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.