SNAA266A April 2015 – November 2015 TDC1000 , TDC1000-Q1 , TDC1011 , TDC1011-Q1
Ultrasonic sensing utilizing Time Of Flight (TOF) measurement techniques are used in liquid level and fluid identification sensing in the automotive, consumer and medical markets. Ultrasonic (TOF) sensing can yield high accuracy and high reliability with low-power consumption for all of these markets. In order to achieve the best cost-to-performance combination, care must be taken in selecting the proper transducer. Cost-sensitive applications can be serviced by utilizing bare (unsealed) transducers making measurements directly through container walls. This application note discusses how to select the most appropriate transducer for liquid level sensing and fluid identification applications. In addition to sensor selection, proper techniques for mounting transducers on the outside of tanks for rapid prototyping is also addressed in this application note.
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Selecting the right transducer starts with understanding what and how you want to make your level sensing or fluid identification measurement. TI’s TDC1000 handles ultrasonic TOF measurements and can work with transducers that have a resonance frequency from 30 KHz to 4 MHz. When choosing a transducer, the following questions need to be answered: What frequency? What size? Which Piezo material? Where does it need to be mounted? What temperature range? Each of these questions will be discussed in more detail below.
The frequency you choose depends on your application. Every transducer will resonate at multiple frequencies depending on its piezoelectric material composition and its geometry. A deep discussion of this topic is not within the scope of this document. As such, this application note only discusses transducers of the disc variety working in axial or thickness mode.
where:
ѳ = Beam divergence angle
V = Sound Velocity in the material (m/sec)
D = diameter of transducer (m)
F = Frequency of transducer (Hz)