Digital Tachometer Calibration Procedure- Non-contact type Using Fluke 754 Process Calibrator

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Do you want to make sure that the rpm reading of the tachometer that you are using is accurate?

In this article, I will share with you a simple and effective way on how to calibrate a Digital Tachometer, the Amprobe Tach20, a non-contact and contact type in one. But in this procedure, we will focus on the non-contact type, we will calibrate the tachometer using its laser pointer.

I will also share with you on how to verify the reading of your tachometer if it is within specifications or not.

If you already have a  Fluke 754 Process Calibrator, then this is an additional capability and an added value because we will use it as our reference standard. This is another useful feature of Fluke 754.

For more details regarding its capabilities, visit this link

We will use a simulated signal (frequency) generated by Fluke 754 with the addition of a LED as the source of our reference value.

In this procedure, there are no adjustable parts so adjustment is not an option, we will verify only the accuracy of the handheld digital tachometer in a non-contact way.

First of all, let us define what a tachometer is.

A Tachometer is an instrument used to measure the speed of a rotating body. A shaft or a motor for example. The unit of measurement is in revolutions per minute (rpm), m/sec or ft/min.

There is a tachometer installed in a car that measures its speed and it is mostly known as the speedometer. The tachometer that I will introduce here is the Handheld Digital Tachometer that is commonly used in industries that measure the speed of a rotating body or a shaft in a motor or simply a fan.

It is a handheld type that you can carry anywhere and used via its laser pointer as a non-contact or through its nozzle (with accessories) as a contact measurement. This is the Amprobe Tach20 Digital Hand-Tachometer.

How to Use a Non-Contact Tachometer (Amprobe Tach20)?

You can use a Tachometer either contact or non-contact depending on the setup and convenience on how you can measure a rotating body.

It is very simple to use, For a non-contact measurement,  just point or aim the laser of the tachometer on a rotating shaft with a  reflective tape stick to it. Ensure a steady hand while aiming to get an accurate reading.

Ensure the distance from the measured part is not more than 24 inches for accurate measurements.

Another is by directly touching the rotating body for a  contact measurement, accessories are used for a different type of surface (provided in the set).

The Amprobe Tach20 is a user-friendly, only 3 buttons are used to fully operate the instrument. Just press and measure.

The Principle of operation behind the non-contact type tachometer is that it has a sensor that senses the fluctuation of light or the switching off/on of a light source or a changing color (a reflection of white and dark color) while a body is oscillating or rotating.

This fluctuation or oscillation has a corresponding frequency in which converted to speed and displayed as RPM. In this setup, the light in the LED is generated by an oscillating sinewave with the corresponding frequency.

Below is a conversion of Frequency (Hz) to Revolutions Per Minute (RPM).( visit WIKI for more explanation)

                           1 Hz = 60 RPM

For the 60 Hz above, expect the output to be 3600 RPM (60×60).

Why do we need to calibrate A tachometer?

A tachometer is used to verify the speed of a rotating motor that produces a specific product or monitors a specific process. By achieving the desired speed, quality and safety are achieved.

Every motor has moving parts that are exposed to wear and tear and therefore needs to be monitored constantly. Also, since most are operated today electronically, we cannot remove the effect of drift and other environmental pressures (temperature, dust, vibrations, etc).

 Tachometer Calibration Procedure 

This RPM calibration procedure is simple to do. I am using the model Tach20 from Amprobe but this is applicable to all tachometers with a non-contact capability using a laser pointer (optical sensor).

Observe the following before calibration:

  • Be sure to check first the functionality of the tachometer (power on, good battery, good physical condition, clean…).
  • Stabilize the instruments to a suitable environment condition ( monitor temperature and humidity) – check this link for more info regarding temperature and humidity.
  • Warm up the reference standard by powering on for at least 30 mins. before using to ensure stable functionality ( good performance)
  • Prepare your Measurement Data Sheet (MDS) to record necessary details of the Amprobe Tach20 Tachometer (brand, model, serial, etc)

Tachometer Calibration Standard

Tachometer Reference Standard
Tachometer Reference Standard

The equipment we need is:

  1. Fluke 754 Process calibrator
  2. A piece of LED (normal 5mm LED)  
  3. A connecting wire or connector.


    Calibration Set up:

Calibration Set up
Tachometer Calibration Set up
  1. Power on Fluke 754, select the source function 
  2. Press the  Frequency/Hz button.
  3. Set the voltage to 2V and Set the Waveform to a square wave
  4. Press done.
  5. Connect the LED using the connector provided in the port under source (see pic). (a pair of connecting probes can be used also).
  6. Press frequency ( Hz) button ( same as 2nd step button)
  7. Set the required frequency range (an example is 60 Hz)
  8. Press enter

    You can use any LED that is powered by an acceptable voltage with a known Frequency. In this pict, I use a Fluke 5522A process calibrator to simulate the frequency and voltage.
    You can use any LED that is powered by an acceptable voltage with a known Frequency. In this pict, I use a Fluke 5522A process calibrator to simulate the frequency and voltage.

    Calibration Procedure:

  9. At this stage, the LED has lighted, Focus the tachometer on the lighted LED with a distance of 3 to 5 inches (until 24 inches) Ensure stable aiming of the light to get the most accurate reading.     
  10. Wait until the reading has stabilized then record. (perform at least 3 trials)
  11. Change the frequency range then repeat steps 6 to 9 until the required set points are reached.
  12. Complete your MDS record
  13. End of verification

How to Perform Tachometer Verification?

Verifying the RPM reading using a frequency of 1500 Hz which is equal to 90,000 rpm.
Verifying the RPM reading using a frequency of 1500 Hz which is equal to 90,000 rpm.

What we need during tachometer verification is the specification of the tachometer or the user tolerance. This is our basis to decide whether the tachometer will pass or fail the verification.

Below is an example:

as per specification, the Amprobe Tach 20 tachometer has an accuracy  =  0.02% of reading.
tachometer expected reading = 60 000 rpm
tachometer actual reading = 59998

  • determine the accuracy value in rpm: 0.02/100*60000 = 12 rpm.
  • and now the tolerance is +/- 12 rpm,
    • therefore, the verification result is PASSED as per the actual reading of 59998.


There you go, I  have presented and discussed what a tachometer is, including the setup and procedure for calibrating a Digital Handheld Tachometer using a Fluke 754 with a piece of Light Emitting Diode (LED). The procedure is so simple that you can do this anytime you want to verify the accuracy of your tachometer.

I also included the procedure on how to verify the accuracy of the tachometer and determine if the reading is pass or failed.

Ensure that  Fluke 754 is calibrated in order to have a reliable and traceable calibration. Verify the calibration status of your reference standards by reviewing its calibration certificate. How to properly review a calibration certificate? Visit this post, click here

To view it in Amazon, click here Amprobe TACH-20 Tachometer with Contact and Non-Contact Measurement

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2 Responses

  1. John Price
    | Reply

    Can you provide the specifications on the LED light that was used?
    This is something that I would like to do in our Metrology Lab but the choices of LED’s are endless.

    • edsponce
      | Reply

      Hi Mr. John,
      Appreciate your comment. I only used a normal 5mm LED. you can check the specs in this link.
      I would be happy to hear if it will work perfectly for you.

      Thanks and regards,

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