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7/29/2019 Wiring for CAN Bus
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24 January 2013Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 1
Wiring for CAN bus
ATLAS
DCS
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24 January 2013Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 3
Introduction
Definition of our CAN bus application
ATLAS
DCS
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24 January 2013Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 4
MAXIMUM CABLE LENGTH
The limitation come from : ELMB supply drop through cables
CAN supply drop through cables
CAN bus limitation (from signal point of view)
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Stphane Detraz PH-ESS 5
CAN BUS LIMITATION
CAN bus length main limitations
(from signal point of view)
Signal round-trip delay Oscillator tolerance between nodes
Signal amplitude drop
The two first effects are not discussed during this
Presentation.
However, as rule of thumb, the following bus line length can
be achieved
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24 January 2013Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 6
Bit rate / Bus length relation
with CAN bit timing parameters being optimized formaximum propagation delay!
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24 January 2013Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 7
CAN bus signal
Maximum number of nodes :
The maximum number of nodes which can be connected to a
network depends on the minimum load resistance a transceiver is
able to drive :The PCA82C250 transceiver provide an output drive capabilitydown to a minimum load of 45
which give a maximum number of 112 nodes for 120
termination!
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24 January 2013Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 8
CAN bus signal
Maximum bus line length
Is given by the minimum differential voltage at the receiving node
for a dominant bit level.
A receiver recognizes a dominant bit if the differential voltage isabove 1V.
We can use the following diagram to calculate the maximum buslength.
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24 January 2013Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 9
CAN bus signal
From the precedent diagram we canfind the following formula :
Tdiff
diffT
SMth
outdiff
RnR
RR
VV
VL
*1
**1*
*2
1
maxmin_
min_min__
max
With :
is the cable linear resistance 0.0375 /m for NE06
Vdiff_out_min is the transceiver min. diff. output voltage for a dominant bit level 1.5V
Vth is the dominant state receiver threshold voltage 1V
VSM is a safety margin voltage which can be determined as : K*(Vdiff_out-Vth)With 0K1 e.g K=0.8 0.4V
RT is the termination resistance 120
Rdiff_min is the minimum transceiver differential input resistance 20k
Nmax is the maximum number of node on the bus lets say 30
Whoua!!
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24 January 2013Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 10
CAN bus signal
The result for NE06 cable & 30 nodes is :
111m!
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Stphane Detraz PH-ESS 11
Standard configurationATLAS
DCS
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Stphane Detraz PH-ESS 12
Cable characteristic impedance
The ISO 11898 CAN standardprescribes that the cable impedance
be nominally 120.But an impedance interval of 108 to132 is permitted.
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Stphane Detraz PH-ESS 13
Cables datasheets
NG18 (SCEM : 04.21.52.218.9)
NE06 (SCEM : 04.21.52.110.0)
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Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 14
Cable propagation delay
Signal velocity in cable :
Lossless lumped equivalent circuit
11
LC
[m/s]
[H/m][F/m]
Example : 2x0.5mm2 NE P cable
L : 0.65H/m
C : 0.075nF/mV = 0.143m/ns
Thus tp = 698ns for 100m
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Stphane Detraz PH-ESS 15
Signal reflection
Example with 100m of 90 cable and 250 Kbaud CAN speed
The bit duration is : 4s
The reflection duration : 1.4s
In this case (120 termination) :1st reflection level : V1 = Vs*Ctl = Vs*1.143 (+14%)
2nd reflection level : V2 = Vs*Ctl*[1+Crl*Crs] = Vs*0.98 (-2%)
3rd reflection level : V3 = Vs*Ctl*[1+Crl*Crs+(Crl*Crs)2] = Vs*1.003
Ctl : load transmission coefficient
Crl : load reflection coefficient
Crs : source reflection coefficient
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Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 16
Signal reflection
t t
D=100mZs0 Zc=120
V1=1.71V
V2=1.47V
V3=1.504V
Crs=-1Crl=+0.143
Ctl=+1.143
+0.21V
-0.21V
Z0=90
-0.03V
+0.03V
0.7s0s
1.4s2.1s
Bounce diagramSignal wave form & noise margin
SUMMARY
0.4V1.5
V
1.7
1V
1.4
7V
0.05V0.08V
1V
1.4s
Minimun voltage for
dominant state
Maximun voltage for
recessive state
0.47V margin
0.32V margin
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Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 17
Solutions proposed
The thick cable and connectors associated
ATLAS
DCS
Components:
Female Connector
Burndy 19 pins female connector => SCEM 09.31.05.552.4
Pins => SCEM 09.21.05.450.6
Thick Cable => SCEM 04.21.52.218.9
Male Connector
Burndy 19 pins male connector => SCEM 09.31.05.548.0
Pins => SCEM 09.21.05.440.8
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Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 18
Solutions proposed
The junction boxJunction Box:
2: CAN L 1: VCP 11: VDG
4: VDG 2: VCP 12: VDG
5: Shield 3: VCP 13: VDG
6: VCG 4: VCG 14: VDG
7: CAN H 5: VCG 15: VDP
8: VDP 6: VCG 16: VDG
9: VCP 7: VDP 17: CAN H
8: VDP 18: CAN L
9: VDP 19: Shield
10 : VDP
ATLAS
DCS
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Sbastien Franz PH-ATI-DC
Stphane Detraz PH-ESS 19
Solutions proposed
The thin cable and connectors associated
ATLAS
DCS
Components with single connectors:
Female Connector
Hood => SCEM 09.21.23.150.3
DC sub-D 9 female connector => SCEM 09.21.21.010.2Pins => SCEM 09.21.21.310.3
Thin Cable => SCEM 04.21.52.110.0
Male Connector
Hood => SCEM 09.21.23.150.3
DC sub-D 9 male connector => SCEM 09.21.21.020.0
Pins => SCEM 09.21.21.330.9
Components with double connectors:
Connectors
Female connectors from Phoenix Contact with two cables
entries
Thin Cable => SCEM 04.21.52.110.0
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Stphane Detraz PH-ESS 20
Solutions proposed
The prices for the thin cable :
The 3 twisted pairs cable: 1.60 CHF/m
Two single connectors (a male and afemale): 18.31 CHF
One double connector : 34.61
ATLAS
DCS
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Stphane Detraz PH-ESS 21
Monitoring board
Supply topology CAN supply
ELMB digital supply
ELMB ADC supplyD-SUB 9 pins
HAVE TO BE REPLACED BY LOWER VALUE RESISTORS
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Stphane Detraz PH-ESS 22
Monitoring board
Function Name Average QuiescentCurrent
ELMB digital VDP 13mA
ELMB Analog(ADC) VAP 11mA
CAN VCP 20mA
Monitoring
(without Air Flow)
VAP 35mA
Air Flow VAP 25mA @ Ta=45C
TOTAL VAP+VDP = 59mA without Air flow
84mA with Air flow @ Ta=45C
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Stphane Detraz PH-ESS 23
The simulation tool
The front panel
ATLAS
DCS
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Stphane Detraz PH-ESS 24
The simulation tool
Tests of the software
ATLAS
DCS
Evolution of the IO controler voltage
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
0 5 10 15 20 25 30
Nodes number
Uelmbs(V)
exp
Simulation
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Some examplesATLAS
DCS
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Conclusion
This design of the wiring will workwithout problem for our CAN bus
applications. Wiring of the first rack monitoring
boards will begin next Monday (16/05)
=> Test in real conditions
ATLAS
DCS
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AND NOW
MAKE A REALISTIC TEST (Planed week 19)
With 30 monitoring card & around 100m of thick cable.