基于锁相环的谐振筒式液体密度传感器检测系统

Detection System for Cylinder Short Shell Resonant Liquid Density Sensor Based on Phase-Locked Loop

为实现液体密度的在线测量，设计了一种基于谐振原理的液体密度传感器检测系统，并进行了检测实验．液体密度传感器由薄壁短管式谐振筒和检测系统构成，所设计的检测系统以锁相环为核心，可实现无相差的频率跟踪，并由单片机对频率进行测量、控制和输出显示．实验测试结果表明：在1～5 kHz频率范围内，检测系统能够实时跟踪谐振频率的变化，频率跟踪不确定度为0．01 Hz；20℃下的传感器系数K0、K1、K2分别为153．8670 kg／m^3、－3．3214×10^6kg／（m^3· s）、1．7667×10^10kg／（m^3·s2）．在密度为700～1200 kg／m^3的测量范围内，传感器综合测量精度为0．076％．

To achieve the online measurement of liquid density , a detection system for the liquid density sensor based on the resonance principle was designed and tested .The liquid density sensor is composed of a short shell resonant cylinder and a detection system .Based on phase-locked loop （ PLL） circuit, the system can realize frequency tracking without phase difference , and the resonant frequency was meas-ured , controlled and displayed by the single chip microcomputer .The test result reveals that the system shows excellent resonant frequency tracking performance in the range of 1—5 kHz, with frequency track-ing uncertainty of 0.01 Hz.And the transducer factors are K0 =153.867 0 kg/m^3 ,K1 =-3.321 4 ×10 ^6 kg/（ m^3·s） and K2 =1.766 7 ×10^10 kg/（ m^3· s2 ） at 20 ℃.Comprehensive measurement precision of the sensor is 0.076%in density range of 700—1 200 kg/m^3 .