Portable optical and contact tachometers are instruments for measuring the rotational speed (RPM) of shafts, motors, fans, turbines and rotating components in general. They come in two main technologies: optical tachometers (non-contact, based on a laser or LED beam reflected from a mark on the shaft) and contact tachometers (with a measuring wheel applied to the rotating component or to the surface of the product). They are widely used in the predictive maintenance of industrial machinery, in speed checks on production lines, in the control of electric and combustion engines, and in materials testing laboratories.
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Optical tachometers
Optical tachometers use a light beam (visible red laser, class 2 for safety) aimed at the rotating shaft: a reflective mark (an adhesive label supplied with the instrument) or a contrasting colored area reflects the beam intermittently during rotation, generating pulses at the integrated photodetector. The pulse frequency corresponds to the rotational speed in revolutions per second, converted automatically into RPM. Typical working distances are 50-500 mm, with a measuring range up to 99,999 RPM. Typical precision is 0.05% of the reading plus 1 digit. They require no physical contact with the shaft, which is particularly important for high-speed or hazardous components.
Contact tachometers
Contact tachometers use a measuring wheel (with a calibrated circumference, generally 6 inches or 200 mm) mounted on the body of the instrument; the wheel rests on the rotating shaft or on the surface of the moving product (strip, wire, sheet metal) and turns by friction. An internal optical encoder counts the pulses per second in order to derive the linear speed (m/min) or, knowing the shaft diameter, the rotational speed. The typical range is up to 99,999 RPM for measurement on a shaft, and up to 1500 m/min for measurements on moving products. They are useful wherever a reflective mark cannot be applied.
Combined models
Most professional instruments on the market are of the combined type (optical plus contact): a single instrument with an integrated optical sensor and a mechanical accessory for contact measurements (with an interchangeable wheel or rod). The operator selects the mode on the display according to the application, which optimizes the investment. The advanced functions integrated are: recording of maximum, minimum and mean values for analyzing speed stability; GO/NOGO thresholds with an audible signal; an internal data logger holding thousands of values; Bluetooth/USB data output; and PC software for archiving and spectral analysis.
Applications
Typical use is in: predictive maintenance of electric motors and industrial fans (checking actual speed against nominal speed); control of the operating speed of pumps, compressors and gearboxes; calibration of variable speed drives (inverters); verification of analog tachometers and panel indicators; control of line speed in continuous production (conveyor belts, processing lines for paper, plastic, textiles and metals); measurement of the linear speed of extruded, drawn and rolled products; and verification of yarn speed in the textile industry.
Standards and calibration
Calibration of portable tachometers is carried out with reference rotation generators (rotating discs with calibrated marks, driven at a known speed by a high-precision encoder) calibrated to ISO 17025. The check covers several points across the measuring range, with calculation of the percentage error. The typical calibration interval is every six months or annual for formal quality control applications, and every two years for general use. Ambient conditions (temperature, vibration) have little influence on the performance of modern digital models.
Selection criteria
Selecting the right tachometer takes into account: the speed range typical of the applications; the preferred mode (optical for non-contact, contact for measurement on a line or for surfaces where no reflective mark can be applied); the accuracy class; the advanced functions (memory, data output, software); portability (size, weight, battery life); and mechanical robustness for workshop use.
Related products
The RODER instruments for this application. Go to the relevant catalogue pages for models, technical data and documentation.
Contacts & Information
Contact for general information : info@roder.it
Machine Vision Division of RODER : www.rodervision.com
RODER Instruments Division : www.innovacheck.com
More about RODER : about us
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Note: Some images on this website have been intentionally generated using artificial intelligence (AI). This is because, for many applications and projects, photographs of the actual installation or system cannot be disclosed owing to confidentiality agreements, contractual clauses and non-disclosure agreements (NDAs).
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