DE7837694U1 - ELECTROCHEMICAL PROBE FOR DETERMINING THE OXYGEN CONTENT IN GAS, IN PARTICULAR IN EXHAUST GAS - Google Patents

Description

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12-12.1978 Zr / Sm

ROBERT BOSCH GMBH, 7OOO Stuttgart 1

Electrochemical probe for the determination of the
Oxygen content in gases, especially in exhaust gases

State of the art ι

The invention is based on an electrochemical measuring sensor for determining the oxygen content in gases, in particular in exhaust gases, according to the genus of the main; claim. It is such a sensor from the
DE-OS 25 ^ 7 683. which provides a plate-shaped electrolyte plague i with both sides coated, has the measurement gas \ lapped electrodes and a dependent on the oxygen content of the measuring gas voltage signal
(potentiometric sensor). Furthermore, from the | DE-OS 19 5 ¹ I 663 such a sensor is known, which also has a plate-shaped plague electrolyte with both I

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December 12, 1978 Zr / Sm

ROBERT BOSCH GMBH, 7OOO Stuttgart 1

Electrochemical measuring sensor for the determination of the oxygen content in gases, especially in exhaust gases

summary

A sensor for the oxygen partial pressure in Proposed gases, which has a plague electrolyte plate mi ^ - at least one pair of electrodes; each pair of electrodes is arranged on the same side of the solid electrolyte plate and exposed to the measurement gas. Advantageous arrangements of heating elements and temperature sensors and preferred embodiments are also proposed of electrodes- Also the installation of several sensor elements in the same sensor and the use for potentiometric and / or polarographic measurements are claimed. The construction of such sensors is both inexpensive and suitable for mass production as well as very flexible in terms of their special design.

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side applied electrodes surrounded by the measuring gas has; but a voltage is applied to its electrode is, as a result of which a dependent on the oxygen content of the measurement gas, limited by gas phase diffusion electric current provides the output of the probe (polarographic probe); in this DE-OS a separate heating element for the sensor is described, which sets the solid electrolyte to the desired working temperature. Mention should be made to ν this last-mentioned polarographic sensor as well

nor the DE-OS 27 11 880. according to which the gas to be measured through a porous coating must diffuse on the measuring electrode; this probe has a tubular plague electrolyte, one end portion of which is closed and its interior is supplied with a reference gas (air) will.

Advantages of the invention

In contrast, the electrochemical sensor with the characterizing features of the main claim has the advantage that it is industrially easy and inexpensive to manufacture, the use of a lower thermal capacity and thus a faster response of the Meßfi'hlers allowed _s easy, suitable for large series supplement with heating element and / or allows temperature sensors, also allows the formation of a potentiometric or a polarographic sensor or even the combination of several potentiometric and / or polarographic sensor elements in a single sensor; the advantageous developments of the main claim

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written sensor are listed in the subclaims.

drawing

, Embodiments of the invention are in the drawing and in the following description in more detail explained. Show it

Figure 1 shows the longitudinal section through a potentiometric sensor according to the invention in an enlarged view namely with the view of the front of the sensor element,

FIG. 2 shows the longitudinal section through the measuring sensor according to FIG. 1, but with the view of the rear side of the sensor element,

FIG. 3 shows the end section close to the exhaust gas of an enlarged, potentiometric sensor element with comb-shaped Electrodes and particularly advantageously arranged heating element,

\ Tj 4 shows the emission of a proximal end portion, shown enlarged polarographic sensor element with comb-shaped electrodes,

FIG. 5 shows the end section close to the exhaust gas of an enlarged, polarographic sensor element with a different electrode arrangement (hook / plate), FIG. 6 shows the front side of the end section on the measuring gas side of an enlarged sensor element with two Electrode pairs,

FIG. 7 shows the longitudinal section through a measuring sensor according to the invention, shown enlarged, with several potentiometric sensors and / or polarographic sensor elements and

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FIG. 8 shows the cross section through the end section on the measuring gas side of an enlarged sensor element block.

