Extech Tachometers & Stroboscopes

Rotational speed measurement instruments for maintenance, production and quality control teams — supplied across South Africa and neighbouring countries from our Cape Town base.

A tachometer is an instrument that measures the rotational speed of a shaft, disc, fan or wheel and displays it in revolutions per minute (rpm). It does this by counting rotation events over an accurately timed interval, either by touching the rotating part with a contact tip or wheel, or by detecting a reflective marker optically from a distance.

A stroboscope solves a different problem. It fires a xenon or LED flash lamp at an operator-adjustable rate, measured in flashes per minute (FPM). When the flash rate is synchronised with the rotation rate of the machine, each flash illuminates the part in the same angular position, and the part appears to stand perfectly still while it continues to run at full speed. That frozen image lets an inspector examine a moving component — a fan blade, a printing cylinder, a textile spindle, a coupling — without stopping the line. Because the synchronised flash rate equals the rotation rate, a stroboscope also functions as a non-contact tachometer.

The four measurement methods, and when each one is right

Every instrument on this page uses one or more of four methods. Choosing the wrong one is the most common reason a tachometer purchase disappoints, so it is worth understanding the trade-off before comparing models.

How to choose the right tachometer

Work through these five questions in order. In our experience the first two eliminate most of the range before rpm specifications are even considered.

• Can you safely touch the shaft end? If yes, a contact instrument such as the 461750 or 461891 is the simplest and cheapest answer, and it needs no consumables. If no — guards, hot surfaces, high speed, awkward access — you need a non-contact model and you can stop considering contact-only units.
• How far will you be standing from the target? This is the specification most often overlooked. The 461895 uses visible light and needs to be within roughly 150 mm. The 461920, RPM33 and RPM250W are laser guided to about 500 mm. The RPM10 and 461995 reach 2 m, which is what you want when a fixed guard or walkway keeps you back from the machine.
• Do you need rpm, or linear surface speed, or both? Belt, web and wire applications need the surface wheel accessory, which comes as standard on the 461750, 461891, 461895, 461995 and RPM10. Laser-only models such as the 461920 and RPM250W cannot measure linear speed.
• Do you need to see the part, or only measure it? Crack detection, print registration, spindle and coupling inspection all require a stroboscope: the 461825 for a portable battery unit, or the 461830 for a fixed mains-powered installation on a production line.
• Does the reading need to be recorded? If measurements feed a condition monitoring record, the RPM33 stores ten data sets with maximum, minimum and average values, the RPM250W streams live readings to the free ExView app on iOS and Android, and the TA503C kit logs 2,000 records for USB download.

Extech tachometers — contact models

Extech tachometers — non-contact laser models

Extech tachometers — combination contact and non-contact

Combination instruments carry both a contact tip and an optical head in one body, so a single tool covers the accessible shaft ends and the guarded ones. For a maintenance team buying one tachometer, this is almost always the right category.

Extech stroboscopes and panel instruments

Extech tachometer and stroboscope comparison

All specifications below are manufacturer figures for the current Extech catalogue. Where a model offers both measurement methods, both ranges are shown.

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Also available from the Ecotao online store

Two further rotational speed instruments are stocked outside the Extech range and can be ordered directly online. Both are worth considering where data logging or battery-powered stroboscopy is the priority.

Applications across South African industry

The instruments above are used in the same broad way everywhere, but the specific reason for the measurement changes with the industry — and that reason is what determines which model actually suits.

Mining, quarrying and bulk materials handling

Conveyor belt speed is the measurement that recurs most often. A weightometer computes tonnage from belt speed multiplied by belt load, so an error in assumed belt speed becomes a direct error in reported tonnage. A contact tachometer with a surface wheel — the 461750, 461891, 461895, 461995 or RPM10 — reads belt speed directly in m/min and is the standard field check against the installed speed sensor. On drive motors and gearbox output shafts behind guards, the 2 m laser reach of the 461995 or RPM10 lets the reading be taken without removing the guard, which matters both for permit-to-work reasons and for time.

