INFICON BCG450 ATM to Ultra-High Vacuum Triple Gauge - Manual (Page 30)

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The Atmosphere Switching Function is used to define an atmospheric pressure
threshold where a (semiconductor) relay "Atmospheric pressure reached" is acti-
vated or deactivated
1) .
The atmospheric pressure threshold is user programmable as a percentage of the
ambient atmospheric pressure (100%)
2) .
A separate sensor built into the gauge (measuring ambient atmospheric pressure )
is used as a reference.
The following rule applies:
Atmospheric pressure × N
Atmospheric pressure threshold = —————————————
100
where:
Atmospheric pres-
sure threshold [mbar] : If chamber pressure rises above this value, the
"Atmospheric pressure reached" relay is activa-
ted
3)
Atmospheric pres-
sure [mbar] : Ambient atmospheric pressure (100%)
(measured outside the vacuum chamber)
N [%] : User programmable percentage value
(admissible range: 1 … 140% 2) , default = 99%)
The measuring range of the gauge is limited to 1500 mbar. If the calcu-
lated atmospheric pressure threshold exceeds 1500 mbar, the relay will
never be activated. Keep this in mind when choosing N.
It is possible to calibrate the atmospheric pressure sensor ( → 45).
1) Depending on gauge version, access to "Atmospheric pressure reached" relay
contacts differ:
BCG450: A hard wired (semiconductor) relay contact is available
between pins 1 and 4 at the sensor cable connector ( → 19
and 32).
BCG450-SD/SP: The function of the setpoint relays SP A/B ( → 20) can be
reprogrammed to perform as "Atmospheric pressure
reached" relays. Reprogramming is carried out via fieldbus.
(further information → [1] or [2]).
(Default setting: relays are assigned to (SP A / B) setpoints)
2) Programming of the percentage N can only be carried out via the serial inter-
faces (RS232, DeviceNet or Profibus, → 33, [1] or [2]).
3) A fixed hysteresis of 2% of the atmospheric pressure threshold is programmed
( → example below).
4.6 Atmosphere Switching
Function
4.6.1 Functional Principle