, Description of the exemplary embodiments

The electrochemical measuring sensor 10 shown in FIGS. 1 and 2 for the determination of the oxygen content in gases, in particular in exhaust gases, consists essentially of the actual sensor element 11, which is rectangular in cross section, on which a temperature sensor 12 and a heating element are additionally provided 13 is arranged, a metallic housing 14 which is provided with an external thread 15 and a key hexagon 16 for installation in a tube (not shown) carrying the measuring gas and in its longitudinal bore 17 a holder 18, 18 ^T and a seal 19 for the sensor element 11 is fixed and fastened, and of a protective jacket 20 which surrounds the area of the sensor element 11 exposed to the measurement gas at a distance.

The sensor housing 14 is provided in its longitudinal bore 17 with a shoulder 21 on which the protective jacket 20 rests with its flange 22; the protective jacket 20 is made of ceramic and has an opening 2k for the measurement gas in its bottom 23. The ceramic holder 18, which is disk-shaped, has an opening 26 for the implementation of the sensor element 11 and, by means of an edge 25, a recess for receiving the seal 19 (cement, glass) for the sealing installation, rests on the protective jacket flange 22 of the sensor element forms. On the edge 25 of the holder 18 lies the

standing components of the sensor 10 can be arranged and possibly also to be used additional Sealing rings in this area were not shown. In the outside of the holder 18 is next to the mounting <bore 28 a fixing groove 32 for a connection cable (not shown) is molded in.

The sensor element 11 has an oxygen-ion conductive Pestelektrolytplatte 33 mm in cross-section a width of 8 and a thickness of O ₃ has 8 mm and consisting essential of stabilized zirconia. This solid electrolyte plate 33 protrudes with its one end portion in the flushed by the measuring gas, surrounded by the protective jacket 20 area of the sensor 10, leads through the adapted opening 26 in the holder 18, through the seal 19 and through the longitudinal opening 27 in the holder 18 'and

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essential cylindrical, ceramic holder 18 'on, \

which limits the seal 19 towards the top. This f

Bracket 18 'also has a longitudinal opening 27 §

for the sensor element 11 and an IJ at its upper end

Drilling 28 of the longitudinal opening 27, into which the exhaust f

the distal end portion of the sensor element 11 protrudes; Yes

to fix the bracket 18 'in the correct position in relation to f

on the bracket l8 is on the edge 25 of the bracket |

18 has a fixation nose 29 formed thereon, which is inserted into a non |

designated, appropriately arranged blind hole in the \

Bracket 18 'protrudes. The outside of the bracket |

18 'has a shoulder 30 on which the flange 31 I

of the sensor housing l4 rests and consequently the ¹

Protective jacket 20 _f the brackets 18 and 18 'and the off |

seal 19 in the sensor housing 14 defines; Compensation |

elements that i

The coefficients of the sizing made from different materials

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ends with its other end portion in the holder | Counter bore 28; for locking the sensor element 11 in the longitudinal direction, the plague electrolyte plate 33 has a transverse bore 34 in which the seal 19 is located anchored. For additional fixation, the plague electrolyte plate 33 is provided with a collar-like cuff 35 || supported in the bracket 18 'by the counter bore 28 extends into the longitudinal opening 27 and is Jj preferably made of plastic (e.g. made of silicone rubber) ®

On the front side 36 of the plague electrolyte plate 33 are in the area surrounded by the measuring gas, two spaced-apart, plate-shaped electrodes 37 and 38 according to known methods Suitable processes (printing, spraying, vapor deposition) are applied and this is also applied to the Plague electrolyte plate 33 applied conductor tracks 39 and 39 'connected; the conductor 39 runs on the left long side and the conductor track 39 'on the right Long side on the front -36 of the plague electrolyte plate 33 · Both conductor tracks 39 and 39 'are at the in de ±' «

Js mounting counter bore 28 located end portion of the

r solid electrolyte plate 33 and serve there as electrical connection contacts. The electrode 37, which consists for example of platinum, and the electrode 38, which consists of a catalytically less active material such as the electrode 37 (eg gold) and preferably also the sections of the conductor tracks 39, 39 'located in the area surrounded by the measurement gas covered with a porous protective layer, which consists, for example, of magnesium spinel, but is not shown.

