aircraft instrument

1. NITTE MEENAKSHI
INSTITUTE OF TECHNOLOGY
An Autonomous Institution affiliated to Visvesvaraya Technological University, Belagavi with A+ Grade by NAAC
UGC | Approved by UGC/AICTE/ Govt. of Karnataka | Bengaluru
DEPARTMENT OF AERONAUTICAL ENGINEERING
Accredited by NBA (Tier- I)
FLUID MECHANICS - 21AE34
Presentation on
“SPEEDOMETERS”
Odd Semester
2022-23
Presented By:
PRAJWAL CHAR Y P | 1NT21AE056
RUTHIKA U ARASHINKAR | 1NT21AE066
TEJAS K | 1NT21AE083
ULLAS GOWDA A | 1NT21AE087
Guided By:
MRS. SREELAKSHMI
Assistant Professor- Dept. of AE, NMIT

2. I N T R O
D E S I G N D E V E L O P
C H A L L E N

3. I N T R O D U C T I O N
• Speedometer is a type of gauge that shows the speed a vehicle is moving.
• It usually shows the speed in miles per hour (mph) for countries that use the statute mile for
distances or Kilometres per hour (kph) for countries that use the metric system.
• Originally, a speedometer was an option that car owners could buy to put on their car. Beginning
about 1910 it was built into all cars.
B A C K

4. D E S I G N D E V E L
1. Mechanical speedometer uses a rotating cable attached to transmission gears.
2. Cable is directly attached to a permanent magnet in the speedometer assembly.
3. Magnet rotates at a rate proportional to the speed of the vehicle.
4. Magnet manipulates an aluminum ring, pulling it in the same direction as the revolving
magnetic field.
5. Aluminum ring's movement is counteracted by a spiral spring.
6. Attached to the aluminum ring is a pointer which indicates the speed of the vehicle.
7. As the vehicle slows, the magnetic force on the aluminum ring decreases and spring pulls the
pointer back to zero.
B A C K

5. D E S I G N D E V E L
8. Electronic speedometers are present in late-model cars.
9. Pulse generator installed in the transmission measures the vehicle's speed.
10. Pulse generator communicates the speed via electric or magnetic pulse signals.
11. Pulse signals are translated into an electronic read-out or used to manipulate a traditional
magnetic gauge assembly.
B A C K

6. C H A L L E N G E S
Mechanical wear and tear: Mechanical speedometers, which use gears and cables to measure the
speed of the vehicle, can wear out over time, leading to inaccuracies and even complete failure of the
speedometer.
Electronic interference: Electronic speedometers, which use sensors and digital displays, can be
affected by electrical interference from other devices in the vehicle. This can cause false readings or
even temporary loss of the speedometer display.
Weather conditions: Speedometers can be affected by extreme weather conditions, such as extreme
heat, cold, or moisture. This can cause malfunctions or false readings.
Tire pressure: The tire pressure of a vehicle can have an impact on the accuracy of a speedometer. A
low tire pressure can cause a false reading, leading to incorrect speed measurements.
Installation errors: Speedometer errors can also occur if the speedometer is not installed properly, or if
there are problems with the wiring or connections.
B A C K

7. S I G N A L P R O C E S S
C A L I B R A T
D I S P L A Y

8. S I G N A L P R O C E
Speedometers typically use a signal processing technique called pulse counting to
measure the speed of a vehicle. Here's how it works:
1.The speedometer mechanism consists of a sensor that is usually located at the wheel of
the vehicle. This sensor is usually a magnetic or a Hall-effect sensor that generates
electrical pulses in response to the rotation of the wheel.
2.These pulses are fed into an electronic circuit that counts the number of pulses
generated by the sensor in a given time period.
3.The circuit converts the pulse count into a frequency, which is proportional to the speed
of the wheel. For example, if the wheel is rotating at a speed of 60 mph, the sensor might
generate 60 pulses per second.
B A C K

9. S I G N A L P R O C E
B A C K
4. The frequency signal is then processed by an amplifier and a filter to remove any noise
or interference in the signal.
5. The filtered signal is then passed to an analog-to-digital converter (ADC) that converts
the analog signal into a digital representation that can be processed by a microcontroller.
6.The microcontroller then calculates the speed of the vehicle based on the pulse count
and the time period over which the pulses were counted. The calculated speed is then
displayed on the speedometer.
7.In modern vehicles, the signal processing circuitry and the speedometer display are
usually integrated into a single module, which is connected to the wheel sensor via a
cable or a wireless link.

