Measured Value Determination With Incremental Or Pulse Encoder - Siemens SIMATIC ST-1500 Function Manual

2.2 Basics of counting, measuring and position input (TM Count, TM PosInput, Compact CPU)
2.2.9.2

Measured value determination with incremental or pulse encoder

Measuring range (TM Count and TM PosInput)
The measuring functions have the following measuring limits:
Measurement type
Frequency measurement
Period measurement
Velocity measurement
* Applies to 24 V incremental encoders and "quadruple" signal evaluation.
** Applies to RS422 incremental encoders and "quadruple" signal evaluation.
All measured values are returned as signed values. The sign indicates whether the counter
value increased or decreased during the relevant time period.
Measuring range (Compact CPU)
The measuring functions have the following measuring range limits:
Measurement type
Frequency measurement
Period measurement
Velocity measurement
* Applies to 24 V incremental encoders and "quadruple" signal evaluation.
All measured values are returned as signed values. The sign indicates whether the counter
value increased or decreased during the relevant time period.
Measuring principle
The technology module assigns a time value to each count pulse. The measuring interval is
defined as the time between each last count pulse before and during the previous update
time. The measuring interval and the number of pulses in the measuring interval are
evaluated to calculate measured variables.
If there is no count pulse within an update time, the measuring interval is dynamically
adjusted. In this case, a pulse is assumed at the end of the update time and the measuring
interval is calculated as the time between that point and the last pulse which occurred. The
number of pulses is then 1.
The feedback bit STS_M_INTERVAL indicates whether a count pulse occurred in the
previous measuring interval. This allows for a differentiation between an assumed and an
actual count pulse.
Counting, measurement and position detection
Function Manual, 12/2017, A5E32009889-AG
The basics of counting, measurement and position detection
Low measuring range limit
0.04 Hz
1.25 µs* / 0.25 µs**
Depending on the configured number of "increments per unit" and the
"time base for velocity measurement"
Low measuring range limit
0.04 Hz
2.5 µs*
Depends on the configured number of "Increments per unit" and the
"Time base for velocity measurement"
High measuring range limit
800 kHz* / 4 MHz**
25 s
High measuring range limit
400 kHz*
25 s
55