earth_america
user_standard Iniciar sesión
action_search_stroke
earth_america
Log on to rate and give feedback 1 2 3 4 5 Log on to rate
0
Concepto

Concepto


Productos AS-C, AS-B, AS-P
Funcionalidades: Hardware
Versión del producto: 1.8, 1.9
10/06/2016

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.

With dual end-point bias, a strong and constant bias level is present over the complete length of the bus. The dual end-point bias uses a pair of 1000 ohm resistors at each end. This combined parallel resistance of 500 ohm still encounters the significant unit load reduction as with Configuration 3, but now supports the RS-485 maximum 1200 m (4000 ft) network length. Para obtener más información, consulte Legrand Configuration 3: Terminated Bus with Single End-point Bias .

When using AS-P or AS-B positioned at the head end of the network, you can use the 5 V available on the Bias+ terminal to provide the head-end bias. You use an external 5 V DC power supply to provide the bias at the far end of the network. When using Automation Server, you use external 5 V DC power supplies at both ends of the network to provide the network bias. The recommended power supplies are discussed separately. Para obtener más información, consulte Power Supply Selection for Legrand Configuration 4 .

Connect a 1000 ohm bias resistor from the TX/RX+ terminal (see the figure below) to the 5 V bias supply (connect the resistor to the Bias+ terminal on AS-P or AS-B, or to the positive terminal on the external 5 V DC power supply). Connect another 1000 ohm bias resistor from the TX/RX- terminal to the 5 V bias supply (connect the resistor to the RET terminal on AS-P or AS-B, or to the negative terminal on the external 5 V DC power supply). Connect an external 5 V DC power supply to the RS-485 bus pair through two 1000 ohm bias resistors at the far end of the cable.

Connect a 120 ohm termination resistor across the + and - data lines at the head end of the bus (typically at the SmartStruxure server device). Connect another 120 ohm termination resistor across the + and - data lines on the last node at the far end of the bus.

Connect the two RS-485 common wire pair and the shield to earth ground terminal rail in the panel with the SmartStruxure server device. This is the only ground connection of the shield for these conductors. The shield drain wire from the cable segments are twisted together and passed by each node.

Both conductors of the second twisted pair cable are used to connect RS-485 Common on the meters.

Use only twisted pair bus cable specified for use with RS-485 (for example, Belden 9842 or equivalent). Para obtener más información, consulte Cable Selection (Legrand Power Meters) .

The example diagram below shows the alternate RS-485 terminal block connections for the different SmartStruxure server device models.

The example diagram below shows the RS-485 Com B connections on Automation Server and AS-P. The guidelines are the same for Com A.

 
action_zoom_plus_stroke Legrand configuration 4 – terminated bus with dual end-point bias (for models 04677, 04680, 04684, or 14669)
Figura: Legrand configuration 4 – terminated bus with dual end-point bias (for models 04677, 04680, 04684, or 14669)

Each of the models 04677, 04680, and 04684 presents an RS-485 network load of 1.32UL, and the model 14669 has a network load of 1.75UL. The SmartStruxure server device has a network load of 0.5UL. To determine the number of nodes (meters) the bus will support, we first determine the remaining available unit load capacity after subtracting the base load of the SmartStruxure server device, and the load produced by the bias resistors.

For networks connecting only with Legrand meters, the initial unit load budget is 48UL. For networks with one or more other Modbus devices that are not isolated, the initial unit load budget is 32UL. The SmartStruxure server device has a unit load of 0.5UL. The dual 1000 ohm bias gives a unit load of 24UL (12,000 / 500). Subtracting these two loads from the initial budget gives a remaining capacity of 23.5UL (all isolated) or 7.5UL (mixed).

For isolated network, the calculated maximum node count is:

  • For models 04677, 04680, and 04684: 23.5 / 1.325 = 17.7 nodes (meters)

  • For model 14669: 23.5 / 1.75 = 13.4 nodes (meters)

For mixed network, the calculated maximum node count is:

  • For models 04677, 04680, and 04684: 7.5 / 1.325 = 5.6 nodes (meters)

  • For model 14669: 7.5 / 1.75 = 4.2 nodes (meters)

You can accommodate the load from a mixed combination of model 14669 meters and the others by simply summing their individual Total Unit Load values. Para obtener más información, consulte General Legrand Power Meter Properties . The maximum recommended limit is reached when that sum reaches 23.5UL (for all isolated) or 7.5UL (for mixed network).

Consulte también

  • Legrand Power Meters
  • Legrand Configurations
  • Legrand Configuration 3: Terminated Bus with Single End-point Bias
  • Cable Selection (Legrand Power Meters)
  • General Legrand Power Meter Properties