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Tabletop centrifuges are very popular in the market

2018/5/2 14:47:52      click :

It is well known that in the era of rapid development of technology, the variable speed AC will gradually replace the DC speed control, speed control system is the central part of the desktop centrifuge, by the control, power driver and of the three elements of the electrical components, mainly to control the speed of the motor. DC speed contributed in the development process of the centrifuge, its main feature is a good start and braking, wide range of speed, simple structure, low cost, theory and practice are more mature and so on, so The first in the eighties centrifuge has been widely used and so mature, so before the eighties has been widely used in a centrifuge, and the application is still ongoing improvements, such as DC motors improved head wear Copper resistance and carbon brushes to delay cycles of life motor change and long centrifugal desk brushes.

Step-down DC drive scheme SCR DC is a classic, simple structure, mature technology, the basic needs of the speed of the centrifuge, and therefore it is widely used at home and abroad centrifugal. Its main disadvantage is the rectified difference of wave, great ripple of the current, with tendency to stop the phenomenon of light load, to maintain a direct DC current, the need to add a heavy smoothing inductor, increasing the volume and the weight of the table centrifuge. In the 1980s, with the development of fully controlled power devices such as power transistors and FET, the switching power conversion technology is gradually applied, such as Germany Eppendorf 5410 and 5402 in a DC speed control system Centrifugal centrifuge, which technology is mainly through a DC chopper frequency, regulate the working relationships of the impulses change the secondary voltage as a DC power supply. Since the switching frequency is high, generally lower than the own inductance only 50 kHz was filtered to get a smooth continuous motor current, overcomes the drawbacks of phase control of the DC speed thyristor, and the speed of therefore, smoother, wider range of speed.
Open-loop speed control centrifuge table is the simplest program of speed control, or even a dozen discrete components or a collector to form a system, so it has some inexpensive internal centrifuge still using this program, The main disadvantage is the need for manual speed control, can not control the motor current, the speed accuracy and the added technical value are relatively low. Given the limitations of open-loop Benchtop Centrifuge velocity, the most widely used in the home and abroad centrifugal feedback loop control speed double current mode both have speed feedback, its main advantage is the automatic control of speed, acceleration speed, speed overshoot Small, high precision, current limiting function to avoid motor overcurrent damage.

Although the DC speed long history and technology matures, but the mechanical switch DC motor switching is your Achilles heel, which limits the motor speed, switch causes interference, such as need to be replaced carbon brushes so that the speed early or High-speed centrifuge the program had to use indirect gear shift or other methods, which increases the cost and size, which reduces the service life and reliability. In the late seventies, outdoor tabletop speed centrifuge in the first frequency control technology, mainly by changing the speed regulation of the supply frequency induction motor. Since the induction motor without mechanical switch, not only eliminates the trouble of replacing the carbon brushes, but also increase the speed of the motor, or even hundreds of thousands rpm tabletop centrifugal speed, can drive directly, greatly simplifying the structure of the centrifuge.

After the nineties, foreign manufacturers of centrifuges main line of products that are used almost frequency control technology, regardless of speed, high-speed or low-speed centrifuge, our country is now classified as a research programs Centrifugal table, some manufacturers have introduced new generation of Tabletop centrifuge. Depending on the AC motor, frequency control is also somewhat different, currently there are three centrifugal motors in a table. Its start and stop acceleration rate is twice as fast as similar centrifuges, but currently the most popular and most mature or Tabletop centrifuge.