DE7229690U - pH flow transmitter for operational pH measurements - Google Patents

Description

Flow giver. for_Betricbs ₌ 2H. measurements

The invention relates to a pH flow transmitter for operational pH measurements, in which a measuring electrode with a glass-like, pH-sensitive Layer and a comparison electrode over a diaphragm with a liquid that can be circulated in a flow channel! related to the pH value of which is to be measured. i

The pH value is known to be an indicator for the hydrogen ion activity v / aqueous liquids and it is often used as a measured variable in liquid analyzes. The measurement of the ' pH value is measured using glass and reference electrodes, and they j is based on the fact that certain glasses or similar substances develop a potential in relation to aqueous solutions that of depending on the hydrogen ion concentration in the aqueous reading is. The connection between this potential and the hydrogen ion concentration is shown by the well-known Nernst'-see Equation described.

The practical structure of pH measuring devices differs fundamentally according to whether it is a laboratory measuring device or a an operating measuring device. Basically, pH value transmitters have a measuring electrode and a comparison electrode, that is to say one so-called electrode chains, which are inserted or can be used in a suitable vessel. In the case of laboratory measuring devices, for example, one wants the pH value even in very small amounts of liquid

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measure, and furthermore it is mostly desirable to be able to easily change the electrodes in order to also be able to measure the concentrations of others being able to measure ions. On the other hand, enough in the later Qualified personnel are available so that cleaning and maintenance of the electrodes are not difficult. In particular the necessary care can be taken when handling the electrodes in the laboratory in order to ensure a mechanical Avoid breaking the glass electrodes.

However, other aspects must be taken into account when designing operational measuring devices. Usually stand once there is always enough liquid available, so that a particularly small volume does not need to be grounded needs. On the other hand, the measurement task is also generally fixed, so that it is also important that the Electrode does not arrive. On the other hand, industrial measuring devices should Work continuously and maintenance-free as possible, so that the question of cleaning the electrodes becomes particularly important. Operating measuring devices must also be constructed to be more robust than laboratory measuring devices.

The known Betriebsaneßgeräte for measuring the pH value in flowing liquids, so-called pH flow transducers for operational pH measurements have a flow channel or a flow-through vessel in which rod-shaped glass electrodes are used are. The ongoing cleaning of the glass electrodes is difficult because the glass electrodes form a flow resistance to which dirt settles. It is known to remove this dirt have become additional mechanical cleaning devices for the rod-shaped glass electrodes within the flow-through vessel to order, which, however, could not fully satisfy. Furthermore, it has become known, the electrodes to be designed as rotating electrodes, so that due to the

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Centrifugal force self-cleaning occurred. But even this construction is too open.

The invention is based on the object of a pH flow transmitter for creating operational pH measurements that is easy and is robust and in which additional devices for cleaning the electrode chains are not required.

This object is achieved according to the invention in that the inner wall of the flow channel is at least partially formed by the pH-sensitive layer of the measuring electrode and that The diaphragm of the reference electrode is flush with the inner wall of the flow channel into an ^ opening in the Wall of the flow channel ends.

This achieves that, so that layers of dirt can not be deposited from a certain flow rate of the to-monitoring ^ n liquid to by turbulence formation at the Innr ^ wall of the flow channel and dam.r I erosion occurs at the pH-sensitive layer bezip ^ or so that layers of dirt that have already formed are removed again by themselves.

To increase the mechanical stability ϊεε, it is advisable to use the! Establish flow channel from a metallic pipe or the like and the inner wall of this space needs to be coated with the pH-sensitive layer.

This embodiment has the advantage that not only the mecha-j niche stability is increased, but at the same time also a; Shielding against electrostatic and / or electromagnetic j Errors given 3.0t.

You can use the current measuring electrode and the reference electrode in 7, / ei axiM arranged one behind the other, closed

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Arrange ring roughness, the open inner channels of which the flow j form a channel.

Another embodiment that results in a shorter overall length, can include that the reference electrode of the measuring electrode in an annular space arranged concentrically around the flow channel and the comparison electrode arranged in a further annulus which is arranged concentrically around the annular space of the measuring electrode he 'um.

There are sr il be noted that the invention is applicable not only to pH flow transmitter, but that sensitive to other ions flow transmitter can be set up according to the invention, for which purpose it is only necessary to replace the pH-sensitive layer with a layer of other ions sensitivity and to choose other electrodes if necessary.

In the following, the invention will be described in conjunction with the drawings on the basis of exemplary embodiments.

Figures 1 and 2 show two embodiments of the invention Flow transmitter for operational measurements.

