Siemens SIMATIC S7-300 FM 350-1 - Period Measurement Mode

Operating Modes, parameters and commands
7.4 Measuring modes
FM 350-1 Counter module
146 Manual, 05/2011, A5E03648639-01
7.4.5 Period measurement
Period measurement
In period measurement mode, the FM 350-1 indicates the dynamic measuring time as a
period. If the period is less than the update time, then an average is calculated for the period.
The value of the calculated period is displayed in units 1 μs or 1/16 μs. You can read the
measured period at the feedback interface (Bytes 0 to 3).
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Figure 7-34 Period Measurement with Gate Function
Update Time
The FM 350-1 updates the measured values cyclically. You specify the update time with the
"Update time" parameter. You can change the update time during operation.
Table 7- 38 Calculating the Update Time
Value range of n
Boundary conditions Update time
n
min
n
max
Non-isochronous mode Any T
DP
n × 10 ms 1 12000
T
DP
< 10 ms n × T
DP
(10 ms/T
DP
[ms] ) +1
1)
12000 Isochronous mode
T
DP
≥ 10 ms n × T
DP
1 120000 ms/T
DP
[ms]
1)
1
The decimal places obtained after division by T
DP
are omitted.
It is prohibited to exceed these limits. If these limits are exceeded, the FM 350-1 generates a parameterization error and
does not switch to isochronous mode.