Arab Academy for Science and Technology and Maritime Transport
College of Engineering and Technology
Mechatronics Engineering Department
EE218
Digital Tachometer
Submitted by: Mohamed Amir EL Refaie
‫محمد امير الرفاعي‬
ID: 18104034
Supervised by
Dr. Salwa
3/6/2020
Electrical and Control Engineering Department
Arab Academy for Science and Technology and Maritime Transport
Cairo 2020
CONTENTS
CONTENTS.................................................................................................................................................. I
LIST OF FIGURES .................................................................................................................................... II
LIST OF TABLES ..................................................................................................................................... III
1.1 Construction ...................................................................................................................................... 1
2.1 Theory of Operation ...................................................................................................................... 1,2
3.1 Measurement Range (Span) ............................................................................................................. 3
4.1 Applications ....................................................................................................................................... 4
I.
LED Tachometer ......................................................................................................................... 4
II. Non-Contact Tachometer ........................................................................................................ 4,5
III. Contact Tachometer .................................................................................................................... 5
5.1 Advantages and Disadvantages........................................................................................................ 6
6.1 Data Sheet Example ....................................................................................................................... 7,8
APPENDIX 1 ............................................................................................................................................... 8
APPENDIX 2 ............................................................................................................................................... 9
REFERNCES ............................................................................................................................................ 10
I
LIST OF FIGURES
Figure 1 Digital Tachometer Construction ................................................................................................... 1
Figure 2 Principle of operation of normal tachometer .................................................................................. 2
Figure 3 Principle of operation of digital tachometer………………………………………………………………………………3
Figure 4 LED Tachometer………………………………………………………………………………………………………………………..4
Figure 5 Non contact Tachometer………………………………………………………………………………………………………..5
Figure 6 Contact Tachometer…………………………………………………………………………………………………………………..5
II
LIST OF TABLES
Table 1 Ranges of different applications ...................................................................................................... 3
Table 2 Technical specification ................................................................................................................. 6,7
III
1.1 Construction
This Digital Tachometer consists of optical sensor, signal conditioning, microcontroller,
display, memory and external port (for the controller) as shown in Figure (1).
The optical sensor transmits to the signal conditioning, the signal conditioning transmits to
the microcontroller, the microcontroller transmits to display, memory and it transmits and takes
back from the external port.
Figure 1 Digital Tachometer Construction
2.1 Theory of Operation
Pulses are taken care of by the tachometer at the frequency that should be measured. A
scale factor is applied and connected to produce readings of a few types like flow rates, linear
speed and so on.
The voltage is created by means of a changeless magnet on the pole. There is a toothed
wheel made of iron, which gets magnetized as the magnet passes the teeth. At that point, as the
1
magnet rotates away from the teeth, the wheel becomes de-magnetized. As these progressions
happen, an electric field conforms to the permanent magnet. This field influences the electric
charges in a wire coil that surrounds the magnet, generating both power and electricity. As the
tooth moves toward the magnet, the current moves in one direction. As the tooth moves from the
magnet, the current changes the direction oppositely. The tachometer reads the frequency with
which the coil's current changes direction. Furthermore, if the engine turns all the more rapidly,
the change in the magnetic field turns out to be increasingly radical, producing higher voltage.
Motors with ignition systems, not always, utilize a little generator joined to the engine drive
shaft. In such case, the tachometer becomes a voltage meter, meaning that it checks the pulsations
of voltage within the ignition system. The output voltage is proportional to the shaft's speed so
measuring voltage is changed over into an precise estimation in RPMs. Figure (2) shows the
principle of operation of a normal tachometer. A tachometer that does not require any physical
contact with the turning shaft is called a non-contact digital tachometer. In this sort, a laser or an
optical disk is connected to the rotating shaft, and it can be studied by an IR beam or laser, which
is coordinated by the tachometer. Figure (3) shows the principle of operation of a digital
tachometer.
