Spider DSA User’s Manual
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In this picture, three Spider-81 and four Spider-80x modules are used. The
Ethernet port of each Spider is connected to one of the Ethernet ports on the
Spider-HUB. One of the Ethernet ports on Spider-HUB is connected to the host
PC.
A remaining Ethernet port on the Spider-HUB can be connected to the “next
cluster” or configuration so that the channel count can be further expanded.
Ethernet Switches for Spider Systems
Crystal Instruments’ Spider platform uses 100 Mbps Ethernet for data transfer
and synchronization. Although Spider modules can work with any standard
Ethernet switch, some switches will have better performance than others.
Switches that support the IEEE 1588 Precision Time Protocol (PTP) version 2 will
allow significantly higher synchronization performance than switches that lack
PTP support. For the best performance, Crystal Instruments’ Spider-HUB should
be used. The IE 3000 series industrial switches by Cisco also support PTP and can
be used for high-precision synchronization.
A Spider system with multiple modules uses PTP to synchronize the internal
clocks of each module over the Ethernet network so that all input channels can be
accurately phase-matched. Each module is connected to a central switch that
routes messages from each connected module through its ports. PTP
synchronization will work regardless of whether the switch is PTP-enabled or not.
PTP works by measuring the signal path delay between each module. The more
precisely this delay can be measured and predicted the more accurately the clocks
can be synchronized. With a regular, non-PTP switch, the delay through the
switch can vary greatly depending on the network load. This adds an unknown
variable into the PTP delay calculation and limits the accuracy of the clock
synchronization. PTP-enabled switches dramatically improve the ability of the
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