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4.2 Integration with systems
Conceptually there are two modes of operation, Interrogated and autonomous.
Integration mode requires a master to request the ISA500 to make a measurement
and report this back.
The ISA500 can be interrogated by the user defined interrogation string, or by the
TTL trigger input. Upon interrogation the ISA500 will make a measurement and
report back the result over the configured output, whether this be a serial string or
analogue voltage / current loop output.
Autonomous mode will make a measurement and output the result over serial or
analogue at a specified time interval.
The ISA500 can be configured to operate in one or both of these modes at the
same time.
ISA500's with the HMRU option make use of the same interrogated and
autonomous mechanises to output heading pitch and roll data over the serial
interface.
4.3 Understanding advanced features
Some serial output strings for altitude measurement report back the energy level of
the echo and a correlation factor.
The energy level ranges from 0 to 1 where 1 represents full saturation of the ISA500
receiver. An energy level of 0.707 (square root of 2) is the theoretical perfect level
as it represents the energy of a pure sine wave with an amplitude utilising the
maximum dynamic range of the ISA500.
The correlation factor ranges from 0 to 1 which represents a quality factor of the
returned echo. A value of 1 would represent a return echo of perfection with
negligible noise and distortion.
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