Cedar Rapids, Iowa | From experience I have observed that sometimes one could "get by" with only a single terminator in a system especially on a test stand. Other times not so.
This ultimately depends on how much capacitance the bus has. Generally the longer the wires, the more capacitance. The type of insulation on the wires can also have an effect on the capacitance.
Think of an air hose in your shop. When you plug the air hose in, it gets pressurized. When you unplug it, Pssssh, the air comes out of the hose. If you have a short hose, like 10 feet long, the air comes out in half a second. If you have 200 feet of hose connected, it may take a couple seconds for the air to get out. Longer hose = more air being stored in the hose = more capacitance.
Electrically, a smaller value resistor is the equivalent of a larger hole for the air to escape. That's why 60 ohms of resistance (two terminators) will bleed off the voltage twice as fast as if you only have 120 ohms of resistance (only one terminator). If you happen to be working with a bus that is short, there is probably less capacitance, and so the voltage can still be bled off in a time that is short enough for the CAN nodes to be happy. All that really matters is that the voltage returns to zero quickly enough for the 1s and 0s to be determined. |
CANBus terminators... what are they anyway?
