7 Increasing Node Count, Extending Reach
Creating prototype systems and making measurements becomes more expensive and time consuming as the number of nodes increases. Further variations, like experimenting with different BINs, requires even more combinations and measurements. A small number of good reliable measurements enables the creation of reliable modes that can then be used in simulation tools to create realistic results and enable comparison of various network configurations. Simulations based on models that match the previous results created jitter vs noise tolerance plots, which can be used to identify configurations that have the desired noise tolerance at reasonable jitter margins. These simulations are used to determine working topologies.
- High node density - how many nodes can be supported in a given condition, and how close can they be spaced.
- Maximum segment length - how long can a segment be, and how many (equally spaced) nodes can it support
High Node Density
When using a large number of nodes, an important parameter is how closely they can be to each other. The methods above were used to determine the minimum distance between nodes for a system, assuming a required noise tolerance of 200mV. If it is possible to avoid using a Common Mode Choke (CMC), minimum node spacing is 5 cm for up to 20 nodes, and 25 cm for up to 50 nodes. as shown in Table 7-1. More nodes may be possible with lower noise tolerance.
| Number of Nodes | Minimum Distance between Nodes | Total Length at Minimum Distance |
|---|---|---|
| 8 | 5 cm | 35 cm |
| 10 | 5 cm | 45 cm |
| 20 | 5 cm | 95 cm |
| 40 | 25 cm | 9.75 m |
| 50 | 25 cm | 12.25 m |
A Common Mode Choke (CMC) causes the node spacing to increase, as shown in Table 7-2.
| Number of Nodes | Minimum Distance between Nodes | Total Length at Minimum Distance |
|---|---|---|
| 8 | 20 cm | 140 cm |
| 10 | 40 cm | 360 cm |
| 20 | 60 cm | 1140 cm |
| 40 | 80 cm | 3120 cm |
| 50 | 90 cm | 4410 cm |
Maximum Segment Length
Maximum segment length, using the same configuration as above, is simpler. For 200mV noise tolerance, without a common mode choke, up to 50 nodes can support a total mixing segment length of 50 m. With a common choke, this drops to 45m.
If the end system can tolerate 100mV of noise, a 2 node system using cables 2 or 3 will function at a length of 100m. This has been shown working correctly under laboratory conditions.