Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-07-24
2004-02-03
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S400000, C204S435000
Reexamination Certificate
active
06685807
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a measuring probe for potentiometric measurements. The probe has a housing of an electrically insulating material surrounding an enclosed space that contains a primary reference element and an electrolyte. The housing has at least one opening through which the electrolyte can be brought into contact with a sample solution on which a measurement is to be performed. The enclosed space is filled with an ion-permeable, micro-porous, high-viscosity polymer substance which, in combination with the electrolyte, forms a filler mass of the measuring probe. The invention also relates to a method of monitoring the state of aging of the measuring probe, and it further relates to the use of the measuring probe for applications in process monitoring and process control.
A widely used kind of measuring probe for potentiometric measurements of ion concentrations or redox potentials is equipped with a diaphragm of porous material. The diaphragm serves to bring a reference—and/or bridge electrolyte, normally in the form of a liquid contained inside the measuring probe, into contact with a test solution. Particularly in chemical or micro-biological process-monitoring and process-control applications, the diaphragm may be subject to contamination which can falsify the results of the measurements.
Another measuring probe, known from DE 34 05 431 C2, belongs to the same general category of measuring probes but does not have a diaphragm and is significantly less prone to contamination. It has a housing of an electrically insulating material with at least one enclosed space containing a reference element and an electrolyte. The housing has at least one opening through which the electrolyte can be brought into contact with the test medium on the outside of the housing, i.e., a liquid solution on which a measurement is to be performed. The enclosed space inside the housing is filled with an ion-permeable, micro-porous, high-viscosity polymer substance which, in combination with the electrolyte, forms a filler mass of the measuring probe. This type of construction assures that the electrical potential measured at the reference element is highly constant even if the solutions being measured are strongly contaminated. In addition, the measuring probe can sustain pressure levels significantly in excess of 10 bar.
Measuring probes of the foregoing description are known to have the problem that as the cumulative operating time of the probe advances, the electrolyte that is initially contained in the polymer substance will to an increasing degree migrate into the test solution, resulting in a progressively spreading electrolyte deficiency in the polymer substance inside the housing. The increasing electrolyte deficiency in the polymer substance is also referred to as the aging process of the measuring probe and produces the undesirable effect that, when the electrolyte deficiency eventually reaches the reference element, there will be a change in the electrical potential measured at the reference element. To avoid the risk of erroneous measuring results, it is therefore necessary to monitor the aging process of the measuring probe. In particular, it should be possible to detect sufficiently in advance, i.e., with an adequate pre-warning interval, when the electrolyte deficiency is approaching the reference element.
According to DE 34 05 431 C2, the problem of detecting the advancement of the electrolyte deficiency can be solved by using an electrolyte consisting of a suspension of homogeneously distributed particles of a neutral salt with ions of equal transport number in an aqueous solution of the neutral salt. The polymer substance and the neutral salt suspension together form a gel that has a turbid appearance due to the salt particles in suspension. The state of aging of the measuring probe can be visually detected, as the turbidity disappears progressively with the advancement of the aging process. The reason for the decrease in turbidity is that the suspended neutral salt particles continuously pass into solution until a final state has been reached where there are essentially no suspended particles left and, as a result, the turbidity is strongly diminished. It has been found that in the aging process, a clearly visible boundary develops between a turbid portion of the gel where the neutral salt particles are homogeneously suspended and a comparatively clear portion where the neutral salt particles have passed into solution. As the boundary advances over time from the opening in the housing towards the reference element, the state as well as the speed of aging of the measuring probe can be determined from a visual observation of the boundary in the polymer gel.
However, the measuring probe according to DE 34 05 431 C2 has several drawbacks. To monitor the state of aging, it is necessary to be able to clearly see inside the enclosed space of the measuring probe. This precludes the use of a non-transparent material for the housing, and it also presents a problem with a transparent housing if the latter becomes contaminated by surface deposits. A further severe problem occurs if the gel in the enclosed space becomes discolored or contaminated, e.g., by the infusion of colored substances or infiltration of dirt particles from the test solution, which could make it practically impossible to visually detect the boundary of the electrolyte deficiency. It also has to be counted as a drawback that the electrolyte needs to be a suspension of homogeneously distributed particles of a neutral salt with ions of equal transport number in an aqueous solution of the neutral salt, a condition that excludes other kinds of electrolytes from being used in the measuring probe.
OBJECT OF THE INVENTION
A first object of the present invention is to provide an improved measuring probe that is free of the aforementioned drawbacks. A further object of the invention is to provide a method of monitoring the state of aging of a measuring probe, and a third object is to propose a use of the improved measuring probe.
SUMMARY OF THE INVENTION
A measuring probe according to the present invention has a housing of an electrically insulating material surrounding an enclosed space that contains a primary reference element and an electrolyte. The housing has at least one opening through which the electrolyte can be brought into contact with the outside of the housing, i.e., with a sample solution on which a measurement is to be performed. The enclosed space is filled with an ion-permeable, micro-porous, high-viscosity polymer substance which, in combination with the electrolyte, forms a filler mass of the measuring probe. The measuring probe of the present invention has a secondary reference element contained inside the enclosed space and arranged in such a manner that an electrolyte deficiency advancing from the opening towards the primary reference element arrives at the secondary reference element before it reaches the primary reference element.
In the measuring probe according to the foregoing description, the state of aging is monitored by using a method that is likewise part of the present invention, with the steps of
a) detecting continually or at intervals the difference (V
1
−V
2
) between the respective electrical potentials V
1
and V
2
of the primary and secondary reference element, and
b) generating a signal when the difference between the potentials exceeds a previously specified threshold value, and/or if the difference between the potentials changes at a rate that exceeds a previously specified threshold rate.
The invention also encompasses the use of the inventive measuring probe in process-monitoring and process-control applications.
With the inventive concept of arranging a secondary reference element in the enclosed space of the measuring probe so that an electrolyte deficiency advancing from the opening towards the primary reference element reaches the secondary reference element before it arrives at the primary reference element, it is no longer necess
Friedrich Kueffner
Mettler-Toledo GmbH
Tung T.
LandOfFree
Measuring probe for potentiometric measurements, method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Measuring probe for potentiometric measurements, method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Measuring probe for potentiometric measurements, method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3283113