Operating instructions

8 METTLER TOLEDO DE40/50/51 Density Meter
Note: The DE40/DE50/DE51 calculate the relative density: the density of water at 4 °C
(d
t
t
) or at the measurement temperature (d
t
t
) is available as a reference. For this
purpose, the density of pure water as a function of temperature is stored in the
instruments.
Density
3. The density
3.1 Definition
The density ρ is the quotient of the mass m and the
volume V of a substance (mass density). As the
density depends primarily on the temperature, the
latter must always be specified.
The relative density is the ratio of the density ρ of a
substance to the reference density ρ
ο
of a reference
substance under conditions which must be
specified separately for both substances.
3.2 Measurement principle
The density measurement of the DE40 and the
DE50/DE51 is based on the electromagnetically
induced oscillation of a glass U-tube.
One complete back and forth movement of a vibration
is a period, its duration is the period of oscillation T.
The number of periods per second is the frequency f.
Each glass tube vibrates at a so-called characteristic
or natural frequency. This changes when the tube is
filled with substance. The frequency is a function of
the mass. When the mass increases, the frequency
decreases, in other words period of oscillation T
incrases.
A magnet is fixed to the measurement tube in the
DE40/DE50/DE51 which is made to oscillate by a
transmitter. A sensor measures the period of
oscillation T.
Amplitude
Time
Oscillation
period T
f =
T
1
[s
-1
]
ρ =
V
m
[kg/m
3
] or [g/cm
3
]
d =
ρ
0
ρ
[1]
Magnet
Oscillator/
Vibration meter
Measurement tube of defined
volumetric capacity