Page 102 February 2020 – TD 266 OPERATING MANUAL – ZPulse® DCS 4420/4830/4520/4930
CHAPTER 7 Electro Magnetic Compatibility
In order for a manufacturer to legally produce and sell a product, it has to apply for CE marking. This means that the
commercialized product is conform to the CE applicable standards and can freely circulate within the EFTA (European
Free Trade Association) & European Union countries. The applicable directive for the Acoustic Doppler products is the
EU EMC 89/336/EMC (all electrical and electronic appliances) which mainly focus on the electromagnetic disturbances
the sensor can generate, which should not exceed a level allowing radio and telecommunication equipment to operate
as intended, and that the sensor has an adequate level of intrinsic immunity to electromagnetic disturbance to be able to
operate as intended. This chapter describes the requirements for the Electromagnetic Compatibility (EMC) of the
sensor; EMC filter and protection solutions required for the Doppler Current Sensor.
7.1 EMC Filter and Protection
The sensor is designed to have an extremely high amplification in the Doppler frequency range around 2 MHz. This also
means that severe common mode noise on the power lines may affect the Doppler measurements if the noise
frequencies are close to 2 MHz. This can be checked from the signal strength when connected to the power of the
system.
Two different options are delivered from the factory, one for underwater/buoy systems and one for cable to land
systems.
7.1.1 Underwater/Buoy systems
A common mode line filter on the power lines has to be inserted between the sensor and the system. This filter should
be as close as possible to the cable output from the system and the ground connection on the filter has to be connected
to the common chassis ground of the system or a common ground structure. The chassis ground serves as a return
path for noise currents decoupled by the common mode filter. This is necessary since the noise currents should have a
low impedance path back to the noise source in the system.
This common mode filter may be left out if the system designer knows (from EMC emission tests) that the system does
no emit any noise on the cable to the sensor in the range around 2 MHz.
7.1.2 Cable to land systems
A Filter Box with surge protection on all lines is delivered together with the cables. This box also has the same built in
common mode filter as delivered for underwater systems. This box needs a good connection to earth to divert any large
surge currents to earth. Cable screen from sea side cable and land side cable needs a good connection to the chassis
of the box.
Surge current are generated from nearby lightning and can cause surge currents in the kilo-ampere range on a cable.
The sensor has some protection built-in but the safest is to remove as much as possible of these large surge currents
on the land side of the cable.
If using the SeaGuard DCS or SeaGuardII DCP with Real-Time cable to land, the same filter box is delivered together
with the instrument and should be installed the same way. The operating manual for SeaGuardII, TD 303, gives more
information on the available cables.
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