Agriculture, irrigation and food processing

Irrigation pump sets, grain handling augers, milling equipment and packing line drives all depend on running at design speed. Under-speed on a centrifugal irrigation pump reduces head disproportionately — head falls with the square of speed — so a pump that seems only slightly slow can be badly short on delivery pressure. Checking actual shaft rpm against the pump curve before condemning an impeller is a five-minute measurement that regularly saves a stripdown. Slow-turning augers and mixer drives are where the 0.5 rpm minimum of the 461891 earns its keep.

Printing, packaging and textiles

This is stroboscope territory. Print registration problems, web flutter, doctor blade behaviour and textile spindle condition are all visible only while the machine runs, and only a stroboscope makes them visible. The 461825 handles this portably across a print floor; the 461830 is set up on a tripod over one line for continuous watching. The 461825's coarse and fine flash adjustment is the feature that matters here — registration faults appear as small periodic movements that are lost unless the flash rate can be trimmed precisely onto synchronisation.

HVAC, building services and facilities maintenance

Fan and pump speeds drift after belt changes, pulley swaps and drive resets, and an air handling unit running below design speed under-delivers airflow with no obvious symptom until a space fails to hold temperature. Non-contact measurement is essential here because fan shafts sit inside AHU casings behind guards. The RPM10 is a particularly efficient choice for building services rounds: it captures fan speed and motor or bearing temperature in one pass, which halves the number of instruments carried up a plant room ladder.

Manufacturing, workshops and quality control

Machine tool spindle speeds, mixer and agitator speeds, centrifuge speeds and test rig calibration all require a verified rpm figure rather than a dial setting. Where the figure feeds a quality record, the 0.05% accuracy of the 461891 or the logging capability of the TA503C is what makes the measurement defensible. Where a technician simply needs to confirm a variable speed drive is doing what the controller claims, the RPM33 or 461920 is enough.

Getting an accurate reading in practice

Instrument accuracy is rarely the limiting factor on a real measurement. These are the errors that actually show up in the field.

• Use one tape strip per revolution. Two strips on the same shaft double the reading. If a shaft already carries a reflective marking from a previous job, check for a second one before trusting the number.
• Keep the tape strip narrow. A wide strip on a slow shaft can register as two pulses as it passes through the beam. Extech supplies replacement reflective tape as the 461937 roll, which is worth stocking — tape is a consumable that gets used up marking machines.
• Mind the angle. Most laser tachometers want to be roughly perpendicular to the tape. The RPM250W tolerates up to 30° off perpendicular, which is a real advantage in cramped plant rooms where a square-on position is not available.
• Press contact tips squarely and steadily. A cone tip held at an angle, or a surface wheel held too lightly against a polished belt, will slip and under-read. Light steady pressure perpendicular to the surface is the technique.
• Check the shiny-surface trap. A polished or chrome shaft can return enough light to trigger a false pulse without any tape at all. If a non-contact reading looks impossibly high, that is usually why.
• Work down, not up, with a stroboscope. Start at the highest flash rate and reduce until the first stationary image appears. Starting low and increasing will find a harmonic first and give a reading that is a fraction of the true speed.

Frequently asked questions

What is the difference between a tachometer and a stroboscope?

A tachometer returns a number: it counts rotations over a timed interval and displays the result in revolutions per minute. A stroboscope returns a picture: it fires a flash lamp at an adjustable rate, and when that flash rate matches the rotation rate the moving part appears frozen in space.

Use a tachometer when you need a speed value to compare against a nameplate or setpoint. Use a stroboscope when you need to see the part while it is running — to inspect a fan blade for cracks, check a printing register, or watch a coupling for wobble. The Extech 461825 does both in one battery-powered instrument.

What is the difference between a contact and a non-contact tachometer?

A contact tachometer is pressed against the end of a rotating shaft using a cone or flat tip, or against a moving surface using a wheel. It works on dull, dark or wet surfaces and needs no preparation, but the shaft end must be reachable and safe to touch.

