The fan/pump is started by pressing [Auto On] button on the LCP and applying a start signal. The speed is adjusted manually by pressing the [ ] or
▲
[ ] navigation keys on the LCP to a level where the feedback is around the system setpoint.
▼
NB!
It is not possible to run the motor at maximum or minimum speed, when manually adjusting the motor speed due to the need of giving
the motor a step in the speed during autotuning.
PID autotuning functions by introducing step changes whilst operating at a steady state and then monitoring the feedback. From the feedback response,
the required values for par 20-93 PID Proportional Gain and par 20-94 Integral Time are calculated. Par 20-95 PID Differentiation Time is set to value 0
(zero). Par. 20-81 PID Normal / Inverse Control is determined during tuning process.
These calculated values are presented on the LCP and the user can decide whether to accept or reject them. Once accepted, the values are written to
the relevant parameters and autotuning mode is disabled in par 20-79. Depending on the system being controlled the time required to carry out autotuning
could be several minutes.
It is advised to set the ramp times in par. 3-41/3-42 or par. 3-51/3-52 according to the load inertia before carrying out PID autotuning. If PID autotuning
is carried out with slow ramp times, the auto-tuned parameters will typically result in very slow control. Excessive feedback sensor noise should be
removed using the input filter (parameter groups 6-*, 5-5* and 26-*, Terminal 53/54 Filter Time Constant/Pulse Filter Time Constant #29/33) before
activating PID autotuning. In order to obtain the most accurate controller parameters, it is advised to carry out PID autotuning, when the application is
running in typical operation, i.e. with a typical load.
20-70 Closed Loop Type
Option:
Function:
This parameter defines the application response. The default mode should be sufficient for most applications.
If the application response speed is known, it can be selected here. This will decrease the time needed for
carrying out PID autotuning. The setting has no impact on the value of the tuned parameters and is used only
for the autotuning sequence.
[0]
*
Auto
[1]
Fast Pressure
[2]
Slow Pressure
[3]
Fast Temperature
[4]
Slow Temperature
20-71 PID Performance
Option:
Function:
[0]
*
Normal
Normal setting of this parameter will be suitable for pressure control in fan systems.
[1]
Fast
Fast setting would generally be used in pumping systems, where a faster control response is desirable.
20-72 PID Output Change
Range:
Function:
0.10
*
[0.01 - 0.50]
This parameter sets the magnitude of step change during autotuning. The value is a percentage of full speed.
I.e. if maximum output frequency in
par 4-13/4-14, Motor Speed High Limit
is set to 50Hz, 0.10 is 10% of 50Hz,
which is 5Hz. This parameter should be set to a value resulting in feedback changes of between 10% and 20%
for best tuning accuracy.
20-73 Minimum Feedback Level
Range:
Function:
-999999.000 User Units
*
[-999999.999 to Value of par. 20-74]
The minimum allowable feedback level should be entered here in User units as defined in par 20-12. If the level
falls below par 20-73, autotuning is aborted and an error message will appear on the LCP.
VLT
®
HVAC Drive Programming Guide
3. Parameter Description
MG.11.C5.02 - VLT
®
is a registered Danfoss trademark
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