The SAL T2 measures longitudinal relative speed through water as well as two-axis true speed over ground. In combination with an external Rate of Turn Gyro a full docking log functionality is achieved.
Electronics Unit – ELC
The ELC controls the measurements. It contains two independent units, one for speed through water measurement and one for speed over ground measurement. Both measuring functions are based on the acoustic correlation principle. The basic concept is the measurement of the time delay between the characteristics of reflected sonic patterns sensed by the receivers. Echo signal modulation is used for speed estimation. The speed is estimated from the fix distance between sensor elements divided by the estimated time delay from correlation, where two signals are compared by shifting one relative to the other in time, and choosing the time shift where the maximum similarity is found. The speed data calculated in the ELC is sent as serial IEC61162-1 / NMEA messages for further processing in the LPU or directly to any other user.
Transducer – TRU
The combined transducer is mounted in a sea valve arrangement suitable both for single and double bottom designs. The transducer incorporates as standard a 30 metres cable for connection to the ELC. This one combined transducer that is equipped with separate crystals for relative water speed and true speed over ground. The crystals work both as transmitters and receivers.
Log Processing Unit – LPU
The LPU is mounted on the wheelhouse area and receives the NMEA message from the ELC. The LPU has various options to perform message conversion and calculations and has also variety of inputs for receiving data from other units e.g. Rate of Turn Gyro for docking functionality. Various outputs are available for external users, such as autopilot, radar, AIS, VDR, fin stabilizers, etc. Serial Digital Indicators – SD4 The SD4 series of indicators gives a flexible solution to the presentation of longitudinal and transverse speeds and distance measurement or docking information.