A non-contact photo or laser tachometer reads a strip of reflective tape stuck to the rotating part, measured from a distance, so it is the safer choice on guarded machines, high speed shafts and hot equipment. Combination models such as the 461995, RPM33 and 461895 carry both methods in one instrument, which is why they are the most common choice for a general maintenance toolkit.

Do I need reflective tape to use a laser tachometer?

Yes, in almost every real case. A photo or laser tachometer detects the change in reflected light as a marker passes the beam once per revolution. Machined steel, painted casings and rubber couplings do not give a reliable pulse on their own, so a short strip of retro-reflective tape is applied to the rotating part. One strip per revolution gives a direct rpm reading.

Extech supplies reflective tape with most of its non-contact models and also sells it separately as the 461937 replacement roll, which is worth keeping in the toolbox because the tape is consumed as machines are marked.

Will the Extech 461830 StroboTach work on South African 230 V mains?

Not directly. The 461830 is built for a 115 VAC 60 Hz supply, so on a South African 230 V 50 Hz socket it requires a step-down transformer of adequate rating.

The 220 VAC 50 Hz version, the Extech 461831, has been discontinued by the manufacturer, and Extech names the 461825 Combination Photo Tachometer and Stroboscope as its replacement. For most South African users the practical answer is the battery-powered 461825, which carries no mains constraint at all and can be walked to any machine on site. Contact us before ordering a mains stroboscope so the supply voltage is confirmed against your site.

How far away can an Extech laser tachometer measure from?

Measuring distance varies significantly across the range and is often the deciding specification. The 461895 uses visible light and works to about 150 mm. The 461920, RPM33 and RPM250W are laser guided to roughly 500 mm. The RPM10 and 461995 reach up to 2 m, which matters when a guard, walkway or hot surface prevents you from getting close to the shaft.

If the shaft you need to read sits behind a fixed guard, size the instrument on measuring distance first and on rpm range second — almost every model covers far more rpm range than a typical industrial drive will ever need.

How accurate are Extech tachometers?

Most of the range is specified at 0.05% of reading, which on a 1,500 rpm motor is under one revolution per minute. The RPM250W is tighter at 0.04%, and the entry level 461750 PocketTach is specified at 0.1% of reading plus 2 digits.

In practice, tachometer error is rarely the limiting factor. Poorly applied reflective tape, a tape strip wide enough to be counted twice per revolution, or a contact wheel slipping on a polished surface will each introduce far more error than the instrument specification.

Can a tachometer measure conveyor belt speed?

Yes. Contact tachometers fitted with a surface wheel read linear speed directly rather than rotational speed, which is the correct way to check a conveyor, a web line or a wire drawing machine. The 461750 covers 1 to 1,999.9 m/min, and the 461891, 461895, 461995 and RPM10 cover 0.05 to 1,999.9 m/min.

Hold the wheel against the belt surface with light steady pressure and perpendicular to the direction of travel. On mining and quarry conveyors this is the standard method for verifying belt speed against a weightometer calibration.

Which Extech tachometer should I buy for general motor and pump maintenance?

For a general maintenance toolkit, a combination contact and laser instrument covers the widest set of situations from a single purchase. The RPM33 is the value option, reading 2 to 20,000 rpm by contact and 2 to 99,999 rpm by laser to 500 mm with ten stored data sets.

The RPM10 adds a built-in infrared thermometer reading −20 to 315 °C, so one instrument checks both the speed and the bearing or housing temperature on the same walk-round — a common choice for condition monitoring routes. If your team already records readings on a phone, the RPM250W streams live rpm to the free ExView app for trending and reporting.

Are any of the Extech tachometers on this page discontinued?

No. Every Extech tachometer and stroboscope listed on this page is current in the manufacturer catalogue as at September 2026.

The one discontinued model worth knowing about is the Extech 461831, the 220 VAC 50 Hz version of the StroboTach, which is no longer manufactured and for which Extech recommends the battery-powered 461825 as the replacement. If you are replacing an older instrument, quote the model number on the label when you contact us so the closest current equivalent can be identified.