In industrial production, mechanical operation and maintenance, and scientific research experiments, the rotation speed of rotating machinery is a key parameter to judge the operating status and performance of equipment, and tachometer, as a special measuring instrument, has become an important tool to ensure the stable operation of equipment with its various types and adaptation capabilities.
1. Types and characteristics of tachometers
Tachometers can be divided into four categories according to the structural principle, and can be divided into fixed and portable according to the method of use to meet the needs of different scenarios.
Classification according to structural principles
1. Mechanical tachometer: including centrifugal, timed and vibrating types, centrifugal type is common. The balance of centrifugal force and spring tension indicates the rotation speed, the structure is simple, no power supply is required, and it is suitable for scenarios with low accuracy requirements (such as small motor inspection), but the accuracy is only 1~2 levels, which is greatly affected by vibration and temperature.
2. Magnetoelectric tachometer: including magnetic induction, electric and electric pulse. The electric type is composed of generator, cable, motor and meter head, with good vibration resistance and can be installed in different places, widely used in diesel engines and marine equipment, with an accuracy of 0.5~1 level, and the electric pulse type can also link the data acquisition system.
3. Strobe tachometer: with degree dial reading, digital display and mechanical strobe type, working based on the strobe effect of visual persistence. Non-contact measurement, no need to connect the rotating shaft, suitable for high-temperature and high-speed scenarios (such as turbines), with an accuracy of 0.1 level, and can also observe the still image of the rotating body to judge equipment failure.
4. Electronic calculated tachometer: including handheld digital type and sensor-counter combination type. The handheld model is compact and portable, using photoelectric or Hall sensors to collect signals, digital display, accuracy level 0.01, suitable for on-site rapid measurement; combined type is mostly used in fixed scenarios, can continuously monitor and store data, and is suitable for large equipment (such as compressors).
Classification by method of use
Fixed type - installed on the equipment, connected to the shaft through the transmission device, working in a vertical state, suitable for long-term monitoring of fixed equipment (such as machine tool spindles), but with poor flexibility.
Portable - independent adult, with rubber or metal connectors to temporarily connect the shaft (non-contact type does not need to be connected), horizontal state work, suitable for mobile maintenance, some contact types need to pay attention to the installation coaxiality.
In addition, although the speed odometer and speedometer measure the line speed, their principle is similar to that of the magnetoelectric tachometer, only through the scale and transmission ratio adjustment function.
2. Selection principle of tachometer
The selection should be based on the scenario, requirements and equipment characteristics:
Precision requirements——For scientific research or precision calibration, choose strobe type and electronic calculation type (level 0.1 and above); choose mechanical type and ordinary magnetoelectric type (level 1~2) for daily inspection.
Equipment working conditions- High-speed equipment (such as high-speed motors) should avoid mechanical types, choose magnetoelectric and strobe types; choose non-contact type for high temperature and corrosive environments; fixed equipment for long-term monitoring, portable for mobile maintenance.
Operating conditions——If there is no power supply, choose mechanical and battery-powered handheld models; The electronic calculation formula of the automatic production line needs to be selected with data linkage and signal output; If the space is small, choose a non-contact strobometer.
For example, a handheld digital tachometer is used to measure household fans, a fixed electronic calculation formula is used to monitor thermal power turbines, and a strobe instrument is used to detect high-temperature gears.
3. Verification of tachometer
In order to ensure accurate measurement, the tachometer needs to be regularly verified by the "tachometer calibration table" (including the steady speed source and indicator instrument), and the commonly used indicator instruments are:
1. 0.5 level standard tachometer - after adding the correction value, the tachometer of 1.5 and below can be verified, which is easy to operate.
2. Digital tachymeter - JSS-2 type (photoelectric sensor + 6-digit frequency meter), SZ-4 type (photoelectric sensor + 4-digit counter), 0.1 level standard can be established when the speed source is stable, suitable for medium and high-precision calibration.
3. Strobe disk - use a standard quartz oscillator, the accuracy is 2 orders of magnitude higher than 0.1 level, and the 0.1 level standard can be built to verify all tachometers of 0.5 level and below.
The verification process is: connect the test subject and the speed source, output the standard speed, compare the reading with the standard value, and judge whether the accuracy is qualified.
4. Summary
There are many types of tachometers, covering the needs of multiple fields, and the selection needs to comprehensively consider the accuracy, working conditions and operating conditions, and regular verification is the key to ensure the reliability of the data. With the development of technology, tachometers are upgrading to high precision, intelligence, and harsh environment resistance, which will better support the efficient and safe operation of rotating equipment in the future.
