Technical data

Table Of Contents
SFBs for Integrated Control
System Software for S7-300/400 System and Standard Functions - Volume 2/2
27-16
A5E00739858-01
Description
The PULSEGEN function transforms the input variable INV ( = manipulated value
of the PID controller) by modulating the pulse duration into a pulse train with a
constant period, corresponding to the cycle time at which the input variable is
updated and which must be assigned in PER_TM.
The duration of a pulse per period is proportional to the input variable. The cycle
assigned to PER_TM is not identical to the processing cycle of the SFB/FB
"PULSEGEN." The PER_TM cycle is made up of several processing cycles of
SFB/FB "PULSEGEN," whereby the number of SFB/FB "PULSEGEN" calls per
PER_TM cycle is the yardstick for the accuracy of the pulse duration modulation.
t
INV
QPOS_P
(LMN)
0
50
100
1
0
t
PER_TM
PULSEGEN cycle
30
50
80
(=CONT_C cycle)
Pulse Duration Modulation
An input variable of 30% and 10 SFB/FB "PULSEGEN" calls per PER_TM means
the following:
"One" at the QPOS output for the first three calls of SFB/FB "PULSEGEN" (30%
of 10 calls)
"Zero" at the QPOS output for seven further calls of SFB/FB "PULSEGEN"
(70% of 10 calls)