One of the most essential parts of a deployment, if not the most essential part, is the power supply to the instrument.
Supplied voltage can be somewhat confusing, as it may depend on point of reference and different configurations require different voltage for seemingly the same job.
We will try to break it down into simple terms.
The two most important things you need to consider are:
- The instrument needs enough voltage to operate fully and emit sound waves.
- The instrument has a maximum voltage rating.
Over-voltage will lead to broken electronic circuits, or worse.
When we are talking about voltage relative to the instrument, we are talking about the measured voltage that is supplied to the instrument. So the voltage you can measure on the wet end of the cable.
When a current flows through an electrical circuit, for instance through a cable, you will have a voltage drop.
The amount of voltage drop along a cable is a function of the current draw (I), linear resistance of the cable (Rl), and the cable length (L);
Vdrop = I*Rl*L.
The typical current draw during the measurement cycle for an AWAC is 1 amp.
The Nortek offshore cable has a linear resistance of 10.6 Ohms/km.
A cable of 1 km will accordingly have an expected voltage drop of 10.6 volts.
This has to be taken into consideration when designing a power supply.
At Nortek we provide the following solutions to combat the downsides of longer cables and to ensure high quality data during the whole deployment:
- For transmission over 50m we recommend the use of the RS422 communication protocol, as the 232 protocol is the simplest form of serial data transmission and will be too slow and might cause loss of data.
- Online cables. These cables are tougher and are designed to be deployed under water and survive the harsh conditions over a long period of time.
- DC/DC converter. This converter is placed inside the instrument, scales down the incoming voltage to 15V, and has an input range of 24-48V giving a lot more freedom and peace of mind when designing a power supply.
- Interface Box. We recommend this for all applications over 100m and for customers that are less familiar with electronics and want a simple and reliable solution. This is a product we have tried and tested over many years.
The interface box is powered by 220 AC voltage and communicates with the instrument only via RS422 and uses a specific round connector at the dry end.
Output is 48 DC voltage.
Having a stable supply is just as important as having the correct voltage. An unstable supply of power can lead to bad data and intermittent issues. In case of bad power surges without interface box or DC/DC it can be fatal to the electronics.
In the case of multiple power sources instruments will draw current from the highest Voltage source untill the sources have equal voltage, then it will draw from both sources.
Check out the data sheet for your specific instrument for exact requirements.
Voltage input range:
AWAC and 2D profiler 9-18V
Midlife (aqd/aqp/vector/vectrino) 9-15V
The above voltages are without DC/DC
-> With DC/DC 24-48V
AD2CP (Signature/DVL) 12-48V
Signature 55/100/250 15-48V
Ethernet for the AD2CP electronics has to be powered individually (This is often forgotten), the cable has a power jack breakout cable at the dry end together with the RJ45 contact.
The instrument comes with a power supply from Nortek as standard.
This powersupply has an output of 24 VDC (2.5A)
This will power the whole instrument.
Ethernet will not work if power is supplied over the serial port or from a battery. Only connect power to the port you will use.
Picture is from the Signature Operations manual.
Do not connect power before all contacts are secured and connected properly.
And as always; if you need further help please send us an email to firstname.lastname@example.org with a detailed explanation and we will help you as quickly as possible.