IKA labworldsoft - Manual (Page 44)

- 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 ODEZRUOGVRIW 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 .