AS-B
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1471 Topic(s)
Concept
The recommendations include two different configuration options to choose from with differences in performance and/or resources required.
Concept
Dual end-point bias applies a separate 5 V DC supply at each end of the network to generate the RS-485 bias. Instead of a single pair of 510 ohm resistors, the dual end scheme uses a pair of 1000 ohm resistors at each end. The dual end-point is the best technique for avoiding the drop in the bias voltage over extended cable lengths as you move away from the bias connection location. By applying bias at the two termination points, the arrangement maintains an equal bias across the complete length of the cable.
Concept
This configuration is the simplest to arrange and supports bus lengths out to 150 m (500 ft) on 24 AWG (0.20 mm²). The automation server should be configured with two 510 ohm bias resistors. One resistor connecting the + data line to the Bias+ terminal on the automation server and the other resistor connecting the – data line to the RET terminal on the automation server. The bias is required to support the transceivers in the VT/VZ nodes and the termination of the bus. AS-P servers and AS-B servers provide 5 V for bias, which supports 120 ohm termination resistors at the two ends of the bus. This will achieve the minimum idle line bias voltage of +200 mV required by the transceivers. Low resistance bias configurations (with 5 V supplies) add significant common mode load on the RS-485 network. The common mode load (Unit Load) of the bias network must be summed with the accumulated unit load of the collection of VT/VZ thermostats/controllers to identify the total unit load on the bus.
Concept
This application note provides recommendations and guidelines for the configuration of RS-485 communications between the automation server and Viconics room controllers. The recommendations are associated with the Viconics VT/VZ/SE 7xxx series thermostats / room controllers configured with the Viconics plug-on MS/TP network adapter. This information is intended to supplement the instructions you receive with the various RS-485 network devices. The guidelines focus on the arrangement of the electrical interface to the automation server's RS-485 port in regards to biasing, termination, cable selection, cable lengths, and cable routing. The guidelines on maximum unit load (node count) and common mode voltage tolerance are associated with AS-P and AS-B servers.
Concept
The information in this section provides recommendations for the RS-485 interface port configuration between the automation server and RS-485 network devices. This information is intended to supplement existing guides for the automation server and for the various RS-485 network devices.
Concept
This configuration applies to the situation where existing MNB devices with bias capability (MNB-300 or MNB-1000) are not available on the network segment, and it is preferred not to add external supplies.
Concept
Mid-point bias refers to the technique of using a separate 5 V DC power supply and locating it at the middle of the total network cable length. This technique takes advantage of the maximum DC differential resistance at the center to maximize the bias voltage applied through the typical pair of 510 ohm resistors from the 5 V bias supply. The higher bias voltage level now applied in the center can extend up to 600 m (2000 ft) in both directions from the center using 24 AWG (0.20 mm²) size cable (or larger).
Concept
When MNB-300 or MNB-1000 devices are not available within 60 m (200 ft) of the end of the cable, the dual end-point bias configuration can still be deployed as seen here in Configuration 2 using a separate 5 V DC supply at each end of the network to generate the RS-485 bias. The same as Configuration 1, this arrangement provides the best performance on systems where bias is needed. The dual end-point avoids the drop in the bias voltage seen with the single end-point bias arrangements. By applying the bias at the same location as the termination, the arrangement maintains an equal bias across the complete length of the cable. This technique does not encounter the positional sensitivity of Configuration 3 in locating the middle point of the network.
Concept
Dual end-point bias applies a separate 5 V DC supply at each end of the network to generate the RS-485 bias. Instead of a single pair of 510 ohm resistors, the dual end scheme uses a pair of 1000 ohm resistors at each end. The dual end-point is the best technique for avoiding the drop in the bias voltage over extended cable lengths as you move away from the bias connection location. By applying the bias at the same location as the termination, the arrangement maintains an equal bias across the complete length of the cable. This technique avoids the positional sensitivity of Configuration 3 in locating the middle point of the network and provides a superior bias reliability. This Configuration 1 differs from Configuration 2 only in the use of MNB-300 or MNB-1000 devices to provide the bias supply source.
Concept
This application note provides recommendations and guidelines for the configuration of RS-485 communications between the automation server and MNB BACnet devices. This information is intended to supplement the existing configuration documents such as the “TAC I/A Series MicroNet BACnet Wiring and Networking Practices Guide (F-27360-10)”. The guidelines focus on the arrangement of the electrical interface to the automation server's RS-485 port in regards to biasing, termination, cable selection, cable lengths and cable routing. The guidelines on maximum unit load (node count) and common mode voltage tolerance are associated with AS-P and AS-B servers.