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Parameter description
7.4.3 Function Blocks
The Function Blocks contain the fundamental automation functions of the fieldbus device.
There are various types of function blocks such as Analog Input Function Block , Analog Out-
put Function Block and PID Block.
Each of these function blocks is used to process various application functions (automation
tasks) in the entire system. In this way, local control functions, for example, can be carried
out directly in the field, self-diagnosis of the device can be performed and device errors such
as a control loop fault can be reported automatically to the automation system.
The function blocks process the input values according to their specific algorithm and their
parameters internally available. They create output values which are made available by con-
necting individual function blocks among one other to further process them in other function
blocks.
7.4.3.1 Analog Output Function Block
The Analog Output Function Block processes an analog signal received from an upstream
connected block (e.g. PID Block) into a correction value that can be used for the downstream
connected Transducer Block (e.g. valve positioner). For this purpose, it contains scaling func-
tions and ramp functions.
The AO Block receives its set point depending on the mode (MODE_BLK) from the CAS_IN,
RCAS_IN or SP input variables. Taking into account the PV_SCALE, SP_HI_LIM and
SP_LO_LIM, an internal operating set point is formed from the SP_RATE_UP and
SP_RATE_DN.
An output value OUT is formed corresponding to the IO_OPTS and XD_SCALE parameters.
The output value is passed on to the downstream connected Transducer Block over the
CHANNEL.
The AO Block has a fault state handling. It is initiated when a fault condition (of the valid set
point) exists longer than the time determined in FSTATE_TIME or the SET_FSTATE parameter
in the Resource Block is enabled.
FSTATE_TIME, FSTATE_VAL and IO_OPTS determine the fault state handling.
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EB 8383-1 EN
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