Data Integration — NMEA Output

Some sensor data collected by Medusa gamma-ray spectrometers can be broadcast over the RS-232 serial port using a NMEA-like protocol, similar to NMEA-0183. The typical baud rate is 115,200 baud.

This output format is useful for integrating with external hardware that expects NMEA-style serial data, such as GIS loggers or survey equipment. For more detailed data, use the JSON output format instead — see JSON Format.

To enable NMEA output, set the RS-232 output mode to Medusa NMEA strings under Settings → Communication → RS232.

Info

Note: The NMEA output is a subset of the data available in JSON format.

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Sentence Reference

Raw Spectrum — $MSSPE

The raw spectrum sentence contains the integer counts per channel for the current measurement.

Info

Note: This sentence may be longer than the 82-byte limit specified by NMEA-0183. To reduce the length, use the Channels to sum setting under Settings → Communication → RS232 — for example, combining 8 channels of a 512-channel spectrum produces 64 output channels. This only affects the NMEA output; the full-resolution spectrum is always stored onboard.

Example:

$MSSPE,1634718239893,1.001,0.982,64,0,113,574,450,369,259,186,...

#	Example	Format	Description
0	$MSSPE	%s	Sentence label
1	1634718239893	%d	Unix timestamp in milliseconds since Jan 1st 1970
2	1.001	%.3f	Real time in seconds
3	0.982	%.3f	Live time in seconds
4	64	%d	Number of channels in this output
5	0	%d	Counts in the first channel
6 .. 4+resolution	113 .. 1	%d	Counts in the remaining channels

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Activity Concentrations — $MSACT

Info

Note: Energy stabilization is required before activity concentrations can be calculated. Depending on the crystal size, this may take several minutes after startup.

Example:

$MSACT,1634738741388,1.002,0.983,0.682,1365.484,136.370,136.429,14.500,86.641,19.458*58

#	Example	Format	Description
0	$MSACT	%s	Sentence label
1	1634738741388	%d	Unix timestamp in milliseconds since Jan 1st 1970
2	1.002	%.3f	Real time in seconds
3	0.983	%.3f	Live time in seconds
4	0.682	%.3f	Stabilization parameter
5	1365.484	%.3f	Activity concentration for ⁴⁰K in Bq/kg
6	136.370	%.3f	Uncertainty in ⁴⁰K concentration
7	136.429	%.3f	Activity concentration for ²³⁸U in Bq/kg
8	14.500	%.3f	Uncertainty in ²³⁸U concentration
9	86.641	%.3f	Activity concentration for ²³²Th in Bq/kg
10	19.458	%.3f	Uncertainty in ²³²Th concentration

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PTH Sensor — $MSPTH

Example:

$MSPTH,1634738741389,1007.000,30.000,112.000*47

#	Example	Format	Description
0	$MSPTH	%s	Sentence label
1	1634738741389	%d	Unix timestamp in milliseconds since Jan 1st 1970
2	1007.000	%.3f	Pressure in hPa
3	30.000	%.3f	Temperature in °C
4	112.000	%.3f	Humidity in %

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GPS — $MSGPS

Example:

$MSGPS,1634738741389,53.211048,6.612187,2.857,1634636299006*6E

#	Example	Format	Description
0	$MSGPS	%s	Sentence label
1	1634738741389	%d	Unix timestamp in milliseconds since Jan 1st 1970
2	53.211048	%.3f	Latitude in degrees
3	6.612187	%.3f	Longitude in degrees
4	2.857	%.3f	Altitude in metres
5	1634636299006	%d	GPS timestamp

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Stabilized Counts — $MSSC

The stabilized counts sentence reports the number of counts in fixed energy windows of the stabilized spectrum. Because it uses the stabilized (energy-corrected) spectrum, the count values are temperature-independent. To convert to count rate, divide by the live time.

Example:

$MSSC,1634738741389,1.000,967,816,672,524,318*0B

#	Example	Format	Description
0	$MSSC	%s	Sentence label
1	1634738741389	%d	Unix timestamp in milliseconds since Jan 1st 1970
2	1.000	%.3f	Live time in seconds
3	967	%d	Total counts in the spectrum
4	816	%d	Counts in the region ≥ 100 keV
5	672	%d	Counts in the region ≥ 200 keV
6	524	%d	Counts in the region ≥ 300 keV
7	318	%d	Counts in the region ≥ 400 keV