Transcript Wiring for CAN bus - CERN - PH-ESE group

Wiring for CAN bus
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
ATLAS
DCS
1
Table of contents







ATLAS
DCS
Introduction
CAN standards
Layout of a standard rack configuration
Cable requirements
Solutions proposed
The rack monitoring board
The simulation tool
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
2
ATLAS
DCS
Introduction
Definition of our CAN bus application
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
3
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)

17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
4
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…

17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
5
Bit rate / Bus length relation
…with CAN bit timing parameters being optimized for
maximum propagation delay!
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
6
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 capability
down to a minimum load of 45Ω…
… which give a maximum number of 112 nodes for 120Ω
termination!
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
7
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 is
above 1V.
We can use the following diagram to calculate the maximum bus
length.
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
8
CAN bus signal
From the precedent diagram we can
find the following formula :
RT * Rdiff _ min
1  Vdiff _ out _ min 


Lmax 
*
 1 *
2 *   Vth  VSM
 Rdiff _ min  nmax  1* RT
Whoua!!
With :
ρ is the cable linear resistance → 0.0375 Ω/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 0≤K≤1 e.g K=0.8 → 0.4V
RT is the termination resistance → 120Ω
Rdiff_min is the minimum transceiver differential input resistance → 20kΩ
Nmax is the maximum number of node on the bus → let’s say 30
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
9
CAN bus signal
The result for NE06 cable & 30 nodes is :
111m!
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
10
Standard configuration
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
ATLAS
DCS
11
Cable characteristic impedance

The ISO 11898 CAN standard
prescribes that the cable impedance
be nominally 120Ω.
But an impedance interval of 108 to
132Ω is permitted.
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
12
Cables datasheets

NG18 (SCEM : 04.21.52.218.9)

NE06 (SCEM : 04.21.52.110.0)
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
13
Cable propagation delay
Lossless lumped equivalent circuit

Signal velocity in cable :

1
1

LC

[m/s]
[H/m]
17 July 2015
[F/m]
Example : 2x0.5mm2 NE P cable
L : 0.65µH/m
C : 0.075nF/m
V = 0.143m/ns
Thus tp = 698ns for 100m
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
14
Signal reflection

Example with 100m of 90Ω cable and 250 Kbaud CAN speed
The bit duration is : 4µs
Ctl : load transmission coefficient
Crl : load reflection coefficient
The reflection duration : 1.4µs
Crs : source reflection coefficient
In this case (120Ω 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
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
15
Signal reflection
SUMMARY
D=100m
0.47V margin
Zc=120Ω
Z0=90Ω
1.4µs
0µs
0.7µs
+0.21V
0.08V
-0.21V
2.1µs
-0.03V
0.05V
V2=1.47V
1V
+0.03V
V3=1.504V
Minimun voltage for
dominant state
Ctl=+1.143
t
t
Bounce diagram
17 July 2015
0.4V
Maximun voltage for
recessive state
0.32V margin
Crl=+0.143
Crs=-1
1.5V
1.4µs
V1=1.71V
1.71V
1.47V
Zs≈0Ω
Signal wave form & noise margin
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
16
Solutions proposed

ATLAS
DCS
The thick cable and connectors associated
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
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
17
Solutions proposed

ATLAS
DCS
The junction box
Junction Box:
2: CAN L
4: VDG
5: Shield
6: VCG
7: CAN H
8: VDP
9: VCP
17 July 2015
1: VCP
2: VCP
3: VCP
4: VCG
5: VCG
6: VCG
7: VDP
8: VDP
9: VDP
10 : VDP
11: VDG
12: VDG
13: VDG
14: VDG
15: VDP
16: VDG
17: CAN H
18: CAN L
19: Shield
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
18
Solutions proposed

ATLAS
DCS
The thin cable and connectors associated
Components with single connectors:
Female Connector
Hood => SCEM 09.21.23.150.3
DC sub-D 9 female connector => SCEM 09.21.21.010.2
Pins => 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
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
19
Solutions proposed

ATLAS
DCS
The prices for the thin cable :
– The 3 twisted pairs cable: 1.60 CHF/m
– Two single connectors (a male and a
female): 18.31 CHF
– One double connector : 34.61 €
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
20
Monitoring board

CAN supply
Supply topology
ELMB digital supply
D-SUB 9 pins
ELMB ADC supply
HAVE TO BE REPLACED BY LOWER VALUE RESISTORS
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
21
Monitoring board
Function
Name
Average Quiescent
Current
ELMB digital
VDP
13mA
ELMB Analog
(ADC)
VAP
11mA
CAN
VCP
20mA
Monitoring
VAP
(without Air Flow)
35mA
Air Flow
25mA @ Ta=45°C
VAP
TOTAL VAP+VDP = 59mA without Air flow
84mA with Air flow @ Ta=45°C
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
22
The simulation tool

ATLAS
DCS
The front panel
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
23
ATLAS
DCS
The simulation tool

Tests of the software
Evolution of the IO controler voltage
12.5
12
11.5
Uelmbs (V)
11
10.5
exp
Simulation
10
9.5
9
8.5
8
0
5
10
15
20
25
30
Nodes number
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
24
Some examples…
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
ATLAS
DCS
25
ATLAS
DCS
Conclusion
This design of the wiring will work
without problem for our CAN bus
applications.
 Wiring of the first rack monitoring
boards will begin next Monday (16/05)
=> Test in real conditions

17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
26
AND NOW

MAKE A REALISTIC TEST (Planed week 19)
With 30 monitoring card & around 100m of thick cable.
17 July 2015
Sébastien Franz PH-ATI-DC
Stéphane Detraz PH-ESS
27