Monday, 3 October 2016

Pulser - Receivers in ultrasonic testing

Ultrasonic pulser - Receivers are well suited to general purpose ultrasonic testing. Along with appropriate transducer and an oscilloscope, they can be used for flaw detection and thickness gauging in a wide variety of metals, ceramics,and composites. Ultrasonic pulser - Receivers provide a unique, low - cost ultrasonic measurement capability. The pulser section of the instrument generates short, large amplitude electric pulses of controlled energy, which are converted into short ultrasonic pulses when applied to an ultrasonic transducer. Most pulser section have very low impedance out puts to better drive transducers. Control functions associated with the pulser circuit include.
1)   pulse length or damping (The amount of time the pulse is applied to the transducer)
2)    pulse energy (The voltage applied to the transducer. Typical pulser circuits will apply from 100 volts 800volts to a transducer)  in the receiver section the voltage signals produced by the transducer, which represent the received ultrasonic pulses, are amplified. The amplified radio frequency (RF)  signal is available as an output for display or capture for signal processing. Control functions associated with the receiver circuit include.
3)   signal rectification ( The RF signal can be viewed as positive half wave, negative half wave or full wave
4)    Filtering to shape and smooth return signals.
5)     Gain, or signal amplification.
6)      Reject control.
The pulser - Receiver is also used in material characterization work involving sound velocity or attenuation measurements,  which can be correlated to material properties such as elastic modulus. In conjunction with a Stepless gate and a spectrum analyzer, pulser - Receivers are also used to study frequency dependent material properties or to characterize the performance of ultrasonic transducers. 

Transducer modeling in ultrasonic testing.

In high -technology manufacturing, part design and simulation of part inspection is done in the virtual world of the computer.  Transducer modeling is necessary to make accurate predictions of how a part of component might be inspected, prior to the actual building of that part. Computer modeling is also used to design ultrasonic transducers.
As noted in the previous section, an ultrasonic transducer may be characterized by detailed measurements of its electrical and sound radiation properties. Such measurements can completely determine the response of any one individual transducer.
There is ongoing research to develop general models that relate electrical inputs (voltage, current) to mechanical outputs (force,velocity)  and vice - versa. These models can be very robust in giving accurate prediction of transducer response, but suffer from a lack of accurate modeling of physical variables inherent in transducer manufacturing. These electrical -mechanical response models must take into account the physical and electrical components in the figure below.
The Thompson -Gray measurement model, which makes very accurate predictions of ultrasonic scattering measurements made through liquid - solid interfaces, does not attempt to model transducer electrical -mechanical response. The Thompson -Gray measurement model approach makes use reference data taken with the same transducer (s) To deconvolve electro - physical characteristics specific to individual transducer.
The long term goal term goal in ultrasonic modeling is to incorporate accurate models of the transducer themselves as well as accurate models of pulser-receivers, cables, and other components that completely describe any given inspection setup and allow the accurate prediction of inspection signals.