Install the TIU

Transducer Interface Unit

The Transducer Electronics Modules (TEMs) are supplied installed in a box called the Transducer Interface Unit (TIU). This has a separate DC or mains supply. The TEM USB connectors are brought out the rear of the unit using cables inside the housing.

A number of different configurations is available for TIUs, depending on how they are to be used.

Installation

Place the TIU on a firm surface.

USB Connection

If the USB connection is made direct from the TIU to the PC, the USB cable needs to be kept short in order to provide reliable communications. 

If the TIU must be mounted at a distance from the PC, consider the use of a COTS USB extender system, such as a USB-to-Ethernet converter.

Transducer Connections

The transducer connections are made with rugged, polyurethane, marine-grade cable. These are rather stiff, and care must be taken in planning the route that these cables take to reach the TEMs. Otherwise, the cables may tend to lie in a location that obstructs the operator's access to the PC or other systems. The connector is about 120 mm long. Allow a bend radius of about 50 mm.

Connect the transducer connectors to the connections on the front of the TEMs. The selection of the TEMs in terms of port or starboard transducer is made in the Swath software Sonar set-up dialog. Conventionally, the top TEM is connected to the port transducer. It is advisable to mark the transducer connectors with red and green tape to identify which one is which.

Power Connections

Connect the power to the power inlet port on the TEM housing. The TIU takes DC power, 9 to 32 V, and it is supplied with a mains-to-DC converter unit.

DC power can be provided from a ship's power system or from a separate battery. The TIU works with one or two 12 V lead-acid batteries.

If working with mains power, connect the mains-to-DC converter to the mains supply and the output lead to the TIU.

Ground Connection

The TIU has a connector for signal ground; this can be used to reduce the effect of electrical "noise" on the sonar signals.

Grounding and Earthing

Proper earthing and grounding of the system is very important for two essential reasons:

It also reduces the risk of accidentally connecting a power source across a ground connection.

Mains safety earth

For personnel safety, the mains power supply earth (if used: some systems are supplied with DC power) must be connected right through the system. Ensure that the earth connection to all the units that take mains power is effective. If in doubt, consult the person responsible for the vessel’s electrical supply.

Noise reduction

Ships can be very electrically noisy. This noise can be picked up by the Bathyswath and degrade the depth measurements. Correct earthing can significantly reduce this noise. The earthing arrangement that gives the best results on any vessel can only be found by experiment. This is because each vessel has different noise characteristics and earthing arrangements.

This part of setting up a Bathyswath system is very important, and should not be skipped or rushed. High external noise is a common cause of poor survey results.

The TEM Signal Ground is brought out to a connector on the back of each TEM. The ground is also bonded to the metalwork of the housings. One significant source of noise is the difference in potential between the sea and the electronics. This potential can be induced by electromagnetic noise. Connecting the Signal Ground to a good sea-earth can reduce this effect. This can be done by:

  • On pole-mounted systems, run a wire between the TEM Signal Ground connector and the metalwork of the pole. Use a wire with a good cross-section, and ensure that the connection to the pole is robust. Keep seawater out of the copper cores of the wire, as corroded wires make very poor contact. Inspect the cable at regular intervals when in use, and replace it if the cores become very dull in colour or show other signs of corrosion.
  • On hull-mounted systems, connect the Signal Ground to the vessel’s sea-earth.

Establish a star network (where all grounds connect to a single point) or a distributed star (a set of stars connected together), and avoid earth loops. This is not always simple, as there may be earth connections between the components of the system that are not obvious. This is illustrated in the figure.earthing diagram

Make a drawing of the cables and connections of the system as it is installed on the boat, including auxiliary systems and power supplies. Not only will this help in detecting problems, but also it will be useful for re-installing the system if it needs to be removed for storage or use on another vessel.

It is not necessary to connect the earths of the two TEMs together if they are installed in the same housing, as their grounds are also connected together via the chassis.

