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Page 1IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA
Preliminary Drive Noise
Measurements
David D. Brandt
Rockwell Automation
Page 2IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 2
Purpose
• The purpose of this presentation is to:
– Present “first pass” measurements of Drive
noise induced in a communication cable
typical of the 1000 m link segment
– Consider whether a more extensive
evaluation is warranted
Page 3IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 3
Drives• Drives operate motors at variable speed from a
fixed frequency (60 Hz) line– VFD = Variable Frequency Drive
• Typically 3Φ line voltage is rectified to DC (480 Vac -> 678 Vdc)
• The DC is switched in pulses via PWM to a 3ΦMotor cable, where the inductance in the motor integrates the current into a sinusoid– Typical PWM rate is 2-4 kHz, sometimes higher
• Drive cables, grounding, and proximity are significant and common sources of interference in industrial facilities
Page 4IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 4
Communication link• Belden 3076F cable (10 m)
– ISA/SP-50, FOUNDATION Fieldbus or PROFIBUS
– 18 AWG stranded (7x26), twisted balanced pair, foil shield, drain wire, polyolefin insulation
• BH Electronics 040-0055 BALUN on each end– 100 Ω differential termination for
cable pair
– 50 Ω SMAs for measurement of CM and DM
– Optional shield termination via case
– 2.4 dB maximum insertion loss
Page 5IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 5
Interference source
• Drive: PowerFlex 755, 7.5 hp– PWM configured to 12 kHz
• Motor: Reliance Electric Duty Master, 10 hp– No load
• Cable: Carol 4C 10 AWG– No Shield (systems below 10 hp are often
unshielded)
Page 6IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 6
Cable placements
• The communication cable was placed in parallel to the motor control cable
• Two variations– Adjacent
– Approximately 20 cm separation
Page 7IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 7
Communication shield termination
• The shield GND was through the BALUN
– On the measurement, GND included the oscilloscope
– On the other end in one of 3 ways:• Isolated from Drive and Motor
• Tied to the Motor’s frame ground via metal plate
• Tied to the Drive’s metal mounting plate
Page 8IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 8
Measurements
• Tektronix TDS 3054, 500 MHz, 5 GS/s
• 2 channels attached to BALUN
– Ch1 to BALUN CM• 50 Ω
– Ch2 to BALUN DM• 50 Ω
• 20 MHz BW limit
• FFT calculation
Page 9IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 9
Setup summary
TDS
3054
Scope
P2
P1040-0055
BALUN
CM
DM
A
B
C
040-0055
BALUN
CM
DM
A
B
C
3076F
Cable
c1
c2
S
c1’
c2’
S’
10 m
Carol 4C 10 AWG, unshielded
12 m
Adjacent or 20 cm
PF755
VFD
460V
R,S,T,
PE
3Φ Chassis
RE
10HP
Motor Frame
R,S,T,
PE
Floating or
through oscilloscope or
@Drive
Through PE
Small chassis plate
Through PE
Large plate
Measurement @ Drive or @Motor
Floating or
through oscilloscope or
@Motor
Motor speed
0 Hz is held in position
60 Hz is run at full speed
Page 10IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA
Testing with adjacent cables
Page 11IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 11
Setup: Adjacent cables, Isolated GNDs, 0 Hz
Measurements: Drive end
• ~6x voltage
reduction
• ~24 kHz
DM
CM
Page 12IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 12
Setup: Adjacent cables, Isolated GNDs, 0 Hz
Measurements: Motor end
• CH2 visually
appears to
be 100 mV
Pk-Pk
– 50 mV
differential
• Pk-Pk does
not appear
accurate
Page 13IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 13
Setup: Adjacent cables, Isolated GNDs, 0 Hz
Measurements: Motor end
• Add FFT
– Rectangular
window
– dBV
• 25 MHz
span
• Pk between
1.5 - 2 MHz
Page 14IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 14
Setup: Adjacent cables, Isolated GNDs, 60 Hz
Measurements: Drive end
• Motor “at
speed”
• Reduced
peaks
• More noise
between
peaks
Page 15IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 15
Setup: Adjacent cables, Isolated GNDs, 60 Hz
Measurements: Motor end
• Motor “at
speed”
Page 16IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 16
Setup: Adjacent cables, GND BALUN at motor, 0 Hz
Measurements: Drive end
• Motor GND appears to add little to Pk noise
• ~8x voltage reduction
• FFT Pkabout 3 MHz (shifted)
Page 17IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 17
Setup: Adjacent cables, GND BALUN at motor, 60 Hz
