Variations
Conceptually, online cable systems are quite simple. In real life, the story is a little less simple and long cables are both a technical and practical challenge. To address these challenges, we have taken many years of experience and designed what we believe to be a very good technical solution.
All cabled observation systems are not the same and Nortek has spent quite a bit of time coming up with a design that we believe will work in most oceanic conditions. The two main elements are:
First, the instrument is connected to a 2-m extension cable that is molded onto our tough online cable. To make sure the instrument connector does not easily come loose, a braided jacket ("Chinese fingers", see element 0 in the drawing below) with a strength of several 100 kg is attached to the online cable and should be attached to the deployment frame before or during deployment.
For cables longer than 50m the online cable connects on shore to the "interface box" (see element 3 in drawing below), which supplies 48 VDC power and RS-422 communication. To reduce the voltage, a DC-DC converter is mounted inside the instrument. The DC-DC converter comes in two physical versions, one that fits inside the AWAC housings and one that fits in all other housings.
The exception to the 50m limitation is the 470 kHz 2D Continental. This system can run up to 200m online cable with 18 VDC input voltage (preferably the Nortek 18V interface box) and no DC/DC converter in the instrument. The penalty of such a solution is a voltage drop over the cable that leads to less acoustic output power which, in turn, means less range. A 48 VDC interface box will not experience this effect.
470 kHz 2D Continental systems with longer than 200m cables should always include a 48 VDC interface box and DC-DC converter in the instrument.
To reduce the problem of wear and tear, we recommend a segmented cable where the segments are linked with an underwater matable connector that can be detached or attached by a diver (optional diver tool is available). For example, it is possible to use four 250-m segments instead of one 1000-m segment. For problems with cables that are being pulled, the strain relief mechanism is designed to take a load of 200kg and then cause the underwater matable connectors to come apart. In many cases, this means that it is possible to get the system back and up and running replacing the damaged cable segment instead of the whole cable.
Any Nortek ocean instrument can be used with the online cabled system and the DCDC converter.
Backup Option
It is possible to add backup batteries and memory to online systems. The battery will ensure that the instrument continues to collect data even if the cable is disconnected and the extra memory ensures that the data are stored.
This backup option is ordered as part of the standard instrument and it is similar to what it is normally used for stand-alone instruments. The Interface Box with 48V output combined with the DC-DC converter inside the instrument are important elements in the backup option to avoid depletion of the backup battery during regular operation.
Please contact Nortek if you have special online requirements that may require subsets or a special version of the online cabled system.