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Also on the face 36 of the plague electrolyte plate 33 is by any known suitable method the temperature sensor 12 (thermocouple) applied, between the conductor tracks 39 and 39 'and close the pair of electrodes 37 and 38. This temperature sensor 12 and its two also to the connection-side end section leading conductor tracks 40 and 40 'are from the plague electrolyte plate 33 by means of a not shown Insulating layer electrically separated; the iso - / "*> Liner layer can consist, for example, of aluminum oxide, which is plasma sprayed onto the plague electrolyte plate 33 is applied. Alternatively - even if functionally less good - such a temperature sensor could also be used be arranged on the back 4l of the plague electrolyte plate 33.

On the back 4l of the plague electrolyte plate 33 is the layered heating element in the area around which the measuring gas flows 30 (e.g. made of platinum) by any known, suitable process (printing, spraying, vapor deposition) applied and with s-one two to the electrical connection area leading conductor tracks 42 and 42 'from the solid electrolyte plate 33 by means of a .not shown Isolation layer separated; this insulation layer can for example consist of aluminum oxide and through Plasma syringes can be applied to the plague electrolyte plate 33. To avoid adverse reactions between the To avoid heating element 13 and the measurement gas, it is useful if the heating element 13 on its outside with a dense layer is covered, which is also not shown in the drawing and, for example, made of glass can exist. Instead of arranging such a hot element 13 on the backside of the plague electrolyte plate 4l

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A heating element can also be located on the plague electrolyte plate front 36, if necessary even can

also on the front 36 and on the back 4l each

Y a heating element can be applied.

. . In the Figure 3 is the transmitter portion of a meßgasseitige \ represented sorelementes 43, wherein the solid electrolyte

': plate 44 on its front side 45 comb electrodes 46 and

% _t 47 carries. These comb electrodes 46 and 47 mesh with theirs! .) Comb teeth 46 'and 47' into one another and thereby form a space 48. On the back of this plague electrolyte plate 44 is on an insulation (not shown)

layer a layer-shaped heating element 49 arranged in such a way that that it runs in that area in which on the plague electrolyte plate front side 45 the gap 48 corresponds between the comb teeth 46 ', 47' (shown in phantom); due to such an arrangement of the heating element 49 is in particular that area the plague electrolyte plate 44 heated in which the oxygen '■■ ion flow takes place. It should be mentioned that the comb teeth 46 '

or 47 'can also be designed in such a way that the with

the tine feet connected to the conductor tracks 50 and 50 'are wider and / or thicker than the free ones Ends of the comb teeth 46 'and 47'; this measure makes it possible to achieve approximately the same current density in the various Sections of the electrodes 46 and 47 instead of rectilinear sides of the comb teeth 46 ', 47' can zigzag sides can also be used; this measure leads to an improvement in the electrode activity of the Sensor element 43. This sensor element 43 is in a Housing 14 can be installed, as shown in FIGS. 1 and 2.

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The above-described sensor 10 with sensor elements 11 or 43 is known to work as an oxygen concentration chain with ion-conducting solid electrolyte and gives a dependent on the oxygen partial pressure of the measuring gas Voltage signal, like the one already mentioned, in DE-OS 25 47 683 described sensor does.

The section of a sensor element shown in Figure 4 is also in a sensor 10 according to Figures 1 and

C 2 can be installed; the measuring gas-side end portion of this sensor element 51 differs from the sensor element 43 in Figure 3 in structure only in that the porous protective layer is converted into a diffusion barrier 53 for the oxygen molecules in the measuring gas ^{on one electrode 52, for example made of platinum, with its comb teeth 52 r;} This diffusion barrier 53 can - like the porous protective layer - also consist of magnesium spinel, but must - be designed in a certain porosity and / or layer thickness according to the desired type of sensor. It should be mentioned that the diffusion barrier 53 may also cover the electrode 54 and then

, acts as a porous protective layer. A voltage (about 1 volt) is applied to the electrode 52 and the counter electrode 54 of a measuring sensor with such sensor elements 51, which can also be made of platinum, and the level of the electric current limited by gas phase diffusion represents a value dependent on the oxygen partial pressure of the measuring gas; Measuring sensors with such sensor elements 51 are referred to as polarographic measuring sensors, as they are described, for example, in DE-OS ¹ η 19 54 663 and 27 11 880 already mentioned.

