Hitachi WJ200-001S Instruction Manual page 118

PID Loop Configuration
The inverter's PID loop algorithm is configurable for various applications.
PID Output Limit - The PID loop controller has a built-in output limit function. This
function monitors the difference between the PID setpoint and the loop output (inverter
output frequency), measured as a percentage of the full scale range of each. The limit is
specified by parameter .

When the difference |(Setpoint – loop output)| is smaller than or equal to the 
limit value, the loop controller operates in its normal linear range.
 When the difference |(Setpoint – loop output)| is larger than the  limit value,
the loop controller changes the output frequency as needed so that the difference
does not exceed the limit.
The diagram below shows PID setpoint changes and the related output frequency
behavior when a limit value in  exists.
Output limit
PID Setpoint
Output freq.
Output limit
Deviation (error) Inversion - In typical heating loops or ventilation loops, an increase in
energy into the process results in an
PV). For cooling loops, an increase in energy into the process results in a
In this case, the Loop Error = –(SP – PV). Use  to configure the error term.
 =
SP
+

PV
%


Error Freq.
PID
calculation
-
PV from process with
positive correlation
Limit imposed
on output
increasing
PV. In this case, the Loop Error = (SP –
 =
SP
-

+
PV
Limit imposed
on output
t
decreasing
Error Freq.
PID
calculation
PV from process with
negative correlation
333
PV.