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Topic: Underwater ROV, slow rs 485 communication Part 1 of 2 (Read 5786 times) previous topic - next topic


Aug 31, 2013, 06:35 pm Last Edit: Aug 31, 2013, 07:04 pm by mrburnette Reason: 1

Resistors set the DC impedance but the AC component is more complex.  My suggestion to the Op is to go back to basics, ensure that they have a 120 Ohm twisted-pair cable per the   Maxi document: http://www.maximintegrated.com/app-notes/index.mvp/id/763 As described in the section Characteristic Impedance of Twisted-Pair Wire.

The cable should be specified for underwater use... But the issue is the water-air interface to the surface.  Special shielding arrangements in the cable manufacture will minimize this point of mismatch.

The reduction in data rate may actually increase throughput if resends are the a large component of overall bandwidth.

Moving to outbound send using fiber for the data is the obvious gold-plated remedy, but there is no reason that the existing design should not perform adequately, IMO.


References: Geomeasurements by Pulsing TDR Cables and Probes
By Kevin M. O'Connor, Charles M. Dowding


The OP hasn't really given any hardware details on the wiring and hardwire control setups. Was any preliminary testing or hardware setups used to arrive at the current ROV configuration?  Previous ROV discussions that might be of interest.

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