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Introduction 3098 Technical Manual
1-4
When the enclosure is sealed, the complete instrument is insulated so that rapid changes in ambient temperature will not
upset the temperature equilibrium of the unit and produce thermal shock errors.
Note that the 3098 may have been supplied without an enclosure - see Important Notice on page 1-1.
1.2.1 Meter Sensing Element
The gas density meter consists of a thin metal cylinder which is activated so that it vibrates in a hoop mode at its natural
frequency. The gas is passed over the inner and outer surfaces of the cylinder and is thus in contact with the vibrating
walls. The mass of gas which vibrates with the cylinder depends upon the gas density and, since increasing the vibrating
mass decreases the natural frequency of vibration, the gas density for any particular frequency of vibration can be
determined.
A solid state amplifier, magnetically coupled to the sensing element, maintains the conditions of vibration and also
provides the output signal.
1.2.2 Installation
The 3098 has been designed to be installed wall mounted, a typical installation set-up being given in figure 1-3 below.
SIGNAL
CONVERTER
HAZARDOUS AREA SAFE AREA
VENT TO
ATMOSPHERE
VALVE F
GAS
LINE
GAS FOR
CALIBRATION
VALVE A
VALVE B
ISOLATION
VALVE
PRESSURE
REGULATOR
ELECTRICAL
CABLE
SAFETY
BARRIERS
IN OUT
VALVE C
Figure 1-3: Typical 3098 Specific Gravity Measuring System