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 vari-
able. The cycle assigned to PER_TM is not identical to the processing cycle of the FB
PULSEGEN. The PER_TM cycle is made up of several processing cycles of FB PUL-
SEGEN, whereby the number of FB PULSEGEN calls per PER_TM cycle is the yardstick
for the accuracy of the pulse duration modulation.
An input variable of 30% and 10 FB PULSEGEN calls per PER_TM means the following:
n "1" at the QPOS output for the first three calls of FB PULSEGEN (30% of 10 calls)
n "0" at the QPOS output for seven further calls of FB PULSEGEN (70% of 10 calls)
With a "sampling ratio" of 1:10 (CONT_C calls to PULSEGEN calls) the accuracy of the
manipulated value in this example is restricted to 10 %, in other words, set input values
INV can only be simulated by a pulse duration at the QPOS output in steps of 10 %. The
accuracy is increased as the number of FB PULSEGEN calls per CONT_C call is
increased. If PULSEGEN is called, for example 100 times more often than CONT_C, a
resolution of 1 % of the manipulated value range is achieved.
Application
Block Diagram
Accuracy of the Manipu-
lated Value
VIPA SPEED7
Standard
PID Control > FB 43 - PULSGEN - Pulse generation
HB00 | OPL_SP7 | Operation list | en | 18-30 849
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