Concept
Legrand Configurations
The recommendations include four different configuration options to choose from with differences in performance and/or resources required.
Legrand Configuration 1: Terminated Bus with No Bias Requirement
This configuration is recommended when using any combination of Legrand meter models 04677, 04680, and 04684. The configuration does not apply to the model 14669. The configuration uses 120 ohm End Of Line (EOL) termination resistors and requires no extra biasing.
For more information, see Legrand Configuration 1: Terminated Bus with No Bias Requirement .
Legrand Configuration 2: Unterminated Bus with Minimal Bias
This configuration uses no bus termination, which means reduced data rates and cable lengths. The configuration applies to any combination of Legrand meter models 04677, 04680, 04684, or 14669.
For more information, see Legrand Configuration 2: Unterminated Bus with Minimal Bias .
Legrand Configuration 3: Terminated Bus with Single End-point Bias
A third configuration option is available where low resistance bias is added to the automation server to allow termination to be applied on a network containing one or more model 14669 meters. The configuration applies to any combination of Legrand models 04677, 04680, 04684, or 14669. AS-P and AS-B servers provide a 5 V bias voltage supply, which supports 120 ohm termination resistors at the two ends of the bus.
For more information, see Legrand Configuration 3: Terminated Bus with Single End-point Bias .
Legrand Configuration 4: Terminated Bus with Dual End-point Bias
A fourth configuration option is targeted at recovering the full 1200 m (4000 ft) capability of the RS-485 network while accommodating the standard 120 ohm End Of Line (EOL) terminations for better high speed data quality. This technique applies a 5 V bias at each end of the network. Biasing the network from both ends completely eliminates the dropping failsafe bias voltage as the cable length extends toward the remote terminator. This configuration option can be used for any combination of Legrand models 04677, 04680, 04684, or 14669.
For more information, see Legrand Configuration 4: Terminated Bus with Dual End-point Bias .
Power Supply Selection for Legrand Configuration 4
The power required from the 5 V DC supply for the bias circuit is extremely small (approximately 5 mA) so just about any small isolated 5 V DC supply will have more than necessary power rating. A low noise power supply with an output isolated from local ground is recommended to minimize the injection of differential noise onto the bus.
For more information, see Power Supply Selection for Legrand Configuration 4 .
Configuration Summary
The four configuration options described above are summarized in the following tables.
Configuration 1 provides the best performance and simplest configuration, but it is not applicable to the model 14669.
|
Model |
Max Cable Length |
Max Data Rate |
Max Node Count, All Isolated |
Max Node Count, Any Non-isolated |
|
04677, 04680, 04684 |
1200 m (4000 ft) |
76,800 bps |
35.8 |
23.7 |
|
14699 |
1200 m (4000 ft) |
76,800 bps |
Not supported |
Not supported |
Configuration 2 is useful for lower data speed over shorter distances in low noise environment.
|
Model |
Max Cable Length |
Max Data Rate |
Max Node Count, All Isolated |
Max Node Count, Any Non-isolated |
|
04677, 04680, 04684 |
150 m (500 ft) |
19,200 bps |
33 |
20.9 |
|
14699 |
150 m (500 ft) |
19,200 bps |
25 |
15.7 |
Configuration 3 is a common configuration that supports full data speed over shorter distances covering many application needs.
|
Model |
Max Cable Length |
Max Data Rate |
Max Node Count, All Isolated |
Max Node Count, Any Non-isolated |
|
04677, 04680, 04684 |
150 m (500 ft) |
76,800 bps |
18.1 |
6 |
|
14699 |
150 m (500 ft) |
76,800 bps |
13.7 |
4.5 |
Configuration 4 supports long length and maximum data rates with all four models. Node count reduced due to bias requirements.
|
Model |
Max Cable Length |
Max Data Rate |
Max Node Count, All Isolated |
Max Node Count, Any Non-isolated |
|
04677, 04680, 04684 |
1200 m (4000 ft) |
76,800 bps |
17.7 |
5.6 |
|
14699 |
1200 m (4000 ft) |
76,800 bps |
13.4 |
4.2 |
Legrand Power Meters
Legrand Configuration 1: Terminated Bus with No Bias Requirement
Legrand Configuration 2: Unterminated Bus with Minimal Bias
Legrand Configuration 3: Terminated Bus with Single End-point Bias
Legrand Configuration 4: Terminated Bus with Dual End-point Bias
Power Supply Selection for Legrand Configuration 4