FORM 2
THE PATENT ACT 1970
(39 of 1970)
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See Section 10, and rule 13)

1. TITLE OF INVENTION
METHOD FOR REDUCING A CONTENT OF FOREIGN MOLECULES DISSOLVED IN A
PRESSURE TRANSFERRING FLUID OF A PRESSURE TRANSDUCER
a) Name : ENDRESS+HAUSER GMBH+CO. KG
b) Nationality : GERMAN Company
c) Address : HAUPTSTRASSE 1,
7 9 6 8 9 MAULBURG,
GERMANY

3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention
and the manner in which it is to be performed : -

The invention relates to a method for reducing content of foreign molecules in
gaseous or liquid form dissolved in a pressure transfer liquid of a pressure
measuring transducer.
Pressure transfer liquids are applied in a large number of pressure measuring
transducers in pressure measuring technology, in order to bring a pressure to be
measured to a pressure sensor. Liquids, such as e.g. silicone oils, whch are as
incompressible as possible and have thermal coefficients of expansion as small as
possible, are preferably used as pressure transfer liquids.
Typically, pressure measuring transducers have a pressure receiving chamber closed
outwardly by an isolating diaphragm; the pressure receiving chamber is connected
via a passageway to a pressure measuring chamber, in which the pressure sensor is
located. The pressure receiving chamber, the pressure measuring chamber and the
passageway are filled with the pressure transfer liquid, which in measurement
operation transmits an external pressure to be measured acting on the isolating
diaphragm to the pressure sensor.
Examples of this are pressure measuring transducers, in which semiconductor
sensors, e.g. silicon chips having doped resistance elements, are applied as pressure
sensors. Usually, semiconductor sensors comprise a membrane-like pressure sensor
chip, which is supported laterally in the pressure measuring chamber.
Semiconductor sensors are, as a rule, very sensitive and are therefore not directly
exposed to a medium, whose pressure is to be measured.
Pressure measuring transducers having upstream pressure transfer means are an
additional example. In measurement operation, the pressure transfer means has a
pressure receiving chamber arranged at a measuring location and closed by an
isolating diaphragm; the pressure receiving chamber is connected via a pressure
transfer line to the pressure measuring chamber of the pressure measuring
transducer; the pressure sensor is located in the pressure measuring chamber; the
pressure measuring chamber is arranged remotely from the measuring location.
In such case, it is of special importance for the accuracy of measurement of the
pressure measuring transducer that the pressure transfer liquid contains as few
foreign molecules dissolved in gaseous or liquid form as possible. Gases and/or
liquids dissolved in the pressure transfer liquid acting on the isolating diaphragm,
can, under certain circumstances, especially at high temperatures and/or low
pressures, lead to gas bubbles forming very suddenly in the liquid, which drastically
changes the transfer behavior of the pressure transfer liquid. Depending on the
amount of trapped foreign molecules, this results, in certain circumstances, in
considerable temperature dependent and/or pressure dependent measurement
errors. For instance, water molecules contained in liquid form or in gaseous form as
steam in the liquid are especially common and problematic. Due to its vapor
pressure increasing exponentially with temperature, water forms steam bubbles at
relatively low temperatures very suddenly under certain circumstances.
Currently, to remove foreign molecules dissolved in the pressure transfer liquid, the
pressure transfer liquid is regularly pretreated in a vacuum distillation method,
before the liquid is introduced, as a rule under vacuum conditions, into the pressure
measuring transducer.
Vacuum distillation methods have the disadvantage that the distillation temperature
is limited by the thermal stability of the pressure transfer liquid.
Additionally, through the vacuum distillation method, an increasing portion of
additional components is withdrawn from the liquid with rising distillation
temperature. This unavoidably leads to an increase in the viscosity of the liquid,
which is disadvantageous for low loss pressure transfer; the increase in the viscosity
of the liquid can likewise only be counteracted by limiting the distillation
temperature.
Due to limitations for the distillation temperature, a residual content of foreign
molecules, which cannot be made smaller, remains dissolved in the pressure transfer
liquid even after the distillation method.
Foreign molecules, such as e.g. water and air are, however, not only contained in the
pressure transfer liquid provided for filling, but, can also cling on the inner walls of
the measuring transducer to be filled, and find their way into the pressure transfer
liquid from there. In order to decrease the number of foreign molecules clinging on
the inner walls, the internal spaces are preferably baked before being filled; the
internal spaces are heated at high temperature under vacuum for a short time; this
loosens the clinging foreign molecules from the inner wall and then they are sucked
out via the applied vacuum. However, a residual content of foreign molecules
clinging on the inner walls also remains here; this residual content can be released in
dissolved form into the pressure transfer liquid after the filling.
