What is a tachometer?

A tachometer is an instrument used to measure the rotational speed of a shaft or disk, expressed in revolutions per minute (RPM), revolutions per second (RPS), or radians per second (rad/s). There are several types, each with its own method of measurement:

Types of Tachometers:

• Mechanical Tachometers: These use a rotating shaft connected to the measured shaft via a flexible coupling. This rotation drives a centrifugal governor or a magnetic drag system which moves a pointer across a calibrated scale. They are relatively simple and robust but are prone to inaccuracies and have limited dynamic range.

• Contact Tachometers: These require physical contact with the rotating shaft, typically using a sensor that detects the passage of markings or pulses on the shaft. This could be a simple optical sensor or a more sophisticated inductive sensor. They are susceptible to wear and tear from contact and are not suitable for all applications.

• Non-Contact Tachometers: These use various methods to measure rotational speed without touching the rotating shaft. Common types include:

  • Stroboscopic Tachometers: A strobe light flashes at a controllable frequency. When the flash rate matches the shaft's rotation, the shaft appears to stand still, allowing the RPM to be read directly from the strobe light's setting. They are accurate but can be difficult to use and require good visibility of the rotating component.
  • Photoelectric Tachometers: These use a light source and a photodetector to measure the time between interruptions of the light beam by markings or slots on the rotating object. They are versatile and can measure high speeds accurately.
  • Laser Tachometers: These use a laser beam to measure the time between reflections from markings on a rotating object. They offer high accuracy and can measure from a distance, making them suitable for hazardous environments.
  • Eddy Current Tachometers: These use an eddy current probe that is positioned near the rotating shaft. The probe's output voltage is proportional to the shaft's speed. They are non-contact, robust, and provide a good signal.

Applications of Tachometers:

Tachometers are widely used in various industries, including:

• Automotive: Measuring engine speed in cars, motorcycles, etc.
• Industrial Machinery: Monitoring the speed of motors, pumps, turbines, and other rotating equipment.
• Aviation: Measuring engine RPM in aircraft.
• Manufacturing: Monitoring the speed of production lines and machinery.
• Medical Equipment: Measuring the speed of rotating components in medical devices.

Choosing a Tachometer:

The selection of a suitable tachometer depends on several factors, such as the required accuracy, the speed range, the type of application, the environmental conditions, and the budget. Factors like whether the application requires contact or non-contact measurement, the size and accessibility of the rotating component, and the desired output (analog or digital) are also important considerations.