Parker PID00A-40 Series, Operation Manual, Page: 39 / 44

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Electronics for Closed Loop Control
Series PID00A-40X Operation Manual
PID00A_10 5715-616 UK.indd CM 14.11.14
Parker Hannifin Corporation
Hydraulics Group
to reduce static error, reduce following error or in-
crease actuator stiffness. High values of P cause
faster system response, whether you need it or not.
As the system frequency response gets too close
to the frequency response of one of your compo-
nents, the system response becomes oscillatory.
•
Valve
The frequency response of the valve can be
obtained from the datasheets. As a first guess, it
needs to be at least twice the system frequency
response.
• Position transducer
Some analog output transducers will present
problems because of filtering intended to smooth
the output. This is most important for this appli-
cation, because in this case the actual velocity
feedback signal will be calculated from the posi-
tion transducer signal. To ensure best system
dynamic, sensors with integrated D/A-converter
should operate with a most high sampling rate.
Magnetostrictive transducers with digital output
often have a low sampling rate, because an in-
teraction with the achievable resolution. Please
obtain detailed information from the transducer
supplier.
• Drive
There is a mode of instability caused by a com-
bination of the mass of the load and the com-
pressibility of the hydraulic fluid in the system.
This frequency is often surprisingly low when
using long stroke cylinders.
Update rate of the controller
The controller updates the electrical output to the
valve at 1000Hz. This rate is fast enough to have
negligible effect in almost all hydraulic applications,
but it does set an absolute limit on the response
of the system.
Generating feedback signals
The electronics derives the feedback signal for the
velocity control from the differentiation of the posi-
tion transducer output signal. The disadvantage of
such a circuit is the creation of noise in the feed-
back signal. Thus different filter algorithms are im-
plemented. To match the functionality of a certain
feedback generator to the utilized position trans-
ducer, the parameters below have to be adjusted:
T-portion of PT1-filter – P28
This parameter is usable for the adjustment of the
low pass filter damping of the differentiated feed-
back signal. The higher this parameter value is,
the better is the smoothing of the feedback signal
within the controller, but all the damping of the fil-
ter. Thus the level of the parameter has negative
influences to the dynamic of the control.
Average quantity – E50
To smooth the differentiated feedback signal sev-
eral values will be sampled resulting in an aver-
age value. The bigger the number of values will be
selected, the better is the quality of the feedback
signal. This function is dedicated for the noise sup-
pression and has virtually a filter function.
Yet the average quantity creates negative effects
for the dynamic of the feedback signal.
Feedback velocity – E70
This parameter enables the generation of the ve-
locity-feedback signal from a position transduc-
er signal.
Sensor length – E73
The specification of the sensor length is required
for calculating the velocity.
MAX velocity – E74
Required to match the maximum velocity with
100% command signal span. Example:That re-
sults for a command signal span of 0...10V a ve-
locity which is adjusted by this parameter.
The performance of the velocity signal may
be examined via the diagnostic function of the
operating software. For this purpose begin
with starting of the ProPXD-Software.
• Type the key combination “CTR + S + E”
• The service window will be opened, type the
passwort “service”
• Select test point
“MP5
”
• Close the service window
• Release the diagnostic screen via the menu
“service” below “monitor”
• Tick the
“monitor output signal”
box
• The button “start” activates the display of the
feedback signal