A Comprehensive Guide to Tachometers and Their Applications

There are several main types of tachometers, each best suited to different uses and applications. In addition to electronic and mechanical tachometers, as explained above, the two principal types are contact and non-contact tachometers. These can then be broken down further as detailed in the sections below. 

Contact Tachometers

Contact tachometers require contact with a rotating object to measure its RPM. They work by using an optical encoder or a magnetic sensor, depending on the particular model. Direct contact with the shaft or rotating component must be maintained in order to achieve an accurate reading. 

Non-Contact Tachometers

Non-contact tachometers can perform measurements without the need for direct contact with the object. They commonly work with lasers or infrared light and are ideal for use with hazardous, hard-to-access, or mobile objects.

Laser Tachometers

Laser tachometers feature a laser on the end of the device which can be pointed at a rotating object to measure RPM via a direct reading function. They are a type of non-contact tachometer and are ideal for use in difficult to access areas, such as tight spaces or working with industrial machinery. Laser tachometers feature varying detecting distances depending on the particular model, but 1-2m is standard. 

Optical Tachometers

Optical tachometers include an optical sensor which is used to measure the rotational speed of the wheel, motor, or shaft. They use a laser or beam of light to measure the RPM and are also able to measure any differences in frequency of the reflected light. 

Using a tachometer is relatively straightforward, but the specific steps will depend on the type of tachometer you are using. Most commonly, you will be using an electronic or digital tachometer, which we will cover in more detail below.   

How to Use a Digital Tachometer?

Digital tachometers, also known as electronic tachometers, are the most common type of tachometer used today. They offer precise and accurate readings of RPM and are relatively simple to operate. Here's a step-by-step guide on how to use a digital tachometer: 

1. Power On: Ensure that the digital tachometer is powered on and the display screen is visible. 

2. Select Mode: Some digital tachometers have multiple modes for different types of engines. Select the appropriate mode based on your specific application. 

3. Choose Measurement Method: Digital tachometers can be used as both contact and non-contact devices. If you are using it as a contact tachometer, ensure that the sensor is in direct contact with the rotating object. If you are using it as a non-contact tachometer, follow the manufacturer's instructions for the correct distance and alignment with the rotating object. 

4. Point the Tachometer: If you are using a non-contact digital tachometer, point the device towards the rotating object. For laser tachometers, ensure that the laser is aligned with the object. For optical tachometers, maintain a clear line of sight between the sensor and the rotating component.  

5. Read the Display: Once the digital tachometer is in position, it will start to measure the RPM. Read the RPM value displayed on the screen. Some tachometers may also have additional features such as data logging or maximum/minimum RPM recording.  

6. Record Data: If necessary, record the RPM data for your specific application. Some digital tachometers have the ability to store measurements for later analysis. 

Digital tachometers are commonly used in automotive, industrial, and laboratory settings. They provide accurate RPM measurements, making them essential tools for monitoring and maintaining machinery and equipment.  

Testing a tachometer is an important part of ensuring that it is functioning correctly and providing accurate readings. There are a few different methods for testing a tachometer, but the most common is to use a known RPM source to compare the tachometer's reading with the actual RPM.  

In the case of a vehicle tachometer, you can use a handheld digital tachometer to compare the reading with the vehicle's tachometer. This will help you to determine if the vehicle's tachometer is providing accurate readings.  

For electronic or digital tachometers, there are typically self-test functions that can be used to verify the accuracy of the device.  

Wiring a tachometer is a common task for automotive enthusiasts and professionals. Tachometers are often added to vehicles to provide real-time feedback on engine RPM, which can be useful for performance tuning and monitoring. Here's a step-by-step guide on how to wire a tachometer to your vehicle: 

1. Choose a Mounting Location: Select a suitable location on the dashboard or instrument panel to mount the tachometer. Ensure that the tachometer is easily visible to the driver. 

2. Route the Wires: Route the tachometer wires from the back of the unit to the engine compartment. Use existing wire channels or create new ones as needed. Be sure to avoid sharp edges and hot engine components to prevent wire damage. 

3. Connect the Power Wire: Identify a switched 12-volt power source in the fuse box. This ensures that the tachometer only receives power when the ignition is turned on. Use a fuse tap to connect the power wire of the tachometer to the selected power source. Be sure to use the appropriate fuse rating for the tachometer. 

4. Connect the Ground Wire: Locate a suitable grounding point in the engine compartment. Clean the connection point to ensure a solid electrical connection. Connect the ground wire of the tachometer to the grounding point using a ring terminal and secure it with a bolt or screw. 

5. Connect the Tachometer Signal Wire: Identify the tachometer signal wire on your vehicle. This wire is usually located at the ignition coil, distributor, or ECU. Consult your vehicle's wiring diagram to find the correct wire. Use a wire splice connector to tap into the tachometer signal wire without cutting it. Connect the tachometer signal wire from the tachometer to the tapped wire. 

6. Secure the Wires: Use zip ties or wire loom to secure and protect the tachometer wires along their entire route. Ensure that the wires are neatly organized and do not interfere with any moving parts. 

7. Test the Tachometer: After wiring the tachometer, test the unit to ensure it functions properly. Start the engine and observe the tachometer reading. The reading should correspond to the actual engine RPM. If the reading is inaccurate, double-check the wiring connections and consult the tachometer's manual. 

Wiring a tachometer to your vehicle provides valuable engine RPM data, which can be beneficial for performance monitoring and tuning. If you're unsure about the wiring process, it's best to seek assistance from a qualified automotive technician. 

The below diagram shows how to wire a tachometer in an automotive application. It can be used in conjunction with the steps outlined above to provide a visual representation of how to wire a tachometer. Please note that wiring colour codes may vary from those shown in the diagram, depending on the make and model of tachometer you are using. As a result, you should reference the manufacturer’s guidelines for your particular device before installation.

Tachometers can be used in a wide variety of applications across a range of industries and environments. Typical applications could include: 

• Vehicles and automotive
• Boats and marine vehicles
• Machinery and mechanical systems
• Research and development
• Laboratories, test and measurement
• Maintenance and routine industrial operations

We've detailed a few of the most common applications for tachometers below.  

Cars 

In the automotive industry, tachometers are essential instruments used to measure the RPM of an engine. They are commonly found on the dashboard of cars, providing real-time feedback on the engine's performance. Tachometers help drivers to determine the most efficient gear to use and to monitor the engine's condition.  

Tachometers used within vehicles allow the driver to choose the most suitable gear and throttle settings for the current conditions. They are beneficial for optimising performance and protecting the engine from overheating, insufficient lubrication, and causing unnecessary wear and tear to components within the system. 

Boats 

Tachometers are also commonly used in marine applications, where they are often referred to as boat tachometers.