SDS Overview And Description
SDS: The ‘Smart Sensor’ Fieldbus
"Smart Distributed System"
Origin: Honeywell, 1989
Based on CAN (Controller Area Network) technology, borrowed from the automotive industry, and the RS485 Electrical specification.
Maximum Number of Nodes: 64 (126 addresses)
Connectors: 18mm ‘mini’ or 12mm ‘micro’ quick disconnect connectors, or 9 pin D-shell
Distance: 100M to 500M
Baudrate: 125, 250, 500 and 1000 Kbits/sec
Message size: 8 bytes of data per node per message
Messaging formats: Change-of-State, Cyclic, others
Supporting Trade Organization: Honeywell Smart Society, http://www.honeywell.com/sensing/prodinfo/sds/
Typical Applications: Commonly found in assembly, material handling, packaging and high-speed sortation machines. Single-cable wiring of multi-input sensor blocks, smart sensors, pneumatic valves, barcode readers, drives and operator interfaces.
Advantages: Low cost, small physical size of electronics, high reliability, diagnostics, efficient use of network bandwidth, power available on the network.
Disadvantages: Limited bandwidth, limited message size and maximum length; limited number of supporting vendors.
A Different Twist on CAN Technology
SDS, like DeviceNet and CAN-Open, is based on the CAN (Controller Area Network) protocol. CAN was developed by Bosch for networking most of the distributed electrical devices throughout an automobile. CAN is an extremely robust protocol with extensive error detection and correction features which easily withstand the harsh physical and electrical environment presented by a car. It is relied upon for such critical devices as anti-lock brakes and airbags in millions of vehicles worldwide.
Smart Sensors
SDS was specifically designed for material handling applications with the intent that the technology could be embedded in compact sensors, which are directly connected to the network. Currently, sensors as small as 18mm tubular proximity switches are embedded with SDS connectivity. This is possible because the SDS slave protocol is economical in terms of minimal memory, processor and size requirements.
Favored Niches
SDS has been very successful in high speed material handling and sorting applications such as the US Post Office and in PC Assembly facilities. Companies like Dell Computer and Gateway have implemented SDS and PC Control as a standard for their automated assembly equipment.
Diagnostics
SDS also has substantial diagnostic capabilities, which, in conjunction with intelligent sensors, allow the operator to detect when a sensor needs to be cleaned, or is about to fail. Intermittent faults can be 'trapped' and device failures can be anticipated before they occur, thus reducing maintenance costs considerably.
Event-Driven, High Speed Messaging
SDS is event-oriented, meaning that status changes on the network are reported only when they occur, not constantly as in polling systems. This drastically reduces traffic on the network; the speed of an event driven ("change of state") messaging system may be many times that of an otherwise identical polling or strobing protocol at the same baudrate. Successful message transmission is verified by the master, which sends a confirmation signal back to the slave.
Message prioritization in SDS is such that even in the event driven mode, where throughput and response times are typically knowable only on a statistical basis, a worst-case response time can still be guaranteed.
SDS is based on the same RS485 voltage and impedance specifications as DeviceNet and CAN-Open, as well as the same 'Mini' 18mm and 'Micro/Euro' 12mm water-resistant molded connectors which are widely used in machine wiring. Device power (up to 8 amps) is also available on the network taps.
Synergetic’s Diverse Lineup of SDS Solutions:
PC Adapter Cards: We have PC/ISA, PC104, PCI, PCMCIA, CompactPCI*, STD32 and VME* Masters and Slaves for SDS. They use the same configuration tools, hardware and software interface as all of our other Fieldbus interfaces (DeviceNet, Profibus, Interbus, etc…).
*Call for availability
Embedded Master Modules: Our COMMUNICATOR modules are credit-card sized boards that you can design into your controller, PLC, operator interface or other device that you wish to convert to Fieldbus. The same dual port memory, software drivers and configuration tool as our PC card is used regardless of the bus.
COMMMUNICATORS require a custom user
hardware design with the COM module mounted as a daughter board and the Fieldbus connector
on your hardware board. All other Fieldbus components are on the COM module. After
designed, all other COM modules can be plugged into the same socket.
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