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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
5.5. Guideline for closed loop applications
Practical guidelines for the adjustment of the con-
trol parameters are summarized below. They are
divided into different application categories and in-
clude common rules of thumb.
The commissioning of a closed loop systems
requires detailed knowledge of process
control technology. Therefore on-site works
support is recommended.
An incorrect wiring resp. parameter setting may
lead to malfunction and permanent damaging
of electronics and drive system!
5.5.1. Application: Closed loop systems for
position
Introduction
The electronics uses a feedback control loop which
automatically adjusts the electrical input to the
valve amplifier to move the drive to a command-
ed position. At the heart of this feedback loop is
a digital controller which computes and updates
the signal output (set value output) every one
millisecond. The controller has adjustable coeffi-
cients, which must be set by the user for the par-
ticular application.
The controller provides a standard PID control ca-
pability plus extra features you can use to improve
the performance beyond the limits of PID.
Basic information for the control algorithm
Why tuning?
The controller can be used with valves that vary
greatly in flow capacity, frequency response, satu-
ration and deadband, with different kinds of load,
and with cylinders of any area and stroke. The
user must adjust the control coefficients for the
specific system. There are no fixed sets of values
for the controller coefficients that will handle eve-
ry situation well.
The electronics utilizes a “PID” controller for its ba-
sic control action. The name PID comes from the
fact that the controller output is the sum of three
terms, called proportional (P), integral (I) and de-
rivative D), each with a user adjustable coefficient.
The user software provides therefore the parame-
ters P16 (P), P17 (I) and P18 (D).
P
- P16
This term provides an immediate output signal,
proportional to the error between commanded and
measured position. If this parameter is set too high,
sustained oscillations may occur. If it is set too low,
accuracy and speed of response may be poor.
I
- P17
This term causes the output to change at a rate
proportional to the error in measured position over
time (integration time), in a direction to drive the
steady state error to zero. P17 is active within a
window, which might be adjustable by parameter
P26. P26 shall be adjusted in the way that the win-
dow lies near the final position or in the stationary
range of the drive. A too higher value of P17 caus-
es oscillations, in addition to which the selection
of a too lower value may result in a slow action.
D
- P18
The D-term provides an output proportional to the
rate of change of the measured drive position. De-
pending on the polarity of the parameter prefix, this
term causes damping or acceleration. For hydrau-
lic drives this term should be set to a low value.
Parameter ranges
The controller provides two parameter ranges of
BASIC
and
EXPERT
. The
BASIC
mode serves
for adjustment of the fundamental function pa-
rameters, while the application specific setting of
the control coefficients may be made via the
EX-
PERT
mode. The operating mode is selected via
the menu
OPTIONS
.
Simple tuning of a position control loop
Before trying anything complicated, you should
adjust the proportional gain, accessible by P16.
In many cases this coefficient will be all you need,
and you will not have to bother with any of the other
control features. If you do need the other features,
you cannot adjust them properly without first ad-
justing the P-gain. Adjusting the P-gain is done by
setting all the other control coefficients P13 – 19
as well as P26 –28 to zero and increasing P16 to
the highest value that does not result in sustained
oscillations of the drive position.
Summary of Contents for PID00A-40 Series
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