IZMIR INSTITUTE OF TECHNOLOGY
Department of Mechanical Engineering
ME 352 SYSTEM ANALYSIS and CONTROL
HW:
Tachometers;
-How they work?
-Circuit working principles.
Mustafa DÖNGEL
220203009
Date of Submission
05.05.2020
TACHOMETERS
Tachometer operates on a tachometer generator principle, which means when a motor
is worked as a generator it generates the voltage according to the shaft velocity. It is also
known as the counter-revolution, and its operating theory may be mechanical, electronic or
optical. A tachometer's specifications are capacity, precision, RPM rate, readings, and display.
Tachometers may be showing meters analog or digital, this research focuses only on digital
tachometers.[1]
Tachometers are classified depending on two criteria as based on data obtaining
mechanism and data reading mechanism. Data obtaining mechanism is divided into two types;
contact and non-contact types. On the other hand, data reading mechanism can be done by
measuring time or frequency.
Contact digital tachometer that is in contact with the moving shaft is considered a
tachometer of contact form. Generally, this type of tachometer is attached to the computer or
electric motor. This can also be connected to an optical encoder or magnetic sensor, so that it
tests the RPM. Unlike, non- contact digital tachometer not having any physical contact with
the moving shaft is called a wireless non-contact tachometer. In this type, a laser or optical
disk is connected to the spinning shaft, and it can be read by a tachometer-directed IR beam or
laser.[2]
Time measurement digital tachometer that also calculates the velocity by measuring
the time interval between incoming pulses is known as a digital tachometer based on time.
This tachometer's resolution is independent of the measurement speed and it is more effective
for measuring low speed. Besides, Frequency measurement tachometer that measures the
velocity by calculating the pulses frequency is called a digital tachometer based on frequency.
That type of tachometer is constructed using a LED, and this tachometer's revolution depends
on the spinning shaft, and is more precise to calculate high speeds. These tachometers are
low-cost and high-efficiency, in the range of 1Hz-12 KHz.[3]
A simple digital tachometer with IR sensing element, block diagram and electronic
circuit diagram is showed in Figure 1 and 2.
Figure 1 Block diagram of a tachometer via IR sensing element and 8051 MC. [4]
Digital tachometer structure is being established by using various blocks such as an
optical or magnetic sensing unit, a signal conditioning unit, a microcontroller, a memory and a
display. After sensing unit pulses are achieved, pulses are identified for further operation by
the microcontroller via signal conditioning unit. It happens as follows, the output signals from
the sensors are noisy and are thus filtered, amplified, and transcribed in digital sense. A
microcontroller is used to interpret the sensor readings and to process them. It sends that
information to a display device and, by taking appropriate action, alerts the user when the
speed is reduced or increased to a predefined level. Finally, stored data is shown by display
unit which transmitted from microcontroller.
Figure 2 Scheme of design and elements in electronic circuit of IR tachometer.[5]
Whenever the reflective strip on the rotating object passes in front of the sensor
assembly, the reflected light falls on the photo transistor, which allows it to be transmitted
further, and consequently the collector voltage drops to zero (via D4 and Q4 for this circuit).
The quad LM324 is used here as a comparator with reference voltage set at limit voltage
value. If the photo transistor's collector voltage drops below limit voltage, the comparator's
output goes into negative equilibrium, and when the photo transistor's collector voltage
reaches limit voltage, the comparator output goes to positive exposure. 8051 MC counts that
pulses and do the mathematics in order to show results on 3-digit 7-segment display.
REFERENCES
[1] Agarwal, T., Agarwal, T., Michael, A., Agarwal, T., & Michael, A. (2020, April 30). Introduction to
Digital Tachometer Circuit Working with 8051 and Types. Retrieved from
https://www.elprocus.com/introduction-to-digital-tachometer-circuit-working-with-8051/
[2] About Tachometers. (n.d.). Retrieved from https://www.instrumart.com/MoreAboutCategory?
CategoryID=5553
[3] Working Principle of Digital Tachometer at Instronline. (n.d.). Retrieved from
http://www.instronline.com/blogs/working-principle-of-digital-tachometer/260
[4] Agarwal, T., Agarwal, T., Michael, A., Agarwal, T., & Michael, A. (2020, April 30). Introduction to
Digital Tachometer Circuit Working with 8051 and Types. Retrieved from
https://www.elprocus.com/introduction-to-digital-tachometer-circuit-working-with-8051/
[5] Habib, Goad, L., Kristian, Shah, D., Rohit, Deven, … Parmar, V. (2015, April 20). Contactless digital
tachometer using 8051. 3 digit display and measures upto 255 rev/sec. Retrieved from
http://www.circuitstoday.com/digital-tachometer-using-8051
