Technical data

Table Of Contents
SFBs for Integrated Control
System Software for S7-300/400 System and Standard Functions - Volume 2/2
A5E00739858-01
27-17
Block Diagram
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QPOS_P
QNEG_P
MAN_ON
NEG_P_ON
POS_P_ON
INV
SYN_ON,
STEP3_ON,
ST2BI_ON
PER_TM,
P_B_TM,
RATIOFAC
0
1
Accuracy of the Manipulated Value
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 SFB/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.
Note
The call frequency must be programmed by the user.
Automatic Synchronization
It is possible to synchronize the pulse output with the block that updates the input
variable INV (for example, CONT_C). This ensures that a change in the input
variable is output as quickly as possible as a pulse.
The pulse generator evaluates the input value INV at intervals corresponding to the
period PER_TM and converts the value into a pulse signal of corresponding length.
Since, however, INV is usually calculated in a slower cyclic interrupt class, the
pulse generator should start the conversion of the discrete value into a pulse signal
as soon as possible after the updating of INV.
To allow this, the block can synchronize the start of the period using the following
procedure: