Delta AH500 - Choice and Purpose of a Devicenet Terminal Resistor

AH500 Module Manual
10-12
Product picture
Type
Function
TAP-CB01 TAP-CB01: DeviceNet trunk cable
TAP-CB02 TAP-CB02: DeviceNet drop cable
10.3.4 Choice and Purpose of a DeviceNet Terminal Resistor
 Choice of a DeviceNet Terminal Resistor
A DeviceNet network needs to connect a terminal resistor of 121 ohm at both ends of the trunk
cable respectively.
The thick cable represents the main cable and the thin cable represents the sub-cable.
 Purpose of a DeviceNet Terminal Resistor
The terminal resistor is used for eliminating the signal reflection in the communication cable.
All signal transmission cables have the characteristic impedance. The characteristic impedance
of Delta DeviceNet communication cable is about 121 ohm.
When being transmitted to the end of the communication cable, because the impedance of the
end is different from the characteristic impedance, the signal will be reflected, which will
interfere with the new signal and the signal wave form distortion will happen.
The phenomenon of the signal wave form distortion is not obvious in the short-distance
transmission. But the wave form distortion will become severe with the increasing
communication cable. Therefore, the two ends of the trunk cable must be installed with the
terminal resistors respectively.
 Installation Position of a Terminal Resistor
The DeviceNet communication cable consists of five wires such as red wire, blue wire, white
wire, black wire and shielded wire as below.