INTRODUCTION NM-251B is a Speed Log ppm output to NMEA-0183 converter that enables connection of every speed log that uses the “closing” contact interface with digital systems and instruments that comply with the NMEA-0183 standards. The NM-251B is capable of converting the speed log contact closures to a standard NMEA $VWVHW string with checksum error control and output at TTL, RS-422 and RS-232 signal levels.
NM-251B has one input port for connecting to the speed log that can be configured to interface both “closing” contact and optocoupler output type Speed Logs. Further details on how to configure the NM-251B are shown on table Configuration shall be done prior to connecting to the Speed Log or else damage may occur to the instrument.
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