Thermal dispersion technology places two
thermowell protected platinum RTD tempera-
ture sensors in the process stream. One RTD
is heated while the other senses the actual
process temperature. The temperature differ-
ence between these sensors is measured
and is proportional to the mass flow rate
of the fluid.

Thermal dispersion provides a gas flow
measuring solution that is easy to install and
virtually maintenance-free to save you time
and costs. It has no moving parts and is inher-
ently multivariable, measuring both flow and
temperature. Insertion styles are particularly
well suited for larger line size applications
because probe length and the number of
sensors are easily and economically added.

FCI flow meters feature a patented no-moving
parts flow element design that provides
direct mass flow measurement with just
a single process penetration. This saves
space and eliminates unnecessary installa-
tion, expense, and performance degradation
associated with separate temperature and
pressure sensors, and density calculation
devices needed with inferred mass flow
techniques. With no moving parts to plug or
foul, FCI flow meters deliver extensive cost
savings over alternative high maintenance
technologies. The result is an accurate and
highly repeatable mass flow measurement
at the lowest total installed cost

Measurement principle
The clamp on flow transducers are mounted onto the outside of the pipe that is completely filled with the fluid. The ultrasonic signals are emitted alternately by a transducer and received by the other. The physical quantities are determined from the transit times of the ultrasonic signals.
Transit time difference principle
As the fluid where the ultrasound propagates is flowing, the transit time of the ultrasonic signal in flow direction is shorter than the one against the flow direction.
The transit time difference ∆t is measured and allows the flowmeter to determine the average flow velocity along the propagation path of the ultrasonic signals. A flow profile correction is then performed in order to obtain the area averaged flow velocity, which is proportional to the volumetric flow rate.