What is the difference between an engine tachometer and an odometer?
2 Answers
Here is an introduction to the differences between an engine tachometer and an odometer: 1. Different functions: The odometer (mileage meter) is located below the tachometer and displays the distance traveled in numerical form. The engine speed is related to the number of work cycles per unit time or the effective power output of the engine, meaning the engine's effective power varies with different speeds. Therefore, when specifying the engine's effective power, the corresponding speed must also be indicated. Speed is a physical quantity representing the ratio of the number of rotations to time, commonly expressed in engineering as speed = number of rotations/time, and is an important parameter describing rotational motion. In electrical engineering, measuring the speed of motors and their driven equipment often requires the use of a portable tachometer. 2. Different principles: The principle of the odometer: The principle is quite simple. Since the diameter of the car's wheels is known, the circumference of the wheels remains constant. This allows the calculation of how many rotations the wheels make per mile, a number that also remains constant. Therefore, as long as the number of wheel rotations can be automatically accumulated and then divided by the number of rotations per mile, the distance traveled can be obtained. Tachometer principle: The tachometer receives digital pulse signals (emitted by a sensor), processes them, and directly reads them into the CPU's counting port. The software calculates the speed and the corresponding position of the pointer, then through the CPU's control port, amplifies and drives the stepper motor to rotate in positive or negative directions, indicating the corresponding speed value (the pointer is directly mounted on the stepper motor's rotating shaft). Each step of the stepper motor is only 1/3 of a degree.
The tachometer displays how many revolutions the engine makes per minute. When driving, I mainly use it to monitor the engine's operating condition. For example, the optimal shift point for a regular family car is usually between 2000 to 3000 RPM for the smoothest gear change. The odometer is much simpler—it only records the total kilometers the vehicle has traveled. This data is particularly important for used car transactions as it indicates the vehicle's usage intensity. The tachometer changes in real-time; when you press the accelerator, the needle shoots up. In contrast, the odometer is like a snail climbing a hill, slowly accumulating numbers. Additionally, maintenance intervals are based on the odometer—oil changes are typically due every 5,000 or 10,000 kilometers. However, newer cars now also feature a trip odometer, which records the distance of a single journey, making it easier to calculate fuel consumption.
