communication in industry

1. Wireless Industrial
Communications

2. Two Categories – Various Techniques
 Control Systems
 Field Instrumentation

3. Control Systems
 Wired Ethernet has become the default standard
for interconnecting controllers.
 Wiring systems are already in place where
hardware is located.
 Firewall protection for connections outside of
wired LAN thoroughly understood.
 Currently not much interest in wireless
backbone systems using the 802.11 a,b,c…n
Ethernet standard.

4. Field Instrumentation
 Steadily growing interest in wireless field
instrumentation.
 Many industrial installation applications.
 Recommended for data acquisition only.

5. Field Wireless Advantages
 Physical installation can be easier.
 Physical installation can be less expensive due to
wiring, conduit and cable tray associated cost.
 Low instrumentation density applications such
as tank farm monitoring can have significant
savings.

6. Disadvantages
 Battery life, although greatly improved in the last
few years, is under two years under optimal
conditions.
 Consistency of communication performance.
 Security of data.
 Many variations of proprietary systems are not
compatible, although a standard is being / has
been developed.

7. Wireless Techniques
 Analog measurement instruments digitize their
measurement to a digital signal of 1’s and 0’s.
 The digital signal is converted to a radio signal
using various modulation techniques such as
ASK, FSK, PSK or QAM.
 Transmitted via an antenna in an elliptical path
of concentric circles to a receiver’s antenna.

8. Message Packet Content
 Lead In – Identifies the type of transmission,
manufacture, time synchronization.
 Addressing Information – who’s its from, who’s
it’s for.
 Data
 Error Checking

9. RF Propogation
 Range
 Operating distance between two radios that wish to communicate
 Access Point to station
 Station to Station
 Coverage
 Total Area Wherein radios can maintain connection to Access
Point
 Range vs Capacity – The greater the coverage area…
 The more wireless stations can be covered
 The less bandwidth available to each user
 The lower the data rates will be at the edge
 The more likely the chances of “hidden notes”

10. Range Dynamics
 Fundamentals
 RF power is measure in dBm
 0 dBm = 1 milliwatt of power
 +10 dBm = 10 times the power
 20 dBm = 100 milliwatts of power
 Signal Power Dissipation
 Inverse of the square of the distance
 Signal Strength
 Expected power at receiver
 RSSI = Receive Signal Strength Indicator (dBm)

11. Radio Waveforms Characteristics
 Sinusoidal in shape
 Frequency defined
 Transmission Power – TX

12. Frequencies Used
 Regulatory bodies set aside frequency bands for
public and industry use.
 Some frequencies are government licensed and
involve applications, fees and often
implementation delays but permit higher
transmission power levels resulting in greater
distances.
 Most industries use un-licensed frequencies such
as 900 MHZ ad 2.4 GHZ .

13. Frequencies Used
 The radio signal can be comprised of a signal
frequency or a band of frequencies.
 As the frequency band get larger, 900 MHZ to 2.4
GHZ , the number and width or size of the
channels increases.
 Most industrial wireless systems use signals
between 200 MHZ and 5GHZ.

14. Transmission Power
 Government regulations limit transmitting
power to various wattage’s depending on
whether the the frequency is licensed or not, and
frequencies involved.
 Higher transmitter power reduces battery life
also.
 Lower frequencies can be transmitted at higher
power levels potentially increasing transmission
distance.

15. Frequency Considerations
 Higher frequencies support higher data
throughput but shorter transmission distance.
 Lower frequency signals propagate further but
have lower data rates.
 Lower frequencies are less effected by
obstructions in the path of the signal.

16. Frequency vs. Wavelength
 High frequency signals are shorter in length.
 Wavelength (m) = 300 ÷ Frequency (MHZ).
 For 900MHZ, wavelength = 300 ÷ 900 = .33m.
 For 2.4GHZ, wavelength = 300 ÷ 2400=.125m.

17. Received Signal Strength can be Reduced By
 Whether there is a clear line of sight or not.
 Signal Diffraction
 Signal Reflection
 Signal Scattering

18. Signal Diffraction
 If signals encounter a large object, such as
process tanks or buildings between transmitter
and receiver, signals will diffract, spreading out
the energy and reducing intensity at receiver
location.
 The bending of the signal helps though if there is
not a clear line of sight.
 Lower frequencies bend more, which is a good
thing.

19. Signal Reflection
 When signal encounter objects larger then their
wavelength there can be significant reflections.
 Lower frequencies attenuate less when bounced
of solid surfaces.

20. Signal Scattering
 Signal that encounter smaller objects such as
busy piping systems verse large tanks, or leaves
on a tree, can scatter in all different directions
reducing signal intensity at the receiving device.
 Lower frequencies scatter less, which is a good
thing.

