Rotation speed concept

Rotation speed is a physical quantity of the ratio of the number of revolutions of a rotating body to time. In engineering, it is usually expressed as speed = number of rotations/time, which is an important parameter describing the rotation of an object. Electricians often need to measure the speed of a motor and its driving equipment, and a portable tachometer is used. The tachometer is an instrument used to measure the rotational speed and linear speed of a motor. There are many types of tachometers, and portable ones generally include mechanical centrifugal tachometers and digital electronic tachometers.

Working principle

The tachometer will process the received digital pulse signal (sent by the sensor) and directly read it into the counting port of the cpu, and the speed will be calculated by the software to correspond to the pointer Then through the control port of the cpu, after zooming in, the stepping motor is driven to rotate in the positive and negative directions, indicating the corresponding speed value (the pointer is directly installed on the rotating shaft of the stepping motor), and the stepping motor takes only 1/3 degree. .

Technical parameters

Speed: 1~99999 rpm

Frequency: 0.0167~1666.6 Hz

Period: 0.6~60000ms< /p>

Counting: 1~99999

Line speed: 0.1~3000.0 m/min

Measurement accuracy of tachometer: full range error <0.02% exceeding High precision (speed, frequency, period)

Measurement distance of tachometer: photoelectric type: 50~300mm; laser type: 50~3000mm

Display: five significant digits Dynamic liquid crystal floating point display

Signal output: TTL level pulse output

Power supply: two AAA batteries, which can be used continuously for 24 hours

Working advantages

1. The pointer with large static moment is not easy to shake and has strong anti-vibration performance.

2. It adopts a single-chip microprocessor through software design, so it has high precision and strong anti-interference.

3. The hour meter uses liquid crystal display without mechanical parts, so it is more reliable and more contemporary.

Because the pointer indication conforms to the traditional visual recognition habits, and is convenient for computer remote processing and networking requirements, digital stepping motor meters are the development trend of modern automobile meters and motorcycle meters. Switec's stepping Motors have been widely used in various automobiles, motorcycles and engineering machinery instruments at home and abroad. The miniature stepping motor for vehicles is a special new type of automobile instrument accessories. The instrument designed with it not only conforms to the traditional visual recognition habits but also meets the requirements of digital processing. It is an ideal accessory for modern instruments.

Classification of tachometers

Centrifugal tachometers

Centrifugal tachometers are composed of transmission parts, receivers and indicators. It is one of the most traditional rotational speed measurement tools. Its main advantage is simple structure and convenient use, but its disadvantage is that the accuracy is relatively low. Its working principle is a tachometer formed by using the centrifugal force of the rotating mass and the principle of rotation angle or ratio. When the shaft of the tachometer rotates, the weight on the centrifuge leaves the shaft center under the action of inertial centrifugal force, and drives the hands to rotate through the transmission device. The rotation speed of the shaft is determined according to the position of the pointer in the balance between the centrifugal force of inertia and the elastic force of the spring.

Magnetic tachometer

The magnetic tachometer uses a rotating magnetic field to generate rotational force on the metal cap, and uses the balance of the rotational force and the hairspring force to indicate the rotational speed. The magnetic tachometer is a model of the successful use of magnetic force. It is a mechanical tachometer that uses the principle of magnetic force; it is generally installed on-site, and can be installed in short distances with a flexible shaft. The magnetic tachometer is simple in structure. The flexible shaft is easily damaged when installed in a remote location.


Tachometer (4 photos)

The tachometer is generally set in the dashboard and placed symmetrically with the speedometer . The tachometer works according to the principle of magnetism. It receives the pulse signal generated when the primary current in the ignition coil is interrupted, and converts this signal into a displayable speed value. The faster the engine speed, the more pulses produced by the ignition coil, the greater the speed value displayed on the table.

Cars are generally electronic tachometers, with pointer type and liquid crystal digital display type. There is a digital integrated circuit in the meter, which drives the pointer to move or display digitally after calculating the voltage pulse from the ignition coil. There is also a tachometer that takes the pulse signal from the generator and sends it to the tachometer circuit to display the speed value. However, the value is not accurate due to factors such as the slippage of the generator belt.

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