The negatively charged nitrogen-vacancy (NV-) center is a defect in diamonds. The spin-dependent fluorescence of the NV- center is used to optically read out the spin state. By using this property, we can precisely measure external magnetic field changes at room temperature and atmospheric pressure. DC Magnetometry using the Ramsey sequence goes through the following steps: initialize the spin state - Pi/2 Pulse - free precession - Pi/2 Pulse - Optical readout. During free precession, the information of external magnetic field changes accumulates in the phase, and it is maximized when the Pi/2 pulse is accurate. Meanwhile, leveraging the identical N sensor ensembles increases the Signal-to-Noise Ratio (SNR) in the readout process and improves the sensitivity by 1/sqrt(N). However, when utilizing a large diamond ensemble to increase N, areas with underperformed individual sensitivity occur due to microwave (MW) pulse inhomogeneity. Consequently, only NV- centers in the region with uniform MW have been used to measure the magnetic field conventionally. In this study, we introduce a binary selection method to minimize ensemble sensitivity. NV- that can be used as ensemble sensors were identified and numerically characterized. As a result, we were able to obtain at least 2 times more gain.