Fluid-actuated level device

Details Fluid-actuated level device Fluid-actuated level device

2000-08-11

2002-12-17

Fulton, Christopher W. (Department: 2859)

Geometrical instruments

Indicator of direction of force traversing natural media

Level or plumb, terrestrial gravitation responsive

Reexamination Certificate

active

06493954

ABSTRACT:

FIELD OF THE INVENTION
The present disclosure relates generally to devices used in identifying two or more points on a horizontal plane, specifically, a fluid-actuated level device for locating points on a level plane.
BACKGROUND
Numerous level devices have been used to identify points on a horizontal plane. Level devices are particularly useful in the building industries where positioning a structure on a level plane is critical to the design and implementation of the structure. Such structures include, for example, foundations, decks, counter-tops, suspended ceilings, suspended sprinkler systems, pools, fences, and sewer lines. Two level devices are commonly used in the building industries: bubble levels and fluid-actuated levels. Bubble levels are well-known in the prior art. Two types of fluid-actuated levels are generally known in the prior art. Both types operate according to the same general principle: if fluid is allowed to flow through a tube and the end of the tube are raised above the body of the tube, then gravity pulls the fluid such that the fluid-levels at the tube ends settle on the same horizontal plane. The first type of fluid-actuated level generally consists of a sealed tube with a pressure-sensing device connected to a tube end for measuring air pressure in an air cavity at the tube end. The pressure varies with the displacement in air volume at the tube ends caused by the gravitational pull on the fluid; the sensing device may thus be calibrated to a particular air pressure, typically a pressure corresponding to when the fluid-levels in the two ends lie on a horizontal plane. One drawback of the pressure-sensitive fluid-actuated level is its cost, which is often prohibitive for commonplace construction applications.
The second type of fluid-actuated level (generally less costly than the first type) typically uses a fluid-level sensing device connected to an end of an unsealed tube. A fluid-actuated level of this type is disclosed in U.S. Pat. No. 4,434,561 and shown in
FIGS. 1-2
. In
FIG. 1
, fluid-actuated level device
10
has a housing unit
17
and a tube
11
for holding an electrically conducting fluid
18
, typically tap water. Tube
11
has a reference-end
21
, connected to the housing unit
17
, and a working-end
20
. Working-end
20
is used by a worker for locating level points in a proposed horizontal plane, or reference plane. Housing unit
17
has a base electrode
15
and a reference electrode
14
inserted through the walls of the reference-end
21
for detecting the fluid-level in the tube
11
. Electrodes
14
,
15
are connected to a power source
12
and a signal generator
13
, such as a sound or light generator, and form a circuit when connected. In operation, conducting fluid
18
in reference-end
21
submerges base electrode
15
. When a worker lifts the fluid-level in working-end
20
higher, the fluid level in reference-end
21
rises to make contact with reference electrode
14
. When conductive fluid
18
contacts reference electrode
14
, an electrical circuit is formed which enables current from electrical source
12
to actuate signal generator
13
. Signal generator
13
then emits a sound, light or other signal to indicate that the fluid-level in the working-end
20
has contacted the reference plane as defined by the reference electrode
14
; this signal will be called the reference signal. In the prior art, housing unit
17
conceals electrodes
14
,
15
and reference-end
21
; external reference marking
16
, which is aligned with the reference electrode
14
, is therefore placed on the outside of housing unit
17
to indicate the reference plane to the worker.
FIG. 2
illustrates the general operation of fluid-actuated level device
10
. A worker fills tube
11
of fluid-actuated level
10
with fluid and affixes housing unit
17
to, for example, a wall
19
. Housing unit
17
is affixed such that external reference marking
16
is aligned with the proposed reference plane
18
(shown as a dotted-line). Working-end
20
(opposite housing unit
17
) is shown extended across the wall
19
; the water-level in working-end
20
is aligned with reference plane
18
. To discover the reference plane, the worker moves working-end
20
upward until the fluid-level in the working-end
20
reaches the same height as the external reference marking
16
on housing unit
17
. Due to the action of gravity on the fluid in tube
11
(the body of the tube
11
must be positioned below the tube ends), the fluid within housing unit
17
at this point has submerged base electrode
15
and reference electrode
14
; this completes a circuit that activates signal generator
13
. The worker hears a reference signal which indicates the level point. In this manner, the working-end
20
may be used to locate a multitude of level points lying on a reference plane roughly defined by a circle centered on housing unit
17
with a radius equal to the tube length. Level points approximately 100 feet from housing unit
17
may be accurately discovered in this manner. The fluid-actuated device of
FIGS. 1-2
is especially useful when level points are sought by a worker working alone in rough and un-even terrain, or, for example, where level points need to be discovered around a corner structure. In this case, the worker takes working-end
20
around the corner structure and moves working-end
20
in a vertical manner until a reference signal is heard from housing unit
17
.
The fluid-actuated level device of
FIGS. 1-2
has a number of limitations. First, the level device
10
does not communicate to the worker whether the fluid-level in the working-end
20
is positioned too high; on the contrary, a single reference signal is given so long as the fluid-level in the working end is either in the reference plane or at any point above the reference plane. This introduces imprecision when a worker, due to, e.g., fatigue or rough terrain, accidentally adjusts the working-end too high after hearing the signal emitted from the device. Second, normal usage of the level device
10
results in dirt and fluid residue accumulation around the electrodes
14
,
15
in the tube; this may result in a “wicking” effect. Wicking is caused when fluid clings to the dirt and fluid residue around the electrodes to form a conductive bridge between the probes that persists beyond the point at which the fluid-level, under normal conditions, would disconnect the electrodes
14
,
15
. In the prior art, a worker is unable to efficiently detect a possible wicking condition because visual access to the tube
11
and the electrodes
14
15
is not provided. Third, a worker typically affixes the housing unit
17
to a reference plane by aligning a single external reference marking
16
on the outer edge of housing unit
17
to the reference point. Housing unit, however, has a greater width than the tube
11
, and therefore any skew or tilt introduced to the housing unit
17
when affixing it (or using it) results in a degree of imprecision equal to the distance between the horizontal planes defined by the reference plane and the external reference marking
16
(the greater the distance, the greater the degree of potential imprecision).
Fourth, housing unit
17
is typically affixed by driving nails or screws for attaching the housing unit
17
into a structure. This often results in imprecision because the nail or screw is driven at an awkward angle due to a lack of care by the worker or by irregularities in the structural medium (e.g., a knot in wood). Because readjustment is typically burdensome (requiring removal and replacement of the nail or screw), such imprecision is typically tolerated. Lastly, the tube ends should generally consist of transparent or otherwise translucent material to enable the worker to view the fluid-levels; as a result, the entire tube is typically constructed of a single molded piece of transparent plastic. Because the tube may be in excess of one-hundred feet long, the cost of transparent tubing may be significant.
SUMMARY
A fluid-actuated level devi

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