Omron MX2 User Manual page 110

"A" Group: Standard Functions
88
A073
Note The setting
gain. The integrator gain Ki = 1/Ti. When you set
abled.
In standard operation, the inverter uses a reference source selected by
A001
parameter for the output frequency, which may be a fixed value (
variable set by the front panel potentiometer, or value from an analog input
(voltage or current). To enable PID operation, set
inverter to calculate the target freq, or setpoint.
A calculated target frequency can have a lot of advantages. It lets the inverter
adjust the motor speed to optimize some other process of interest, potentially
saving energy as well. Refer to the figure below. The motor acts upon the
external process. To control that external process, the inverter must monitor
the process variable. This requires wiring a sensor to either the analog input
terminal [O] (voltage) or terminal [OI] (current).
S etpoint
E rror
+
S P
P V
When enabled, the PID loop calculates the ideal output frequency to minimize
the loop error. This means we no longer command the inverter to run at a par-
ticular frequency, but we specify the ideal value for the process variable. That
ideal value is called the setpoint, and is specified in the units of the external
process variable. For a pump application it may be gallons/minute, or it could
be air velocity or temperature for an HVAC unit. Parameter A075 is a scale fac-
tor that relates the external process variable units to motor frequency. The fig-
ure below is a more detailed diagram of the function.
Setpoint
(Target)
Standard setting
F001
Multi-speed
setting
A020 A035
to
POT meter on
ext. panel
V/I select
[AT]
Voltage
[O]
Current
[OI]
A076
The PID Disable function temporarily suspends PID loop execution via an
intelligent input terminal. It overrides the parameter
PID execution and return to normal motor frequency output characteristics.
The use of PID Disable on an intelligent input terminal is optional. Of course,
any use of the PID loop control requires setting PID Enable function
The PID Clear function forces the PID loop integrator sum = 0. So, when you
turn ON an intelligent input configured as [PIDC], the integrator sum is reset to
zero. This is useful when switching from manual control to PID loop control
and the motor is stopped.
for the integrator is the integrator's time constant Ti, not the
F req.
P ID
Inverter
C alculation
P rocess V ariable (P V )
Frequency
Scale factor
source select
Reciprocal
A001
1
A075
Process variable (Feedback)
Analog input scaling (OI)
A102
A101
A105
A103 A104
PID V/I input select
Section 3-5
A073
= 0, the integrator is dis-
A071 01
= . This causes the
E xternal
M otor
P rocess
Scale factor
A075
P gain
A072
SP
I gain
+ +
A073
D gain
A074
Scale factor
A075
A071
(PID Enable) to stop
F001
), a
S ensor
F001
Frequency
setting
Monitor
d004
A071 01
= .