Inside or outside the tank? Inside or outside the tank will greatly affect the cost of the transducer. Applications that require transducers to be mounted on the inside of a tank need sealed transducers that are mechanically more complex as they need to withstand chemical (liquid) exposure. On the other hand, applications that allow transducers to be mounted on the outside of a container can utilize bare, unsealed transducers which are much lower cost. These applications also have the added benefit of being non-invasive and can be retrofitted to existing tanks. In general, if an application can tolerate external mounting, total system cost is reduced and the system benefits from higher reliability and accuracy.
Top or bottom of the tank? Top or bottom will also greatly affect the cost of the transducer and the resonance frequency. If the transducer is mounted on the bottom of the tank on the outer wall, the bare transducer type can be utilized. However, if the transducer is mounted on the top in the inner wall, for example to measure level, the conducting medium for the ultrasonic wave is now a gas, and thus the resonance frequency of choice needs to be 40 kHz to 200 kHz depending on the level accuracy requirement and level height that is being monitored. For fluid identification applications, transducers are typically mounted on the outside of the outer wall. Since the transducers will not come in contact with the liquid medium inside the container, the less expensive, bare transducers can be utilized.