It is an object of the invention to provide a method for reducing content of foreign
molecules in gaseous or liquid form dissolved in a pressure transfer liquid of a
pressure measuring transducer
For this, the invention resides in a method for reducing content of foreign molecules
in gaseous or liquid form dissolved in a pressure transfer liquid of a pressure
measuring transducer,
- which has a pressure receiving chamber closed by an isolating diaphragm;
- which has a pressure measuring chamber connected to the pressure receiving
chamber;
- which has a pressure sensor arranged in the pressure measuring chamber;
and
- in which the liquid serves to fill an inner space of the pressure measuring
transducer formed by the pressure receiving chamber and the pressure
measuring chamber connected thereto, and to transfer an external pressure
acting on the isolating diaphragm to the pressure sensor in measurement
operation, wherein
- the liquid is brought into contact with at least one adsorptive body, and
- foreign molecules dissolved in the liquid are bound to the adsorptive bodies
by adsorption.
In a preferred embodiment, the adsorptive bodies comprise zeolite.
Additionally, the invention includes a first embodiment of the method of the
invention, wherein
- the adsorptive bodies, in a pretreatment method for pretreating the liquid for
filling the pressure measuring transducer, are introduced as granular material
into the liquid, where the adsorptive bodies then adsorb foreign molecules;
- the liquid is separated from the adsorptive bodies containing the adsorbed
foreign molecules; and
- the inner space of the pressure measuring transducer to be filled is filled with
the liquid, which has been separated from the adsorptive bodies.
Additionally, the invention includes a second embodiment of the method of the
invention, wherein
- the adsorptive bodies have a particle size, which is small compared to the
dimensions of the inner space of the pressure measuring transducer to be
filled;
- the adsorptive bodies are introduced into the liquid in a pretreatment method
for pretreating the liquid for filling the pressure measuring transducer; and
- the inner space of the pressure measuring transducer is filled with the liquid
containing the adsorptive bodies.
Additionally, the invention comprises a third embodiment of the method of the
invention, wherein
- the adsorptive bodies have a particle size, which is small compared to the
dimensions of the inner space of the pressure measuring transducer to be
filled;
- the adsorptive bodies are introduced into the inner space of the pressure
measuring transducer to be filled; and
- the inner space is filled with the liquid.
Additionally, the invention includes a fourth embodiment of the method of the
invention, wherein
- the pressure measuring transducer has at least one hollow space adjoining the
inner space to be filled;
- adsorptive bodies are introduced into the hollow spaces;
- the hollow spaces are separated from the inner space by a partition, which is
permeable to the liquid and impermeable to the adsorptive bodies; and
- the inner space and the hollow spaces are filled with the liquid.
Additionally, the invention includes an embodiment of the third or the fourth
embodiment, wherein
the pressure transfer liquid is pretreated in a pretreatment method before filling the
pressure measuring transducer with this liquid, in which pretreatment method:
- adsorptive bodies are introduced into the liquid and adsorb foreign molecules
dissolved therein;
- the liquid is separated from the adsorptive bodies and the foreign molecules
bound to the adsorptive bodies by adsorption; and
- the separated liquid, which is free of adsorptive bodies, is used for filling.
Additionally, the , invention comprises a pressure measuring transducer
manufactured with the method of the invention, wherein the pressure measuring
transducer has
- a pressure receiving chamber closed by an isolating diaphragm,
- a pressure measuring chamber connected to the pressure receiving chamber,
- a pressure sensor arranged in the pressure measuring chamber, and
- an inner space formed by the pressure receiving chamber and the pressure
measuring chamber connected thereto and filled with a pressure transfer
liquid; and
- wherein the liquid contains adsorptive bodies,
-- whose particle size is small compared to the dimensions of the inner space
filled with the liquid, and
-- which serve to bind foreign molecules dissolved in the liquid to themselves
by adsorption.
Additionally, the invention comprises a pressure measuring transducer
manufactured with the method of the invention, wherein the pressure measuring
transducer has
- a pressure receiving chamber closed by an isolating diaphragm,
- a pressure measuring chamber connected to the pressure receiving chamber,
- a pressure sensor arranged in the pressure measuring chamber, and
- at least one hollow space adjoining the inner space formed by the pressure
receiving chamber and the pressure measuring chamber connected thereto,
wherein,
-- adsorptive bodies are arranged in the hollow spaces;
- the inner space and hollow spaces are filled with the pressure transfer liquid;
and
- the hollow spaces are separated from the inner space by a partition, which is
permeable to the liquid and impermeable to the adsorptive bodies.
In a further development of the last mentioned pressure measuring transducer, this
has
- at least one hollow space arranged in a diaphragm bed of the isolating
diaphragm, which diaphragm bed adjoins the pressure receiving chamber;
- at least one hollow space adjoining the pressure measuring chamber;
- at least one hollow space adjoining a pressure transfer line connecting the
pressure receiving chamber with the pressure measuring chamber; and/or
- a hollow space, which is arranged in an end of a filling opening of the
pressure measuring transducer and adjoins the inner space of the pressure
measuring transducer.
