3.4 Installation and Commissioning¶
A Safety Simplifier system that uses SimpleCAN is connected the same way as a regular Simplifier CAN bus (see chapter 8, Bus communication via radio and/or CAN-bus, in the Safety Simplifier manual). Downloading the configuration is also done the same way (see 1.10 Downloading Programs).
3.4.1 Technical data for CAN 2.0¶
Cable requirements for CAN 2.0 (ISO 11898-2):
- Cable type
- Twisted pair: standard for CAN_H and CAN_L, to reduce electromagnetic interference (EMI).
- Shielded twisted pair (STP): recommended in high-EMI environments (for example, industrial settings).
- Unshielded twisted pair (UTP): acceptable in low-EMI environments (for example, labs).
- Electrical characteristics
- Characteristic impedance: 120 Ω ±10%
- Capacitance: less than 30 pF/ft (≈ 98 pF/m)
- Conductor size: 22–24 AWG (≈ 0.34–0.25 mm²)
- Termination
- Resistors: 120 Ω at each end of the CAN bus (two in total).
- Purpose: prevents signal reflections and defines the bus idle voltage.
- Cable length vs. baud rate (general values)
| Baud rate | Max cable length |
|---|---|
| 500 kbit/s | About 100 m |
| 250 kbit/s | About 250 m |
| 125 kbit/s | About 500 m |
Table 3.2: Maximum cable length at different baud rates.
These values are based on ISO 11898-2 and can vary depending on cable quality and environment.
Note
The possible distance can be either longer or shorter in practice. Contact SSP North for further advice.
3.4.2 CAN card connection for Safety Simplifier¶
CAN card connection for Safety Simplifier.
Notes from the wiring diagram:
- At both ends of the CAN cable, the resistor switch shall be in position ON (pushed in the direction of the arrow). Each end of the CAN bus is then connected to 120 Ω. An external resistor on the M12 contact on the ends can also be used.
- On all other CAN cards, the resistor switch shall be in position OFF.
- If a screen is used, it should be connected to all CAN cards.
- Maximum stub length: 125 kbit/s — max 2.4 m; 250 kbit/s — max 1.2 m; 500 kbit/s — max 0.6 m.