21. Detrimental Environmental Effects
 Natural
 Manmade

22. Natural Detrimental Effect
 Solar Flares
 Storms
 Lightning
 Rain
 Snow
 Fog

23. Man Made Detrimental Effects
 Lower frequency nose from electrical power
systems is not normally an issue.
 Noise produced by electronic devices that
operate at high frequencies can be a problem.
 Other wireless systems operating at nearby
frequencies can cause undesirable interference.

24. Signal to Noise Ratio
 It’s recommended that the background noise,
which may unfortunately be riding on the back
of on the signal, be at least -100dB below the
signal strength.
 This ensures that the radio signal can be
demodulated back by the receiver with an
acceptable Bit Error Ratio (BER).
 Higher data rates require higher SNR’s.

25. Receiver Sensitivity
 Receiving devices with greater sensitivity and/or
larger antennas can decode weaker signals at
acceptable BER’s
 Receivers are often specified by their ability to
decode weak signals at a particular BER such as -
110 dB @ 1X10-
5 (1 bit error for every 100,000
bits)

26. Error Detection
 Cyclic Redundancy Check – CRC is often used for
error detection.
 When errors are detected the individual corrupt
packet may just be discarded or the entire
message, depending on technique used.
 Automatic Repeat Request (ARM) mechanisms
are the norm.

27. Packet Size
 Unlike Ethernet with a fixed packet size, various
system utilize different sized packets.
 The likely hood of corrupted data relates to the
length of the message x transmitted data rate.
Therefore larger packets have a detrimental
effect on one influencing aspect and a positive
effect on another. By reducing transmission time.

28. Transmission Power
 Doubling the useful transmission distance
requires quadrupling the transmission power.
 If the transmitting power is halved the useable
transmission distance will be around 71%.
 Transmission power is limited by both
governmental regulations and battery life.
 Increasing receiver sensitivity has the same
effect as increasing transmitting power.

29. Frequency Effects on Signal Strength
 Increasing transmission frequency has the same
effect as increasing transmission distance.
 If the transmitting frequency doubles the signal
strength at the receiver drops to ¼.
 New Distance = Old Distance x (old freq/new
freq)1/2
 Higher Frequencies also suffer from multipath
fading more due to phase differences due to
different path lengths.

30. Modulation Types
 Fixed Frequency
 Spread Spectrum

31. Spread Spectrum
 Uses multiple channels within a band of
frequencies.
 Frequency Hopping Spread Spectrum (FHSS) hop
around according to a fixed sequence
(synchronous) or the receiver continuously scans
all the channels (asynchronous) in the band
looking for the next transmission.

32. Transmission Distance
 Transmitting power, receiver sensitivity, antenna
height, and obstruction to the line of sight all
affect maximum transmission distance.
 2.4 GHZ up to 7 Km
 900 MHZ up to 25 km
 Obstructions and path quality can reduce
distance to less the 10% of above quoted values.

33. Mesh Networks
 Rely on multiple devices being able to receive a
message not intended for itself then
retransmitting the signal to the intended device.
 Permits lower transmitting power levels which
increases battery life.
 Networks are highly intelligent and self learning
which increases reliability yet reduces
retransmissions.

34. Standards
 Wireless Hart is a popular standard which
includes 900 MHz and 2.4 GHz, spread spectrum
and mesh technologies.
 ISA 100 802.15.4 is similar to wireless Hart but
also support other protocols.

35. Security
 Wireless systems are inherently not as safe as
wired systems.
 Signals can be jammed by accident or on
purpose. FHSS are much less vulnerable then
fixed frequency systems.
 Many modern systems encrypt data and utilize
WPA2 type security (same technique you likely
use on your home wireless network).

36. Industrial Wifi…
 What’s needed :
 Host system: Any system accepting data produced by the
WirelessHART Field Network (WFN). This could be a DCS,
PLC, RTU, Data Historian, asset management software, etc.
 Join key A 128 bit security key used to authenticate wireless
field devices when joining the network, including
encryption of the join request. A common Join Key may be
used among all devices on a given network, or each device
may have a unique join key.
 Network ID: Each Gateway at a facility or location should be
programmed with a unique Network ID. All authenticated
wireless field devices with the same Network ID will
communicate on the same network and Gateway.

37. Industrial Wifi
 Wireless adapter Enables an existing 4-20 mA,
HART-enabled field device to become wireless.
Adapters allow the existing 4-20 mA signal to
operate simultaneously with the digital wireless
signal.
 Wireless field devices: Field device enabled with
a WirelessHART radio and software or an
existing installed HART-enabled field device with
an attached WirelessHART adapter.

38. Gateway Architecture

39. ISA Drawing Example