wiring for can bus

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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Introduction

Definition of our CAN bus application

ATLAS

DCS


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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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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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Bit rate / Bus length relation

with CAN bit timing parameters being optimized formaximum propagation delay!


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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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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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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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CAN bus signal

The result for NE06 cable & 30 nodes is :

111m!


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24 January 2013

Sbastien Franz PH-ATI-DC


Standard configurationATLAS

DCS


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24 January 2013



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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24 January 2013



Cables datasheets

NG18 (SCEM : 04.21.52.218.9)

NE06 (SCEM : 04.21.52.110.0)


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24 January 2013



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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24 January 2013



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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24 January 2013



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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24 January 2013



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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24 January 2013



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

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24 January 2013



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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24 January 2013



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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24 January 2013



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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24 January 2013



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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24 January 2013



The simulation tool

The front panel

ATLAS

DCS


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24 January 2013



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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24 January 2013



Some examplesATLAS

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24 January 2013



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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24 January 2013



AND NOW

MAKE A REALISTIC TEST (Planed week 19)

With 30 monitoring card & around 100m of thick cable.

wiring for can bus

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