YOKOGAWA STARDOM FCN-500, Engineering Manual

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<9. Advanced Engineering >
194
TI 34P02K35-02E May 31, 2017-00
9.2 Know-how in Use of NPAS_POU
This section describes know-how, settings and precautions relating to the use
of NPAS_POU.
9.2.1 Scan Cycle and Control Cycle
Scan cycle is described in Section 2.2.4, “Determining FCN-500, FCN-RTU Scan
Cycle” and Section 4.1.2, “Control Task Setup.”
When using an NPAS POU, besides scan cycle, the control cycle must also be
considered.
Details about the control cycle of NPAS POU can be found in Logic Designer’s
NPAS POU online help documentation.
● What is Control Cycle?
NPAS POU has four processing functions, namely input processing,
control/calculation processing, output processing and alarm processing.
• Input processing
In NPAS POUs, input processing processes input signals and convert them into
data suited for control calculation and numerical calculation, etc.
In regulatory control POUs, input processing gets PV values from input signals,
while in calculation POUs, input processing gets the CPV (calculated process
value). Totalization and calibration functions are also included in input
processing.
• Control/calculation processing
Control/calculation processing performs the calculation function and control
function of each NPAS POU.