Setpoint Scaling (Sc); Loop Update Time Too Fast (Tf) - Allen-Bradley SLC 500 Series Reference Manual
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Example with the RG bit set: The reset term (TI) of 1 indicates that the integral
value of 0.01 minutes/repeat (0.6 seconds/repeat) is applied to the PID
integral algorithm. The gain value (KC) of 1 indicates that the error is
multiplied by 0.01 and applied to the PID algorithm.
Example with the RG bit clear: The reset term (TI) of 1 indicates that the integral
value of 0.1 minutes/repeat (6.0 seconds/repeat) is applied to the PID integral
algorithm. The gain value (KC) of 1 indicates that the error is multiplied by 0.1
and applied to the PID algorithm.
The rate multiplier (TD) is not affected by this selection.
TIP
Valid on SLC 5/03 and higher processors.
Setpoint Scaling (SC)
Table 9.14 Setpoint Scaling Parameter
Tuning Parameter
Address
Descriptions
SC - Setpoint Scaling Word 0, Bit
5
The SC bit is cleared when setpoint scaling values are specified.
Loop Update Time Too Fast (TF)
Table 9.15 Loop Update Time Too Fast Parameter
Tuning Parameter
Address
Descriptions
TF - Loop Update Too
Word 0, Bit 6 binary (bit)
Fast
The TF bit is set by the PID algorithm if the loop update time specified cannot
be achieved by the controller due to scan time limitations.
If this bit is set, correct the problem by updating your PID loop at a slower
rate or move the PID instruction to an STI interrupt routine. Reset and rate
gains will be in error if the instruction operates with this bit set.
Proportional Integral Derivative Instruction
Data Format Range
Type
binary (bit)
0 or 1
control
Data Format Range
Type
0 or 1
status
Publication 1747-RM001G-EN-P - November 2008
9-11
User Program
Access
read/write
User Program
Access
read/write
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