Siemens Simatic S7 Series

Program instructions
7.6 Counters
S7-200 SMART
224 System Manual, 09/2015, A5E03822230-AC
7.6.3
Noise reduction for high-speed inputs
Counting high-speed pulses with HSC inputs
Note
High-speed input wiring must use shielded cables
Use shielded cable with a maximum length of 50 m, when connecting HSC input channels
I0.0, I0.1, I0.2, and I0.3.
One or both of the following actions may be necessary to correctly operate a high-speed
counter.
● Adjust the System Block digital input filter time of the input channels used by the HSC
channel. In an S7-200 SMART CPU. Input filtering is applied before the counting of
pulses by the HSC channel. This means that if an HSC input pulse occurs at a rate that is
filtered out by the input filtering, then the HSC does not detect any pulses on the input.
You must make sure that you configure the filter time of each input of the HSC to a value
that will allow counting at the rate your application requires. This includes direction and
reset inputs. The following table shows the maximum input frequency that can be
detected for each input filter configuration.
Input filter time
Maximum detectable frequency
0.2 μs 200 kHz for S model CPUs
1
100 kHz for C model CPUs
2
0.4 μs 200 kHz for S model CPUs
100 kHz for C model CPUs
0.8 μs 200 kHz for S model CPUs
100 kHz for C model CPUs
1.6 μs 200 kHz for S model CPUs
100 kHz for C model CPUs
3.2 μs 156 kHz for S model CPUs
100 kHz for C model CPUs
6.4 μs
78 kHz
12.8 μs
39 kHz
0.2 ms 2.5 kHz
0.4 ms
1.25 kHz
0.8 ms 625 Hz
1.6 ms
312 Hz
3.2 ms
156 Hz
6.4 ms
78 Hz
12.8 ms
39 Hz
1
S model CPUs: SR20, ST20, SR30, ST30, SR40, ST40, SR60, ST60
2
C model CPUs: CR40, CR60