|
Linet network |
1. What is Linet
1.1. What is the LiNet network? Linet is a light control network. 'Light', in this context, means it is easy and simple to use. The Linet network is used to control a network of electrically driven or controlled equipment and various types of data acquisition devices. Typical applications include (but are not limited to) lighting control systems, alarm systems, air conditioning, multi-point measurement and control systems etc. A Linet network consist of a controller, transmission media and nodes. One controller per network is needed. Transmission media is topology and polarity free twisted pair cable network, which carries data and small power. Nodes are the 'network cards' of the system. They have ready-made interfaces - switch I/O, PWM (power control) output, analog input, data I/O - for the devices to be controlled. There can be up to 200 nodes in a Linet network. 1.2. What are the products available from the Linet company Linet products are:
1.3. What are the fundamental features of the Linet network Linet was designed from scratch to meet the demand for a control network for simple applications. Its design targets have been: 1) Simple system design and setup. Linet nodes' fixed interface makes system design simple, and prevents network data corruption due to design bugs. As the network controller is used as the set-up tool, no Linet-specific design tools are required. Using controller's menu-driven interface, network setup is so easy everyone can do it. 2) Robustness against external interference. LiNet is reliable. Please see faq 3.2 for more information. 3) Low cost system. Our core product, single-chip IC node, requires only about 4mm2 silicon. In some peer-to-peer networks there are three microprocessors all running 10 MHz in each node, even though the node's function was to switch a lamp on and off. Less is more, we say. 1.4. What are the major differences between Linet and other networks 1) Linet node has integrated, fixed I/O-functions. Use of fixed functions removes need to program the node. This makes the device simple to design and manufacture. If the application required 'distributed intelligence', you can connect a microcontroller to the node. For example, Microchip's PIC-controllers suit well for this. 2) Linet network is a master-slave system. In peer-to-peer networks a 'master' is not needed, but they still need a power supply, so the odds are even. They also require separate set-up tools which, in Linet system, is integrated into the controller. Linet is designed to be the simpliest approach. For instance, Linet can form body of a home automation system consisting of 200 I/O-points, containing only one device that runs a program (which is the controller). In peer-to-peer networks, there are 200 devices all running programs. Which is simplier to keep up? In data acquisition or sub-network applications, when the network is linked to a host system, the controller is obviously used to form the link. This is also possible in peer-to-peer networks but, again, more design effort is needed. 3) Linet uses time division protocol. This gives fixed signal delays, that doesn't depend on system load. Most peer-to-peer networks use CSMA/CD (ie. collision detect). Comparison between network protocols.
2.1. Aren't the markets full of solutions like Linet No. Currently, if you want to build a distributed control system, either you have to use hard-wired control cabling or complex high-end control network. The former is not acceptable in most cases, the latter is fine if you really need all that functionality and complexity. In most control applications however, there is only a need for turning on or off some devices, controlling power of them, or measuring some slowly changing values. In this area, there are no other control networks that are as simple, reliable and easy to use as the Linet network. 2.2. Isn't the Linet network very slow Yes and no. The serial data transmission speed in data mode is 80 bits/sec per node. For example, result of a 12-bit a/d-conversion including error correction can be transmitted approximately four times per second. Is this enough or not, depends on the application. LiNet uses time division protocol, so the data transmission capacity doesn't depend on number of nodes in the network. Therefore you can have up to 200 nodes all transmitting 12-bit values four times per second simultaneously. 2.3. Is Linet an 'open' system Yes. Linet offers the benefits of open systems. The interface
from the node to the device is hard-written on the node (eg. a switch).
The interface from the controller to a host is also documented and open.
3. Questions about Linet technology 3.1. Can I use network cable longer than 200 m Currently we have specified the maximum length of network cable to be 200 meters, and there can be up to 200 nodes connected to the cable. The limitation is based on cable capacitance and resistance. If thinner wire is used, the capacitance decreases but the resistance increases, and vice versa. By lowering the number of nodes in the network, the current in the network decreases and higher resistance can be accepted. Therefore by lowering the maximum quantity of nodes the cable length can be increased. For example, a 600 m. network of 20 nodes has been found functioning. 3.2. Will Linet cause EMC/EMI problems The carrier wave form in Linet network is almost pure sine and it's frequency is moderate 20kHz. Nodes' power consumption is very low so only low levels of power are transmitted through the network. LiNet hardware is designed so that its sensitivity to interference is at its minimum. Signal sensing in the network is done by signal integrating circuits both in the controller and in the nodes. Linet has been tested to fullfill EU EMC regulations according to specifications EN50081-1 and EN50082-1. 3.3. What is signal transmission delay through Linet network Linet uses time division protocol. All 200 nodes have their own time slot in the signal frame, and the frame is repeated 80 times in second. In switch I/O, the node-to-node or node-to-controller delay is 50 msec. Note that this delay is fixed, not depenging on the size or degree of utilization of the network. In data I/O, the data rate is 80 bits/sec per node. Note that this is also the net data rate, as because of the time division protocol, there is no overhead in the transmitted data. 3.4. Can I increase the data transmission capacity of 80 bits/sec The Linet controller software supports dynamic frame size.By selecting the frame size to be 200, 100 or 50 nodes, the capacity will be 80 bits/s, 160 bits/s or 320 bits/s, respectively. 3.5. How has the node been made The node is a mixed-signal IC, consisting of analog, digital and high voltage semiconductor technology on the single piece of silicon. No embedded processors are involved as for the protocol, sequential logic has been used. 3.6. Is the system based on RS485 or other standard No. Linet has been developed from scratch for control networking. It has not been inherited from any data network. Linet is a master-slave system using time division protocol. The carrier is a mix of (bidirectional) data and small power. All signals are sinusoidal, and when a signal is detected, and area from the signal is measured instead of just taking a sample of voltage. 3.8. Can I install the Linet network cable near other conductors Yes. Linet is very strong against external interference, so the twisted pair cable may be installed in the same cable tray or pipe in use by other power and/or data conductors. 3.9. Can Linet nodes be used for PLC (power line communication) No. Linet node has bult-in transceiver, so a dedicated
twisted pair cable network has to be used.
Copyright Linet Oy. All rights reserved. |
Linet Evaluation Kit
|