946 Controller Instruction Manual
pg. 35
11. SET SP displays the entered and saved setpoint trip value. To change the value, scroll to the
value to be changed, highlight by pressing
Enter
, and then adjust to the desired value with the
or
keys. Confirm the change by pressing
Enter
. The range is 1% to 95% of the
manometer’s full scale. When entering the value, the speed of the value change can be increased
by continuously pressing the
or
key.
12. Hyst
When a set point value is changed, the hysteresis value will be changed automatically. If DIR is
set to ABOVE, the hysteresis is automatically set to 0.9xSet point; if DIR is set to BELOW, the
hysteresis is automatically set to 1.1xSet point.
To modify the hysteresis, move the cursor to the hysteresis value and press
Enter
. Use the
or
key to change the value, then press
Enter
again to set the value. When DIR has been set to
ABOVE, the maximum hysteresis value permitted for a Capacitance Manometer is 0.99xSet
point; when DIR is set to BELOW, the minimum hysteresis value is 1.01xSet point.
6.5.3 Setup for a CP (Convection Pirani), Convectron, or PR Sensor
Do not use Convection Pirani or Convectron g auges abo ve 1000 Torr true p ressu re.
Series 946 Control lers are furni shed calibrated for N
2
. They also measure the pres sure of
air correctly within the accuracy of the instrument . Do no t attempt to use a Convecti on
Pirani or Convectr on gauge calibrat ed for N
2
to measure or control the pres sure of othe r
gases such as argo n or CO
2
, unless the gas type setting or accurate conversi on data for
N
2
to the othe r gas is prope rly used. If accurate con versi on data is no t used or
imprope rly used, a potential overpressu re explosion hazard can be created u nder certain
conditions.
For example, at 760 Torr of argon gas pres sure, the indicated pressure on a Convection
Pirani or Convectr on gauge calibrat ed for N
2
is 24 Torr. At an indicated pres sure of 50
Torr, the true pressu re of argo n is considerabl y abo ve atmosp heric pressu re. Thus if the
indicated pres sure is not accurately converted to true pres sure, it is possible to
overpress ure the vacuum system. Overpress ure m ay cause glass compo nents to sh atter
dangerou sly, and if hig h eno ugh may cause metal parts to rup ture thus damaging the
system and pos sibly injuri ng person nel. Read this Section for prope r use of conversi on
data.
A pres sure relief valve should be installed in the system if the possibility of exceeding
1000 Torr exists. For some gase s, be aware the indicated pres sure will be higher than the
true p ressu re. For exampl e, at a true pres sure of 9 Torr for helium the indicated pres sure
on a Convectron gau ge calibrated for N
2
is 760 Torr. The safe way to operate the gauge is
to prope rly use accu rate con version data.
Refer to Figure 6-9 for setting up a Pirani or Convection Pirani sensor.