Optical Modem (optional)

The RBRcervello may be configured at the factory to communicate with sub-surface instruments using a pair of Hydromea LUMA250LP optical modems, permitting deployment in environments that are not sufficiently saline for the standard RBR MLM.

We provide an Optical Modem Kit (RBR P/N 0017848) consisting of a Sub-Surface Optical Modem (SSOM) and Head-End Optical Modem (HEOM) pair, which together form a transparent point-to-point serial connection between a modified RBRcervello and an RBR logger fitted with a specialized power/data battery endcap (BEC).

We advise against modifying the configuration of the modems as shipped from RBR. The shipped configuration should be optimal under most conditions. If you are experiencing problems with the optical modem link, please contact support@rbr-global.com for assistance.

Behavior

Beaconing

The Head-End Optical Modem is configured to transmit a beacon message every second.

To save power, the Sub-Surface Optical Modem is configured to go to sleep if 30 seconds pass without it receiving a beacon message.

This should not affect Cervello’s data transmission.

No-attempt window

To save power while the Wirewalker profiling float is out of optical communications range, the Cervello will turn off the Head-End Optical Modem for a configurable “optical modem discovery no attempt window” if the optical communications link is broken. The optimal value of this setting will vary depending on the Wirewalker’s maximum profiling depth and can be calculated as:

T = 2*(max_profiling_depth - 1.2*modem_max_range)/(0.5m/s)

This calculation does not include any safety factor on the profiling depth, and the profiling speed may change depending on the ballasting and wave conditions.

Maximum optical modem range.

The optical modem’s maximum range will be no more than 7m in clear water.