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Operation
The basic theory of operation for an electrolytic tilt
sensor is as follows. Figure 1 depicts a single axis tilt
sensor. An electrically conductive fluid (electrolyte) is
sealed within a glass or ceramic cavity, to conduct
between a common, positive and negative electrode.
When at electrical null (i.e. level), both electrodes are
evenly submerged within the fluid, which remains level
due to gravity. This produces a balanced (equal) signal
output between the positive and negative electrodes, and
common.
As the sensor is rotated about its sensitive axis, the
amount of surface area submerged within the fluid will
increase for one electrode, and simultaneously
decrease for the other, thereby creating an imbalance
in the output (see figure 2). This imbalance, or
ratio, of one electrode to the other is directly
proportional to the angle of rotation.
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The illustrations above depict a relatively simple
‘open-cavity’ design, which would have a total
sensing range of approximately +/- 70 degrees. All
fluid filled type tilt sensors are limited to a
total sensing range of less than +/-90 degrees, as
the electrodes will become either totally
retracted or submerged when approaching that angle.
Once this occurs, the sensor is in what is known as
‘over-range’ or ‘saturation’, and no variation in
the output will be observed. This limitation can be
overcome with an approach, which incorporates a
second tilt sensor offset 90 degrees (in the
sensitive axis) to the first. This design
successfully provides a full 360 degree sensing
range, but requires a sophisticated multiplexing
routine within the electronics to discern the
correct angular position.
For narrow angle range measurements of below
+/-15 degrees, the geometry of the sensor
changes dramatically. To maintain acceptable
accuracy and sensitivity, the radius of the
fluid cavity must greatly increase (see
figure 3). Electrode alignment within the
cavity also becomes extremely critical. This
highly developed design produces the most
accurate tilt sensors available on the
market, with sub-arc second resolution.
Furthermore, by altering the profile of the
internal cavity, excellent results have been
achieved in attenuating sensitivity to
vibration, a typical problem with fluid
filled devices.
Dual Axis Tilt Sensors
When dual axis (X and Y) tilt sensing is required,
two sets of electrodes are required. The second
set of electrodes must be accurately positioned,
perpendicular (orthogonal) to the first set.
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