Transcript ppt

TCSP – Reliability and Safety
Reliability Analysis
• Major component chosen for analysis:
• Switching Regulators (LM2679SD-5.0, LM2679SD3.3)
• Hottest running components
• Microcontroller (MCS12A64CFUE)
• Most complex component
• Quad 2 to 1 Multiplexer (SN74CBT3257)
• Failure leads to crashing
• Linear Amplifiers for thermopiles (AD8626)
• Failure would cause unstable flight, possibly crashing
FMECA
Criticality Levels
• High – Could cause personal injury
• Medium – Inhibits ability to fly autonomously
• Low – Inhibits ability to take photos or other
inconveniences
FMECA
Block A - Microcontroller
FMECA
Block A - Microcontroller
Failure
No.
Failure Mode
Possible Causes
Failure Effects
Method of
Detection
Criticality
Remarks
A1
Microcontroller
outputs no data
Out of spec supply
voltage, U1 failure,
clock failure, PLL
failure, software
bug, bypass caps
shorted
No display on
LCD, does not
work in
autonomous
mode
Observation
MediumHigh
This failure would be
elevated to high
criticality if a shorting
component caused
excess heat
dissipation
A2
Some pins are
always 0 or 1
Over-voltage on
pin could have
burned up the
driver, software
bug
Erratic system
behavior,
excessive
heating of the
microcontroller
Observation
MediumHigh
This failure would be
elevated to high
criticality if a shorting
component caused
excess heat
dissipation
FMECA
Block B - Regulators
FMECA
Block B - Regulators
Failure
No.
Failure Mode
Possible Causes
Failure Effects
Method of
Detection
Criticality
Remarks
B1
Vout,5 = 0V or
Vout,3.3 = 0V
Failure of U6 or
U7, Shorted
capacitor in Block
B, no feedback,
external short
System shows
no operation
Observation
High
If a short is causing the
lack of output,
excessive heat is being
generated which could
injury the user
B2
Vout,5 > 5V or
Vout,3.3 > 3.3V
Failure of U6 or U7
Could damage
any of the ICs
on the board,
system
probably nonfunctional
Observation
High
Possibility of injurious
heat dissipation
B3
Vout,5 or Vout,3.3
not regulated
enough
Failure of a
capacitor in Block
B that becomes
and open circuit
Erratic
microcontroller
failure, perhaps
repeated
resetting
Observation
Medium
Unlikely to cause harm,
but results in non-flyable
plane
B4
Vsense > 5V
R20 fails and
causes a short
Microcontroller
reports
unreasonable
battery voltage
Observation
Low Medium
Probably just a
nuisance which would
fry a port pin, but could
also cause the entire
microcontroller to fail.
FMECA
Block C – Radio and Servos
FMECA
Block C – Radio and Servos
Failure
No.
Failure Mode
Possible Causes
Failure Effects
Method of
Detection
Criticality
Remarks
C1
Autopilot /
Manual
multiplexer
signal incorrect
U18 failure, or
failure of any of the
resistors or
capacitors directly
before it
Plane does not
properly switch
between
manual and
autopilot
Observation
High
If this failure arose
during a flight, the
plane could crash,
possibly injuring a
person
C2
Inputs do not
propagate
through
multiplexer
U13 or R40 failure
Servo motors
do not respond
to manual input
or autopilot
Observation
High
This would cause the
plane to crash,
possibly injuring
someone
C3
Multiplexer
always output
either manual
or autopilot
values
S pin of U13
shorted to Vcc or
ground
Cannot switch
operating
modes
Observation
High
Could cause injury if
the drive motor
powered up
unexpectedly on the
ground
FMECA
Block D – Thermopile Amplifiers
FMECA
Block D – Thermopile Amplifiers
Failure
No.
Failure Mode
Possible Causes
Failure Effects
Method of
Detection
Criticality
Remarks
D1
Vref = 0V
U14 failure, could
also have its input
or output shorted
to ground
Thermopiles do
not sense sky
properly,
unstable flight
Observation
High
Could cause injury if
crash induced
D2
Vref > 2.5V
U14 failure
Thermopiles do
not sense
ground as well,
jittery flight
Observation
High Medium
Could lead to
crashing
D3
Amplifier output
is very small
Failure of U9 or
U10, Failure of any
of the resistors in
Block D such that
they become
shorts
Plane cannot
stabilize
Observation
High
Would lead to
crashing in autopilot
mode, and possibly
injure the operator
D4
Thermopile
values read in
are erratic
Connection to
thermopiles could
be faulty
Jittery flight
Observation
Medium
Could lead to
crashing
FMECA
Block E – GPS and MicroSD
FMECA
Block E – GPS and MicroSD
Failure
No.
Failure Mode
Possible Causes
Failure Effects
Method of
Detection
Criticality
Remarks
E1
Unable to
communicate
with MicroSD
card
Failure of U2, U3,
or U4; Any resistor
in the SD circuit
becomes open; SD
card corrupt;
software
System unable
to read
MicroSD card,
displays error
message
Observation
and BIST
Medium
No risk of injury, but
the plane cannot
operate
autonomously
E2
Unable to
communicate
with GPS
receiver
Failure of U15,
U16, or U17;
resistor in GPS
circuit becoming
open; faulty cable;
software bug
System unable
to get a GPS
lock, waits
indefinitely and
will not allow
autonomous
flight
Observation
and BIST
Medium
No risk of injury, but
the plane cannot
operate
autonomously
FMECA
Block F – Camera and LCD
FMECA
Block F – Camera and LCD
Failure
No.
Failure Mode
Possible Causes
Failure Effects
Method of
Detection
Criticality
Remarks
F1
LCD_TX signal
always idle
Failure of U12,
short or open
circuit of any of the
capacitors or
resistors
connected to U12
LCD is always
blank
Observation
Low
This is a nuisance,
but the plane will
operate properly
F2
Camera shutter
trigger always
open
Failure of U11,
software
malfunction
Camera never
takes photos
Observation
Low
The plane will fly, but
no photos will be
taken
Questions?