• 1 revolution = 2
11
= 2048
If the encoder does not have an electronic nameplate (SSI and partly also BiSS),
ec40 singleturn res. must be adjusted according to the data sheet specifications
(=> see 6.1.6.6, "The digital data word“).
The resolution is 2
ec40
, one revolution corresponds to:
• 1 revolution = 2
ec40
•
Example:
ec40 = 12
• 1 revolution = 2
12
= 4096
6.1.3.5 For all encoders
In addition to the resolution, the control characteristics of a drive are significantly
influenced by the accuracy of the position.
The accuracy is reduced compared to the position resolution by errors in the en-
coder, in the signals, the encoder mounting on the motor, the signal transmission,
the input circuit, the encoder evaluation, the signal detection, etc.
Example:
A "system accuracy" of ± 60 angular seconds and a resolution of "positions/U =
2048 (11 bit)" is specified for an Endat encoder in the catalogue.
The resolution of the digital position is calculated by the 11 bit specification:
360° / 2
11
= 0.176° per bit = 0.176 ∙ 3600 angular seconds = 632 angular seconds
per bit
If the 1Vss signals are evaluated, the position value has a resolution of 22 bit. This
corresponds to a position resolution of
360° / 2
22
= 0.000086° per bit = 0.000086 ∙ 3600 angular seconds = 0.31 angular
seconds per bit
In this case, the error of the position, which already results from the encoder (± 60
angular seconds) is many times greater than the resolution (0.31 angle seconds).
Scan time snd speed fluctuations
The speed is calculated from position differences. Therefore, the non-infinite reso-
lution of the position mathematically always leads to a fluctuation of the speed.
The finer the resolution of the position, the lower the speed fluctuations.
The scan time is the second influencing variable on the speed fluctuation, i.e. the
time between the two position values from whose difference the speed is calcu-
lated. The greater the scan time, the lower the speed fluctuation.
From these two mathematical correlations there is a minimal fluctuation of the
speed, which always occurs at fluctuation of the position by 1 increment and it can
be calculated as follows:
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