Additionally, the invention comprises a pressure measuring transducer
manufactured with the method of the invention, wherein the pressure measuring
transducer has
- a pressure receiving chamber closed by an isolating diaphragm,
- a pressure measuring chamber connected to the pressure receiving chamber,
and
- a pressure sensor arranged in the pressure measuring chamber; wherein
- the inner space formed by the pressure receiving chamber and the pressure
measuring chamber connected thereto is filled with a pressure transfer liquid;
and
- at least one adsorptive body in the form of a molded body is arranged in the
inner space or an adjoining hollow space.
In a first further development of the last mentioned pressure measuring transducer,
one of the adsorptive bodies is an adsorptive body that is arranged in a hollow
space, which is closed to the environment, that adjoins the pressure receiving
chamber on its side lying opposite the isolating diaphragm, and that is embodied as
a diaphragm bed for the isolating diaphragm.
In a second further development of the last named pressure measuring transducer,
one of the adsorptive bodies is a tubular adsorptive body inserted in a line
connecting the pressure receiving chamber to the pressure measuring chamber.
In a third further development of the last named pressure measuring transducer, one
of the adsorptive bodies is a displacement body inserted in the inner space of the
pressure measuring transducer.
In a further development of the last named further development, the adsorptive
body inserted as a displacement body is provided with electrical connections, via
which a capacitance of the adsorptive body dependent on the state of the pressure
transfer liquid soaking the adsorptive body can be measured by means of a
capacitance measuring circuit connected thereto.
The method of the invention offers the advantage that the adsorptive bodies
permanently remove the foreign molecules from the liquid; the foreign molecules are
then no longer available for forming gas bubbles in the pressure measuring
transducer.
The invention and further advantages will now be explained in greater detail based
on the figures of the drawing, in which seven examples of embodiments are
presented. Equal elements are provided with the equal reference characters in the
figures. The figures of the drawing show as follows:
Fig. 1 schematically, a pressure measuring transducer with a thereto
connected apparatus for pretreating the pressure transfer liquid and
for filling the pressure measuring transducer;
Fig. 2 a pressure measuring transducer having an inner space filled with a
pressure transfer liquid, wherein adsorptive bodies are introduced into
the inner space;
Fig. 3 the pressure transfer means of the pressure measuring transducer of
Fig. 1, wherein hollow spaces containing adsorptive bodies are
provided in the diaphragm bed of the isolating diaphragm,
Fig. 4 the measuring transducer housing of the pressure measuring
transducer of Fig. 1, in which a hollow space containing adsorptive
bodies is provided in the pressure measuring chamber;
Fig. 5 the connection piece of the pressure measuring transducer of Fig. 1,
with a hollow space with adsorptive bodies arranged in the filling
opening and a hollow space with adsorptive bodies bordering the
pressure transfer line;
Fig. 6 the pressure transfer means of the pressure measuring transducer of
Fig. 1, in which the diaphragm bed of the isolating diaphragm is
formed by an adsorptive body formed as a molded part and arranged
under the pressure receiving chamber, and an additional tubular
adsorptive body arranged in the line of the pressure transfer means;
and
Fig. 7 an example of an adsorptive body applied as a displacement body.
Fig. 1 shows, schematically, a pressure measuring transducer together with an
apparatus connected thereto for pretreating the pressure transfer liquid and for
filling the pressure measuring transducer.
The pressure measuring transducer has a pressure transfer means having a pressure
receiving chamber 3 closed by an isolating diaphragm 1. Pressure receiving chamber
3 is connected via a pressure transfer line 5 to a pressure measuring chamber 9
enclosed in a measuring transducer housing 7 located remotely from the pressure
receiving chamber 3. In pressure measuring chamber 9, a pressure sensor 11, e.g. a
semiconductor sensor, is arranged, which in measurement operation serves to
measure an external pressure p acting on isolating diaphragm 1. For this, the inner
space of the pressure measuring transducer formed by pressure receiving chamber 3,
line 5 and pressure measuring chamber 9 is filled with a pressure transfer liquid,
which in measurement operation serves to transfer the pressure p acting on isolating
diaphragm 1 to pressure measuring chamber 9 and therewith to pressure sensor 11
located therein.
The pressure measuring transducer shown here represents only one example of a
pressure measuring transducer, in which the invention is applicable. The invention
is also applicable in connection with differently embodied pressure measuring
transducers, which have an inner space filled with a pressure transfer liquid for
transmitting a pressure to be registered metrologically to a pressure sensor arranged
in the inner space.
The pressure transfer liquid is preferably a hydraulic liquid, e.g. a silicone oil, which
is as incompressible as possible and which has a thermal coefficient of expansion,
which is as small as possible.
Ordinarily marketed, pressure transfer liquids always contain a residual content of
foreign molecules, especially water and air, in gaseous or liquid form dissolved
therein. This residual content cannot be withdrawn from the liquid due to
limitations of the distillation temperature even using a vacuum distillation method.
