SeaDaq

Network Layout

A typical SeaDaq data acquisition system is shown above. The SeaDaq network is connected to a media converter which transmits the data over single-mode OC-3 fiber optic cable to another

The general layout of the network system is shown above.

Nodes are generally wired up using category 5 twisted pair cable with up to 100m between nodes. Each node has a receiver and transmitter and takes data from the previous node, appends its own data and then transmits it using its output port as shown below. Each receiver and transmitter is a single twisted pair of wires which is transformer isolated from the power signal. The bandwidth of the transmission path is around 39MHz. Power is also distributed using this cable. If a large number of nodes is present that exceeds the current carrying capacity of the cable then either a separate power cable can be used, or separate pairs of the cable can be used. At the termination end, the cable can go into a standard ATM network interface card, or into a fiber optic media conversion for transmission over greater distances. The media converter will convert the STM-1 electronic signals into OC-3 optical signals. The transmission length is increased to 2km using multimode fiber and 20km using single-mode fiber.

The data appended to the data-stream includes the analog data from each channel in 24 bit format, i.e. 3 bytes from each of the 8 channels making 24 bytes in total. This data is combined into a frame of up to 9600 bytes containing a series of samples together with framing data required for re-assembly of the data-stream at the PC end.