Reference electrode for ion activity measurement, especially for pH measurement.

The invention relates to a reference electrode for a measuring chain for measuring the ionic activity, such as the pH. For electrochemical potential measurements such as the pH measurement, a measuring electrode which is responsive to the ions to be measured and a reference electrode is provided. Both electrodes are immersed in the medium to be measured. By a measuring device (mV meter, pH meter), the potential difference between the two electrodes is measured. The display unit is a measure of the ion concentration. In the hydrogen ion activity measurement (pH measurement), in which a measuring electrode is used which responds to hydrogen ions, which means that the potential dependent with respect to the reference electrode of the hydrogen ion concentration, the potential of the reference electrode but is independent constant, typically a pH -Wertmessgerät used. The pH meter is an mV meter, which is calibrated in pH values. The object of the reference electrode is to be independent of the state and the nature of the medium to be measured in an ion-conducting contact on the medium to be measured to the measuring electrode and to have an independent on the ion concentration constant self-potential. Such a reference electrode, for example, is known from DE-OS 30 36 354th In this known Refe rence electrode a downwardly open chamber is provided with a coating of glass. The lower open end is closed by a porous plug, which ensures an ion-conducting contact on the medium to be measured to the measuring electrode, the chamber is filled with a saturated aqueous solution of potassium chloride and silver chloride. Inside the chamber, surrounded by the chloride solution, there is a galvanically chlorinated silver wire or silver plate, of or connected with a cable to the encoder.

Such an arrangement is not only expensive to manufacture, but also has the following disadvantages:<ul><li>The porous plug (diaphragm) leaking potassium chloride and silver chloride chemical reactions with the medium to be measured may occur that clog the diaphragm and can interrupt the ion-conducting contact.</li></ul>

This known arrangement is pressure resistant to diffusion of the medium to be measured to avoid only by an expensive pressure equalization valve inside the electrode through which the operational reliability may be affected.

The Elektolytvorrat inside the chamber is reduced due to the flow during the measurement process through the diaphragm. Topping up is essential.

This known arrangement has only limited temperature resistance.

It is therefore an object of the invention to provide a reference electrode that simply having the structure and greater operational reliability.

The solution of the problem according to the invention characterized by a glass tube whose lower end is closed by a, consisting of porous ceramic plug and filled with an electrolyte of potassium chloride and silver chloride, in a galvanically chlorinated silver wire is, of a way of a connecting cable meter is connected, and wherein the glass tube is surrounded by an existing electrically conducting plastic sheath.

For more information on the material of the jacket can be taken from the dependent claims. 2 and 3

An electrode with the electrode of the invention comprises a further, known per se, measuring electrode, as this example is known from DE-AS 23 56 719th Between the reference electrode and the measuring electrode a measuring device (mV meter, pH meter) is connected with high input resistance. The scale of the meter is calibrated in mV or pH.

Another solution of the problem according to the invention characterized by a galvanically chlorinated silver wire with a coating of a polymer such as Polyvinylesther, which finely divided silver chloride is added. The chlorination of the silver wire is effected in a galvanic Procedure means of a solution of hydrochloric acid, potassium chloride, and potassium nitrate, or other suitable material. In this reference electrode is a particular chamber, such as a glass tube into which a liquid is filled, is avoided. This electrode is thus executed completely dry.

The wrapping of the polymer may additionally be admixed other salts. This can be particularly finely divided potassium chloride or lithium chloride.

An electrode with the electrode of the invention has a more well-known in itself, separate measuring electrode. This electrode can be designed as single-rod or as a two-rod measuring chain. The reference electrode and the measuring electrode are (, pH meter mV meter) connected to a measuring device, the scale of which is calibrated in mV or pH values.

The reference electrode of the invention is generally suitable for ion activity measurement. It is suitable as described for the measurement of the hydrogen ion activity (pH), as well as for any other anions such cations using for suitable measuring electrodes, which are not to be described in more detail here. In addition, there is the choice of the conductive additive in the polymer is important because a washout by the medium to be measured of the conductive additive in the form of salts can not be avoided, whereby the measurement can be influenced itself. It is therefore recommended as a conductive additive for the measurement of, for example chlorine, bromine, iodine, silver, mercury, potassium cyanate and a conductive additive potassium nitrate or sodium nitrate.

Further details of the invention are disclosed in claims 11 and 12 as well as the drawings of the embodiments specifically for pH measurement.

It show the<ul><li>Fig. 1 is a reference electrode according to the invention in a longitudinal section;</li><li>Fig. 2 is a Double electrode for the pH measurement with the reference electrode according to the invention,</li><li>Fig. 3 is a combination electrode for the pH measurement with the reference electrode according to the invention,</li><li>Fig. 4, a reference electrode according to the invention in a dry execution,</li><li>Fig. 5 is a Double electrode with a reference electrode according to FIGS. 4 and</li><li>Fig. 6 shows a combination electrode with a reference electrode in accordance with FIG. 5 shows.</li></ul>

The proportions of the individual components in the drawings do not correspond to real conditions in order to allow a good visibility.

In the drawings, the reference electrode 2, a glass tube 22 with the same, with 21, which consists of conductive plastic jacket surrounding the glass tube concentrically, respectively. The glass tube 22 is closed at its lower end by an existing porous ceramic plug 25th In the glass tube 22, an electrolyte 24 is contained, as well as a supply of powdered silver chloride 26, to ensure saturation of the consisting of potassium chloride and silver chloride aqueous electrolyte 24th In these electrolyte of the galvanically chlorinated silver wire immersed 23 and establishes the electrical contact with the connection cable third

When Double electrode shown in Fig. 2 except the reference electrode 2 a measuring electrode 1 is provided, both of which are immersed in the process medium. 7 The measuring electrode 1 has a glass tube 10, the lower spherical member 13 consists of electrically conductive glass, and responsive to the measured hydrogen ion. The glass tube 10 is filled with an electrolyte, in which a galvanically chlorinated silver wire 11 is located which is like the galvanically chlorinated silver wire 23 is connected via connection cable 3 to the measuring device 5, the scale is calibrated in mV / pH.

In the illustrated in Fig. 3 electrode with a reference electrode 2 according to the invention is in turn with 10, the glass tube of the measuring electrode, referred to be spherical member made of electrically conductive glass, with 11 of the galvanically chlorinated silver wire 13, which is immersed in the electrolyte is filled in the glass tube 10 and is connected to the connecting cable 3 to the measuring device. The glass tube 10 is surrounded by an existing conductive plastic sheath 21st Within the jacket 21, the glass tube 22 is disposed. The chlorinated silver wire 23 is also connected via connection cable 3 to the measuring device.

In the illustrated in Fig. 4 the second embodiment of the invention with 41 of the galvanically chlorinated silver wire 42 and with the polymer, by adding electrically conductive sheath which surrounds the chlorinated silver wire, is shown.

In the illustrated in Fig. 5 embodiment of the invention the same reference numerals are as stated above valid. Both the reference electrode 2 and the measuring electrode 1 are immersed in the medium to be measured. 7 The electrical contact to the measuring device 5 is made via a cable connection formed as coaxial cable. 3

In the combined electrode shown in Fig. 6, the glass tube 10 of the measuring electrode of one of the polymers referred to above existing with conductive additive jacket 42 comprises concentric. Within the enclosure 42 a chlorinated silver wire 41 is arranged, which is like the chlorinated silver wire 11 is connected via connection cable 3 to the measuring device. The chlorinated silver wire 41 together with the sheath 42, the reference electrode.