In addition to water molecules, foreign molecules especially well soluble in silicone
oils, such as e.g. oxygen, nitrogen and carbon dioxide play an important role here.
According to the invention, the content of foreign molecules in liquid or gaseous
form dissolved in the pressure transfer liquid is reduced by bringing the liquid into
contact with at least one adsorptive body 13 and, via this contact, foreign molecules
dissolved in the liquid are bound to the adsorptive bodies 13 by adsorption. In this
way, the adsorbed foreign molecules are withdrawn from the liquid and cannot form
gas bubbles in the liquid in measurement operation.
The adsorptive bodies 13 preferably comprise zeolite. Zeolites are alumino-silicates,
whose crystal lattice has a cage structure with numerous hollow spaces, which are
accessible from all sides through pores.
Zeolites are obtainable both as a granular material as well as sintered formed bodies
with a relatively freely selectable form. Since zeolites can only adsorb molecules,
which can pass through their pores, they are suited especially well to selectively
adsorb the disturbing foreign molecules, especially water, oxygen, nitrogen and
carbon dioxide, contained in pressure transfer liquids. The adsorption takes place at
room temperature so that this method is also suitable for liquids, which have very
low thermal stability. Since the exclusively targeted, low molecular weight materials
are removed from the liquid by adsorptive bodies 13, the targeted disturbing content
of low molecular weight foreign molecules in pressure transfer liquids is reduced
through this method without the viscosity of the liquid being detectably increased.
The method of the invention can be executed at different stages of the manufacturing
process of the pressure measuring transducer.
In a first variant of the invention, the method is executed in the form of a liquid
pretreatment method, to which the liquid is subjected before it is filled into the inner
space of the pressure measuring transducer. This variant can be executed, for
example, with the apparatus illustrated in Fig. 1 for pretreating the pressure transfer
liquid and for filling the pressure measuring transducer.
In such case,, the pressure transfer liquid is filled into a supply container 15, in which
adsorptive bodies 13 are preferably introduced in the form of a fine grained
granulate. Preferably arranged in supply container 15 is mixer 17, which mixes the
content of supply container 15 at the beginning of the pretreatment method and
thereby effects a uniform distribution of the adsorptive bodies 13 in the liquid as
indicated in Fig. 1.
Preferably, an inner space 19 of supply cont.ainer 15 remaining above the liquid level
is evacuated via a vacuum pump 21 connected thereto via a valve V. In this way,
foreign molecules emerging upwardly from the liquid are sucked out and an intake
of foreign molecules from the environment is prevented.
Adsorptive bodies 13 remove foreign molecules from the liquid until either
dissolved foreign molecules are no longer. contained in the liquid or the loading
capacity of adsorptive bodies 13 is reached.
The adsorbed foreign molecules are then bound to adsorptive bodies 13 and can
accordingly be separated from the liquid together with adsorptive bodies 13. For
this, the force of gravity is preferably utilized, which causes the adsorptive bodies 13
to sink to the floor of supply container 15. After adsorptive bodies 13 sink, a layer of
adsorptive bodies 13 is located on the floor of supply container 15. The height H of
the layer, as indicated by the dashed line in Fig. 1, is a function of the dimensions of
supply container 15 and the amount of adsorptive bodies 13 introduced earlier
therein. Located above this layer is the liquid separated from the adsorptive bodies
13. The liquid freed from the adsorbed foreign molecules can now be removed, for
example, via an outflow 25 equipped with a controllable valve 23 and arranged
above the height H of the layer of adsorptive bodies.
Alternatively, a filter 27 can be provided in front of outflow 25, in order to prevent
adsorptive bodies 13 from leaving supply container 15.
For filling the inner space of the pressure measuring transducer, outflow 25 is
preferably connected directly to a filling apparatus (here shown schematically only),
via which the liquid freed from the adsorbed foreign molecules is introduced into
the inner space of the pressure measuring transducer. The pressure measuring
transducer has for this a filling opening 29, via which the inner space to be filled is
accessible.
A number of different filling apparatuses and filling methods known from the state
of the art can be applied for the filling. Preferably, as shown in Fig. 1, the filling
occurs under vacuum. For this, the vacuum pump 21 is connected to the inner space
via an evacuation line 31 equipped with a valve V and opening into filling opening
29 for evacuating the inner space. Then, the inner space is filled with the liquid freed
from the adsorbed foreign molecules via outflow 25 fed into filling line 33 opening
into filling opening 29. Then, the filling apparatus is removed and the filling
opening 29 sealed pressure, and gas, tightly by a closure (not shown here).
To the extent that adsorptive particles 13 are applied, which have a particle size,
which is small compared to the dimensions of the inner space of the pressure
measuring transducer to be filled, a second variant of the invention can alternatively
be applied, in which the inner space is filled with liquid containing adsorptive
bodies 13. In this case, the inner space is preferably directly filled with the liquid
containing adsorptive bodies 13 'after the introduction of the adsorptive bodies 13
into the liquid. Also, a homogeneous distribution of adsorptive bodies 13 is
preferably effected here by mixer 17. In contrast to the earlier described method, the
filling here, however, occurs during the mixing procedure or immediately thereafter,
so that the adsorptive bodies 13 have no time to settle on the floor of supply
container 15. Filter 27 is not used in this case.
