A phase-locked loop system for the monitoring of resonance frequency using LabVIEW and a software-defined radio platform

In a large range of applications, resonant sensors can be properly employed, as its resonance frequency is used indirectly to infer the measurement parameters. There are different approaches for extracting the resonance frequency, and one of the most efficient and explored methodologies is the phase-locked loop (PLL) system. One possibility to implement this system is with off-the-shelf analog devices and data-acquisition platforms. This alternative is relatively easy to implement, but there are some inconveniences, such as the need for several connections with coaxial cables between the devices, the considerable occupied space to implement the circuit, the use of adapters, increased propensity to external noise, both electrical and mechanical, besides the difficulty of making changes in the circuit topology. In this work, the use of a software-defined radio (SDR) platform with the LabVIEW environment is demonstrated as an alternative of a faster and reliable PLL implementation with only one component. A resonant cavity sensor is used to validate the implemented system. The preliminary results show that the system was able to properly track the resonance frequency of the sensor and that it can be a very useful platform to test different control strategies.