Abstract:
A device and method for preparing an electrochemical sensor may enable the sensor head thereof to be provided with an electrolyte and a membrane. The device may include a retaining means for the sensor in addition to means for depositing the electrolyte and means for depositing the membrane.

Description:
PRIOR APPLICATION DATA 
     The present application is a national phase application of International Application PCT/CH2002/000431, entitled “DEVICE AND METHOD TO PREPARE ELECTROCHEMICAL SENSORS” filed on Aug. 6, 2002, incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     The invention relates to an apparatus for the preparation of an electrochemical sensor. 
     BACKGROUND OF THE INVENTION 
     Electrochemical sensors are known, the measuring principle of which is based on ion diffusion. This ion diffusion takes place, using a suitable electrolyte, usually via a semi-permeable membrane, for example a glass for H +  and Teflon for CO 2 . Such electrochemical sensors enable primarily the H + -concentration to be measured and indirectly, via the measurement of the H + -concentration, also the concentration of, for example, CO 2  or O 2  to be determined. The measurement of the H + -concentration takes place with a pH electrode, also termed a glass electrode. 
     A modification of the pH electrode is the pO 2  electrode, also termed a Clark electrode, which serves for the measurement of the O 2  concentration. 
     A further modification of the pH electrode is the pCO 2  electrode also termed a Severinghaus electrode which permits the measurement of the CO 2  concentration. In the Severinghaus electrode the CO 2  diffuses through a membrane (Teflon) into an electrolyte with an NaHCO 3  solution with: CO 2 +H 2 O&lt;-&gt;H 2 CO 3 &lt;-&gt;H + +HCO 3  applying. The H + -concentration is measured with the pH electrode and the CO 2  value derived therefrom. 
     Such electrochemical sensors are used amongst other things for the measurement of blood gas values such as the CO 2  concentration or the O 2  concentration in the blood. The electrochemical sensor is applied to a position of the human body with a good circulation of blood in order to measure the transcutaneous carbon dioxide partial pressure (tCpCO 2 ) or the transcutaneous oxygen partial pressure (tcpO 2 ). Extensive information concerning these generally known measurement methods are for example to be found in the following review article “Noninvasive Assessment of Blood Gases, State of the Art” by J. S. Clark et al., Am. Rev. Resp. Dis., Vol. 145, 1992, pp 220-232. 
     It is also known to provide the electrochemical sensor with additional sensors, for example with LEDs and photoelectric sensors in order to simultaneously carry out a pulsoximetric measurement. A combination sensor of this kind for the combined measurement of the oxygen saturation of the haemoglobin in arterial blood and also of the arterial carbon dioxide partial pressure is known from the document EP 0 267 978 A1. This combination sensor includes as an electrochemical sensor, a Severinghaus electrode for the measurement of the transcutaneous CO 2  partial pressure and also an arrangement for the measurement of the oxygen saturation (SpO 2 ) by means of pulsoximetry. 
     A disadvantage of electrochemical sensors is the fact that their preparation and maintenance is very demanding and requires trained specialist personal. For the Severinghaus electrode the semi-permeable membrane and the electrolyte which is located between the membrane and the sensor head must, for example, be regularly exchanged in order to ensure a problem-free operation. This servicing work is very demanding because the measurement accuracy is dependent on the thickness of electrolyte layer and also on the precise arrangement of the membrane. The reproducability of the measurement accuracy is of central importance, because vital parameters, such as the CO 2  content in blood are measured with the electrochemical sensor. A faulty measurement of this parameter could prove lethal for a patient. The electrochemical sensor is, moreover, frequently used in a hectic environment, such as in an intensive care station in the hospital. The electrochemical sensor is however also increasingly frequently used in the home area (home care) in order to monitor patients at home. 
     SUMMARY OF THE INVENTION 
     It is thus the object of the present invention to design the preparation of the electrochemical sensor reliably and simply. 
     The invention is in particular solved with an apparatus for the preparation of an electrochemical sensor in order to provide its sensor head with electrolyte and a membrane comprising a holding means for the sensor, a means for the dispensing of the electrolyte and also a means for the dispensing of the membrane. 