Fig. 2 shows an example of a pressure measuring transducer filled with a liquid
containing adsorptive particles 13. As an alternative to the example of an
embodiment illustrated in Fig. 1, a pressure measuring transducer lacking an
upstream pressure transfer means is presented here. This embodiment has a
compact measuring transducer housing 35, on whose front side a pressure receiving
chamber 39 closed outwardly by an isolating diaphragm 37 is located. Pressure
receiving chamber 39 is connected via a short passageway extending in the interior
of transducer housing 35 to a pressure measuring chamber 41 arranged in measuring
transducer housing 35. Pressure sensor 11 is located in pressure measuring chamber
41.
The same end result as regards the filled pressure measuring transducer is
alternatively also achievable by introducing the adsorptive bodies 13 into the inner
space before filling the pressure measuring transducer. The pressure measuring
transducer is then subsequently filled with pressure transfer liquid. Also in such
case, the adsorptive bodies 13 must naturally have a particle size small compared to
the dimensions of the inner space to be filled, in order to assure unhindered pressure
transfer through the liquid. Also in this way, adsorptive bodies 13 get into the liquid
and bind foreign molecules dissolved in the liquid by adsorption.
In such case, the liquid, with which the inner space of the pressure measuring
transducer containing adsorptive bodies 13 is filled, can naturally be supplementally
subjected to the pretreatment method described above, in which the liquid, before it
is used for filling, is mixed with adsorptive bodies 13, which are separated together
with the adsorbed foreign molecules from the liquid before the filling. Then, the
pressure measuring transducer is filled with the liquid, which is pretreated using the
pretreatment method in this way and is hee of adsorptive bodies. This variant offers
the advantage that the content of foreign molecules dissolved in the liquid clearly
already reduced by the pretreatment method is still further reduced by adsorptive
bodies 13 contained in the pressure measuring transducer.
Alternatively to the introduction of adsorptive bodies 13 into the inner space of the
pressure measuring transducer, adsorptive bodies 13 can also be introduced in one
or more hollow spaces, serving here to accommodate adsorptive bodies 13 likewise
formed as granulate and connected to the inner space of the pressure measuring
transducer to be filled with the pressure transfer liquid. The hollow spaces are
closed to the inner space by a partition, such as e.g. a metal grate, which is
permeable to the liquid but is impermeable to adsorptive bodies 13. The foreign
molecules dissolved in the liquid located in the hollow space(s) are also here bound
to adsorptive bodies 13 through adsorption, and are thus permanently removed
from the liquid.
Since adsorptive bodies 13, in such case, remain in the hollow spaces, they bring
about no degradation of the pressure transmitting properties of the liquid in the
inner space. This variant is also especially applicable in pressure measuring
transducers, which have inner spaces with small dimensions. Since adsorptive
particles 13 do not penetrate into the adjoining inner space, the particle size of
adsorptive bodies 13 here does not need to be small compared to the dimensions of
the inner space of the pressure transducer.
The hollow space@) can be arranged at different locations in the pressure measuring
transducer.
Thus, for example, as shown in Fig. 3, at least one hollow space 43 can be sunk into
the diaphragm bed 45 of isolating diaphragm 1. Fig. 3 shows four hollow spaces 43
in the diaphragm bed 45 of isolating diaphragm 1 of the pressure measuring
transducer illustrated in Fig. 1. Adsorptive bodies 13 are located in each hollow
space 43. Hollow spaces 43 face directly into the pressure receiving chamber 3 and
are closed toward pressure receiving chamber 3 by the partition 47, which is
permeable to liquid and impermeable to adsorptive bodies 13. For the manufacture
of this variant, adsorptive bodies 13 are introduced into the hollow spaces 43
beforehand, wluch are then sealed by partition 47, e.g. a metal grate. Then isolating
diaphragm 1 is welded in place. Preferably, pressure receiving chamber 3 and the
adjoining hollow spaces 43 are heated strongly once under vacuum before the filling
of the liquid. This procedure, which is referred to as baking, causes at least a large
part of foreign molecules, especially possible residual moisture, clinging to the
interior of the pressure transfer means, to be released, so that it can be sucked out.
Adsorptive bodies 13 comprising zeolite offer, in such case, the advantage that they
can, in given cases, freely release already adsorbed molecules at high temperatures,
especially at temperatures above 250°C, so that these molecules are likewise sucked
out and therefore the adsorptive bodies 13 reach their maximum adsorptive capacity
before contact with the filled pressure transfer liquid.
Fig. 4 shows an additional hollow space 49 - here arranged in pressure measuring
chamber 9 of the pressure measuring transducer of Fig. 1 - provided instead of or
supplementally to hollow spaces 43 for accommodating adsorptive bodies 13.