Figure 5 represents a section of a sensor element 55, in which on a solid electrolyte plate 56 the

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both electrodes 57 and 58 have a different configuration "*

have as the electrodes in the examples described above : One electrode 57 , which in the case of a polarographic sensor would be covered with a layered diffusion barrier 59, is designed as a plate and the other electrode 58 as a hook, which the plate-shaped electrode 57 at a distance surrounds; the porous protective layer on the hook electrode 58 has not been shown. If such a sensor element 55 is to be used as a potentiometric measuring sensor, it can retain the same structure, but if necessary the thickness and / or the porosity of the protective layer and the electrode material must be adapted to the requirements. It is advantageous if the heating element (not shown) arranged on the rear side of the plague electrolyte plate 56 runs essentially in that area in which the intermediate space 60 between the electrodes 57 and 58 is located on the front side of the solid electrolyte plate 56 shown.

In the figure 6 the meßgasnahe section is shown of a sensor element 61 f, on the Pestelektrolytplatte 62 even two electrode pairs 63/63 'and 64/64' arranged with their non-designated conductors and a temperature sensor 65 are. Both electrode pairs 63/63 'and 64/64' can expediently be applied to a single side of the plague electrolyte plate 62; the distance between the pair of electrodes 63/63 'and the pair of electrodes 64/64' is chosen such that the two do not functionally influence each other. What has been said about protective and diffusion layers and the selection of the electrode material in the examples described above applies here accordingly.

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Speaking, in particular in the respect that the electrode pairs 63/63 'and 64/64' both for a potentiometric measurement or both for a polarographic measurement or one pair of electrodes for a potsntiometric and the other electrode pair for a polarographic measurement can be used. The temperature sensor 65 (thermocouple) is electrically separated from the solid electrolyte plate 62 and the electrode pairs 63/63 ^T and 64/64 'by means of an insulation layer 66. As in the other examples, a heating element can be arranged on the rear side of the solid electrolyte plate 62.

An embodiment of a related sensor 67, in which there are several sensor elements 68, 69 in a metallic sensor housing 70, is from the Figure 7 shows: With the sensor elements ^ 8 and 69, which are fastened in a single housing 70, are sensor elements, as they are in the preceding Examples are described. They are preferably arranged in pairs and parallel to one another, hold somewhat spaced from one another and - if necessary - their heating elements 71 and 71 'are as close together as possible turned to make good use of the heating energy. In most cases it is sufficient if only one of the two is used in pairs arranged sensor elements 68 (or 69) is provided with a heating element 71 (or 71 ') and the two Sensor elements 68 and 69 are arranged close together or even lie directly on top of one another; the heating element 71 (or 71 ') is from the solid electrolyte plates 72 and 73 kept electrically insulated (e.g. by means of insulating layer (s) not shown or an air gap) .

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In the figure, 8 of the meßgasseitige end portion of a sensor element block shown 74: This sensor element block 74 has two electrolyte plates 75 and 76 which with their area occupied by Isolationsschxchten 77 and 77 'i backs facing each other and a two Community

1 include heating element 78; on the outside

i:

■ i facing sides carry the plague electrolyte plates 75 and

76 each have a pair of electrodes 79 and 80 (or also several pairs each) and possibly not shown

; '^ Temperature sensors, which are also not shown, the insulation shafts from the plague electrolyte plates

I and / or. 76 are electrically isolated. Per sensor element

I block 74 represents a permanently assembled unit

and can be carried out simultaneously or consecutively for potentiometric and / or polarographic measurements are used will.

The sensor 67 shown in Figure 7, which has the two sensor elements 68 and 69 (or one or contain several sensor element blocks 74 according to FIG , can), has the metallic sensor housing 70 with

an external thread 80 and a key hexagon 82 for installation in a tube (not shown) in which the

