Abstract
A simple and sensitive transducer making use of a vibrating glass tube was applied for detecting the small difference of density between water samples.
The glass tube of about 10cm long filled with a sample of about 1cm3 is vibrated electromagnetically in its bending mode and the variation of the vibration frequency due to the difference of density of water in the tube is detected. For compensating the effect of temperature variation, a pair of vibrating tubes are used together and the density of a water sample is compared with that of standard water.
The procedure of measurement is as follows. The standard water is poured into one of the vibrators and the sample into another, the vibration period of each vibrator is measured with an electric counter, then the difference of density between the standard water and the sample water can be calculated from the difference in period.
It has been confirmed that the density can be compared with a better precision than 1ppm only by controlling the room temperature at (20±0.5)°C.
