Table of Contents

## Overview:

In this article, learn **what is pulse per mile with definition**, **pulse per mile calculator with formula**, What is VSS and more in detail. Generally Pulse per mile is calculated in vehicles to measure speed with the help of VSS through Speedometer. To be clear read the below definition and formula to better understand and calculate PPM(Pulse Per Mile) for vehicles.

## What is Pulse per Mile?

As we all know speed of the vehicles is measured in miles per hour or kilometers per hour. To measure this speed a Reluctor gear along with sensor is fitted on axle cases or on transmission. These sensors are also called as **VSS(vehicle speed sensor)**. There are two types of sensors reluctance sensor which generates sine wave and Hall effect sensor generates a square wave in the output signal.

The Reluctor gear has certain number of tooth, when it rotates a magnetic sensor which is fixed generally on case reads the number of teeth moved in certain time. Each tooth movement is counted as one pulse. For example, If the Reluctor gear has 30 teeth and if it takes one complete rotation then 30 pulses are generated.

## Definition:

**“The number of pulses generated when a vehicle travels one mile of distance is called Pulse per mile or Pulses per mile”**.

## Pulse per mile calculator for a car or vehicle

Generally the speedometer or Odometer will do all the internal calculations and just show the speed of the vehicle. Now lets know in details how the calculations were done and write the formula.

**Pulse per mile** depends on the Axle ratio, vehicle or car tire diameter, number of teeth on the Reluctor gear.

**Axle ratio: ***Axle ratio* is the number of revolutions the output shaft or driveshaft needs to make in order to spin the axle one complete turn.

Now coming to the car tire we need to measure the diameter of the tire to calculate the circumference of the tire.

As the tire is in the shape of circle, the circumference of the vehicle tire is : π.d

as we measure the tires in inches, we get circumference in inches.

now lets calculate the number of times the tire revolves for one mile. One Mile = 63360 inches.

No. of revolutions of tire in 1 mile = 63300/π.d

Now we need to multiply with axle ratio as the drive shaft revolves the ratio times than tire axle. Our reluctor gear is fixed on drive shaft.

Related article: Rotary encoder with Arduino in detail with example codes

Number of revolutions of Reluctor gear =(63360/π.d) x Axle ratio.

Now, finally we need to multiply the no of revolutions of reluctor gear with the number of tooth the reluctor gear has. As we already learnt that one tooth movement capture is equal to one pulse.

## Pulse per mile formula

**Pulse per mile = ((63360/π.diameter of tire) x Axle ratio) x no. of tooth.**

## Lets check with an example:

- Lets imagine the tire diameter d = 26 inch.
- Axle ratio = 3.73
- No. of tooth on reluctor gear = 10.

**Pulse per mile = ((63360/3.14 x 26) x 3.73) x 10**

=((63360/82) x 3.73) x10

=(772 x 3.73) x10

=2880 x 10 = 28800 pulses/mile.

Also read: DIY Tachometer to Measure Accurate RPM using Arduino