Pid Functions - Danfoss VLT FCD 311 Design Manual

Gal/min. (GAL/MIN)
3 3
Ft /min. (FT /MIN)
Gal/h (GAL/H)
3 3
Ft /h (FT /H)
Lb/s (LB/S)
Lb/min. (LB/MIN)
Lb/hour (LB/H)
Lb ft (LB FT)
Ft/s (FT/S)
Ft/min. (FT/MIN)
Function:
Select among different units to be shown on the dis-
play. The unit is read out if an LCP control unit can
be connected, and if Reference [unit] [2] or
Feedback [unit] [3] has been selected in one of pa-
rameters 009-012 Display read-out, and in Display
mode. The unit is used in Closed loop also as a unit
for Minimum/Maximum reference and Minimum/Max-
imum feedback.
Description of choice:
Select the required unit for the reference/feedback
signal.
FCD 300 Regulators
The FCD 300 has two integrated PID regulators, one
to regulate speed and one to regulate processes.
Speed regulation and process regulation require a
feedback signal back to an input. There are a num-
ber of settings for both PID regulators that are made
in the same parameters, but selection of regulator
type will affect the selections that have to be made
in the shared parameters.
In parameter 100 Configuration it is possible to se-
lect regulator type, Speed regulation, closed loop [1]
or Process regulation, closed loop [3].
Speed regulation
This PID regulation is optimised for use in applica-
tions in which there is a need to maintain a
particular motor speed. The parameters that are
specific for the speed regulator are parameter 417 to
parameter 421.
Process regulation
The PID regulator maintains a constant process
mode (pressure, temperature, flow, etc.) and adjusts
the motor speed on the basis of the reference/set-
point and feedback signal.
A transmitter provides the PID regulator with a feed-
back signal from the process as an expression of the
process's actual mode. The feedback signal varies
as the process load varies.
= factory setting. () = display text [] = value for use in communication via serial communication port
MG.04.A1.02 - VLT is a registered Danfoss trade mark
®
VLT FCD Series
[31]
This means that there is a variance between the ref-
[32]
erence/setpoint and the actual process mode. This
[33]
variance is compensated by the PID regulator by
[34]
means of the output frequency being regulated up or
[35]
down in relation to the variance between the refer-
[36]
ence/setpoint and the feedback signal.
[37]
[38]
The integrated PID regulator in the frequency
[39]
converter has been optimised for use in process ap-
[40]
plications. This means that there are a number of
special functions available in the frequency converter.
Previously it was necessary to obtain a system to
handle these special functions by installing extra I/O
modules and programming the system. With the fre-
quency converter the need to install extra modules
can be avoided. The parameters that are specific to
the Process Regulator are parameter 437 to param-
eter 444.

PID functions

Unit of reference/feedback
When Speed regulation, closed loop is selected in
parameter 100 Configuration the unit of reference/
feedback is always rpm.
When Process regulation, closed loop is selected in
parameter 100 Configuration the unit is defined in
parameter 416 Process units.
Feedback
A feedback range must be preset for both regulators.
At the same time this feedback range limits the po-
tential reference range so that if the sum of all
references lies outside the feedback range, the refer-
ence will be limited to lie within the feedback range.
The feedback signal must be connected to a termi-
nal on the frequency converter. If feedback is
selected on two terminals simultaneously , the two
signals will be added together.
Use the overview below to determine which terminal
is to be used and which parameters are to be pro-
grammed.
Feedback type
Pulse
Voltage
Current
A correction can be made for loss of voltage in long
signal cables when a transmitter with a voltage out-
put is used. This is done in parameter group 300
Min./Max scaling.
Terminal Parameters
29, 33 305, 307, 327,
328
53 308, 309, 310
60 314, 315, 316
85