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- Frequency is regarded as one of most important indices for the operating power systems. Several digital techniques for measuring frequency have been presented in the last decades. This paper proposes a design and implementation an adaptive scheme using phase angle difference calculation for frequency measuring in power system. The advantages of the proposed technique are demonstrated by fault signals from EMTP simulation and user defined arbitrary signals by Excel program. The proposed technique is compared with the conventional methods. Performance test results indicate that the proposed technique provides accurate measures in presence of noise and harmonics and in case faults and is suitable for measurement near-nominal, nominal, and off-nominal frequencies. We can see that It will be useful in microprocessor based relays and digital meters that need to measure power system frequency.