A tachometer measures the rotational speed of an engine or motor, typically expressed in revolutions per minute (RPM). These devices, available in both analog and digital formats, are commonly found in automobiles and aircraft.
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In this article, we will explore the different types of tachometers, their working principles, applications across various industries, and recent advancements in tachometer technology.
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What is a Tachometer?
A tachometer is a device that measures rotational speed—typically tracking how fast an engine’s crankshaft or a motor’s rotor is spinning. It works by generating a signal that corresponds to the rotation speed, usually displaying the measurement in revolutions per minute (RPM). If you've ever noticed a gauge in a car with a needle moving as you press the gas, that’s the tachometer. It usually features a dial, a needle, and markings that indicate safe and potentially damaging speed ranges.
Most modern vehicles now use digital tachometers integrated into the dashboard, but the core function remains the same. Depending on the method of measurement, tachometers either determine speed by counting the frequency of pulses generated by the rotating shaft or by measuring the time between each pulse.
The term “tachometer” comes from the Greek words tachos (speed) and metron (measure). Early mechanical versions worked using centrifugal force—the outward push experienced by objects in a spinning system. By the early 19th century, these devices were adapted for measuring machine speed, and by the 1840s, they became a standard feature in locomotives and other vehicles.
Beyond engines, tachometers also have specialized applications. In medicine, for example, a haematachometer can be placed inside an artery or vein to estimate blood flow based on the speed of a tiny spinning turbine. This helps diagnose circulation issues, such as arterial blockages.1-3
Understanding Tachometer Types and Their Principles
Not all tachometers are the same. They come in different designs, each suited for specific uses. Let’s take a closer look at how they’re classified based on their working principles, data collection methods, and measuring techniques.
Tachometer Classification Based on Working Principle
Analog Tachometers
Analog tachometers have a classic needle-and-dial design, displaying RPM in a straightforward way. They rely on mechanical or electromechanical systems to turn rotational movement into an electrical signal. Many use a frequency-to-voltage converter to translate speed into voltage, which is then displayed on an analog meter.
These tachometers are simple and reliable but lack modern features like data storage and precise deviation calculations. They’re commonly found in older vehicles and machinery where basic real-time speed monitoring is enough.3
Digital Tachometers
Digital tachometers take mechanical speed and convert it into digital signals, offering real-time, highly accurate readings. These models detect shaft rotation and display RPM on an LCD or LED screen. For example, an infrared module can detect interruptions in a beam caused by the rotating shaft, producing pulses that are counted to determine speed.
Unlike their analog counterparts, digital tachometers provide clear, easy-to-read numerical displays and often include memory storage for data analysis. They’re widely used in cars, planes, and medical equipment. However, they can be sensitive to slight positional changes, and rapidly fluctuating speeds can make it tricky to get a stable reading.2,4
How Tachometers Collect Data: Contact vs. Non-contact
Now that we've explored how tachometers display and process speed readings, let's look at how they collect data—whether through direct contact with a rotating object or using non-contact methods.4
Contact Tachometers
As the name suggests, contact tachometers must physically touch the rotating shaft to measure speed. They typically use optical encoders or magnetic sensors to detect motion, converting mechanical movement into RPM readings. These devices work best when direct interaction with the rotating part is feasible and when precise measurements are required. They usually measure speeds between 0.5 and 10,000 RPM and often feature five-digit LCD displays.4
Non-Contact Tachometers
Non-contact tachometers measure rotational speed without touching the object, making them ideal for high-speed applications. These devices use lasers or optical disks to detect motion and are commonly found in vehicles such as buses, trains, and airplanes.
They work by detecting pulses from a shaft encoder. When a reflective surface on the shaft interrupts a light beam, pulses are generated and counted by an electronic circuit to determine speed. These tachometers are highly accurate, particularly at high speeds, and are essential when physical contact could interfere with performance.5
How Tachometers Measure Speed: Time vs. Frequency
Now that we’ve looked at how tachometers collect data, let’s see how they interpret that data to determine speed. Depending on the approach, they can measure speed based on either time intervals or frequency calculations.
Time Measuring Tachometers
Time-based tachometers measure speed by calculating the time between incoming pulses. These are especially useful for low-speed applications, as they maintain reliable resolution regardless of the speed.
