INFICON SKY CDGxxxD (Profibus) - Manual (Page 39)

tira54e1-a (2009-01) CDGxxxD.cp
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11 Trip Point Function Block (Relay 1 and 2)
The Trip Point Object models the action of trip points for a device, often
corresponding to physical outputs (Discrete Output Object). Each Trip Point
channel has a pointer (Analog Sensor Input Object Instance ID) to a source Analog
Sensor Input Instance.
A trip point value, designated as a High or Low trip point, is compared to the
specified instance of an Analog Input Sensor Process Value parameter. This trip
point is intended to be used as a process control indicator only, as distinguished
from the Analog Input Sensor Function Block Object’s Alarm and Warning trip
points.
All the necessary calculations and the setting/resetting (triggering) of the relays are
done by the basic device itself.
Two different functionalities are implemented: Setpoint function and Atmosphere
(ATM) detection. The Setpoint function is realized via the Low trip Point function
and the ATM detection via the High Trip point function. The two functions are
mutually exclusive, only one of them can be active at a time.
The basic device switches to the desired function according to the value
"Percentage of ATM" (ID 201). See section 11.2.11.
If "Low Trip Enable" (ID 20) is set, the Setpoint function is activated.
The parameter "Percentage of ATM" (ID 201) is automatically set to "0" and
therefore the ATM function is disabled. Low Trip Point is compared to the Analog
Input Sensor Function Block Instance 1 (CDG) ProcessValue to generate a trip
point condition.
Status will be set if the input (ProcessValue) is at or below the Low Trip Point. If the
pressure (input) increases above "Low Trip Point + Hysteresis", the Status will be
reset.
This functionality is used to compare the pressure measured by the CDG with the
atmospheric pressure.
The parameter "Percentage of ATM" (ID 201) is used to define a value "Percentage
of Atmosphere". This value will be multiplied with the pressure from the Analog
Sensor Instance 2 (ATM Sensor). Then this result will be copied into parameter
"High Trip Point" (ID 202). If a value other than "0" is written to Percentage of
Atmosphere (ID 201), the parameter "Low Trip Enable" (ID 20) is automatically set
to "0". High Trip Point is compared to the Analog Input Sensor Function Block
Instance 2 (ATM) ProcessValue to generate a trip point condition.
Status will be set if the input (ProcessValue) value is at or above the High Trip
Point. If the pressure (input) decreases below "High Trip Point – Hysteresis", the
Status will be reset.
11.1 Trip Point Function
Block behaviors
11.1.1 Setpoint function
11.1.2 Atmosphere detection