FIG. 1 shows a section through an embodiment of a flow transmitter according to the invention, in which the measuring electrode and the comparison electrode have been accommodated in concentrically arranged cells. "1" denotes a flow channel through which a flow to be monitored | Fluid can be circulated and which at the same time forms the inner wall of an annular space 2, the outer wall of which is denoted by 3. The outer wall 3 in turn forms the inner wall of a RmgrauEies U _1, the outer wall of which has been designated with "5".

The annulus 2 is in a known manner with a buffer solution

Pat4F1 (670 10000 / KE)

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filled and in this buffer solution is the lead electrode 6
the measuring electrode arranged, which tightly through the ring space 4
is passed through, so that their supply line is accessible from the outside.

The ring space 4 is also filled with a liquid,
which is connected to the flow channel Λ via a diaphragm 7 in terms of potential, the one without electrical or potential
Compound through the buffer solution in the annulus 2 passes.
A reference electrode 8 de: · comparison electrode is arranged within the annular space.

It should be noted that the diaphragm 7 of the reference ^{electrode is} flush with the inner wall of the flow channel Λ
concludes «

The flow channel 1 can be made of a pH-sensitive glass. A potential jump forms on this glass wall, which is a measure of the hydrogen ion concentration in the liquid to be monitored, which flows in the flow channel. The size of this potential can be expressed as a voltage
measured between the measuring and comparison electrodes
become what is well known.

To reduce the risk of breakage and the electrical shielding |

to improve the flow channel 1 can also from j

a metal pipe or the like. Then i

it is necessary to have a pH j sensitive layer made of glass or a similar material

to attach. This layer is shown in dashed lines and has been designated by j “9”.

If instead of the pH-sensitive glass as a material for! the flow channel or the layer 9 a material;

Pet 4 F 1 (670 10000 / Kb)

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verv / ends that responds to other ions, so you can with the Flow transmitters also measure the concentration of other ions. j

FIG. 2 shows in perspective another embodiment j of the invention, which differs from the embodiment according to FIG. 1 j The only difference is that the two annular spaces in which the j lead electrodes of the measuring and comparison electrodes are arranged are arranged axially one behind the other. It was therefore the same for the individual components of this embodiment! Reference numerals as in the embodiment according to FIG. 1 are omitted / ended. It should be noted that in this embodiment the pH-sensitive Layer only covers the inner wall of the annular space 2 in which the lead electrode for the measuring electrode is arranged. A more detailed description of this embodiment can therefore be dispensed with.

The inner diameter of the flow channel 1 is chosen so that at the expected flow velocities at the Inside wall of the channel 1 erosions occur, which prevent dirt from settling or dirt that has settled is eliminated. If necessary, you can use an additional circulation pump, which can be done in conjunction with conventional flow sensors is already known.

Experiments have shown that the measured pH value with stationary liquid in the flow channel and with turbulent flowing The fluid fluctuates so little that these fluctuations are in the range of the tolerable errors.

As with any conventional flow transmitter, the potentials measured with a flow transmitter according to the invention are also temperature dependent. How this temperature dependency can be compensated is known, and this is not the subject of the invention, which is seen in that by a

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ill ti

Erosion of the sensitive layer of the measuring electrode caused by turbulence in the one to be monitored ?! Liquid evoked v: ird, a self-cleaning of the sensitive layer occurs, the additional Makes devices for cleaning the electrodes superfluous.

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Claims (1)

Pa. tec SO urchins 1, pH flow transmitter for operating pH measurements, in which one Measuring electronics with a glass-like, pH-sensitive ScMchi ■ and a Yergyich electrode via a diaphragm with a fluid that can be circulated in a flow channel whose pH value is to be monitored or measured, thereby marked t, that the inner wall of the flow channel is at least partly from the pH-sensitive layer of the electrode is formed and the junction of the comparison electrode! flush with the inner wall of the flow channel? - j send in an opening in the wall of the flow channel i ends. 2. pH flow transmitter according to claim 1, characterized in that that the flow channel made of a metallic pipe or the like and the inner wall of this tube is covered with the pH-sensitive layer. 3 » pH flow transmitter according to claim 1 or 2, characterized in that the discharge electrode of the measuring electronics is concentric in one of the flow channels Pat4 F 1 (670.10000 / KE) 7229690 03/18/76 -2- surrounding annulus and the reference electrode of the reference electrode are arranged in a further, concentrically arranged around the first annular space further annular space. 4. pH flow transmitter according to claim 1, characterized in that that the lead electrode of the measuring electrode and rie lead electrode the comparison electrode in zv / ei axially one behind the other arranged annular spaces are arranged, the inner openings form part of the flow channel. Pal Λ i I (B ¹ O tüOOC / KE) 7 ?? 9690