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Programming Function Blocks and Features
Video Recorder – User Manual 90
4.8 Program Control Loops
Control Loop Programming Structure
Programming a control loop requires configuring at least 3 function blocks: an Analog Input (AI), a loop
algorithm and an Analog Output (AO). The term AO is applied to any type of control output; current
(CAT), or time proportioning (DAT). The structure of the instrument permits many variations on this
concept by allowing Calculated Values (CVs), both digital and analog, to be used as inputs to the
different parameters within the control algorithms. It also allows a single parameter to be read by any
number of function blocks in the unit.
Loop Characteristics
Table 4-8 lists loop characteristics to be aware of when configuring your instrument.
Table 4-8 Loop Characteristics
Characteristic What to be aware of
Choice of algorithm type Two PID algorithm types, interactive and noninteractive. Noninteractive is the
default type; however, this may be changed.
Gain or proportional band PB is the default; however this may be changed.
7 loop types available If the loop type is changed after a configuration is completed, all previously
programmed entries will be deleted.
Diagnostic routines You will be prompted to save your entries when leaving the loop program
sequence. Diagnostic routines are executed at this time to verify all entries are
complete and compatible. A FAIL message at this time may indicate incomplete
entries or incompatible selections.
Split output tuning When programming Split Output control loops, tuning parameter set #1 is
automatically applied to output values between 0 and +100. Tuning parameter
set #2 is automatically applied to output values between 0 and -100.
Programming loop
parameters
Control loop programming may require entry of numerical values, analog
parameters or discrete parameters as determined by the specific loop feature. In
some cases the choices may be a numeral, an analog parameter or OFF. For
parameter choices, refer to Table 3-2 for definitions of the discrete and analog
parameter types available. OFF or NONE are listed as menu choices where
applicable. Scroll to locate.
Minimum programming
requirements
Many of the prompted entry fields for control loops are optional. As a general
rule, the minimum entry information for control loops includes the Process
Variable (PV) with range limits, set point value, some combination of gain, reset
and rate, and a source for the feedback. In most cases, the feedback source will
be the back-calculation output (BC) value of the analog output (AO) function
block.