Parameters
M-Max Series Adjustable Frequency Drive
MN04020003E—October 2013 www.eaton.com
99
PID Controller, Actual Value Message FBV
The upper and lower actual value limits (P9.15, P9.16) are
“process messages”. They cannot be used for monitoring
the actual value signal. FBV is not a fault message.
When P5.1–P5.3 = 25, you can set the digital output or a
signalling relay for the FBV.
The FBV actual value message enables the M-Max PID
controller to implement a direct “two-stage control”, as is
commonly used for HVAC applications.
Example:
Ventilation system with two fans (frequency
inverter). Under normal operating conditions, the
maximum output power of fan 1 (M1) is sufficient
to maintain the actual value (PV) at the reference
value. When fan 1 is fully used and additional
airflow is required, a second fan (M2) with
constant power is a simple solution.
Block Diagram, Ventilation with “Two-Stage Control”
With the closed-loop control example shown here, the
sequence is based on the signal diagram in the figure on this
page. The process variables in the limit values are shown in
percent (%). The output frequency (Hz) is shown
superimposed in the same diagram.
●
Start of fan motor M1 with FWD signal. The actual value
(PV) is below the limit value of P9.16. The FBV output
(P5.1–P5.3 = 25) then switches and fan motor M2 (Start)
starts automatically
●
The actual value rises and reaches the upper limit (P9.15).
The FBV output is automatically switched off (= fan M2
Off). Fan M1 remains in operation and works in linear
control mode. In a correctly set up system, this is the
normal operating range
●
If the actual value drops below the limit value (P9.16), the
FBV output is switched. and fan M2 is activated again to
support fan M1
●
When the FWD signal is removed from frequency
inverter 1, the inverter goes from RUN to STOP mode and
decelerates the drive over the set ramp time
●
When frequency inverter 1 is stopped, the FBV output is
automatically de-energized so that fan M2 also stops
Item
Number
Description
1
Output frequency (Hz)
2
Actual value (process variable PV)
FWD: Start signal, clockwise rotating field.
FBV: Actual value message, limit values exceeded (P9.15, P9.16).
P9.15
P9.16
FWD
FBV
t
%
1
2
Item
Number
Description
1
Frequency inverter with PID controller for M1 fan motor
2
Motor starter (frequency inverter, soft starter, contactor) for
M2 fan motor
FWD: Start signal drive 1.
FBV: Actual value message of drive 1 for activating drive 2.
Start: Start signal, drive 2.
PV
FWD
M2
M1
FBV
Start
0–10V/ 4–20 mA
1
2
