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Basis of Ultrasonic Signal Generator

08 Jan, 2016 Ultrasonic Generator
ultrasonic signal generator

Ultrasonic signal generators are used to convert AC electricity at voltage of 220V to 380 Volts and at a frequency of 50 or 60 Hz into a high-frequency electrical energy which can drive the ultrasonic devices. With the development of ultrasonic technology, signal generator are widely applied in the fields of industrial cleaning, welding, drilling, polishing, homogenization, etc.

Principle of ultrasonic signal generator


The generator produces a signal (can be sine signal or pulse signal) with certain frequency, which equals to the frequency of transducer. The complete generator circuit should also have mature feedback system, mainly to provide two feedback signals as follows:

The first is to provide the output power signal. We know that when the voltage changes, the output power will increase or decrease along with it, and further causes the unstable mechanical vibration. So that the power amplifier can be adjusted through the power feedback signal to stabilize the energy output.

The second is to provide the frequency tracking signal. At the resonant frequency, ultrasonic devices can steadily operate with highest efficiency. However the resonant frequency point may drift smally in some cases such as assembly or aging of electrical elements. The frequency tracking signal can be used to track the frequency of ultrasonic transducers in a certain range, to help ultrasonic generator to maintain the optimal working condition.

Types of ultrasonic signal generator


Ultrasonic signal generator can be divided into self-exitation generator and separate-excitation generator according to circuit design.

The self-excitation circuit has no signal source, and conbine the oscillation, power amplifier, output transformer and transducers as a closed loop to meet the requirement of amplitude and phase feedback, and eventually become a power amplification oscillator which have the same resonant frequency with transducers. Self-excitation generators are commonly used to drive small number of transducers, but for a large number of transducers, they can't be adjusted to achieve resonance effect. So at present, for most of the high-power ultrasonic application, separate-excitation circuit are preferred.

Separate-excitation generator mainly contains two pars of oscillator and amplifier in structure. In general, the ultrasonic energy is applied to the transducers through the coupling of output transformer. The circuit is composed of signal source and signal amplification.

Signal source uses CPU as the core for signal generation and operation, generally driven by voltage of 12-15V, and provide square wave signal for signal amplification circuit. Many functions such as timing control can be realized by controlling the signal output of signal source. Low voltage control can ensure the safety and reliability.

Signal amplification is used to amply the signal, and then output to the ultrasonic transducer. Different output circuit and voltage greatly affect the transmission efficiency, low output voltage means the high energy consume inner the generator and cause the overheat of transducers. For good results, appropriate adjustment of the circuit can increase the output voltage for transducers.

Matching design of signal generator


Ultrasonic generators are different from common amplifiers in matching with ocsillators. Common amplifiers relate to only impedance transformation, that means to make maximum power amplifier output power rating via matching the internal resistance of the source with the load resistance. Beyond this, ultrasonic generators offer turning match for transducers, utilize impedance elements with a certain value, and adjust it vibrate at the same frequency to the impedance of load to make the system work in the optimal condition.

 
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