     The holding means, the means for the dispensing of the electrolyte and also the means for the dispensing of the membrane are jointly arranged in the same apparatus, which has the advantage that the sensor head can be reproducibly and very precisely provided with the electrolyte and also equipped with the membrane. The apparatus is preferably designed such that the sequence of preparation of this sensor is compulsorily guided in that first the electrolyte is dispensed and thereafter the sensor head can be equipped with the membrane. 
     The holding means, the means for the dispensing of the electrolyte and also the means for the dispensing of the membrane are advantageously arranged within a common housing, so that they are not accessible from the outside during the preparation of the sensor. 
     The means for the dispensing of the membrane and for the placement of the same of the sensor head preferably has a spring which is arranged such that the membrane is dispensed with a reproducible pressing force onto the sensor head and secured to it. Moreover, the means for the dispensing of the membrane advantageously has a pressing body with a pressing surface which, during the dispensing of the membrane, arealy contacts the membrane in order to reproducibly displace the electrolyte located between the membrane and the sensor head in such a way that the sensor connected to the membrane has a reproducible layer thickness of electrolyte, in particular a uniform layer thickness of electrolyte, between the sensor head and the membrane. This apparatus has the decisive advantage that every sensor equipped with the membrane has an essentially identical layer thickness of electrolyte. This increases the measurement reliability and reduces faulty measurements. The apparatus of the invention has the advantage that the preparation of the electrochemical sensor is essentially determined by the characteristics of the apparatus and no longer by the experience and ability of a specialist. Thus, even in a stress situation, such as, for example, results at an intensive care station, a reliable preparation of the electrochemical sensor is ensured. Moreover, it is also possible for an inexperienced person to reliably prepare the sensor, for example in the home area. 
     The apparatus of the invention also has, in a preferred embodiment, a means for cleaning the sensor head and also a means for the removal of an old membrane. An already used sensor can thus be put into the apparatus of the invention, wherein, with compulsory guidance the old membrane is first removed from the sensor, thereafter the sensor head is cleaned, the sensor head is provided with electrolyte and finally the sensor is provided with a new membrane. 
     In an advantageous design all consumed parts which are required for the preparation of the electrochemical sensor are arranged in a common carrier, with this carrier being designed as an exchangeable part preferably as a disposable or throw-away part. In this connection, prior to each preparation of an electrochemical sensor a new common carrier is first to be laid into the apparatus of the invention. 
     It is however also possible to conceive the entire apparatus of the invention as a disposable part or throw-away part so that no common carrier has to be exchanged. This apparatus contains all the means required for the preparation of an electrochemical sensor and does not therefore have to be opened. This apparatus is thus particularly simple to operate. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to embodiments. There are shown: 
         FIG. 1   a  a longitudinal section through an electrochemical sensor without a membrane set in place; 
         FIG. 1   b  a longitudinal section through an electrochemical sensor with a membrane set in place; 
         FIG. 2  a side view of a schematically represented apparatus for the preparation of an electrochemical sensor; 
         FIG. 3  a longitudinal section through a sensor held in a holding means; 
         FIG. 4  a longitudinal section through a means for the dispensing of the electrolyte; 
         FIG. 5  a longitudinal section through a means for the dispensing of the membrane; 
         FIG. 6  a longitudinal section through a means for the cleaning of the sensor head; 
         FIG. 7  a side view of the means for the cleaning of the sensor head; 
         FIG. 8  a longitudinal section through a means for the removal of the membrane; 
         FIG. 9  a view onto a common carrier; 
         FIG. 10  a cross-section through an apparatus for the preparation of an electrochemical sensor; 
         FIG. 11  a side view of the housing of the apparatus for the preparation of the sensor; 
         FIG. 12  a view onto the housing of the apparatus for the preparation of the sensor; 
         FIG. 13  a perspective view of the common carrier; 
         FIG. 14  a further perspective view of the common carrier; 
         FIG. 15  a partial view of the section along the section line A-A of  FIG. 11 . 
