Continuous measurement of density of liquid - vibrates liquid at resonant frequency in quartz measuring cell and has sensor to convert signal into voltmeter output

摘要

The density of a liquid flowing through a measuring cell is measured by vibrating it at its resonant frequency. This frequency varies as a function of the density and allows continuous measurements to be made. A quartz measuring cell (14) comprises two concentric tubes mounted vertically and supported (20) rigidly. The cell is vibrated by an annular electrodynamic system (34). The vibration is sensed by an electromagnetic sensor (42, 44) and applied to a low frequency amplifier (46) the output of which is used to drive the vibrator (34) via a lamp (49). The amplifier output is applied to a frequency-to-voltage converter (50). The voltage is amplified (52) and a potentiometer (54) allows the output on a numerical voltmeter (58) to be set to zero when water is circulated.