Thesis - Leigh Moody.pdf - Bad Request - Cranfield University

Chapter 3 / Sensors
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3.2 Generic Sensor Modelling
Figure 3-1 captures the generic approach applied to sensor modelling.
When a sensor is active its reference input is derived locally from reference
state vector at the sensor update rate.
A feature of this program and the AMIS is
the way in which the sensors are isolated
from the reference environment. Figure
3-2 shows the sensors receiving data
derived from the reference-state vector
rather than the reference environment
directly. In the AMIS the reference
environment is defined by internal models,
or by external data sources such as
telemetry, HardWare-In-the-Loop (HWIL),
and other simulations such as the Route
Generation Program.
Although this design approach leads to
some inefficiency, it results in a singlethread
modular structure. The interface
between reference models and state vector
can be fixed early in the design and data
pre-processors put in place. Sensor models
can then be developed in isolation without
knowledge of the referenced model beyond
the content of the reference state vector.
Returning to Figure 3-1. The sensor
dynamics and time dependent errors are
modelled at the sensor reference rate,
whether they are superimposed on the
reference input or not, so as to avoid
discontinuities in the output when toggling
measurement availability or changing the
output rate. The errors induced by
Analogue-to-Digital Conversion (ADC)
are an exception. These are applied at the
output rate so as to respect the Zero-Order-
Hold (ZOH) process on which they are
based.
The output interface model described in §0 can be characterised to represent
system errors induced by various forms of digital interface between the
sensors and state observers. The measurement errors are determined in each
sensor module by comparing the reference input with the output from the
digital interface.
3.2-6
NO
YES
SENSOR
CONTROLLER
SENSOR
AVAILABLE
YES
SENSOR INPUT DERIVED
FROM REFERENCE
TARGET,
MISSILE & SATELLITE
DYNAMICS
HIGH FREQUENCY
ERROR DYNAMICS
PERFECT
SENSOR
NO
SUPERIMPOSE
MEASUREMENT
ERRORS AT
TRANSMISSION RATE
SENSOR TO
FUSION FILTER
INTERFACE
NEXT SENSOR
Figure 3-1
Generic Sensor Error Model