3/35 9.1 Time,Frequency,and Phase-Angle Measurement Ei sin wt E。sin(wt+p 11N11113s1901t11共11/ 180 0 Fosin wt Calibrated phase-shift device Figure 9.3b Phase Angle from Lissajous Figure-Straight line An alternative method employing the same basic principle but a null technique. The calibrated phase-shift circuit is adjusted until the ellipse degenerates into a straight line.Then the phase angle is read directly from the phase-shifter dial. When the "sinusoidal"signal are noisy and/or distorted,special phase meters and tracking filters may be necessary for accurate measurement. 14/35 9.2 Liquid Level Using Motion Force Tx Measurement and/or control of liquid level in tanks is an important function in many industrial processes and in more exotic()applications, such as the operation and fueling of large liquid-fuel rocket motors. Motion Force transducer transducer (o) (61 Figure 9.4 Liquid Level Measurement Strategies -Fig.9.4(a):a simple float is coupled to some suitable motion transducer to produce an electrical signal proportional to the liquid level. -Fig.9.4(b):a displacer which has negligible motion and measures the liquid level in terms of buoyant force by means of a force transducer.Figure 9.3b Phase Angle from Lissajous Figure – Straight line z An alternative method employing the same basic principle but a null technique. The calibrated phase-shift circuit is adjusted until the ellipse degenerates into a straight line. Then the phase angle is read directly from the phase-shifter dial. When the “sinusoidal” signal are noisy and/or distorted, special phase meters and tracking filters may be necessary for accurate measurement. 9.1 Time, Frequency, and Phase-Angle Measurement 13/35 z Measurement and/or control of liquid level in tanks is an important function in many industrial processes and in more exotic(特殊) applications, such as the operation and fueling of large liquid-fuel rocket motors. 9.2 Liquid Level – Using Motion & Force Tx Figure 9.4 Liquid Level Measurement Strategies ▬ Fig. 9.4(a): a simple float is coupled to some suitable motion transducer to produce an electrical signal proportional to the liquid level. ▬ Fig. 9.4(b): a displacer which has negligible motion and measures the liquid level in terms of buoyant force by means of a force transducer. 14/35