Siemens SIMATIC S5-115U, User Manual

Page: 412 / 676

Integral Blocks S5-115U Manual
Table 11-11. Format of the Transfer Block (Continued)
Data Word Name Comments
22
24
29
48
X
Z
XZ
YA
a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
Actual value (- 2047 to+2047)
Disturbance variable (- 2047 to+2047)
Derivative time (- 2047 to+2047)
Output variable (- 2047 to+2047)
All parameters (with the exception of the control word STEU) must be specified as 16-bit fixed
point numbers.
Note
The PID algorithm uses the data words that are not listed in the table as auxiliary flags.
Initializing and Invoking the PID Controller in the STEP 5 Program
A number of different PID controllers can be implemented by calling OB251 repeatedly, so make
sure that the relevant controller DB has been invoked before calling OB251.
Note
Important controller data are stored in the high-order byte of control word DW 11
(DL 11). Make sure that only T DR 11/SU D 11.0 to D 11.7 or RU D 11.0 to D 11.7
operations are used to modify user-specific bits in the control word.
Selecting the Sampling Interval
The value selected as sampling interval must not be excessiveley high in order to be able to use
the well-known analog method in the case of digital control loops.
Experience has shown that a sampling interval of approximately 1/10 of the counter constant
T
RKdom
*
produces a control result comparable to the equivalent analog result. Dominant system
time constantT
RKdom
determines the step response of the closed control loop.
T
A
=1/10
•
T
RKdom
In order to ensure the constancy of the sampling interval, OB251 must always be invoked in the
service routine for timed interrupts (OB13).
* T
RKdom
=Dominant system time constant of the closed control loop
11-38
EWA 4NEB 811 6130-02b