Communication Protocols and Cable Networks

Transcription

1 Usage Guidelines Communication Protocols and Cable Networks SensorNet, RS-422, and How they are Different and When to Use Them. About this Guide This guide explains the difference between American Dynamics video system dome control protocols (SensorNet, RS-422, and ) and cable networks and when to use each. You should carefully plan the network layout before beginning an installation. For additional information see Application Note AN_0026. If you need assistance... Contact your sales representative. American Dynamics and the American Dynamics logo are registered trademarks of Sensormatic Electronics Corporation. Belden is a registered trademark of Belden Inc. Other product names (if any) mentioned herein may be trademarks or registered trademarks of Sensormatic or other companies. No part of this guide may be reproduced in any form without written permission from Sensormatic Electronics Corporation Tyco International Ltd. and its Respective Companies. All Rights Reserved. Brief Description SensorNet, RS-422, and are proprietary serial data communications protocols. SensorNet SensorNet uses two wires to provide half-duplex, multi-drop, differential communications. Advantages: High speed, 2-wire non-polarized, high noise/surge/static immunity, long cable length, drives 32 devices, upload firmware to domes, ping communications test utility. Disadvantages: Proper termination required for reliable communications. Network Topologies: Star,. RS-422 Duplex RS-422 uses four wires to provide duplex, multi-drop, differential communications. Advantages: No termination required, allows more repeaters per line. Disadvantages: Slower speed, 4-wire polarized, less noise immunity. Simplex RS-422 uses two wires to provide simplex, multi-drop, differential communications. Advantages: Two wires, no termination required, allows more repeaters per line. Disadvantages: Slow speed, one-way communications, polarized wiring, less noise immunity. Network Topologies:. uses two wires to provide simplex, multi-drop, differential communications. Advantages: Moderate speed, high noise/surge/ static immunity. Disadvantages: Polarized wiring, not high speed, drives three devices. Proper termination required for reliable communications. Network Topologies:. RP 03/2008 USAGE GUIDELINES 1 of 6

2 Protocol Comparison Table 1 shows the differences between the various protocols: SensorNet, RS-422, and. Note that each protocol requires certain types of cable. For more information, refer to application note AN Table 1. Differences between protocols Cable Type Wire Gauge Max. Length Unshielded (Belden 8442 / or 0.326mm 2 (22AWG) 1000m (3300ft) with repeater 1500m (5000ft) without repeater SensorNet (Belden 8760 / or mm 2 (18AWG) 600m (2000ft) with repeater 900m (3000ft) without repeater Unshielded (CAT-5) mm 2 ( 24AWG) 1000m (3300ft) with repeater 1500m (5000ft) without repeater Duplex RS Twisted Pair (Belden 8102 / or mm 2 ( 22AWG) 1000m (3300ft) Simplex RS-422 (Belden 8102 / 88102, 8760 / or mm 2 ( 22AWG) 1000m (3300ft) (Belden 8760 / or mm 2 ( 18AWG) 1500m (5000ft) Connection Non-Polarized Non-Polarized Non-Polarized Polarized Polarized Polarized Termination Yes Yes Yes No No Yes Data Rate Max. Devices 32 per line 32 per line 32 per line 10 per line 10 per line 3 per line Max Address Network Topologies, Star, Star, Star Note: In some environments, high noise on the network may limit cable distances to less than the maximums indicated in the table. Notes: For SDU-3 through SDU-7: If using the dome pig-tail connector, terminate as usual (see Table 2). If using the I/O board connectors, terminate the I/O board as usual (see Table 2), but you must always terminate the pig-tail connector so that the dome does not incorrectly think the pig-tail connector is being used. This pig-tail termination does not appear on the network. USAGE GUIDELINES 2 of 6

