The present invention relates to a high-sensitivity and accuracy
pressure meter, of the type comprising: a support structure: a switching member
engaged to the support structure and operatively associated with a signalling
circuit for selectively switching over said circuit from a first use condition
to a second use condition and vice versa; transducer means put into fluid communication
with an environment to be checked so that, upon pressure variations in the environment
itself, switching-over of the signalling circuit between the first and second
use conditions is caused upon command of the switching member.
In particular, the pressure meter in reference is designed to be
used when very low pressure variations need to be detected in environments in which
the actual pressure, that is the detectable difference in pressure relative to
the surrounding atmosphere is very limited too, in the range of 0.05 to 3 millibar.
It is known that pressure meters generally provide the use of a switching
member, usually consisting of a microswitch engaged to a support structure and
operable upon command of transducer means put into fluid communication with an
environment to be checked for the purpose of causing, following pressure variations
in said environment, switching of the operating state of an electric signalling
circuit connected to the microswitch. In particular, the transducer means usually
comprises a diaphragm made of elastomeric material, sealingly engaged on the periphery
thereof to an appropriate support structure so that the opposite faces of said
diaphragm respectively communicate with one environment which is generally the
environment the pressure of which is to be checked, and a second environment which
is generally the outside atmosphere.
Thus the diaphragm is subjected to elastic deformation as a result
of variations in the differential pressure taking place between the two environments.
The deformations in the diaphragm give rise to an axial displacement
of a transducer rod slidably guided in the support structure and acting on the
microswitch so as to cause switching of the operating state of the electric circuit
when the differential pressure exceeds a predetermined threshold.
The foregoing being stated, it is to be pointed out that the use
of the above described pressure meters brings about several problems and difficulties
in those cases in which switching of the electric circuit is required following
very low variations in the differential pressure, even in those environments in
which the gauge pressure is only marginally higher than the pressure of outside
atmosphere. This situation takes place for example when a pressure meter is to
be associated with a flue of a boiler or the like in order to give an alarm signal
and/or to control the boiler turning off, should the exhaust gas pressure increase
beyond a predetermined limit, in the case of an accidental obstruction of the
flue, for example.
Under situations of the above kind where the pressure meter must
be capable of detecting pressure variations in the order of millibar fractions,
inertias due to the elastic strength and weight of the diaphragm as well as to
the passive resistances and weight of the components connecting the diaphragm to
the microswitch, create important hindrances to the achievement of the desired
operating features. Practically, even if diaphragms having a great surface extension
and a very reduced thickness are used, which diaphragms are very resilient but
on the other hand have problems as regards brittleness and porosity, it is impossible
to achieve satisfactory results with the use of a pressure meter, in terms of
sensitivity, accuracy and reliability in operation.
In addition, it is noted that diaphragms made of elastomeric material
are subjected to modify their modulus of elasticity as a result of the natural
aging of the material of which they are made thereby jeopardizing the pressure
The main object of the present invention is to obviate the problems
of the known art, by providing a pressure meter which exhibits greatly improved
features as regards sensitivity, accuracy and reliability in operation with respect
to conventional diaphragm pressure meters and which, at the same time, is of very
simple construction so that costs for manufacturing it can be very reduced.
The foregoing and further objects that will become more apparent
in the following description are substantially attained by a high-sensitivity and
accuracy pressure meter, characterized in that said transducer means comprises:
at least one movable element having a plate-like conformation, disposed in a plane
parallel to a base wall of the support structure and operatively connected to
said switching member; at least one plenum chamber element made of flexible material
and internally defining a branching chamber hermetically isolated from the outside
atmosphere and communicating with the environment to be checked, said plenum chamber
element being operatively interposed between said base wall and movable element,
in order to move said movable element away from the base wall and cause the intervention
of the switching member following variations in the inner volume of the plenum
chamber itself, as a result of pressure variations in the environment to be checked.
Further features and advantages will better be understood from the
detailed description of a preferred embodiment of a high-sensitivity and accuracy
pressure meter in accordance with the present invention, given hereinafter by
way of non-limiting example with reference to the accompanying drawings, in which:
- Fig. 1 is an exploded perspective view of the pressure meter in reference;
- Fig. 2 is a transverse sectional view of the pressure meter in question.
Referring to the drawings, a high-sensitivity and accuracy pressure
meter in accordance with the invention has been generally identified by reference
The pressure meter 1 comprises a support structure 2 designed to
be fastened to any supporting table. In the embodiment show, the support structure
2 is substantially defined by a box-shaped body 3 closed at the top by a cover
4 provided with engagement tabs 5 to be snap fitted into corresponding seatings
6 defined in the side walls of the box-shaped body.
Rigidly engaged to the support structure 2 is a switching member
7 operatively associated with a respective signalling or control circuit 8. More
particularly, in the embodiment shown the switching member 7 consists of a microswitch
fastened to the cover 4 and interlocked to the signalling circuit 8 in order to
selectively change it over between a first use condition to which for example the
absence of current flow through the circuit may correspond, and a second use condition
in which the passage of a current flow is produced in order to signal a state of
alarm to known and conventional devices (which therefore are not herein shown)
connected to the electric circuit 8 itself.
For certain applications, provision may be made for a pneumatic switching
valve member and respective fluid-operated circuit or equivalent means, in place
of the microswitch 7 and respective electric circuit 8.
The activation of the microswitch 7 takes place upon command of transducer
means 9 housed in the box-shaped body 2 and arranged to act on a push-button element
7a being part of the switch and oriented towards the inner part of the box-shaped
body 2 through an opening 10 formed in the cover 4.
