900240 Rev. B
3/01
page 16
4.3
Measurement Parameters
Parameters in this section affect the measurement functions of the compass board. “Mag sample rate” is a key setting
that affects both continuous and strobe mode measurements. In continuous mode, either 1, 2, 4, or 8 magnetometer
measurements are averaged per tilt measurement depending on the “Mag sample rate” setting.
In strobe mode, measurements are suspended until an NMEA query command is received. When this occurs, “Mag
sample rate” determines how many magnetometer readings are collected per tilt measurement as above, and “Strobe
mode count” determines the number of readings to be averaged before returning the resulting requested sentence. A
“Strobe mode count” of zero will result in 256 samples being averaged, which will require 18.6 seconds between the end
of the query request and the start of the output sentence.
The “Mag units factor” setting is used to convert normalized magnetometer readings to milliGauss for output in XDR
and CCD messages. The intent is to provide outputs with approximate field strength units so that the magnitude of the
numbers make sense.
Parameter Name
Description
Command Syntax
Mag sample rate
Query
Response
Magnetometer sampling rate
13.75 , 27.5, 55, 110 Hz
This parameter will determine the number
of magnetometer readings averaged per
heading output. Set to 13.75 Hz for low
power consumption
m=1 for 13.75, m=2 for 27.5, m=4 for 55,
m=8 for 110 Hz
#BA6=1*39<CR><lf> for 13.75 Hz
#BA6=2*3A<CR><lf> for 27.5 Hz
#BA6=4*3C<CR><lf> for 55 Hz
#BA6=8*30<CR><lf> for 110 Hz
#BA6?*0A<CR><lf>
#m*hh<CR><lf>
Strobe Mode Count
Query
Response
Number of heading measurements to be
average before issuing an output in Strobe
Mode operation (0 to 255)
N= Number of reading to average (0 to 255)
#BA7=nn*hh<CR><lf>
#BA7?*0B<CR><lf>
#N*hh<CR><lf
>
Set / Reset
Query
Response
Controls the magnetometer Set/Reset
operation.
Set / Reset ON (Set/Reset at 13.75 Hz)
Set/Reset OFF
ON
OFF
#FA0.6=1*23<CR><lf>
#FA0.6=0*22<CR><lf>
#FA0.6?*10<CR><lf>
#1*31<CR><lf>
#0*30<CR><lf>
Set / Reset interval
(ddd)
Query
Response
Time interval between magnetometer
Set/Reset calibrations in seconds:
0 = disable, 255 = 4 min, 15 sec (=max)
Use long time interval to reduce power
consumption. Use continuous or short time
intervals for high repeatability.
(This parameter applies only when Set
Reset is turned OFF)
T= Time between Set Reset in Seconds
#BA9=ddd*hh<CR><lf>
ddd= Set/Reset interval in seconds
#BA9?*05<CR><lf>
#T*hh<CR><lf>
Mag units factor
Conversion factor for normalized Mag
readings to mGauss.
