3/35 9.1 Time,Frequency,and Phase-Angle Measurement The most convenient and widely utilized instrument for accurate measurement of frequency and time interval is the electronic counter-timer. Time and frequency standard is a piezoelectric crystal oscillator( 电晶体振荡器)； Typical frequency is 107 Hz,drift in frequency may be of the order of 3 parts in 107 Hz; .Quartz crystal clocks use various approaches to deal with the effects of temperature on the clock frequency,which is about 3 ppm (parts per million)for 0~50 C. 4/35 9.1 Time,Frequency,and Phase-Angle Measurement Signal Amplifier and shaper Gate 106 10310103 100 10 回回@回回回回 Decimal-Counting Units Gate control 102 10°6 10-3 10-4 sec sec sec Crystal oscillotor 10 MHZ Time-base dividers Fig.9.1(a)Frequency measurement The signal goes through a gating circuit to the decimal-counting units for a precisely timed interval(EPUT =event per unit time). Use a 2nd signal in place of the crystal oscillator to get the frequency ration of the two signals.9.1 Time, Frequency, and Phase-Angle Measurement ‹ The most convenient and widely utilized instrument for accurate measurement of frequency and time interval is the electronic counter-timer. z Time and frequency standard is a piezoelectric crystal oscillator (压 电晶体振荡器); z Typical frequency is 107 Hz, drift in frequency may be of the order of 3 parts in 107 Hz; z Quartz crystal clocks use various approaches to deal with the effects of temperature on the clock frequency, which is about 3 ppm (parts per million) for 0~50 ℃. 3/35 Fig. 9.1(a) Frequency measurement - The signal goes through a gating circuit to the decimal-counting units for a precisely timed interval (EPUT =event per unit time). - Use a 2nd signal in place of the crystal oscillator to get the frequency ration of the two signals. 9.1 Time, Frequency, and Phase-Angle Measurement 4/35