Siemens SIMATIC S7 System Manual page 295

The following table lists the values for generating the example waveform. The profile table,
for this example, is in V memory and starts at VB500. You can use any block of V memory
that is available for a PTO profile table. You can include instructions in your program to load
these values into V memory, or you can define the values of the profile in the data block.
Table 7- 19
Address
VB500
VD501
VD505
VD509
VD513
VD517
VD521
VD525
VD529
VD533
The PTO generator begins by running Segment 1. After the PTO generator reaches the
required number of pulses for Segment 1, it automatically loads Segment 2. This continues
until the last segment. After the number of pulses for the last segment is reached, the
S7-200 SMART CPU disables the PTO generator.
For each segment of the PTO profile, the pulse train begins at the starting frequency
assigned in the table. The PTO generator increases or decreases the frequency at a
constant rate to achieve the ending frequency with the correct number of pulses. However,
the PTO generator limits the frequency to the starting and ending frequencies specified in
the table.
The PTO generator performs repeated additions to the working frequency to create a linear
change in frequency over time. The constant value added to the frequency has a limited
resolution. This limited resolution can introduce some truncation error into the resulting
frequency. Thus, the PTO generator does not guarantee that the pulse train frequency can
reach the ending frequency that was specified for that segment. In the figure below, you can
see that the truncation error affects the accelerating PTO frequency. The output should be
measured to verify that the frequency is within an acceptable frequency range.
①
②
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
Profile table values
Value
3 Total number of segments
2,000 Starting frequency (Hz)
10,000 Ending frequency (Hz)
200 Number of pulses
10,000 Starting frequency (Hz)
10,000 Ending frequency (Hz)
3,400 Number of pulses
10,000 Starting frequency (Hz)
2,000 Ending frequency (Hz)
400 Number of pulses
Desired frequency plot
Actual frequency plot
Program instructions
7.7 Pulse output
Description
Segment 1
Segment 2
Segment 3
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