Siemens SIMATIC S7-1500 System Manual page 188

Configuring
9.9 Configuration of digital inputs/outputs (X142)
Example 2: "Multiple periods" measurement method
With a machine, the speed of a shaft is to be determined via a single encoder based on a
rotating slotted disc.
The pulses are to be acquired on the SIMATIC Drive Controller using a digital input/output
(X142) in the event/period duration measurement operating mode.
Due to the accuracy requirements and high speed, the cycle duration is determined over
multiple periods.
Figure 9-26
In the "Multiple periods" measurement method, the cycle duration is determined by counting
the number of 41.67 ns increments between the last rising edge of the last measuring cycle
and the last rising edge of the current measuring cycle with the period duration counter N
In addition, the number of rising edges N
The period duration is calculated based on the count values, taking into account counter
overflows, as follows:
If you know the number of pulses emitted by the encoder per revolution of the shaft, you can
calculate the speed at which the shaft rotates.
Calculation example
N = 48 pulses are emitted per revolution of the shaft (N
S
pulses per revolution of the encoder).
186
Simple encoder on a shaft, multiple periods measurement method
for the same period is determined.
E
is also referred to as the number of
S
System Manual, 11/2023, A5E46600094-AD
.
P
SIMATIC Drive Controller