Do not coil up un-used parts of the earth wire: cut it to length. Coils can cause the earth wire to pick up external electrical interference. For the same reason, do not run the earth wire close to mains wires or the active signal wires from other electrical systems.

If noise is still a problem, try connecting Signal Ground to mains earth. However, before attempting this, ensure that mains earth is effective and safe (see above).

To evaluate the amount of noise pick-up, start the Bathyswath system running as in normal survey mode, but with the transmit signal turned off. Make sure that the transducers are plugged in to the TEMs, and are in the water, and that all auxiliary systems (attitude, position, etc.) are operating and plugged in to the Bathyswath system. However, if one or more of these systems are not available at the time of the test, use the ‘Test Mode’ option under ‘Configuration’ in the Swath program. Disable all of the angle and phase filters. Look at the ‘Cross Profile’ window. If noise is low, then this display will show a random ‘cloud’ of noise points. If there is significant noise pick-up, then the display will show a straight line issuing from each transducer. Depth measurement is severely compromised when these straight lines continue to exist when the transmit signal is enabled and the system is measuring a seabed.

Open an ‘Amplitude’ window. The vertical scale is signal amplitude, and the horizontal scale is range. The TEM output is logarithmic, so one division at the bottom of the window represents much less of a step in signal than one division at the top.

With the transmit signal disabled, the noise level should be below the second division of the screen, less than 10,000 for the arbitrary 16-bit numerical scale, and as low as possible. If it is above this, effort should be taken to reduce it, and if it is approaching the middle of the scale (30,000), system performance will be very severely degraded. It is not advisable to proceed to survey with this level of noise still present. The target level can be established by replacing the transducer plug with one that shorts out the signal inputs. Note that the signal level rises considerably if nothing is connected to the TEM’s transducer connector at all; this is normal, and so noise reduction investigations must be done with the transducers plugged in and in the water.

Examine the amplitude display for repeating ‘waves’ or ‘spikes’ of signal noise. These may be caused by electrical or acoustic interference from other systems, or they may come from the power supply used. These should be identified and eliminated. Try turning off or disconnecting other systems on the boat, to see if the noise signal changes.

If noise pick-up persists:

  • Try other combinations of earthing. Some earth connections will make things worse, by introducing ground loops where two items are already grounded together by another route.
  • Ensure that the transducer cables do not run around or next to any other cables, especially mains, Ethernet, and auxiliary sub-systems (position, attitude, etc.).
  • Look for external sources of interference. Radio and radar transmissions can be particularly troublesome, as they operate at similar frequencies to the Bathyswath sonar.
  • Try changing the physical location of the components of the system.
  • Disconnect the auxiliary inputs to the system to see if the noise level falls. It will be necessary to set the corresponding ‘attitude derivation’ or ‘position derivation’ to ‘Use Fixed Value’ in the dialogs under the Configuration menu in the Swath program, in order to maintain a visible output in the Amplitude window. This is achieved in one step using the ‘Test Mode’ command under ‘Configuration’. (Tip: save a session file with the ‘Use Fixed Value’ settings; call it ‘TEM_test.sxs’ or similar). Once a particularly noisy auxiliary item has been identified, it can be targeted for careful earthing. One cause of noise is a sensor that is poorly earthed internally or in its own sub-system. If this cannot be rectified, consider the use of an opto-isolator in the serial line from the auxiliary system. These can be obtained from must suppliers of industrial computing equipment.
  • Ensure that connections to metalwork are electrically and mechanically robust. For example, aluminium forms a layer of oxide that is an excellent electrical insulator. It is usually necessary to use a self-tapping screw or similar to obtain a good earth. If the ship has a metal structure, then consider setting up an earth bolt, firmly electrically and mechanically bonded to the metal. This can form the ‘star point’ of the earthing system.
  • If some instruments are powered from a separate 12V or 24V DC system, try running an earth to the negative rail.
  • Try changing the power supply: for example, some mains inverters give out a very ‘spiky’ waveform, which can appear very strongly in the sonar signal. If the PSU cannot be changed, try using a line voltage conditioner unit.