Tachometer

Quick Answer: The Tachometer is a handheld instrument that measures rotational speed, usually displayed in revolutions per minute (RPM), for motors, fans, shafts, pulleys and wheels. A tachometer is used in engineering and physics labs and in maintenance work to check speed without stopping the machine.

Optical and Contact Measurement

Handheld RPM meters work in one of two ways. An optical (photo) type shines a light or laser beam at a small strip of reflective tape stuck to the rotating part and counts each flash that comes back. A contact type has a rubber-tipped spindle pressed into the centre hole of a shaft, and many accept a small wheel for measuring the surface speed of belts and conveyors. Some models combine both. The title does not say which this is, so method, range and accessories should be confirmed when ordering.

Optical measurement keeps hands away from moving parts and adds no load to small motors, which matters when testing a toy motor or a desk fan in a practical. Contact measurement needs no tape and works wherever the shaft end is accessible, but it slightly loads the shaft and needs the spindle held steady and in line.

In the physics lab, RPM links directly to angular velocity (ω = 2πN/60 radians per second for N revolutions per minute), so a measured speed can be used to check rotating-disc, centripetal-force or dynamo experiments. For the vibration those machines produce, see the vibration meter.

Specifications

Applications

• Checking motor speeds on engineering trainers and machine-shop lathes
• Verifying fan and blower speeds during HVAC maintenance
• Converting measured RPM to angular velocity in rotational-motion practicals
• Comparing the speed of a DC motor at different supply voltages in electrical experiments

Care & Handling

• Tie back loose hair, sleeves and lanyards before measuring near rotating parts.
• For optical use, apply reflective tape to a clean shaft while it is stopped, and never reach in while it turns.
• Hold a contact spindle squarely on the shaft centre; an angled tip slips and gives low readings.
• Keep the lens and rubber tips clean, and store the instrument in its case.

Why Choose LabEquip

Polytechnic workshops, mechanical engineering labs and maintenance teams are the usual buyers. LabEquip lists the tachometer in General Lab Products; say whether you need optical, contact or combined measurement through the contact page.

Frequently Asked Questions

How much reflective tape should I use?

A single small strip on the rotating part is enough. More than one strip gives several pulses per revolution and a reading that is too high, unless the meter is set to account for them.

Why does the optical reading fluctuate?

Common causes are holding the meter at a steep angle, standing too far away, a shiny shaft that reflects as brightly as the tape, or strong lighting. Cover shiny areas with matt tape and hold the beam steady and nearly square to the target.

Can it measure the linear speed of a belt?

A contact model with a surface-speed wheel can, by rolling the wheel on the belt. Optical models give RPM, which you convert using the pulley diameter.

How do I convert RPM to angular velocity?

Multiply RPM by 2π and divide by 60 to get radians per second. For example, 600 RPM is 10 revolutions per second, or about 62.8 rad/s.

Is it safe to use a contact tachometer on a lathe?

Only with care: keep the spindle in line with the shaft centre, use light pressure and keep hands, sleeves and hair clear of the chuck. Where possible, use optical measurement on exposed rotating parts.

Can it measure a centrifuge’s speed?

Only where the rotor can be seen safely, such as through a viewing port designed for that purpose. Never open a centrifuge lid while it is running to take a reading.

Last Updated: September 2026