Preliminary Considerations
Before energizing the control system, review your application carefully. What would happen if your
system overshoots – will damage result?
In an application where the load moves freely and cannot impact against anything or be crushed by the
actuator, overshoot can be tolerated during the adjustment of the loop.
However, in a clamping application, for example, overshoot could damage the actuator or the load being
clamped.
Stop and ask yourself – "Will my adjustments cause damage if not done properly?" If so, you may have
to modify the equipment for safety reasons so that it can tolerate over-positioning, overspeed, or higher-
than-planned forces during adjustments.
Caution:
A bad setting of the PID parameters may cause the drive to oscillate.
An oscilloscope and a means of generating a square wave (signal generator or system controller) is
required in order to tune a closed loop controller. To adjust the controller parameters, the command
signal into the amplifier should continuously switch between 10-30% and 70-80%. Each signal level
should have a dwell time of several seconds (Figure 2).
Before installing the card, the potentiometers P, I, and D should be at the fully counter clockwise position
and the switches on the card should be set based on the application described in the "Application Notes"
section.
Finally, install the card and connect the command and feedback signals based on the appropriate option
described in the "Control Input Option" section.
Caution:
If the feedback signal is not of the proper polarity, your load will promptly "run away" when the
command signal is applied. This is because the feedback is being added to, not subtracted from, the command
signal at the summing junction, producing a constantly increasing error signal.
Tuning Procedure
1. Connect a monitoring device, such as an oscilloscope or an XY recorder to the COMMAND INPUT, and
the FEEDBACK signals (see "Control Input Options").
Caution:
Care should be taken when taking measurements using TP2. If this test point should become
grounded, the feedback command will change in turn causing unintended operation.
Do not attempt to visually "eyeball" the results of the adjustment. Visual observation of the actuator is
not accurate enough. If you do not know how to operate the monitoring device, seek the assistance
of someone who DOES know how to use it.
2. Energize the system and be sure the servo valve has been mechanically nulled.
3. Apply the step input repeatedly, and slowly increase the Proportional Gain of the amplifier a little at a
time while observing the system response (via the feedback signal).
A position control system, for example, will respond as shown in Figure 3.
As Proportional Gain is increased, the step input will give increasingly faster response. Eventually the
gain will reach a value where the input step will cause the actuator to just barely reach the desired
position.
Continue increasing the Proportional Gain until the system achieves the position that the step input
should produce, as shown in Figure 4.
4. When the Proportional Gain is set high enough so that the step input causes the desired position to
be achieved, measure the response time using the time base of monitoring instrument.
5. Now, continue to raise the Proportional Gain until a moderate overshoot occurs, as shown in Figure 5.
6. Begin increasing the DERIVATIVE Gain now, a little at a time, while observing the response carefully.
The overshoot should begin to reduce as Derivative Gain is increased.
Continue increasing the Derivative Gain, and applying the step input, until the overshoot is
eliminated (Figure 6).
Installation Guide
Servo Amplifier
PID Set-Up Procedure
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©
Danfoss | August 2023
BC459665217198en-000101
