MKS HPS 919 Series, Operation And Maintenance Manual

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Hot Cathode Ionization High Vacuum Senor System
When an LED is on, the measured pressure is below the set point value, the
normally open relay contact is closed, and the normally closed contact is
open. When an LED is off, the measured pressure is above the set point
value, the normally open relay contact is open, and the normally closed
contact is closed.
To prevent the relays from oscillating when the pressure passes by a set
point pressure, the circuit incorporates hysteresis, so that the set point
turns off at a pressure slightly higher than one at which it turns on. The
response time of the relays depends upon the pressure at which the
Controller is operating.
Adjusting the Filament Protection Limit
The life of the filament can be greatly extended if it is shut off at higher
pressures. The lower the pressure at which the filament is shut off, the longer
the life will be. The Series 919 Controller has a filament protection feature
which automatically shuts off the filament. The protection level can be set
between 10
-6
and 10
-2
Torr.
To adjust the protection level to a particular pressure,
1. Depress the Protect push-button on the front panel below the display.
2. Use a small screwdriver to adjust the Protection potentiometer on the
front panel, as shown to the right, until the display shows the
pressure at which you would like to shut off the filament.
Restarting the Filament
If a pressure value for filament protection has been set and the pressure rises
above this value, the filament will shut off automatically. If the pressure falls
back below this value, the filament will not turn on automatically. You must
restart the filament with either one of the following methods.
Local Method
1.
Switch the Filament toggle off.
2. Switch it back on.
Remote Method
1.
With the Filament toggle set to remote, allow pin 10 (filament remote-
enable) of the Accessory connector to go to a TTL high level if not
already high.
2. Return to a TTL low level or ground.
Protection
Adjust Pot
Front Panel
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