How to Test a Tachometer with a Multimeter

How to Test a Tachometer with a Multimeter

Testing your tachometer’s accuracy is important to ensure your vehicle is running smoothly. Learn how to test a tachometer with a multimeter in a few simple steps with our guide. Take control of your vehicle’s performance today.
By the end of this article, you’ll be equipped with the knowledge and tools you need to take control of your vehicle’s performance.

Tachometer is a highly usable device in the car, machines, and different vehicles, which tells us about the speed history of the vehicle, or you can say that you will have information about the speed at which the vehicle was running by knowing the history of the engine of the car.

Difference between a tachometer and a speedometerDifference between a tachometer and a speedometer

The tachometer is sometimes misinterpreted as the speedometer as people think that both meters tell about the vehicle’s speed then, which means that the car’s speedometer is also known as the tachometer, but it is not the truth.

Tachometer is a device that tells about the rotational speed of any engine, and now it can be a car engine or a machine; for those who don’t know that there is a great difference between a tachometer and a speedometer.

The biggest difference, which will make you understand how both these separate terms are that a tachometer does not contain any dials and pointers, so you cannot see the current speed level from the tachometer. You can only understand at what speed the engine or a machine was running before.

The speedometer is the meter that tells you about the current speed of the vehicle or engine, as there are dials and pointers present on the speedometer. So these are separate meters and essential for you at their places.

Types of the tachometer

There are usually two types of tachometers:

  • Mechanical tachometer

The first type of tachometer is a Mechanical tachometer. These tachometers were used in different motorcycles and some old cars, which tell the driver about the engine’s speed. However, with modern technology, this type of tachometer is getting rare. So now these are available in very old vehicles.

  • Digital tachometer

The second type of tachometer is the digital tachometer, also known as the electric tachometer. These tachometers are present in the instrument panel of the different vehicles; they allow the driver to know about the engine’s condition by telling the speed at which the engine was running before.

Why is the tachometer important?

Tachometers are devices that allow you to measure the RPM of the turntable or a shaft, so to adjust the engine’s speed, the drivers must know about the speed history of the engine by using the tachometer.

The tachometer helps the driver select the right gears under different conditions. So, it will be difficult for the driver to select the right speed for their engine if the tachometer stops working properly or starts giving the wrong results. You can understand how dangerous it can be to follow the instructions according to the results provided by the faulty tachometer.

How to read the tachometer?

The tachometer can measure the rotational frequency of any moving part of a machine or engine, so if you want to locate the tachometer of your car, then it is present in the car’s dashboard.

The value of the rotational frequency or the rotational speed of the engine will be displayed on the tachometer as the RPM. The value will go from 0 to 10000 RPM according to the vehicle type and the engine or machine speed.

How to test a tachometer with the multimeter?How to test a tachometer with the multimeter

After learning about the importance and uses of the tachometer, it is important to know what we should do if the tachometer stops working or is not displaying accurate results to you. In this condition, you have to test the Tachometer. You can perform the test on the tachometer by using the digital multimeter.

As it will allow you to know about the type of issue that has occurred in the tachometer of your machine or engine, and in this way, you can better understand the working and the requirements of the tachometer.

Material and tools required:

Here is a short list of important materials you must manage before starting the test.

  • Tachometer
  • Digital Multimeter
  • Safety gloves

How to test a tachometer with the multimeter (quick guide overview):

  • Turn on the digital multimeter
  • Set the digital multimeter to test the frequency of the tachometer. For this, turn the selection knob of the digital multimeter at the frequency symbol Hz.
  • Connect the red lead of the multimeter with the wire of the tachometer connected to the engine cylinder and connect the black lead of the digital multimeter to the GND.
  • Turn the engine ON so that the tachometer will also start measuring the rotational frequency of the engine.
  • Read the rotational frequency value of your tachometer from the display screen of the digital multimeter.
  • Convert the resulting frequency value into RPM.
  • Compare the resulting RPM value with the normal RPM value of the tachometer.
  • A small difference will not be a big deal, but the tachometer is faulty if there is a great difference between the two results.

Below is a step-by-step guide to test tachometer with the multimeter:

How to test at tachometer with a multimeter (step-by-step guide):

Step 1: Turn on the digital multimeter

As you are going to use the digital multimeter to test the rotational frequency of the tachometer of your engines, you have to turn on the digital multimeter so that it can work for you. Do not let the digital multimeter keep ON idly; only turn it ON when ready to use it properly.

Step 2: Set the digital multimeter

After turning ON the digital multimeter, you must set it according to the test you will perform. So you have to measure the frequency of the tachometer, so you have to set the digital multimeter on the frequency settings. You must gently rotate the selection knob towards the frequency mode. Now the digital multimeter is ready to perform the test.

Step 3: Connect the multimeter leads

To measure the frequency of the tachometer, you have to connect the leads of the digital multimeter with the tachometer. Only connect the red lead of the digital multimeter with one of the wires of the tachometer joining the engine cylinder. Connect the black lead of the digital multimeter with the GND.

If you need to know what the GND is, it is any metal part that is getting connected to the body of the car.

Step 4: Turn the engine ON

After setting it all up, you have to turn the engine ON so the tachometer will start measuring the frequency. You are turning the engine to test the tachometer, so ensure the engine remains idle.

Step 5: Measure the tachometer frequency

The digital multimeter will start giving some frequency value of the tachometer, which you can see on the digital screen of the multimeter. This way, the digital multimeter will measure the frequency of the tachometer. You have to note down the resulting value of the frequency.

Step 6: Change the frequency into RPM

You must apply the formula to get the RPM value from the frequency. Now, this step depends upon the type of engine for which the tachometer is working. So you need to know whether the engine is a four-stroke or two-stroke. The large vehicles are mostly four-stroke engines, and the motorcycles are typically two-stroke engines.

If the engine is four strong, you must apply the following formula.

RPM = Hz × RPS × 60 sec

The Hz is the value of the frequency you have measured from the digital multimeter, and the RPS value depends upon the engine type.

  • For the four-stroke engine, you have to put the value of 2 RPS.
  • For the two-stroke engine, you have to put the value 1 RPS.

Step 7: Compare the results

Now you have to compare the RPM’s resulting value with the tachometer’s normal RPM value. If the results are close to 200 revolutions, your meter works well; if the results are far from the normal value, your tachometer faults it.

Final verdict

The tachometers are of great use, especially for car owners. The tachometers are not present in automatic cars, but people often make them installed because it seems quite useful to them to have a meter in their automobiles. The normal working of the tachometer is essential for the driver because it helps them select the right gears and speed adjustment.

Any fault in the tachometer will lead the driver in difficulty, so to save yourself from any problem, it is essential to keep testing the tachometer so that it cannot betray you on the way and you can easily measure the RPM value of your engine.

Testing the tachometer will be fine for those who know how to use the digital multimeter correctly, so if you have experience using the digital multimeter, you can go for the test easily by following the above-given guidelines.

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