Simulation of an Industrial Environment and overview of test results

1. Simulation of an Industrial Environment and overview of test results J. CATRYSSE; KHBO J. Rayée, D. Degrendele; KHBO

2. Increasing use of wireless systems • Advantages: • flexibility • less wiring needed • still improving (power management, interference protection, …) • Disadvantages: • lack of robustness against mechanical and electrical constraints • Wired systems are usually more robust

3. Lack of information about industrial environments • Not much information available about performance of wireless technologies in heavy industrial environments. • In most literature only office use is considered.

4. 3 ways for the characterisation of an industrial environment • Theoretical models • difficulty to quantify parameters • In situ measurements • time consuming • difficulty to implement in real machinery • Simulation setup • controlled measurement environment • all disturbance effects can be taken into account • influence of the effects can be tested separately or together

5. Wireless systems technology • Wireless systems are protected against possible disturbances by using (encoding, spread spectrum, protocol, …) • Makes use of ISM frequencies • free for short range communication • high density of disturbing signals •  Cost/profit analysis to find the most fitting solution

6. Selection of technologies

7. Wireless technologies used • Wireless system S1 - Frequency modulation • a lot of side bands created • if modulation index  •  # side bands  •  S/N-ratio 

8. Wireless technologies used • Wireless system S2 - FHSS • Frequency hopping spread spectrum (FHSS) • this systems hops over a certain sequence of different frequency channels • Adaptive FHSS • detects affected channels and skips them

9. Wireless technologies used • Wireless system S3 - DSSS • Direct Sequence Spread Spectrum (DSSS) • Every information bit is modulated using the same pseudo random bit code. • The energy is spread over a wider frequency spectrum • Per frequency, signal levels are lower, this means less interference to other systems and higher security against intruders

10. Wireless technologies used • Wireless system S4 - Bluetooth • uses FHSS • includes coding schemes (CRC, FEC, …) • P2P as well as piconet configurations

11. Wireless technologies used • Wireless system S5 - DECT • Digital Enhanced Cordless Communication (DECT) • uses Time Division Multiple Access (TDMA) • every user gets certain timeslots allocated • many users possible at the same time

12. Overview of the technical specs of the wireless system

13. Performance of wireless systems • Quantified by the bit error rate • (BER)=(#errorbits) / (total # of bits) • e.g. • Sent: 0110 0001 • Received: 0010 0011 • BER=2/8=25%

14. Possible disturbance effects • Mechanical disturbances • Vibration • Low & high speed movement • temperature • … • Electrical disturbances

15. Mechanical disturbances • Influence depends on the quality of the hardware • this info should be supplied by the manufacturer • Not dealt with in this paper

16. Electrical disturbances • Power reduction at the receiving antenna • reflections • path loss • multipath fading • antenna efficiency • obstructions in the propagation way • Interference signals

17. Electrical disturbances • Path loss • reduction of power due to increasing distance between the RX and TX • path loss can be increased by introducing obstructions in the propagation way • The reduced power at the receiver will increase the likelihood of disturbances in the communication

18. Electrical disturbances • Multipath fading • arises when reflected waves that are out of phase interfere with direct waves • caused by direct waves hitting conducting objects and in this way generating reflected waves

19. Test setup for multipath fading

20. Results of measuring multipath fading • RPR= received power reduction = PRX/PTX • RPR is 10dB less in hall than in open area, although there are reflecting walls

21. Electrical disturbances • Interference • caused by other wireless systems • solution: co-existence plan in some protocols • caused by nearby machinery • hard to predict • typically 170dBµV/m in the [10kHz, 500MHz] range • decreases with increasing frequency

22. Electrical disturbances • Interference caused by nearby machinery • measurements are made in the near field, because: • in practice communication devices are in close proximity to the machinery • in the far field, emissions are limited by the EMC directive & emission standards • simulated by adding an interference antenna

23. Measuring interference of nearby machinery • Measuring in near field using sniffer E- & H- field probes • Measurement results show the envelope of the maximum measured field strengths on different components of the machinery

24. Measuring interference of nearby machinery: welding machine

25. Measuring interference of nearby machinery: frequency converter

26. Measuring interference of nearby machinery: computer

27. Measuring interference of nearby machinery: weaving machine

28. Measuring interference of nearby machinery: electrical motor

29. Measuring interference of nearby machinery: CNC centre

30. Summary of measurements on interference of nearby machinery

31. Simulation of the disturbances using a generic simulator • The communication devices are connected to the PC’s through an RS232-connection

32. Implementation of disturbance effects on the simulator • Mechanical disturbances • vibrations  vibrating table • Electrical disturbances • interference  interference antenna • path loss  introducing a metal plate between RX and TX • multipath fading  adding metal plates behind and next to the RX • ambient noise levels  adding an interference antenna

33. Implementation of disturbance effects on the simulator • Mechanical disturbances • vibrations  vibrating table

34. Generic simulator • 1 vibration table • 2 transmitter TX • 3 interference antenna • 4 metal obstruction • 5 metal plates for reflection • 6 receiver RX • 7 moving table

35. Implementation of disturbance effects on the simulator • Electrical disturbances • interference  interference antenna

36. Implementation of disturbance effects on the simulator • Electrical disturbances • path loss  introducing a metal plate between RX and TX

37. Implementation of disturbance effects on the simulator • Electrical disturbances • multipath fading  adding metal plates behind and next to the RX

38. Measurements • Measurement on the generic simulator • In situ measurements • influence of long distance on path loss • changing mutual height of RX and TX • obstructions in the propagation way

39. Measurements on the generic simulator • Radiated interference + multipath fading • interference antenna generates signal + reflection plates added

40. Measurements on the generic simulator • Multipath fading + path loss • TX & RX enclosed in metal boxes, consisting of single plates

41. Measurements on the generic simulator • Multipath fading + linear movement

42. Measurements on the generic simulator • Vibrations

43. Measurements on the generic simulator • Vibrations, multipath fading, linear movement and radiated interference

44. Summary of the test results (1) • Only S1 (FM) showed degradation under several conditions. These maybe due to limitations of the PCB. • Performance of a certain technology depends on the TX-power and the RX-sensitivity • Bluetooth and DECT have best performance

45. Summary of the test results (2) • Propagation delay time • =timeRX-timeTX • =radio propagation delay + processing delay • Sometime technologies use an automatic repeat, so delay time becomes unpredictable

46. Conclusions • Simulation of an industrial environment described • Different disturbances discussed • Design of a generic measuring setup • Technologies with a lot of encoding (DECT, Bluetooth) provide more reliable communication channels