FAQ – NMEA0183 XDR Sentence (Transducers)

What is the XDR sentence?

The XDR (Transducer Measurement) sentence is a generic NMEA0183 sentence used to transmit measurements from various types of sensors (transducers). It allows multiple measurements to be grouped into a single sentence.

What is the general format of the XDR sentence?

$xxXDR,a,x.x,u,n,a,x.x,u,n,...*hh

Where for each transducer group:

• a: Transducer type (one letter)
• x.x: Measured value
• u: Unit of measurement (one letter)
• n: Transducer name (character string)

The checksum (*hh) is mandatory.

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Which transducers are supported by NavimetriX?

1. Heel/Pitch

Field	Value
Type	A (Angular)
Unit	D (Degrees)
Name	PTCH

Example:

$IIXDR,A,5.2,D,PTCH*XX

This indicates a pitch angle of 5.2°.

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2. Roll

Field	Value
Type	A (Angular)
Unit	D (Degrees)
Name	ROLL

Example:

$IIXDR,A,-1.1,D,ROLL*XX

This indicates a roll angle of -1.1°.

Combined example (Roll + Pitch):

$IIXDR,A,-1.1,D,ROLL,A,5.0,D,PTCH*74

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3. Water Temperature

Field	Value
Type	C (Temperature)
Unit	C (Celsius), F (Fahrenheit), or K (Kelvin)
Name	Must contain water (e.g., WATERTEMP, WaterTemp, water)

Examples:

$IIXDR,C,18.5,C,WATERTEMP*XX
  $IIXDR,C,65.3,F,WaterTemp*XX
  $IIXDR,C,291.65,K,water*XX

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4. Air Temperature

Field	Value
Type	C (Temperature)
Unit	C (Celsius), F (Fahrenheit), or K (Kelvin)
Name	Must contain air (e.g., AIRTEMP, AirTemp, air)

Examples:

$IIXDR,C,22.0,C,AIRTEMP*XX
  $IIXDR,C,71.6,F,AirTemp*XX

Combined example (Water + Air):

$IIXDR,C,18.1,C,WATERTEMP,C,22.0,C,AIRTEMP*49

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5. Barometric Pressure

Field	Value
Type	P (Pressure)
Unit	B (Bars)
Name	Must contain baro (e.g., BARO, Barometer, baro)

Note: The value must be expressed in Bars (1 bar = 1000 hPa). NavimetriX automatically converts it to hPa.

Example:

$IIXDR,P,1.013,B,BARO*XX

This indicates a pressure of 1013 hPa.

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How do I combine multiple measurements in a single sentence?

Transducer groups can be chained in the same XDR sentence (up to 10 transducers per sentence):

$IIXDR,A,-2.5,D,ROLL,A,3.1,D,PTCH,C,18.5,C,WATERTEMP,C,21.0,C,AIRTEMP,P,1.015,B,BARO*XX

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Is the transducer name case-sensitive?

No. Transducer name recognition is not case-sensitive for temperatures and pressure:

• WATERTEMP, WaterTemp, watertemp → all recognized
• AIRTEMP, AirTemp, airtemp → all recognized
• BARO, Barometer, baro → all recognized

Exception: For roll and pitch, the names must be exactly ROLL and PTCH.

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Which talker prefix should I use?

NavimetriX accepts all standard talker prefixes (II, GP, HC, etc.). The examples above use $II (Integrated Instrumentation), but $GP, $HC, or others are equally valid.

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Summary of accepted formats

Measurement	Type	Unit	Transducer Name
Pitch	A	D	PTCH
Roll	A	D	ROLL
Water temperature	C	C, F, or K	contains water
Air temperature	C	C, F, or K	contains air
Barometric pressure	P	B	contains baro