Pathfinder DVL Guide
April
2018
EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
Page 39
Electrical Integration Considerations
Grounding Issues
Multiple grounds connected to a vehicle hull or to a vehicle chassis can have undesirable consequences.
Grounding problems can be avoided by implementing prudent grounding schemes.
The DVL has three isolated grounds in order to achieve the desired performance levels of the instrument.
The grounding systems are as follows:
•
Communication ground
•
Power ground
•
Chassis ground
The grounded systems noted are isolated from each other. The Power Ground is isolated from the Chassis
Ground by an isolation / ground noise filter circuit. This ‘link’ between these two grounds is susceptible
to EMI from outside sources if the isolation is not properly maintained outside the DVL. If the DVL’s
isolation / ground noise filter circuit is shorted, the DVL may experience an increased noise floor, ulti-
mately propagating into the signal receivers.
This same isolation circuit will be shorted if the chassis (DVL GND) is in direct contact with the vehicle
chassis (vehicle GND) and the Power supply ground connected to the DVL is also connected to the ve-
hicle chassis (vehicle GND).
Typically the DVL chassis is anodized, thereby providing electrical insulation when the instrument is
mounted into what are usually metal hulls. The anodized coating is required to maintain chassis ground
isolation.
Another potential electrical path bypassing the isolation/ground filter can occur through seawater. The
current generated can pass via the DVL anode, (or scratches in the DVL coating), through the sea-
water, and then back to the hull (or frame) to the vehicle. The likelihood of this ground path occurring is
increased if the hull of the vehicle is connected to the Power ground of the DVL through the vehicle’s
grounding circuitry. Typically this resistance is very high resulting in only a few microamperes of current
and is limited by the size of the DVL anode and the distance between the Anode and the grounded hull of
the vehicle (the greater the separation the greater the resistance).
For the condition described, if the exposed surface resistance is great, the DVL will not be adversely af-
fected, as is usually the case. For conditions where the surface resistance of the DVL chassis and vehicle
are low, undesired interferences will occur.
Another way that you can have undesired grounding of the DVL to the frame or hull of a vehicle is
that mounting holes can lose their anodized coating by scraping of the anodized inner wall with the
mounting screws. The use of an isolation plate and plastic bushings and washers are good practices to
avoid this grounding path.
In summary, bypassing or shorting the DVL isolation / ground noise filter circuit will increase the sensi-
tivity of the DVL to vehicle noise, which will increase noise floor in the instrument and in the data, thereby
resulting in a reduced operational range and data contamination from interference. Additionally, bypass-
ing of the DVL isolation/ground filter can lead to accelerated corrosion.
Your Pathfinder DVL transducer housing is made of aluminum that is protected by sacrificial
anodes and a hard anodize coat and paint.
Do not connect other metal to the DVL.
Other
metals may cause corrosion damage.
Use M6 isolating bushings and washers when mounting the DVL to a metal structure. Keep
this in mind when fabricating a fixture, which materials to use, or deciding how to place it on
the vehicle.