In accordance with the present invention, the transducer means 9
essentially comprises at least one movable element 11 having a plate-like conformation,
preferably made of foam polystyrene material or any other material suitable for
achieving a sufficient structural stiffness with a relatively low weight. The movable
element 11 is disposed parallel to a base wall 15 of the box-shaped body 3 and
operatively connected to the push-button element 7a of the microswitch 7, possibly
by means of an auxiliary rod 12 extending perpendicular to a base plate 13 fastened
to the movable element itself, for example by gluing. A preloading spring 14 may
be optionally interposed between the plate 13 and cover 4 of the support structure
2 in order to push the movable element 11 away from the microswitch 7 at a given
Still in accordance with the present invention, at least one plenum
chamber element 16 made of flexible material is interposed between the movable
element 11 and base wall 15 of the box-shaped body 3, said plenum chamber element
internally defining a branching chamber "C" hermetically isolated from the outside
atmosphere and communicating, as better specified in the following, with the environment
the pressure variations of which are to be checked.
In a preferential solution, the plenum chamber element 16 is substantially
formed with at least one polyethylene (or similar flexible material) sheet or
tubular element of a thickness in the range of 0.02 to 0.1 mm, folded over according
to respectively superposed first and second layers 16a, 16b sealed with each other
by a heat seal 16a along the respective perimetric edges.
Associated with the plenum chamber element 16 is a connecting member
17 accessible from the outside of the box-shaped body 3 for enabling connection
between the branching chamber "C" and the environment to be checked. Said connecting
member 17, put into the plenum chamber element 16 before heat seals 16c are made
along the perimetric edges of said layers, is essentially provided with a disc-shaped
flange 18 from which a tubular portion 19 extends at right angles thereto, which
tubular portion 19 passes through the first layer 16a of the plenum chamber element
16 and the base wall 15 of the box-shaped body 3 through corresponding access
openings 19a, 19b. A stop nut 20 is screwed down on the tubular portion 19 outside
the box-shaped body 3 and acts on the base wall 15 thereof so as to make the disc-shaped
flange 18 act in an opposing relationship with the base wall 15 in order to exert
a hermetic seal around the access opening 19a of the first layer. For the purpose
of ensuring a perfect tightness around the access opening 19a, an O-ring 18a may
be provided which is engaged to the disc-shaped flange 18 and acts on the first
layer 16a of the plenum chamber element 16.
The tubular portion 19 is designed to be connected to the environment
to be checked, for example by a flexible hose 21 partly shown.
Operation of the pressure meter according to the invention described
above mainly as regards structure is as follows.
Pressure existing in the environment to be checked is transmitted
to the branching chamber "C" defined in the plenum chamber element 16. The action
of said pressure tends to increase the inner volume of the plenum chamber element
16 moving the first and second layers 16a, 16b apart from each other. The action
exerted by pressure is transmitted over the whole surface extension of the movable
element 11 in a resting relationship on the second layer 16b of the plenum chamber
When the pressure value is held below a predetermined threshold,
the weight of the movable element 11 and/or the action exerted by the counterspring
14 are sufficient to keep the second layer 16b of the plenum chamber element 16
close to the first layer 16a as shown in dotted line in Fig. 2. When, on the contrary,
pressure overcomes the predetermined threshold, the action that said pressure
exerts on the surface of the movable element 11 wins the weight proper to said
element and/or the action of the counterspring 14, causing the displacement of
the second layer 16b and the movable element itself away from the base wall 15
of the box-shaped body 3, as shown in solid line in the accompanying figures.
The resulting axial displacement of the auxiliary rod 12 causes the operation of
the push-button element 7a of the microswitch 7 and, therefore, the selective
switching over of the electric circuit 8 from the first to the second operating
condition. The consequent current flow along the electric circuit 8 can be indifferently
utilized for producing an alarm signal or triggering the intervention of any safety
device interlocked to the pressure meter 1.
The invention achieves the intended purposes.
It will be in fact recognized that, although this pressure meter
can be manufactured at very reduced costs by virtue of its simple construction,
it has greatly improved features as regards sensitivity and accuracy in operation
as compared to conventional diaphragm pressure meters. In particular, the described
pressure meter is capable of signalling pressure variations in the order of few
Just as an indication it is to be considered the use of a movable
element acting on the plenum chamber element over a contact surface in the order
of 100 cm² and exerting a force of 2.5 g. The force necessary to actuate the push-button
element of the microswitch can be considered 25 g, so that a thrust greater than
27.5 g should be necessarily exerted on the movable element in order to obtain
the operating intervention of the pressure meter. In such a case it will be sufficient
for the gauge pressure in the checked environment to exceed the value of 0.27
millibar in order to cause the displacement of the movable element and the resulting
switching over of the electric circuit by the microswitch.
Obviously the movable element and/or counterspring may have different
structure and size depending on the differrent requirements.
Advantageously, if on installation the pressure meter is oriented
with the movable element in a horizontal plane above the base wall, the counterspring
can be eliminated and the pressure meter can be calibrated, as regards pressure
threshold, based on the weight of the movable element itself. In this case, if
a microswitch or any other switching element is adopted the operation of which
is not dependent on the presence of spring means, a very precise and constant calibration
of the pressure meter can be achieved, since it does not depend on the variation
of the stiffness coefficient of springs and/or diaphragms as a result of aging.
Obviously modifications and variations may be made to the invention
as conceived, without departing from the scope of the appended claims.