Hollow space 49 is here annular and surrounds the exterior of pressure sensor 11.
The boundary of hollow space 49 is formed here by a partition 51, which is
permeable to the liquid and impermeable to adsorptive bodies 13; partition 51 is
solidly connected to an inner lateral surface 53 of transducer housing 7 surrounding
pressure measuring chamber 9 and to an end face 55 of pressure measuring chamber
9. End face 55 adjoins inner lateral surface 53 of the pressure measuring transducer
on the side facing the pressure transfer means and closes the pressure measuring
chamber on this side.
Fig. 5 shows two additional hollow spaces 57,59, which can be applied instead of or
supplementally to the hollow spaces 43, 49 described above. These two additional
hollow spaces 57,59 adjoin line 5 of the pressure measuring transducer of Fig. 1 and
serve for for accommodating adsorptive bodies 13.
The hollow spaces 57,59 containing adsorptive bodies 13 are arranged in the interior
of a connection piece 61 of the pressure measuring transducer. Connection piece 61
connects measuring transducer housing 7 to the upstream pressure transfer means
and a portion of line 5 extends through connection piece 61.
Hollow space 57 directly borders the portion of line 5 and is separated from this by a
partition 63, which is permeable to the liquid and impermeable to adsorptive bodies
13.
Hollow space 59 is integrated in a region of filling opening 29 adjoining line 5. Fig. 5
shows filling opening 29 to be already sealed by a closure 65. Hollow space 59 is
also closed here by a partition 67, which is permeable to the liquid and impermeable
to adsorptive bodies 13. Preferably, hollow space 59 is formed by a cylindrical insert
69 fitted terminally into filling opening 29. Adsorptive bodies 13 are enclosed in
cylindrical insert 69. Insert 69 is closed on the pressure transfer line side by partition
67 and on its side facing away from pressure transfer line 5 by an additional
partition 71, which is permeable to the liquid and impermeable to adsorptive bodies
13.
This offers the advantage that insert 69 with adsorptive bodies 13 can be introduced
into filling opening 29 before filling the inner space of the pressure transfer means.
Therewith the option is provided to heat the inner space and the adsorptive bodies
13 under vacuum before the filling, and then to fill the inner space under vacuum via
insert 69. In this way, adsorptive bodies 13 have their maximum adsorption capacity
at the beginning of the filling procedure. A further advantage is that the entire
amount of liquid to be filled flows over adsorptive bodies 13 into the inner space,
and, in such case, foreign molecules dissolved in the liquid are adsorbed by the
adsorptive bodies 13.
Adsorptive bodies 13, which remain in the inner space of the pressure measuring
transducer, respectively in the adjoining hollow spaces 43, 49, 57, 59, during
measurement operation offer the additional advantage that they can also adsorb
foreign molecules that initially cling to the inner walls of the inner space or hollow
spaces 43,49, 57, 59 and, under certain circumstances, only detach after a long time
and then enter the liquid.
Alternatively or supplementally to the granular adsorptive bodies 13 described
above, aIso individual adsorptive bodies with greater dimensions, e.g. adsorptive
bodies embodied as one piece, molded parts, can be applied in the pressure
measuring transducer. These adsorptive bodies are preferably sintered zeolite
inlays, which, for their respective location of use in the inner space of the pressure
measuring transducer and/or in an adjoining hollow space opened to the inner
space but otherwise outwardly closed, can be manufactured to accurately fit in the
pressure measuring transducer.
Fig. 6 shows an example of an embodiment for this, in which a first adsorptive body
73 is arranged in a hollow space 75 forming the outer termination of pressure
receiving chamber 3 of the pressure transfer means of Fig. 1 on the side of pressure
receiving chamber 3 lying opposite isolating diaphragm 1. Adsorptive body 73 is
essentially washer shaped and fiIIs hollow space 75. Preferably, the side of
adsorptive body 73 pointing into pressure receiving chamber 3 is formed as a
diaphragm bed, against which isolating diaphragm 1 rests in the case of excess
pressure acting thereon. This adsorptive body 73 serves both for the adsorption of
foreign molecules as well as also for the protection of isolating diaphragm 1 in the
case of overloads acting thereon.
Additionally provided in Fig. 6 is a second, tubular adsorptive body 77, which is
inserted into the line 5 connecting pressure receiving chamber 3 to pressure
measuring chamber 9.
Fig. 7 shows a further example of an embodiment, in which an adsorptive body 79 is
arranged in pressure measuring chamber 9. Adsorptive body 79 fills out a relatively
large part of the inner space of pressure measuring chamber 9 while leaving pressure
sensor 11 and its connection to the pressure supply (not shown here), e.g. pressure
receiving chamber 3, free. Also, this adsorptive body 79 fulfills a double function, in
that, on the one hand, it adsorbs foreign molecules, and, on the other hand, it serves
as a displacement body, whose insertion clearly reduces the amount of pressure
transfer liquid required to fill pressure measuring chamber 9. Correspondingly
formed adsorptive bodies can be applied in all sections of the inner spaces of
pressure measuring transducers as well as in the hollow spaces of pressure
measuring transducers, which border the inner spaces and open to the respective
inner space but are otherwise closed outwardly, in which previously classic, purely
mechanical, displacement bodies were applied.