I sample gas flows. The sample gas side sections of the sensor

I elements 68 and 69 protrude into the longitudinal bore 83 of this

Ϊ Housing 70 and are at a distance from a metallic

; see protective jacket 84 surrounding the one in its bottom

I opening 85 for the measuring gas and at its other end

I cut a splash 86. On this protective

s tel-Plansch 86, which on a shoulder 87 in the housing

\ Longitudinal hole 83 rests, is a metallic reflective

I xionsschild 88 arranged through its central bore

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insulate the sensor elements 68 and 69 and that helps to localize the heat in this area; It is advantageous for the localization of heat if the inside of the protective jacket 84 and the side of the reflective shield 88 facing the protective jacket 84 have a heat-reflecting surface. The flange 90 of a carrier sleeve 91 rests on the edge region of the reflective shield 88 and runs coaxially to the longitudinal housing bore 83. The carrier sleeve flange 90, the reflective shield 88 and the protective jacket 84 are fixed and fixed on the housing shoulder 87 by a beaded edge 92 of the housing 70. The carrier sleeve 91 has above its flange 90 some in one plane, into the carrier sleeve bore 93 pointing beads 94 as supports for a metal disc 95 _s through the central bore 96, the sensor elements 68 and 69 lead and as a support element for a number of superimposed, on the support sleeve 91 abutting insulation disks 97 is used. These insulating disks 97, which are made of ceramic, for example, keep the heat from the sensor element holder 98, which adjoins the insulating disks 97 in the support sleeve 91 and can consist of a plastic (eg a glass fiber reinforced thermoset); Instead of plastic, the sensor element aging 98 can also consist of glass or ceramic. This sensor element holder 98 is advantageously produced by injection molding into the carrier sleeve 91, with the sensor elements 68 and 69, the reflection shield 88 and the insulating disks 97 also being fixed at the same time; During this injection process, fixing lugs 99 are also molded onto the sensor element holder 98, which are anchored in corresponding wall openings 100 of the carrier sleeve 91. In addition, a bore 102 is also formed in the connection-side end face 101 of the sensor element holder 98,

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into which the end sections of the sensor elements 68 and 69 on this side protrude and the one fixing groove 103 for the has connector not shown; A sealing ring 104 is arranged on the holder end face 101, which is used for the tight assembly of sensor 67 and the aforementioned connector.

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Claims (1)

