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14.06.2016 / bja
5.5. Speed
Manufacturer-specific telegrams 101 and 102 as well as PROFIdrive telegrams 82 and 83 deliver speed
information besides the absolute position value.
5.5.1. Speed Measuring Unit
Speed scaling provides four options:
•
rpm
revolutions per minute.
•
steps /10ms
number of steps in the configured singleturn resolution every 10ms
•
steps /100ms
number of steps in the configured singleturn resolution every 100ms
•
steps /1000ms
number of steps in the configured singleturn resolution per second
Scaling is defined by encoder parameterization, see also chapter.
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„Parameterization“.
Each scaling option provides measured value output as a „signed integer“. Positive values indicate the
direction of rotation with rising position values. Which rotational direction is assigned “positive” depends on
the CW/CCW parameter setting.
If speed is outside the +32767 to –32768 range (16 bit speed format), the encoder will output the respective
maximum value. Depending on the applied basic encoder and configuration, the maximum value may be
achieved even at very low speed. The 32 bit speed format will prevent any overrun.
5.5.2. Speed Update Period
Encoder speed is measured during an update period. Input data are updated at the end of each period.
A short speed update period entails a more dynamic speed output, whereas an extended update period
ensures more stable values. The optimum speed update period depends on the application requirements.
The update period can be configured within the range from 1ms to 255 ms.
For configuration refer to chapter 4.6 „Parameterization”.
5.5.3. Speed Filter Depth
The speed information acquired within in the update period can be filtered throughout several update cycles.
Regardless the configured filter depth, the speed information in the input data is updated at the end of every
update cycle.
A shallow filter depth (number of update cycles) entails a more dynamic speed output, whereas a higher filter
depth ensures more stable values. The optimum speed filter depth in interaction with the configured update
time depends on the application requirements.
The filter depth, which is the total number of average update cycles, is configurable within the range from 1 to
255. For configuration refer to chapter 4.6 „Parameterization“.
5.6. Preset function
The preset function in the encoder is triggered as soon as the PLC sets the “Preset-Bit” (see below) in the
output data. The encoder position is set to the given preset value
For optimum alignment of mechanical position to preset we recommend to set the preset value during
encoder standstill, but it may also execute while encoder rotates for less accurate requirements.
It is mandatory to parameterize the required resolution or code sequence (cw/ccw) prior to performing the
preset operation.
Upon performing a preset operation an internal offset is calculated and stored non-volatile in the Flash
memory to make sure the encoder will be at the same position after cycling power.
Although the Flash pr100.000 write cycles, frequent software- or event-triggered preset operations
may consume even this capacity what has to be considered in the PLC software configuration.