3 Cable Network Comparison Cable networks such as Star, and provide the means through which a communications source speaks to remote devices. Table 2 explains what each network is, when to use it, and lists examples. Note: The maximum number of remote devices connected to a network depends on the protocol and the electrical demands of each device. Refer to instructions supplied with the device. Table 2. Network comparisons Cable Network What It Is: Examples: Star Daisy- Chain Use with SensorNet only. Use if you anticipate that the customer will want to relocate devices in the future. The Star network consists of a single driver as the communications source connected to a maximum of four cable segments. Note that the SensorNet/ Distribution Panel (ADACSNETD) and the SensorNet J-Box (RJ6SN) contain multiple drivers. The cable distance is cumulative, meaning that when added together they should not exceed the maximum cable distance of 1000 meters (3300 feet) with unshielded cable or 600 meters (2000 feet) with shielded cable. The Star network is not recommended for high noise environments or long distances due to the extra terminations, which lower the signal to noise ratio. Use with SensorNet, RS-422, or. RS-422 does not require termination. Daisy Chain: A separate cable connects each adjacent device along the chain. Daisy chaining makes it easy to add devices by extending the network from a nearby device. The communications source can connect anywhere along the cable. Use if the cable is to be short and extended in the future, or when the central distribution point and the remote devices are in the same room. : A single cable connects all the devices along the backbone. To add a device, the insulation is stripped and connected to the device. The cable is not cut. The communications source can connect anywhere along the backbone. Use if the cable is to be long and not extended in the future. The backbone operates the same as the daisy chain, but uncut wires may be more conductive and reliable. The communications source is the hub of the star network. Terminate the devices but do not terminate the communications source. CS = Communications Source T = Terminated devices The communications source is at one end of a daisy chain or backbone network. Terminate the communications source and the last device on the cable. CS = Communications Source T = Terminated devices The communications source is in the center of the cable. Terminate the devices on both ends of the cable. Do not terminate the communications source. USAGE GUIDELINES 3 of 6

4 Combining Cable Networks Star, and networks can be used in combination. The diagram below shows the communications source as the hub of a combination of a Star and Daisy Chain/ network. CS = Communications Source, T = Terminated device. Note that the star network is used with SensorNet only. Wire Connection Star and Daisy Chain networks use standard wire connections where the wire is cut and inserted into a connector and tightened down. A network uses a different technique where the cable is not cut. A 2.5cm (1in) section of the insulation is stripped away and the wire is bent (not cut) and inserted into the connector. Each device is connected in this fashion so there are no cuts in the cable. Standard (cut) Daisy Chain (wire is cut) (wire is not cut) Segment Terminations Each communications source or remote device has a termination switch or jumper to prevent signals from reflecting back along a cable. Only terminate a device when it is at the end of a cable. Only terminate the ends of the main (long) cables. Short stubs (less then 3 meters (10 feet)) of the main cable, while not desirable, have a minimal effect and should not be terminated. Note: Because a J-Box Aux Out contains a driver to amplify the signal, it acts as a communications source to the devices connected to it. It is at the end of the cable when a daisy chain or backbone network is used so the J-Box Aux Out should be terminated. It is not at the end of the cable when a star network is used (SensorNet only) so the J-Box Aux Out should not be terminated. USAGE GUIDELINES 4 of 6

