Product version

Log on to rate and give feedback 1 2 3 4 5

0

Concept

Concept

Products: AS-P Smoke Control, Automation Server Smoke Control

Functionalities: Smoke Control

Product version: 1.8

9/26/2016

MS/TP Cable Routing

The MS/TP network cable should be routed in a continuous daisy chain bus configuration. There should not be any Stub connections, Stars or Ring configurations. The bussed cable should pass through each node and be connected with no splits or branches in the cable network.

The following network configuration diagrams (with red Xs) show undesirable arrangements of the connected copper cabling.

action_zoom_plus_stroke

Undesirable Cabling Configurations

Figure: Undesirable Cabling Configurations

You can use repeaters to achieve the star, distributed star (backbone with clusters) and stubs off of the backbone. The repeater separates the cable, while each side (or each port on a multi-port repeater) starts a new wire segment. This avoids the effect of stub or cluster/lump capacitance from distorting the data on the backbone.

No more than 2 repeaters should separate any two nodes on the network. This means after you use a repeater to drop a branch leg off the backbone at multiple locations, you cannot add another repeater on any of these branches because this would create a 3 repeater string to one or more nodes on the network.

MS/TP and Modbus Cable Selection

With RS-485 MS/TP (or Modbus) communications, two conductors are used to pass the differential data (A+ and B- signals) from one node to the next. To maintain the balanced characteristics between the two wires, the cable must provide twisted pairs and be specified for data communications. As the twisted pair passes alongside other cables and equipment in the facility, there are a multitude of noise sources, radiated EMI and electromagnetic fields that will impose noise onto the twisted pair cable.

Although it is definitely the most important characteristic, the balanced performance of the cable requires more than just the twisted pair characteristic. The twisted pair cable can become unbalanced when encountering discontinuities in the capacitance between the two wires, or the capacitance from conductor to shield or the impedance of the wires. This makes it important to select quality cable specified for RS-485 data communications.

The cable supplier must provide a cable specification that includes all of the characteristics listed in the following tables. The recommended specs for these characteristics are listed and provide the best results.

Tip:

You should avoid cable where the manufacturer/supplier cannot provide the full cable specifications.

Table: Recommended Cable Characteristics

Characteristics	Recommendation
Type	Shielded Twisted Pair Low Capacitance
Twisted Wire Size	22AWG - 24AWG
Impedance	120 Ohms
Capacitance (wire to shield)	<25 picofarads per foot
Capacitance (wire to wire)	<14 picofarads per foot
Maximum Length	Up to 4000 ft max Depending on termination and bias restrictions

Table: Recommended Twisted Pair Cables

Manufacturer	Model	Size (AWG)	Pairs	Imp.	Cap1 pf/ft ^a	Cap2 pf/ft ^b	Vel	Ple- num
Belden	3105A	22 Str	1	120	11	20.9	78%
Belden	3107A	22 Str	2	120	11	20.9	78%
Belden	9841	24 Str	1	120	12.8	23	66%
Belden	9842	24 Str	2	120	12.8	23	66%
Belden	82841	24 Str	1	120	12	22	76%	Y
Belden	82842	24 Str	2	120	12	22	76%	Y
Belden	89841	24 Str	1	120	12	22	76%	Y
Belden	89842	24 Str	2	120	12	22	76%	Y
Alpha Wire	6453	22 Str	1	120	11	20.9	78%
Alpha Wire	6455	22 Str	2	120	11	20.9	78%
Alpha Wire	6412	24 Str	1	120	12.8	23
Alpha Wire	6413	24 Str	2	120	12.8	23
General Cable	C0841A	24 Str	1	120	14.2	25.6	66%
General Cable	C0842A	24 Str	2	120	11.4	20.5	66%
Connect-Air	W241P2050FRIB	24 Str	1	120	10.9	19.6	78%	Y
Connect-Air	W221P2010FRIB	22 Str	1	120	10.9	19.6	78%	Y

Cap1 = Capacitance between the two conductors of the pair(s)
Cap2 = Capacitance from each signal conductor to shield

MS/TP Network Bias

The MNB series controllers use an isolated RS-485 transceiver that requires a network bias. (This is true only for the Automation Server (AS-SMK) and not the AS-P (AS-P-SMK)).

The bias consists of a pull-up resistor to 5V (on the TX/RX+ signal) and a pull-down resistor to ground (on the TX/RX+ signal). The purpose of the bias is to ensure a high-level, data condition exists in the quiescent or idle state when no controller is driving the bus.

The MNB-300 controller provides internal bias jumpers to optionally enable the biasing of the network. To accommodate the full network length of 4000 feet, bias is needed at each end of the bus. With a network of 500 feet or less, the bias can be supplied from one location.

When MNB-300 controllers are not used on the network, or not positioned on the end of the bus (or within 200 feet), the external 5V supply can be used to bias the network.

Altronix VR1TM5- Network Bias Supply

You can use the VR1TM5 power supply module to provide 5 volt bias for the MS/TP network for the MNB controllers needing the bias. You use one of the 24 VAC transformers listed in this guide to provide power to the supply module. For more information, see Transformers .

action_zoom_plus_stroke

MS/TP Bias Supply

Figure: MS/TP Bias Supply

You connect the +5 volt and common outputs from the module to two separate 1K ohm ¼ watt resistors. For the resistor connecting to the supply common, connect the other side of that resistor to the TX/RX- network signal. For the resistor connecting to the supply +5 volt output, connect the other side of that resistor to the TX/RX+ network signal. You use two of the bias modules to connect one at each end of the network to accommodate the full 4000 feet length.

action_zoom_plus_stroke

MS/TP Bias

Figure: MS/TP Bias