Understanding the Basics: What is a Tachogenerator?

A tachogenerator, also referred to as a tachometer generator or simply a tach generator, is a versatile rotary electromechanical device used to produce an electrical signal proportional to the shaft rotational speed. Understanding what a tachogenerator is and how it operates provides valuable insight into one of the most common velocity and speed sensing technologies with widespread use across industrial, automation, instrumentation, research, and consumer product applications.

In this article, we will overview the inner workings of basic DC and AC output tachogenerator designs to grasp the essential concepts of how shaft speed and rotation translates into proportional electrical outputs. We’ll also briefly discuss common applications and usage cases where implementing a tachogenerator offers advantages.

Tach Generator Operating Concepts

Fundamentally, a tachogenerator utilizes rotating electromagnetic induction principles to transform mechanical rotation into proportional electrical signals. The faster the speed, the higher the electrical output.

The most basic DC output tachogenerator consists of a multi-pole permanent magnet rotor which spins inside of a stationary wire-wound stator assembly. The rotor drives lines of magnetic flux to intersect across the stator windings. As the rotor poles pass the coil windings, the changing magnetic fields induce voltages by Faraday’s law of electromagnetic induction. Faster rotational speed causes faster magnetic flux cutting through the windings, inducing higher peak AC voltages. Added commutator contacts then convert and rectify the AC into DC output.

More advanced AC output tach designs utilize multiple phase windings instead of commutators to allow cleanly outputting generated sinusoidal waves without significant harmonics for precision speed-proportional signals. The number of pole pairs determines the sinusoidal frequency produced relative to shaft speed.

Calibration and linearity of the output rest upon carefully balancing the electromagnetic circuits and winding parameters to ensure reliable proportional relationships through the entire operating speed range. Ball bearings enable smooth rotation across a wide range of speeds and temperatures. The construct allows fully-enclosed housings to contain lubrication and protect internal components in harsh environments.

Common Tach Generator Applications

Tach generators serve essential roles in measuring, indicating, and controlling rotational mechanical systems. Some common applications which leverage them include:

• Engine, Motor, and Pump Speed Feedback – Essential for monitoring or controlling rotation rates to desired speeds and providing overspeed warnings.

• Rate Tables and Centrifuges – Precisely indicate speeds for setting experimental conditions.

• Power Meters – Measure work performed by calculating speed and torque.

• Cranes, Winches, and Cable Systems – Display lift velocities for safe operation and load control.

• Mixers and Agitators – Maintain proper stirring speeds for processing.

• Machine Tools – Display working speeds like lathes, mills, and drill press spindles.

• Wheels and Axles – Trucks, trains, and equipment traction monitoring.

• Governors and Speed Controllers – Provide feedback for closed-loop control.

• Automotive Tachometers and Bike Computers – Display engine RPM or wheel speeds.

• High-End Audio Turntables – Precisely control record playing speed.

This list barely scratches the surface of the countless essential and ingenious applications leveraging tach generator technologies due to their reliability, accuracy, versatility, and cost-effectiveness for translating mechanical motion into proportional electrical outputs across virtually any rotating shaft speed range.

Tach Generator Advantages

Some key benefits and advantages of tach generators include:

• Direct Shaft Coupling – No belts, chains, gears needed; attaches directly to shaft.

• Rugged and Robust Construction – Proven reliable in harsh environments.

• Wide Speed Ranges – Models supporting from sub 1 RPM to 100K+ RPM speeds.

• Pulse Outputs – Allows simple digital interface signals.

• Accuracy and Linearity – Provides precise, consistent proportional outputs.

• Current Outputs Available – Allows lossless remote transmission.

• Temperature Stability – Consistent performance across operating temps.

• No Contact Brushes – Brushless designs support maintenance-free operation.

• Low-Noise Magnetic Circuits – Avoids electrostatic and brush noise issues.

• Low-Inertia Air-Gap Designs – Prevent loading down rotating shafts.

• Compact and Lightweight – Enable flexibility Embedding Into tight spaces.

These performance advantages allow tach generators to deliver economical, accurate, reliable shaft speed measurements through simple rotary induction processes across an incredibly wide breadth of speed monitoring and control applications - cementing them as a preferred engineering solution versus alternative approaches.

Bottom Line

Tachogenerators represent one of the most prevalent technologies for motion control and instrumentation spanning across both industry and consumer applications. We've explored the electromagnetic fundamentals enabling tach generators to transform rotation into proportional electrical outputs for interfaces and closed-loop control. 

Understanding tach generator operating principles provides deeper insight into an amazingly versatile rotary velocity measurement device with ongoing popularity due to precision, robustness, cost-efficiency and wide implementation. With continually advancing designs and capabilities, tachogenerators will remain a core technology for motion feedback and control for the foreseeable future.