover p
condensed in the cryopump. (Refer to Table 5-2.)