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In Automatic Control, Mechatronics and Robotics technical tasks is desirable to have information about certain parameters to control, supervision or fault detection in a system. This information can be estimates by direct measurement of particular variables or using special devices capable of observing the state of system under control. If the first option is selected a physical sensor is required.

One commonly selected option are the Frequency Domain Sensors (FDS), this devices converts the desired parameter into a square wave with a frequency or period proportional to physical quantity under measurement. In order to reduce time to obtain information for control a system with sufficient quality and good reliability, a high performance method for frequency measurement is desirable.

Historically, many analog and digital frequency measurement techniques have been proposed. In a basic digital measurement technique, the zero crossings of a signal are detected and a square wave is formed, representing transitions between the binary logic levels low and high. Selected digital logic state is detected and counted, and a measure of frequency is determined by the number of complete cycles occurring in the square waveform during a fixed time interval, determined by the counter's time base [1]. This method can be classified as the classical method and their main error source is the *±1* error count derived from the relative timing of gate and signal, which means that the resolution is *1* Hz during a *1*s gate time for all input signal frequencies [2]. For allow high resolution frequency measurements gate time larger than *1*s should be selected.

In reciprocal counting measurement techniques, the gate time is determined by electronic detection of two kinds of same phase difference situations between two pulsed signals with different frequencies [3], or by electronic detection of two coincident pulses of two regular independent pulse trains [5 -6]. In these methods the quantization error (±1 count error) can be overcome satisfactorily [2-3,6]. But, in [3] a high distinguishability analog circuit for phase coincidence detection is required and in [5] the relative methodical error is pulse width dependent for random selection of stop measurement pulse coincidence and, is experimentally probed that relative methodical error can be reduced by two o three orders of magnitude than frequency meters based on classical method [6].

Continuous time stamping principle change the scenario in frequency measurement, because in each measurement has not a defined start (= start trigger event), and a stop (= stop trigger event) plus a dead-time between measurements to read out and clear registers, do interpolation measurements and prepare for next measurement [2]. In this technique Linear regression using the least-squares line fitting is used because for a onesecond frequency measurement in a fast processing counter could contain hundreds o thousands of paced time-stamped events, no just a start event plus a stop event [2]. But fast digital circuits are needed to implement this technique.

However, a fast method for frequency measurement base pulse coincidence principle and rational approximations was proposed and, was shown that under a novel numerical condition for detect the stop trigger event measurement resolution is improved. Instrumental errors are caused only by the reproducibility of the reference frequency and relative measurement error is comparable to the reproducibility of reference oscillator. [7]. Simple digital circuits are needed to practical implementation of this technique.
