Frequency Measuring - Siemens SIMATIC S7-300 FM 350-1 Manual

Operating Modes, parameters and commands
7.4 Measuring modes
7.4.3

Frequency measuring

Frequency Measurement
In the frequency measurement operating mode, the FM 350-1 counts the pulses that occur
within a dynamic measuring time.
The value of the calculated frequency is made available in the unit 10
measured frequency value at the feedback interface (Bytes 0 to 3).
Figure 7-32
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- 32 Calculating the Update Time
Boundary conditions
Non-isochronous mode
Isochronous mode
The decimal places obtained after division by T
1
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.
140
Frequency Measurement With Gate Function
Update time
Any T n × 10 ms
DP
T < 10 ms n × T
DP
T ≥ 10 ms n × T
DP
are omitted.
DP
n
min
1
(10 ms/T [ms] ) +1
DP DP
1
DP
Hz. You can read the
-3
Value range of n
n
max
1000
1000
1)
10000 ms/T
DP
FM 350-1 Counter module
Manual, 05/2011, A5E03648639-01
[ms]
1)