Signal Usage and Analysis - Complete Summary

IG AL AGE




APPLIED SCIENCES
UNI ERSIT OF
AMSTERDAM
ACA
A D A AL I




C
A
2019-2020
MMA




IG AL AGE
A D A AL I
Signal Usage and Analysis summary 1

,Week 1: Role of sensors in aviation




Sensor
A device that senses/detects specific physical properties (pressure, temperature, motion etc.) and
produces related signal.
- Pitot tube, Static ports, Angle of Attack sensor, True Air Temperature probe etc.

Pressure Sensors
Used for: altitude, velocity, fuel, tires…
It can be determined mechanically (manometer), trough change in resistance and separation of
charge.

Piezoelectric materials
A material that produces an electric charge when mechanical stress like pressure is applied to the
crystal. It has many applications like microphones, guitar elements and in aircraft.

Pressure = separation of charge

𝑞 =𝐾∙𝑥 q, charge in Coulomb
K, sensitivity C/m
x, displacement in meters

𝑞
𝐶= →𝑞 =𝐶∙𝑉
𝑉

To determine pressure: 𝑉 = 𝐾! ∙ 𝑝, with Kp sensitivity in V/Nm-2

Temperature Sensors
A sensor used to measure the temperature like the TAT and the temperature of the engine. There are
many ways to measure temperature.
- Mechanical (mercury thermometer), resistive (thermistors and RTD’s), Seebeck effect
(Thermocouples).

1. Thermocouple sensors
An electrical device consisting of two dissimilar electrical conductors forming an electrical
junction. A thermocouple produces a temperature-dependent voltage as a result of
the thermoelectric effect, and this voltage can be interpreted to measure temperature. They are
used in a wide temperature range.

Seebeck Effect
The temperature difference (∆T) in the metal wire creates a voltage difference (∆V).

∆𝑉 = −𝑆(𝑇) ∙ ∆𝑇 : with S(T) being the
Seebeck Coefficient



Signal Usage and Analysis summary 2

, $
SA and SB are constant: 𝑇" = 𝑇# + , T2 is the reference temperature.
(&! '&" )


Type K-thermocouple
Also known as a Chromel-Alumel thermocouple.

𝑇)*+),- = 𝑇-*. + 𝛼/ + 𝛼" ∙ 𝑉 + 𝛼# ∙ 𝑉 # + ___ + 𝛼+ ∙ 𝑉 + Coefficients 𝛼 are tabulated

2. Resistance Temperature Sensors (RTD)
Uses the temperature dependent resistance of a material to determine the temperature and are
more accurate and stable than thermocouples. Made from metals (when a metal heats up, the
resistance increases and is almost linear at low temperatures). Used below 600-800 degrees C.

Thermistor
Made from metaloxides and is used at low temperatures
between 0 and 100 degrees. The relationship between T
and R is non-linear, it changes negatively and sharply with
a positive change in temperature.

𝛽 ∙ 𝑇/
𝑇=
𝛽 + 𝑇/ (ln(𝑅 ) − ln(𝑅/ ))
"
In case 𝛽 is temperature dependent: 0 = 𝐴 + 𝐵 ∙ ln(𝑅) + 𝐶(ln(𝑅))1

Load Cells and Strain Gauges
Electrical resistance changes when forces or pressure is applied:
- Load Cell
- Strain gauge ∆𝑅 ∆𝐿
≅𝐾 (𝐾 ≅ 2)
Strain: ∆𝐿/𝐿 𝑅 𝐿

Week 2: Accelerometers and measurement of signals
Measurement of Acceleration

Linear Angular
Position/Angle x 𝜃
𝑑𝑥 𝑑𝜃
Velocity 𝑣= 𝜔=
𝑑𝑡 𝑑𝑡
𝑑𝑣 𝑑𝜔
Acceleration 𝑎= 𝛼=
𝑑𝑡 𝑑𝑡

Linear Acceleration
Linear acceleration can be measured in two ways: 1. Mass-Spring system, 2. Piezoelectric Crystals

1. Mass-Spring System
𝑘𝑥 = 𝑚 ∙ 𝑎

2
𝑎 = 3𝑥




Signal Usage and Analysis summary 3

, 2. Piezoelectric Crystals
4
𝑎= ∙𝑉
5!∙3


Angular Acceleration
Angular acceleration can be measured through the use of gyroscopes.

1. Classical Gyroscope
- Mechanical device
- Important property: spinning motion preserved.
- Application in aircraft: at least 3 gyroscopes needed to preserve attitude.

2. Laser Gyroscope
Fiber Optic Ring Laser
Two laser bundles, 1 clockwise and 1 - Sagnac Effect:
counterclockwise. - Frequency difference
- Sagnac Effect: phase difference
between cw and ccw laserbundles.
- Phase Difference

Wheatstone Bridge
A circuit used to measure static or dynamic electrical resistance. It has 4 resistors of which 3 are
known. The ingoing voltage Vi is known and the outgoing V0 can be determined.

∆8 5∆9
𝑉/ = 𝑉# − 𝑉" =
8 9

8# 8%
𝑉/ = 𝑉: F8 −8 G
# ;8$ & ;8%


Measurement of Signals

Determination of strain of beam bending
Full Wheatstone bridge strain gauge.

$' 8;∆8 8'∆8 ∆8
$(
= (8;∆8);(8'∆8) − (8;∆8);(8'∆8) = 8

$ ∆8 ∆9
𝐹 = 0 → $' = 8
=0→ 9
=0
(


$ ∆8 ∆9 " ∆8 " $
𝐹 = $' = 8
=0→ 9
=5∙ 8
= 5 ∙ $'
( (


Proximity Sensor
The proximity sensing system indicates whether an aircraft door is open or closed by sensing the
absence and presence of a ferrous metal target. The sensor contains only a passive sensing element
based on the variable inductance principle. This allows the sensor to be highly reliable and operate
in extreme environments.

Measurement of Distance
<) ∙<' ∙4 <) ∙<' (>'?)∙@ <' ∙?∙@ <) ∙<' >∙@ <' ∙@("'<) )?
𝐶= =
==
+ =
= =
+ =
=A <' ∙@("'<) )? =? <' ∙4
=B
= = =B
→𝐶= =




Signal Usage and Analysis summary 4