Preferably, adsorptive body 79 is provided with electrical connections 81, via which
electrical capacitance of adsorptive body 79 can be measured by a capacitance
measuring circuit 83 connected thereto. Since adsorptive bodies 79 have an
extremely porous structure, adsorptive body 79 is saturated after the filling of the
pressure transfer liquid. Correspondingly the capacitance of adsorptive body 79 is a
measure for the capacitance of the pressure transfer liquid, which, in turn, delivers
information concerning the state of the pressure transfer liquid. Correspondingly,
the state of the pressure transfer liquid can be monitored based on the measured
capacitance of adsorptive body 79.
Via the capacitance measurement, it is recognizable directly after the filling of the
pressure measuring transducer whether, as regards the adsorption of the foreign
molecules by adsorptive body 79, a stable equilibrium state has been achieved.
Moreover, based on the capacitance measurement, an increase in the content of
foreign molecules, especially air and moisture, arising in the pressure transfer liquid
in the area of adsorptive body 79 during the operational period of the pressure
measuring transducer can be detected. Such a subsequent increase can be caused
e.g. by damage to isolating diaphragm 1 or an unsealed site in the pressure
measuring transducer.

1 isolating diaphragm
2 pressure receiving chamber
3 pressure transfer line
7 measuring transducer housing
9 pressure measuring chamber
11 pressure sensor
13 adsorptive body
15 supply container
17 mixer
19 remaining inner space of the supply container
21 vacuum pump
23 valve
25 outflow
27 filter
29 filling opening
31 evacuation line
33 filling line
35 measuring transducer housing
37 isolating diaphragm
39 pressure receiving chamber
41 pressure measuring chamber
43 hollow space
45 diaphragm bed
47 partition
49 hollow space
51 partition
53 interior lateral surface of the measuring transducer housing
55 interior end face of the measuring transducer housing
57 hollow space
59 hollow space
61 connection piece
63 partition
65 closure
67 partition
69 cylindrical insert
71 partition
71 adsorptive body
73 hollow space
77 adsorptive body
79 adsorptive body
81 electrical connection
83 capacitance measuring circuit

WE CLAIM :
1. Method for reducing content of foreign molecules in gaseous or liquid form
dissolved in a pressure transfer liquid of a pressure measuring transducer,
- which has a pressure receiving chamber (3, 39) closed by an isolating
diaphragm (1,37);
- which has a pressure measuring chamber (9, 41) connected to the
pressure receiving chamber (3,39);
- which has a pressure sensor (11) arranged in the pressure measuring
chamber (9,41); and
- in which the liquid serves to fill an inner space of the pressure
measuring transducer formed by the pressure receiving chamber (3,39)
and the pressure measuring chamber (9,41) connected thereto, and to
transfer anexternal pressure (p) acting on the isolating diaphragm
(1,37) to the pressure sensor (11) in measurement operation, wherein
- the liquid is brought into contact with at least one adsorptive body
(13,73,77,79), and
- foreign molecules dissolved in the liquid are bound to the adsorptive
bodies (13) by adsorption.
2. Method as claimed in claim 1, wherein
the adsorptive bodies (13,73,77,79) comprise zeolite.
3. Method as claimed in claim 1, wherein
- the adsorptive bodies (13), in a pretreatment method for pretreating the
liquid for filling the pressure measuring transducer, are introduced as
granular material into the liquid, where the adsorptive bodies (13) then
adsorb foreign molecules;
- the liquid is separated from the adsorptive bodies (13) containing the
adsorbed gas molecules; and
the inner space of the pressure measuring transducer to be filled is
filled with the liquid, which has been separated from the adsorptive
bodies.
4. Method as claimed in claim 1, wherein
- the adsorptive bodies (13) have a particle size, which is small
compared to the dimensions of the inner space of the pressure
measuring transducer to be filled;
- the adsorptive bodies (13) are introduced into the liquid in a
pretreatment method for pre treating the liquid for filling the pressure
measuring transducer; and
- the inner space of the pressure measuring transducer is filled with the
liquid containing the adsorptive bodies (13).
5. Method as claimed in claim 1, wherein
- the adsorptive bodies (13) have a particle size, which is small
compared to the dimensions of the inner space of the pressure
measuring transducer to be filled;
- the adsorptive bodies (13) are introduced into the inner space of the
pressure measuring transducer to be filled; and
- the inner space is filled with the liquid.