Figure 2 Principle of operation
2
Figure 3 Principle of operation
3.1 Measurement Range (Span)
The measurement range for the digital tachometer differs from an application to another.
Digital Techometer has lots of applications but here are 3 measurement ranges for three different
applications as shown in Table (1).
Table 1 Ranges of different applications
App name
Display
Range
Accuracy
Resolution
Autoranging:
Laser (LED
5 digits LCD
5 to 99,999
±0.01% or ±1
0.001 to 1.0
light source)
display
RPM
Digit
RPM Fixed: ± 1
Digit RPM
0.1 RPM (2 to
Non-Contact
5 digits LCD
1 to 99,999
±(0.05%+1
999.9 RPM) 1
RPM
display
REV
digits)
RPM. (over
1000 RPM)
Contact RPM
5 digits LCD
10.0 to
display
19999RPM
3
0.001/0.01/0.1/1
± (0.1% of
rdg.+2 digit)
4.1 Applications
I. Laser (LED light source)
It is a battery-powered portable non-contact optical tachometer. It works with up to 36
inches from a reflective target. It uses an LED light source to transmit. Its design makes it safer,
as the direct line of sight views both the rotating object and the screen at the same time while
providing a non-slip rubber surface for a single hand operation as well as shown in Figure (4).
Figure 4 LED Tachometer
II. Non-Contact tachometer
The digital tachometer gives fast and accurate non-contact RPM measurements of rotating
objects. The tachometer uses the CPU technique and the photoelectrical technique as shown in
Figure (5).
4
Figure 5 Non contact tachometer
III. Contact tachometer
It is widely used to measure rotational speed of engines, conveyer belts, and other rotating
systems/objects as shown in Figure (6).
Figure 6 contact tachometer
5
5.1 Advantages and Disadvantages
Digital Tachometer has many advantages as:
1. It has linear relationships between output and rotational speed.
2. It is cheap.
3. It doesn’t require maintenance every now and then (Not often at all).
4. It gives free output.
Although digital tachometer has those advantages, it also suffers from some disadvantages
like:
1. Hard to calibrate with.
2. At high speed, it has no linear relationship between speed and output.
6.1 Data Sheet Example
Table 2 Technical Specification
Display
5 digits LCD display
Accuracy
Accuracy : ±(0.05%+1 digits)
RPM Test Range
2 to 99,999 RPM
Count Range
1 to 99,999 REV
Resolution
0.1 RPM (2 to 999.9 RPM) 1 RPM. (over 1000
RPM)
Sampling Time
0.5 sec. (over 120 RPM)
Detecting Distance
50mm to 500mm
6
Time Base
Quartz Crystal
Power Consumption
Approx 45mA
Power Supply
9V Battery or 6V Exterior DC
Operation Temp
0°C to 50°C
Weight
151g
Dimension
160mm × 58mm × 39mm
7
APENDIX 1
8
APPENDIX 2
9
REFERNCES
https://www.youtube.com/watch?v=3l7EJMU_OGo
https://www.slideshare.net/RohitChoudhury1/tachometer-66815270
https://www.elprocus.com/introduction-to-digital-tachometer-circuit-working-with-8051/
https://www.behance.net/gallery/24045013/Principle-Types-and-Application-of-Tachometer
https://www.quora.com/What-is-the-working-principle-of-tachometers
A. & M. College of Texas, 1952
https://www.globaltestsupply.com/pdfs/cache/www.globaltestsupply.com/monarch/tachomet
er/6125_011/datasheet/monarch_6125_011_tachometer_datasheet.pdf
8. http://www.farnell.com/datasheets/1725281.pdf
9. http://content.amprobe.com/DataSheets/TACH-10%20Tachometer.pdf
10. https://www.youtube.com/watch?v=Kowv-nJnX7o
11. https://www.youtube.com/watch?v=_7dPJ5trYDo
1.
2.
3.
4.
5.
6.
7.
10