Extech 461920 Tachometer Mini Laser Photo  Counter.

Mini Laser Photo Tachometer Counter
Make non-contact RPM measurements (2 to 99,999 rpm) of rotating objects by pointing the integral laser (1.6-foot target distance) at the reflective tape placed on the object to be measured.

Features Overview
Measurements are displayed on the easy-to-read large five-digit LCD screen. The memory button holds last reading and recalls min/max readings display. Counter function counts to 99,999 revolutions. Rugged double molded housing for better grip. Complete with 9-volt battery, reflective tape, and user manual.

Tachometer Applications:
Motor speed, moving fans, pumps, and gears, propeller devices, and many other general maintenance, production, and automotive uses.

What is a Tachometer?
A tachometer is a device that measures the angular speed of a rotating shaft in terms of revolutions per minute (RPM). Also, a tachometer can measure linear speed in terms of feet per minute (feet/minute) or meters per minute.

How do Contact Tachometers Operate?
The sensor tip is placed in direct contact with the rotating object. After 2 seconds an accurate reading is displayed. Linear surface speed can also be measured by placing the edge of the wheel on the moving object.

How do Photo (Non-contact) Tachometers Operate?
First, a small piece of reflective tape (approximately 1/4-inch) is mounted on the object to be measured. Second, the light beam or laser is pointed at the revolving tape. The reflection from the tape provides a reading to be displayed and updated once per second. For the most accurate measurements, the distance between the tachometer and the reflective tape should be within 6 inches for a light beam and up to 6.5 feet for a laser. Fluorescent or bright ambient lights may interfere with the measurement.

Which Extech Tachometer Model Is the One for You?
A non-contact (photo) tachometer was designed for applications where it is not feasible to have the tachometer come in contact with the rotating device. This is the case in high-speed applications and/or where the object to be measured is not easily reached. A contact tachometer is also available for applications where direct contact of the tachometer with the object is preferred. You can also select a combination (contact/non-contact) tachometer for the maximum in flexibility.

Accessory: Reflective Tape for Photo Tachometers
For use with any brand Photo Tachometer. Place a piece of reflective tape on the object to be measured and point the tachometer's integral light beam at it. Ten reflective tape strips. Each strip measures 23 x 0.25 inches (584 x 6 mm).