6. Method as claimed in claim 1, wherein
- the pressure measuring transducer has at least one hollow space
(43,49,57,59) adjoining the inner space to be filled;
- adsorptive bodies (13) are introduced into the hollow spaces (43,49,57,
59);
- the hollow spaces (43,49,57,59) are separated from the inner space by
a partition (47, 51, 63, 67), which is permeable to the liquid and
impermeable to the adsorptive bodies (13); and
the inner space and the hollow spaces (43,49,57,59) are filled with the
liquid.
7. Method as claimed in claim 5 or 6, wherein
the pressure transfer liquid is pretreated in a pretreatment method before
filling the pressure measuring transducer with this liquid, in which
pretreatment method:
- adsorptive bodies (13) are introduced into the liquid and adsorb
foreign molecules dissolved therein;
- the liquid is separated from the adsorptive bodies (13) and the foreign
molecules bound to the adsorptive bodies (13) by adsorption; and
- the separated liquid, which is free of adsorptive bodies, is used for
filling.
8. Pressure measuring transducer manufactured with a method as claimed in
one of claims 1,2,4,5 or 7, wherein the pressure measuring transducer has
- a pressure receiving chamber (39) closed by an isolating diaphragm
(371,
- a pressure measuring chamber (41) connected to the pressure receiving
chamber (39),
- a pressure sensor (11) arranged in the pressure measuring chamber
(41), and
- an inner space formed by the pressure receiving chamber (39) and the
pressure measuring chamber (41) connected thereto and filled with a
pressure transfer liquid; and
- wherein the liquid contains adsorptive bodies (13),
- whose particle size is small compared to the dimensions of the inner
space filled with the liquid; and
- which serve to bind foreign molecules dissolved in the liquid to
themselves through adsorption.
9. Pressure measuring transducer manufactured with a method as claimed in
one of claims 1,6 or 7, wherein the pressure measuring transducer has
- a pressure receiving chamber (3) closed by an isolating diaphragm (I),
- a pressure measuring chamber (9) connected to the pressure receiving
chamber (3),
- a pressure sensor (11) arranged in the pressure measuring chamber (9),
- at least one hollow space (43, 49, 57, 59) adjoining the inner space
formed by the pressure receiving chamber (3) and the pressure
measuring chamber (9) connected thereto, wherein
- adsorptive bodies (13) are arranged in the hollow spaces (43,49,57,59);
- the inner space and hollow spaces (43, 49, 57, 59) are filled with the
pressure transfer liquid; and
- the hollow spaces (43,49,57,59) are separated from the inner space by
a partition (47, 51, 63, 67), which is permeable to the liquid and
impermeable to the adsorptive bodies (13).
10. Pressure measuring transducer as claimed in claim 9, wherein the pressure
measuring transducer has
- at least one hollow space (43) arranged in a diaphragm bed (45) of the
isolating diaphragm (1), which diaphragm bed (45) adjoins the
pressure receiving chamber (3);
- at least one hollow space (49) adjoining the pressure measuring
chamber (9);
- at least one hollow space (57) adjoining a pressure transfer line (5)
connecting the pressure receiving chamber (3) to the pressure
measuring chamber (9); and/ or
- a hollow space (59), which is arranged in an end of a filling opening
(29) of the pressure measuring transducer and adjoins the inner space
of the pressure measuring transducer.
Pressure measuring transducer manufactured with a method as claimed in
claim 1, wherein the pressure measuring transducer has
- a pressure receiving chamber (3) closed by an isolating diaphragm (I),
- a pressure measuring chamber (9) connected to the pressure receiving
chamber (3), and
- a pressure sensor (11) arranged in the pressure measuring chamber (9);
wherein
- the inner space formed by the pressure receiving chamber (3) and the
pressure measuring chamber (9) connected therewith is filled with a
pressure transfer liquid; and
- at least one adsorptive body (73,77,79) in the form of a molded body is
arranged in the inner space or an adjoining hollow space.
Pressure measuring transducer as claimed in claim 11, wherein one of the
adsorptive bodies (73) is an adsorptive body (73) that is arranged in a hollow
space (75), which is closed to the environment, that adjoins the pressure
receiving chamber (3) on its side lying opposite the isolating diaphragm (I),
and that is embodied as a diaphragm bed for the isolating diaphragm (1).
13. Pressure measuring transducer as claimed in claim 11, wherein one of the
adsorptive bodies (73) is a tubular adsorptive body (77) inserted in a pressure
transfer line (5) connecting the pressure receiving chamber (3) to the pressure
measuring chamber (9).
14. Pressure measuring transducer as claimed in claim 11, wherein one of the
adsorptive bodies (79) is a displacement body inserted in the inner space of
the pressure measuring transducer.
15. Pressure measuring transducer as claimed in claim 14, wherein the adsorptive
body (79) inserted as a displacement body is provided with electrical
connections (81), via which a capacitance of the adsorptive body (79)
dependent on the state of the pressure transfer liquid soaking the adsorptive
body (79) can be measured by means of a capacitance measuring circuit (83)
connected thereto.