ES441.1 - User’s Guide 65
ETAS Functional Description
5.11 Example
In the automotive sector, measuring the speed of wheels, gears, fans, water
pumps, turbines is essential to be able to determine vehicle velocity or flow, for
example.
For determining the speed in revolutions/minute, an extended configuration of
the number of periods per revolution is necessary.
Application
A speed sensor wheel with 60-2 teeth assembled on the crankshaft returns a
periodically structured signal pattern via a sensor. The number of revolutions per
time unit is a measure of the wheel speed. This wheel, with division into 60,
usually has 58 teeth. The position of the two missing teeth defines the reference
mark for the position of the crankshaft. One revolution of the wheel is thus a
cycle which consists of 60-2=58 periods.
Simplified Example
The configuration principle is demonstrated by the following simplified example.
Fig. 5-32 16-2 "Speed Sensor" Wheel
To be able to determine a speed with the ES441.1, a cycle has to be defined in
the configuration software, for example:
1 revolution = 1 cycle = (16-2) periods
The module always counts complete cycles. The result is a frequency or number
of revolutions per minute.
This mode can be used to determine the average speed with periodic input sig-
nals.
Fig. 5-33 Principle of the Input Signal of a "Speed Sensor" Wheel
Every cycle in the example has 14 periods (see Fig. 5-33 on page 65). One cycle
can be assigned to a full revolution or a section. The measure result does not
depend on the start of the cycle.
15 9 13 1
Cycl e n
15 9 13 1
Cy cl e n + 1
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