5 Installation Tips SensorNet #1: Only terminate a communications source or network device if it is at the end of a cable or endof-line. Each SensorNet device has a termination switch or jumper. Terminating the devices at the ends of the cable prevent the signals from reflecting back along a cable. Proper termination makes communications more reliable. J-Box and distribution panel outputs renew or amplify the signals, so they are considered communications sources. With daisy chain and backbone networks, they are considered end-of-line and should be terminated. With star networks, they are not considered end-of-line and should not be terminated. J-Box and distribution panel inputs are considered network devices. Terminate them only if they are end-of-line. #2: If a repeater must be used, place the repeater midway along the cable. This will ensure that there is a reliable signal at the input to the repeater. #3: No more than four repeaters are allowed between any two devices on the network. Devices include SensorNet Domes, TouchTrackers, SensorNet I/O units, SensorNet to RS-422 converters, SensorNet Distribution Panels, SensorNet links for American Dynamics MPCPU / MP48 / VM96 / AD168 switches, SensorNet J- Boxes, and fiber optic transceivers that contain repeaters between their separate output ports. This 4-repeater restriction includes devices that are not on the same cable segment or leg of the network. Network collisions resulting in loss of data may occur between out-bound (from the communications source) and in-bound (to the communications source) communications. #4: Signal repeaters (J-Boxes, Distribution Panels) should only be cascaded when cable distances exceed the maximum allowed or when noise is an issue. SensorNet devices can operate at signal levels from 0.3 to 5V, but 1 to 5V is recommended. #5: If shielded cable is used, signals may rapidly decline as more devices are connected or as the cable length increases. As a result, the maximum length allowed for shielded cable is reduced. The shield should be connected at the communications source end only. #6: Attach network devices in stages. Check that their response is correct so you can correct the problem before continuing with the installation. Use ping tests to measure failure rate or operate the dome to verify proper operation. #7: No more than 32 devices per cable segment. With a daisy chain or backbone network, a cable segment starts at the first network device on the cable and ends at the last network device on the cable. The network device at the start or end of the cable may be a communications source. With a star network, up to four branches can be supported. All four branches are considered one cable segment for the purpose of determining the cable length. However, the network device at the end of each of the four branches should be terminated to ensure reliable communication. #8: SensorNet can be used with Star, Daisy Chain, or networks. #9: SensorNet connections are not polarized. Advantages of SensorNet 1. The connections are not polarized and the two wires can be connected in any order. 2. Firmware can be uploaded to domes using a PC with a USB-to-SensorNet module (ADACSNET), an MP48 Plus system, or an ADTT16E controller. 3. A ping test can be used to determine the reliability of the network. 4. Remote manual dome reset command from console. 5. SensorNet outputs are transformer coupled to provide 2000V galvanic isolation, to prevent ground loops, and to prevent conducted discharge currents from flowing through the system. 6. SensorNet outputs incorporate TVS surge protection diodes and drivers that can withstand 2000V ESD level surges. 7. SensorNet outputs are protected with PTC self-resetting fuses to guard against inadvertent wiring connection to up to 30Vac class 2 LPS power. USAGE GUIDELINES 5 of 6

6 RS-422 #1: RS-422 does not require terminations. #2: If a repeater must be used, place the repeater midwayt along the cable. This will ensure that there is a reliable signal at the input to the repeater. #3: More than four repeaters are allowed between any two devices on the network. Devices include Domes, RS-422 converters (RCSN422), RS-422 Distribution Panels, RS-422 links for American Dynamics MPCPU / MP48 / VM96 / AD168 switches, and RS-422 J-Boxes. #4: Signal repeaters (J-Boxes, Distribution Panels) should only be cascaded when cable distances exceed the maximum allowed or when noise is an issue. #5: Ground the shield wire at the source device only. This will prevent ground loops. #6: Attach network devices in stages. Check that their response is correct so you can correct the problem before continuing with the installation. #7: No more than 10 devices per cable segment. With a daisy chain or backbone network, a cable segment starts at the first network device on the cable and ends at the last network device on the cable. The network device at the start or end of the cable may be a communications source. #8: RS-422 can be used with Daisy Chain or networks only. #9: RS-422 connections are polarized. Care must be taken to connect the correct wires to the appropriate device terminals. #1: Only terminate a communications source or network device if it is at the end of a cable or endof-line. Each device has a termination switch or jumper. Terminating the devices at the ends of the cable prevent the signals from reflecting back along a cable. Proper termination makes communications more reliable. J-Box and distribution panel outputs renew or amplify the signals, so they are considered communications sources. With daisy chain and backbone networks, they are considered end-of-line and should be terminated. Distribution panel inputs are considered network devices. Terminate them only if they are end-of-line. #2: If a repeater must be used, place the repeater midwayt along the cable. This will ensure that there is a reliable signal at the input to the repeater. #3: No more than three repeaters are allowed between any two devices on the network. Devices include Domes, code converters, Distribution Panels, and links for American Dynamics MPCPU / MP48 / AD168 / AD2150 switches. #4: Signal repeaters (Distribution Panels) should only be cascaded when cable distances exceed the maximum allowed or when noise is an issue. #5: Ground the shield wire at the source device only. This will prevent ground loops. #6: Attach network devices in stages. Check that their response is correct so you can correct the problem before continuing with the installation. #7: No more than 3 devices per cable segment. With a daisy chain or backbone network, a cable segment starts at the first network device on the cable and ends at the last network device on the cable. The network device at the start or end of the cable may be a communications source. #8: can be used with Daisy Chain or networks only. #9: connections are polarized. Care must be taken to connect the correct wires to the appropriate device terminals. USAGE GUIDELINES 6 of 6