User guide

- 44 -
3,'&RQWUROOHU &RQWURO%ORFN
The 3,'&RQWUROOHU control block is a regulator circuit with an input for the 6HW9DOXH, an input for
$FWXDO9DOXH
and an
2XWSXW
.
In contrast to the two-position controller (which may be emulated under
ODEZRUOG
VRIW with a
trigger module), which only recognizes the two states of "ON" and "OFF" the PID controller is a
FRQVWDQW
controller (the manipulated variable is constantly changed) with which much better
controller results may be obtained.
The same applies to information which is available to the controller. The two-position controller
only recognizes three different input signals: the actual value is either too large, too small or lies
within the permissible range. This information does not make it possible to use a continuous
manipulated variable range because it is too imprecise. Instead it is a quantitative measure for the
deviation of the actual value from the set value.
H Z\
serves as such a system deviation

A controller is a transmission element and thus completely determines when the resulting
manipulated variable
XW
is provided for each possible system deviation
HW
. The relationship is
referred to as the &RQWURO$OJRULWKP. An algorithm which has been tried and proven in many
cases shows
3
roportional,
,
ntegral and
'
ifferential behavior and is thus called a
3,'
controller.
The algorithm contains the three free constants
3SURSRUWLRQDOLW\IDFWRU
,,QWHJUDWLRQWLPHFRQVWDQWRUUHVHWWLPH
and

''LIIHUHQWLDOWLPHFRQVWDQWRUUDWHWLPH
which have to be correspondingly adapted to the entry fields in the controller parameter window
and the process which is to be controlled.
(IIHFWVRIWKHFRQVWDQWVRQWKHFRQWUROSURFHVV
The larger the proportionality factor
3
is the faster the system deviation
H
is settled. However
3
may not be too large because the regulator circuit would otherwise oscillate.
A remaining minimal system deviation
H
is lowered through the integral proportion
,
. The reset
time may be too small because otherwise the regulator circuit would become unstable.
The controller dynamic is significantly improved by the differential proportion'. The
proportionality factor
3
may be greater than for a pure
3
or
3,
controller without the regulator
circuit becoming unstable.
In most cases several practical tests are required in order to find the optimal factor settings for a
specific regulatory circuit.
The behavior of the controller can be tested with two control blocks "Set Value" and a result block
digital display.