Measurements: Drive end
Page 18IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 18
Setup: Adjacent cables, GND BALUN at Drive, 0 Hz
Measurements: Motor end
• Drive GND
appears to
add little
Pk noise
• ~20x
voltage
reduction
Page 19IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 19
Setup: Adjacent cables, GND BALUN at Drive, 60 Hz
Measurements: Motor end
Page 20IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA
Testing with 20 cm cable
separation
Page 21IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 21
Setup: 20 cm cable separation, GND BALUN at Drive, 0 Hz
Measurements: Motor end
• ~10x voltage reduction
• Cable separation reduces Pknoise
• Visually appears to be 60 mV Pk-Pk
Page 22IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 22
Setup: 20 cm cable separation, GND BALUN at Drive, 60 Hz
Measurements: Motor end
• Visually
appears to
be 90 mV
Pk-Pk
Page 23IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 23
Setup: 20 cm cable separation, Isolated GNDs, 0 Hz
Measurements: Motor end
• GND coupling
was
dominating
over
capacitive
coupling
between
cables
• Visually
appears to be
20 mV Pk-Pk
Page 24IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 24
Setup: 20 cm cable separation, Isolated GNDs, 60 Hz
Measurements: Motor end
• Visually
appears to
be 25 mV
Pk-Pk
Page 25IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 25
FFT comparisons (partial)
• Noise below 10 MHz
• Noise may come through
capacitive coupling or
shield grounding
Adjacent cables, Isolated GND
20 cm separation, Isolated GND
20 cm separation, Drive GND
Adjacent cables, Motor GND
Adjacent cables, Drive GND
Page 26IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 26
Rise time “rule of thumb”
• BW (GHz) = 0.35 / Rise_Time (ns)
• IGBT (typical)
– Rise = 30 ns
• BW = 11.6 MHz
– Fall = 70 ns
• BW = 5 MHz
Page 27IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 27
Conclusions
• Drive noise can enter differential pair:
– By capacitive coupling of parallel cables
– Through shield sharing common GND with Drive
• Both causes must be addressed to limit noise
• Peak noise relates to 2x the PWM frequency
• A lower level of noise appears continuous
• Good installation practice may reduce noise
well below the 75 mV fieldbus rule of thumb
– This is just one configuration
Page 28IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 28
ISO/IEC Installation standards
Page 29IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 29
Installation practice – common requirements
• IEC 61918, Edition 3, 2013
– “Industrial communication networks –
Installation of communication networks in
industrial premises”
• Basic requirements for installation of media for
communication networks in industrial premises
within and between the automation islands
• Covers balanced cabling
• Versions since 2007
Page 30IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 30
IEC 61918 – Cable separation
• Table of distances between communication
cables and other types of circuits
Page 31IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 31
IEC 61918 – Shield earthing
• 5.7.4 Shield earthing methods
– Generic description of RC and direct
connection options
• 5.7.5 Specific requirements for CPs
– “Additional information regarding the earthing
and shielding installation requirements for a
specific industrial network may be found in the
respective installation profile.”
• 4.4.7.3.2 Star
– “Currents in earth paths generated by high
currents can be controlled by the means of a
star earthing system and by isolating the
signal earth from the equipment earth.”
Page 32IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 32
IEC 61784-5-1 (one of several)
• Industrial communication networks – Profiles – Part 5-1: Installation of fieldbuses –Installation profiles for CPF 1
– CPF 1 = FOUNDATION™ Fieldbus
– Requirements are in IEC 61918:2013 unless amended by “supplementing, modifying, or replacing”
• No amendment to separation requirements
• A.4.4.7.5 Specific requirements for CPs
– “For CP 1/1 four options are available to the planner for shield termination.”
Page 33IEEE P802.3 Maintenance report – July 2008 PlenaryVersion 1.0IEEE P802.3cg 10 Mb/s Single Twisted Pair Ethernet Task Force – May 2017 Interim Meeting, New Orleans, LA, USA Page 33
Next Steps
• Some additional scrutiny on this
configuration
• Characterize the communication cable
• Test with a longer run of cable
• Test with a larger Drive and Motor