Tham khảo tài liệu 'crc press mechatronics handbook 2002 by laxxuss episode 2 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Quartz Oscillator with 1 X 10-9 Frequency Offset Time Seconds FIGURE A sample phase plot. FIGURE The relationship between accuracy and stability. Dimensionless frequency offset values can be converted to units of frequency Hz if the nominal frequency is known. To illustrate this consider an oscillator with a nominal frequency of 5 MHz and a frequency offset of X 10- . To find the frequency offset in hertz multiply the nominal frequency by the offset 5 X 106 X 10-11 X 10-5 Hz Then add the offset to the nominal frequency to get the actual frequency 5 000 000 Hz Hz 5 000 Hz Stability Stability indicates how well an oscillator can produce the same time or frequency offset over a given time interval. It doesn t indicate whether the time or frequency is right or wrong but only whether it stays the same. In contrast accuracy indicates how well an oscillator has been set on time or on frequency. To understand this difference consider that a stable oscillator that needs adjustment might produce a frequency with a large offset. Or an unstable oscillator that was just adjusted might temporarily produce a frequency near its nominal value. Figure shows the relationship between accuracy and stability. Stability is defined as the statistical estimate of the frequency or time fluctuations of a signal over a given time interval. These fluctuations are measured with respect to a mean frequency or time offset. Short-term stability usually refers to fluctuations over intervals less than 100 s. Long-term stability can refer to measurement intervals greater than 100 s but usually refers to periods longer than 1 day. Stability estimates can be made in either the frequency domain or time domain and can be calculated from a set of either frequency offset or time interval measurements. In some fields of measurement stability is estimated by taking the standard deviation of the data set. However standard deviation only 2002 CRC .
