Complete summary of the course Signal Usage and Analysis. Includes all information from the lectures including explanations from the book "Electrical Engineering".
It also includes all formulas that have to be used to solve the problems.
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.
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.
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.
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