This paper present the developments of a low-cost Phasor Measurement Unit (PMU) for smart grid monitoring. This PMU is being developed for large-scale use in the distribution system allowing to monitor local and transmission level events. The device provides magnitude, angle and frequency data of the AC voltage in a synchronized way, between any point in the electrical system, even geographically distant. The instrumentation system is designed to connect in low voltage distribution network. For the acquisition and processing system is employed a general purpose hardware with architecture that allows high precision data and processing performance. The used phasor estimation method is Discrete Fourier Transform with fixed window and adaptive sample rate for minimizing spectral leakage effect. The results of this paper include the validation of instrumentation and acquisition system for steady state conditions.