Siemens S7-300 appendix Measurement principle, Integrated hardware low-pass filter

Technical data of CPU 31xC 6.6 Technical data of the integrated I/O

Measurement principle

31xC CPUs use the measurement principle of actual value encoding. Here, they operate with a sampling rate of 1 kHz. That is, a new value is available at the peripheral input word register once every millisecond. This value can then be read via user program (e.g. L PEW). The "previous" value is read again if access times are shorter than 1 ms.

Integrated hardware low-pass filter

An integrated low-pass filter attenuates analog input signals of channel 0 to 3. They are attenuated according to the trend in the figure below.

Attenuation

	< 1 %
Internal	Attenuation
signal level
	< 1 0 %	strong

attenuation

100%

63%

Inadmissible input frequency

50 Hz 200 Hz 400 Hz Input frequency

Figure 6-3 Low-pass characteristics of the integrated filter

Note

The maximum frequency of the input signal is 400 Hz.

CPU 31xC and CPU 31x, Technical data	6-35
Manual, Edition 08/2004, A5E00105475-05