Biomedical Engineering Reference
In-Depth Information
FIGURE 2-65
Diagram of two
impeller flowmeters.
(a) In-line.
(b) Insertion.
when properly specified and installed, have good accuracy, particularly with low-viscosity
liquids.
A major concern with turbine meters is bearing wear. Bearingless options have been
developed using the liquid itself for lubrication. These are particularly important in medical
applications, particularly implanted ventricular-assist pumps, discussed in Chapter 9.
2.4.13.7 Impeller Flowmeters
Impeller flowmeters, also called paddle-wheel meters, are one of the more commonly
used types. They are a direct offshoot of the old undershot water wheels. In-line meters
are constructed as a unit that includes inlet and outlet orifices, whereas the insertion type
can be installed into existing pipes through a round hole, as shown in Figure 2-65.
In-line meters are more sensitive than axial turbine flowmeters at low flow rates
because the blade incidence angle is much larger. They are also relatively insensitive to
the flow regime (laminar or turbulent).
As with the turbine meters, paddle rotation is usually sensed using a magnetic pickup,
and the flow rate is determined by measuring the pulsation rate.
2.4.14 Temperature Sensors
The measurement of temperature is probably one of the most common sensing require-
ments in the medical field. The human organism can function effectively over only a small