* · 519 2 December 12, 1978 Zr / Sm ROBERT BOSCH GMBH, 7QOO Stuttgart 1 Expectations 1. Electrochemical probe for the determination of the Oxygen content in gases, especially in exhaust gases, t,
with a sensor element which has a substantially rectangular solid electrolyte plate which conducts oxygen ions and which is arranged in the longitudinal direction within a metal housing and on which there are spaced apart electrode pairs exposed to the measurement gas, characterized in that at least one electrode pair (: (37/38; 46/47; 52/54; 57/58; 63/63 ', 64/64; 79, 80) only | on a single side (36; 45) of the solid electrolyte plate (33; 44; 56; 62; 72, 73; 75, 76) is arranged, preferably on the end portion of the solid electrolyte plate (33; 44; 56; 62; 72, 73; 75, 76) near the measuring gas, and that with the electrodes (37, 38; 46, 47; 52, 54; 57, 58; 63, 63 '; 64 ₃ 64'; 79, 80) conductive tracks (39, 39 '; 50, 50') in contact up to the connection area remote from the sample gas the solid electrolyte plate (33; 44; 56; 62; 72, 73; 75, 76) and preferably serve as connection contacts there. ..12 * ■ '■ ·· ■ · «» »Sill 1 II - 2 - R Zr / Sm .5192 2. Electrochemical sensor according to claim 1, characterized characterized in that the length of the gap extending between the electrode pairs (46/47; 52/54; 57/58) (48; 60) is as long as possible, e.g. by using intertwine protruding comb electrodes (46/47; 52/54) or by combining a plate and a hook electrode (57/58). 3- Electrochemical measuring sensor according to one of claims 1 or 2, characterized in that a temperature sensor (12; 65) (eg a thermocouple) is located on the sensor element (11; 6l), which is opposite the. electrically separated from other components by means of an insulating layer (66) and is preferably arranged near the electrodes (37/38; 63/63 ", 64/64 '). 4. Electrochemical sensor according to one of claims 1 to 3, characterized in that there is a layer-shaped heating element (13; 49; 7I / 7I ¹ ; 78) on the sensor element (11; 43; 68, 69; 74), which is opposite is electrically separated from the other components by means of an insulation layer. - 3 - row 5 19 2 Zr / Sm Electrochemical measuring sensor according to Claim 4, characterized in that characterized in that the heating element (13; 49; 71, 71 '; | 78) is on that side (41) of the plague electrolyte plate (33; 44; 72, 73; 75, 76) that the side (36, 45) with the two electrodes (37/38; 46/47; 79, 80) is opposite. 6. Electrochemical sensor according to claim 5, characterized in | characterized in that the heating element (49) on the plague electrolyte plate (44) runs essentially in that region of this side (45), the space on the side (45) of the plague electrolyte plate (44) carrying the electrodes (46, 47) (48) is (46, 47) counter \ between the electrodes. f 7 · Electrochemical measuring sensor according to one of Claims 3 ^ ^v> % ^{to 6, characterized in that conductor tracks (40, 40 ', 42, 42!} ) are also used for the electrical connection of the heating element (13; 49; 78) and the temperature sensor (12; 65), which extend up to the electrical connection area on the The end portion of the sensor element (11, 43, 6l, 68, 69, 74) remote from the measuring gas lead and preferably serve as a connection contact there. - 4 - R. 519 Zr / Sm 8. Electrochemical measuring sensor according to one of claims 1 to 7, characterized in that one of the electrodes (37, 46) catalytically active on the sensor element (11, 43) and the second electrode (38, 47) less catalytically is active as the first electrode (37, 46) and that the conductors connected to the electrodes (37, 33; 46, 47) - ("'■ tracks (39/39 '; 50/50') lead the signal of the sensor (10) acting as an electrochemical cell. 9. Electrochemical sensor according to one of claims 1 jj to 7, characterized in that at least one of the two electrodes (52, 54; 57, 58) with a'Diffusions-. barrier (53; 59) for the oxygen molecules of the measuring gas is provided and that a voltage is applied to the electrodes (52, 54; 57, 58). 10. Electrochemical sensor according to claim 9, characterized in that the diffusion barrier (53, 59) a. f is applied to the electrode (52, 57) porous layer. 11. Electrochemical measuring sensor according to one of claims 8 1 to 10, characterized in that the electrodes exposed to the measuring gas % (37/38: 46/47; 52/54; 57/58; _{63/63 · 3} J 64 / 64 ¹ ; 79, 80) and preferably also the other components exposed to the measurement gas, such as the heating element (13; ~ ../5 ι "· ·« ..I III / 519 - 5 - R. Zr / Sm 49; 71, 71 '; 78), temperature sensors (12; 65) and conductor tracks (39, 39 ', 40, 40', 42, 42 ·, 50, 50 ') - if they ι are not covered by any diffusion barrier (53, 59) - wear a protective layer which is porous in the area of the electrodes (37/38; 46/47; 52/54; 57/58; 63/63 ¹ , 64/64 '; 79, 80). 12. Electrochemical measuring sensor according to one of claims 1 to 11, characterized in that at least one sensor element (11; 43; 51; 55; 61; 68, 69; 74) in this way in the central bore (17; 83) of a tubular metal sensor housing (14; 70) is attached that a seal (19; 97, 98) the sensor element (11; 43; 51; 55; 6l; 68, 69; 74) divided into the area for electrical connection and the area around which the sample gas flows. 13 · Electrochemical measuring sensor according to claim 12, characterized characterized in that the sensor elements (68, 69) are arranged in pairs at a distance from one another in a metal housing (70) are and that the heating elements (71, 71 ') of the sensor elements (68, 69) are preferably facing each other. l4. Electrochemical measuring sensor according to Claim 12, characterized in that the sensor elements are in a metal housing (70) (75/79, 76/80) in pairs directly next to each other * 11 » ^, frm -6- R. 5 192 Zr / Sm gene or are connected to one another and that preferably only a single 'heating element (78) is arranged between the sensor elements (75/79, 76/80), the electrodes (79 ₃ 80) of which point outwards. 15. Electrochemical sensor according to one of claims 1 to l4, characterized in that the exposed to the measurement gas Area of the sensor element (11, 43; 51; 55; 6l; 68, 69; 74) at a distance from a protective jacket (20, 84) is surrounded, which feeds the measured gas to the sensor element (11; 43; 51; 55; 6i; 68, 69; 74) in a metered manner.