Hitachi L2002 Error Inversion, PID Output Limit, PID Loop Configuration, Other PID-relatedtopics:

4–57

L2002 Inverter

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 A078.

•When the difference (Setpoint – loop output) is smaller than or equal to the A078 limit value, the loop controller operates in its normal linear range.

•When the difference (Setpoint – loop output) is larger than the A078 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 A078 exists.

%
Output limit			Limit imposed
				on output
	A078	Limit value

PID Setpoint

Output frequency A078

Limit value

Output limit	Limit imposed
	on output

t

Error Inversion - In typical heating loops or ventilation loops, an increase in energy into the process results in an increasing PV. In this case, the Loop Error = (SP – PV). For cooling loops, an increase in energy into the process results in a decreasing PV. In this case, the Loop Error = –(SP – PV). Use A077 to configure the error term.

A077 = 00					A077 = 01
SP + ∑		Error		Freq.	SP – ∑		Error		Freq.
			PID					PID
			Calculation					Calculation
PV	–				PV	+
		PV from process with					PV from process with
		positive correlation					negative correlation

Operations Monitoring and

Other PID-related topics:

•“PID Control” on page 3–24

•“PID ON/OFF and PID Clear” on page 4–28

•“Output Deviation for PID Control” on page 4–42

•“PID Second Stage Output” on page 4–46