Frequency Measuring Tachometers
These tachometers determine speed by measuring the frequency of incoming pulses, making them ideal for high-speed applications. Many use red LED displays and operate across a frequency range of 1Hz to 12 kHz. They’re known for being both cost-effective and efficient.
Where Tachometers Are Used
Tachometers are found in nearly every industry that involves rotating machinery. Some of the most common applications include:1-5
- Automobiles, airplanes, trucks, tractors, and trains – for monitoring engine and wheel speeds.
- Laser instruments and medical devices – ensuring precision in specialized applications.
- Analog audio recording – maintaining consistent speeds for playback and recording.
- Industrial machinery – preventing wear and tear by keeping speeds within optimal ranges.
What’s New in Tachometer Technology?
Tachometer technology has made huge strides, moving from simple mechanical designs to sophisticated digital systems that deliver high levels of precision. One exciting example comes from a recent study in the Journal of Language and Linguistic Studies, which introduced a digital tachometer capable of measuring speeds up to 800 RPM using a PSoC5LP microcontroller. This system integrates an alphanumeric LCD, an optical sensor, and a DC motor, showing just how much microcontrollers can boost the accuracy and versatility of tachometers.
What makes this study stand out is its use of PSoC5LP interrupts to measure motor speed and update the display every three seconds. This not only showcases the advancements in digital tachometers for industrial and mechanical applications but also highlights their growing importance in education.
By incorporating hands-on microcontroller-based speed measurement, students and engineers alike can gain a deeper understanding of real-world applications. This reflects a broader trend—tachometers are no longer just passive measurement tools; they are becoming smarter, more interactive, and more valuable across different fields.6
The Future of Tachometers
Tachometers are getting smarter, more precise, and a whole lot more automated. Thanks to advancements in sensor technology and microcontrollers, we’re seeing wireless, high-efficiency speed measurement systems that can adapt to various industries. Whether it’s keeping tabs on engine performance in cars or monitoring industrial machinery, these innovations are making tachometers more accurate and versatile than ever.
Looking ahead, tachometers will continue to be a go-to tool in engineering and mechanics. No matter the industry—automotive, aerospace, or manufacturing—these devices will play a crucial role in keeping things running smoothly.
Whether you opt for an analog or digital model or decide between contact and non-contact options, the goal remains the same: reliable and precise speed monitoring. As technology advances, tachometers will likely become even more integrated into smart systems, solidifying their place in modern diagnostics and automation.
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References and Further Reading
- Lynch, K. M., Marchuk, N., Elwin, M. L. (2016). Sensors. Embedded Computing and Mechatronics with the PIC32, 317–340. DOI: 10.1016/b978-0-12-420165-1.00021-4, https://www.sciencedirect.com/science/article/abs/pii/B9780124201651000214
- Shrestha, S., Poudel, U., Rouniyar, P. (2021). Digital Tachometer. https://www.researchgate.net/publication/351784421_DIGITAL_TACHOMETER
- Giyatno, D. W. F. S. N., Orlando, T. R., Supriatin, N. (2018). Analog tachometer as an indicator motorcycle machine wearing based on moving coil. E3S Web of Conferences, 43, 01004. DOI: 10.1051/e3sconf/20184301004, https://www.e3s-conferences.org/articles/e3sconf/abs/2018/18/e3sconf_astechnova2017_01004/e3sconf_astechnova2017_01004.html
- Sharma, H. (2018). Manufacturing of Digital Tachometer. Journal of Emerging Technologies and Innovative Research, 5, 11, 281-284. https://www.jetir.org/view?paper=JETIREY06059
- Kumar, N., Morwal, H., Raj, S., Singh, A. K. (2018). Contactless IR Tachometer. International Journal of Advance Research And Innovative Ideas In Education, 4(3), 45-49. https://ijariie.com/FormDetails.aspx?MenuScriptId=96880&srsltid=AfmBOope7mTDlMfbzpUK6OtQDeTrsjIoe9YD8iCqxB2ACZejjA5dF5tF
- Hurtado, O. G., Camargo, J. R. L., Díaz, M. A. O. (2022). Didactic system for teaching microcontrollers-Case study: design of a digital tachometer. Journal of Language and Linguistic Studies, 18(4). https://www.jlls.org/index.php/jlls/article/view/5069
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