10. D I S P L A Y
Analog Speedometer: An analog speedometer uses a rotating needle on a dial to show
the vehicle's speed. The needle is connected to a gear mechanism driven by the
speedometer's circuitry that moves the needle as the speed changes.
Digital Speedometer: A digital speedometer uses a digital display (LED/LCD) to show the
vehicle's speed, which is driven by the speedometer's circuitry. The speed can be
displayed as a number (e.g. 60 mph) or a graphical representation (bar graph). Some
digital speedometers also show additional information such as the odometer reading, trip
meter, or fuel level.
B A C K

11. C A L I B R A T I O N
•Calibrating a speedometer involves adjusting its reading to match the actual speed of the
vehicle. Here's a detailed description of the process.
1. Equipment: To calibrate a speedometer, you need a GPS/radar gun to measure the
vehicle's speed, tools for removing the speedometer, and an electronic calibrator or
programming tool to adjust the speedometer's output signal.
2. Testing the accuracy: The first step in calibrating a speedometer is to check its accuracy
by comparing the speedometer reading with the speed measured using a GPS/radar gun.
If the speedometer is inaccurate, adjustments may be needed.
3. Removing the speedometer: Some vehicles have a removable speedometer that can be
taken out of the instrument panel for calibration by removing screws or clips. Other
vehicles have an integrated speedometer that cannot be easily removed.
B A C K

12. C A L I B R A T I O N
4. Adjusting the speedometer: A removable speedometer can be adjusted by turning a
screw or adjusting a potentiometer. The amount of adjustment needed depends on the
difference between the speedometer reading and the actual vehicle speed measured by a
GPS/radar gun.
5. Reprogramming the speedometer: If a speedometer cannot be easily adjusted or if the
vehicle has an electronic speedometer, it may need to be reprogrammed using a calibrator
or programming tool. This involves connecting the tool to the vehicle's onboard diagnostic
port and adjusting the speedometer output signal to match the actual vehicle speed.
6. Reinstalling the speedometer: Once a speedometer has been calibrated, it needs to be
reinstalled in the vehicle and tested for accuracy. Further adjustments may be made if
needed until the speedometer reading is accurate.
B A C K

13. T Y P E S
E L E C T R O N
S P E E D O M
M E C H A N I C A L
S P E E D O M E T E R
F U T U R E

14. T Y P E S
• Of all the instruments you can find on a modern dashboard, only one is a legal requirement – the
Speedometer & its built in- milometer (also known as Odometer).
• In common with car speedometer, there is also a speedometer in aircrafts known as airspeed
indicator, this works by measuring the differential pressure between static pressure and total pressure
from Pitot - static tube.
• In car technology or in aerospace applications, the trend is now towards using electronic
speedometer. But most of the vehicle have a mechanical with a needle and calibrated dial to snow the
speed.
• Unfortunately, the design of this speedometer has hardly changed in the last 50 years. •
B A C K

15. M E C H A N I C A L S P
E E D O M E T E R
• This type of speedometer measure the speed of a car by being linked
mechanically with the gearbox output shaft.
• In aircraft, airspeed indicator (ASI) is the only flight instrument that uses
both the static system and the pitot system.
• Static pressure enters the ASI case, while total flexes the diaphragm, which
is connected to the ASI pointer via mechanical linkage.
• The pressures are equal when the aircraft is stationary on the ground &
hence shows the reading as zero.
• When the aircraft in moving, air entering the Pitot tube is at a greater
pressure than the static line which flexes the diaphragm, moving the pointer.
B A C K

16. E L E C T R O N I C S P
E E D O M E T E R
• In common with the trend electronic dashboard instruments, electronic
speedometers are now becoming much more popular, even though
mechanical ones are generally reliable.
• The most common type has a magnet attached to the gearbox output
shaft & an electronic unit positioned close by to act as a pick up.
• Every time the rotating magnet passes the pickup, the unit sends a pulse
of electric current down a wire to the speedometer.
• In modern aircraft, airspeed is usually indicated on a speed tape which
forms part of the Electronic Flight Instrument System Display.
B A C K

17. F U T U R E
• Design firms are currently experimenting with improvements in speedometers
readout an effort to eliminate the moment of distraction needed for the pilot/
driver to look down and gauge his or her speed.
• Digital readouts projected onto the windshield is the next development step.
• Heads-up-display is the current trend, where the pilot / driver doesn't need to
look down rather see the windshield where the required readings are shown,
adjusting them as per our requirement is the next step in development.
• In addition, speedometer projection system will eventually be integrated with
navigation tools, allowing directional information to appeal with gauge readouts.
B A C K