Vacon 50X, User Manual

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fundamentals of pi control vacon 110
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10
Generally, a digital input is used when the process will be operated as both a closed and an open loop and/
or when circumstances may arise where you would want to override the process speed as determined by
the process variable and reference.
Remember: to complete the implementation, you must configure a digital input separately to invoke PI
control.
10.3 Tuning the PI Control Loop
Once the parameters are initially configured, you should tune them so the process control loop operates
as optimally as possible. To make tuning easier, the following recommendations should be observed:
• If your application does not require enabling by digital input, for the duration of
tuning you should select a value for parameter 850 (PI Configure) which does allow
a digital input to enable PI control. Once tuning is finished, you can restore the
parameter to its original value.
• Install a switch to select closed loop and open loop performance.
• Connect a calibration signal to the drive to simulate the effects of the transducer’s
signal. While this is not absolutely required, it can be very helpful.
Once the preparations for tuning are complete, enable PI control via the digital input and set the switch
to open loop. Then operate the drive, utilizing any necessary instrumentation (for example, pressure
gauges, meters, etc.) to characterize the range of the signal supplied from the transducer (for example,
at 3 PSI, the transducer provides 1 V). This will aid in better understanding the operation of the system
and make calibration easier.
Select a mid-range operating point for the system and inject a signal close to that which the transducer
would provide at that point. Vary the signal by the value determined by the set-up technician and deter-
mine whether the proportional response of the system is appropriate. If the questions posed in the pre-
vious section are answered correctly and your initial assumptions prove correct, a combination of input
scaling and proportional gain should make the performance match the system.
Next, examine the transient or short-term effects that are common on all realworld systems. Use the cal-
ibrator to change the feedback signal by some value for a measured interval, with the value and duration
approximating the real system.
For example, say 1 V for 5 seconds was selected. By monitoring parameter 856 (PI Error 2), the effect of
the feedback signal may be observed. The value of this parameter should increase and then settle back
to zero, or perhaps go below zero (negative). The value of the parameter may go positive and negative a
number of times as a response to repeated 5 second transients. Tune parameter 853 (PI Int Gain) to op-
timize this effect to suit the circumstances.
Finally, put the transducer into the circuit and review the results. The results will likely show that the val-
ue of parameter 853 (PI Int Gain) needs to be modified to complete the implementation. Minor adjustment
of the other PI control parameters may also be necessary.
Once the process control loop is optimally functioning, if you changed the value of parameter 850 (PI Con-
figure) for tuning, restore it to its original value.
If you need further assistance or advice, please contact VACON . (See the inside front cover of this manual
for information on how to contact technical support.)