Biomedical Engineering Reference
In-Depth Information
TABLE 2-6
Manufacturers of a Selection of Accelerometers
Manufacturer
Product Range
Columbia Research Labs
99
Dataforth Corporation
1
Dytran Instruments
111
Endevco Corporation
104
Extech Instruments
1
Honeywell Sensing and Control
103
Instrumented Sensor Technology
43
Kistler Instrument Corporation
161
Measurement Specialities
187
MEMSTech
3
Ricker
9
Soltec Corporation
49
Wilcoxon Research
45
2.4.10 Tilt Sensors
Pinball players all know at least one application of tilt sensors. At their most basic, tilt
sensors consist of a pool of mercury and two contacts within a hermetically sealed glass
container that complete a circuit if the device is tilted.
More sophisticated tilt sensors can be manufactured from accelerometers mounted
on three orthogonal axes and equating the relative gravity vector in each. However, most
low-cost tilt sensors exploit the bubble-level principle. Figure 2-54 shows one axis of a
fluid-filled sensor tipped at
∼
15
◦
. As the sensor tilts, the surface of the fluid remains level
due to gravity. The fluid is electrically conductive, and the conductivity between the two
electrodes is proportional to the length of electrode immersed in the fluid. At the angle
shown, for example, the conductivity between pins
a
and
b
would be greater than that
between
b
and
c
.
Electrically, the sensor is similar to a potentiometer, with resistance changing in pro-
portion to tilt angle; therefore, the output can be determined using a Wheatstone bridge
in its dynamic unbalanced configuration. For small angles, typically less than 20
◦
, the
output voltage is proportional to the tangent of the tilt angle. However, as the angle in-
creases, nonlinearities become more pronounced, and more sophisticated microcontrollers
are required to apply corrections to the measurements to maintain accuracy.
FIGURE 2-54
Electrolytic tilt
sensor.
(a) Photographs.
(b) Schematic
showing fluid and
electrodes.
