Planning and Installation Guidelines 21
Planning and
Installation Guidelines
Technical Description
Wireless Proximity Switches / Issue: 09.2004
V 6
2.10
Switching Frequency and Latency
The input module and the communication modules communicate with each other via the air
interface.
Due to this communication and the following processing in the input module and fieldbus
connection (FieldBusPlug), certain delays occur.
Principle
1
st
proximity change is transmitted
2
nd
proximity change is stored, to be transmitted as soon as 1
st
transmission is finished.
3
rd
proximity change -> error message
Air Interface Latency
5 – 20 ms
Overall Latency
(sensor head -> signal available at fieldbus):
typical ~
17ms
99,9% of the events
20ms
max. (worst case)
34ms
(for single events in case of heavy disturbance)
Independant of number of sensors used
Min. Pulsewidth
for signal on fieldbus
~20ms
-> corresponds to
typ. switching frequency of 25 Hz
(worst case: min. switching frequency of 15 Hz )
BUT
: Restrictions to
≤≤≤≤≤
5 events/s
(proximity changes /s)
due to energy availability in worst case spots.
Typical timing patterns can be seen in fig. 2.7
1
5
4
3
2
1
5
4
3
2
1
5
4
3
2
1
5
4
3
2
1
min. 20 ms
5 changes / sec
5 changes / sec
Target change
1 sec
1 sec
Signal on the fieldbus
Target change
Signal on the fieldbus
Fig. 2.7: Timing pattern