     
    
    
     In the following the same reference numerals will be used for the same items. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1   a  shows in a longitudinal section an electrochemical sensor  2  with a sensor head  2   a , glass electrode  2   b , holding grooves  2   c , inner space  2   d  and cable  2   e . The components located in the interior of the sensor  2  are not shown.  FIG. 1   b  shows in a longitudinal section the sensor  2  illustrated in  FIG. 1   a  which is prepared for the measurement in that its sensor head  2   a  is now covered with an electrolyte  3  and a membrane  4  with a holding ring  4   a  is secured to its sensor head  2   a . The electrochemical sensor shown in  FIG. 1   b  could for example contain a Clark electrode or a Severinghaus electrode. 
       FIG. 2  shows, in a side view, a schematically illustrated apparatus  1  for the preparation of the electrochemical sensor  2 . The apparatus comprises a housing  5  consisting of a housing upper part  5   a  and also of a housing lower part  5   b , with the two housing parts  5   a ,  5   b  being mutually displaceably mounted in the direction of the displacement t. The housing lower part  5   b  has an opening  5   m  behind which a holding means  6  for the sensor  2  is arranged. In the housing upper part  5   a  there is disposed a means  7  for the dispensing of the electrolyte and also a means  8  for the dispensing of the membrane. These two means  7 ,  8  are coupled to an actuating means  5   c  in order to move the means  7 ,  8  in the direction of displacement s and thereby to supply the electrolyte  3  or the membrane  4  to the sensor  2  fixed in the holding means  6 . The means  7 ,  8  are disposed in the interior of the housing  5 . 
       FIG. 3  shows, in a longitudinal section, a sensor  2  which is held in the holding means  6  including an abutment part  6   a , a first holding part  6   b  and also a lug  6   c . The sensor  2  can be released from the holding means  6  in that the lug  6   c  is depressed and thereby the first holding part  6   b  released from the engagement in the sensor  2 . It can prove advantageous to close the opening  5   m  shown in  FIG. 2  with a second holding part  6   d , with this holding part  6   d  being so designed that it lies on the sensor  2  and additionally fixes it. 
       FIG. 4  shows a longitudinal section through a means  7  for the dispensing of the electrolyte  3 . The means  6  comprises a container  7   d , filled with electrolyte  7   e , which has a closure  7   f  (for example with a ball). The container  7   d  is mounted in an outlet and holding part  7   a . The outlet and holding part  7   a  can be connected via a web  7   c  to a common carrier  11 . A pressure exerted downwardly onto the actuating means  5   c  is transmitted via the cylinder-like projection  5   d  onto the means  7  so that this is first moved downwardly until the spacer  7   b  contacts the sensor head  2   a . Thereafter the container  7   d  is pressed into the outlet and holding part  7   a , with the closure  7   f  opening with a correspondingly high internal pressure and the electrolyte  7   e  flowing via the passage of the outlet and holding part  7   a  onto the surface of the sensor head  2   a . As soon as the pressure is taken from the actuating means  5   c  the means  7  moves upwardly again and the spacers  7   b  no longer lie on the sensor head  2   a.    
       FIG. 5  shows a longitudinal section through a means  8  for the dispensing of the membrane  4 . The means  8  comprises a holder  8   a  with lugs  8   b  for the holding ring  4   a  of the membrane  4 . The means  8  further includes a piston  8   d  which is displaceably mounted via the guide part  5   e  and which is coupled via a spring  8   f  to the movable housing upper part  5   c  and which has at the bottom a pressing body  8   e  with a contact pressure surface  8   g  which uniformly contacts the membrane  4 . The means  8  can be connected via the holding part  8   c  to a common carrier  11 . The pressure exerted downwardly onto the actuating means  5   c  acts via the cylindrical projections  5   d  onto the spring  8   f  so that the piston  8   d  is moved downwardly. During this movement the lugs  8   b  enter into contact with the sensor  2  and are thereby spread apart, so that the membrane  4  is released and thereafter secured to the sensor  2 . During the mounting of the membrane  4  onto the sensor  2  a comparatively uniform areal force lies over the whole membrane  4 , brought about by the pressing body  8   e , so that the electrolyte  3  located between the sensor head  2   a  and the membrane  4  is uniformly displaced outwardly before the membrane  4  is fixedly connected via the holding means  4   a  to the sensor  2 . The means  8  has the advantage that the maximum pressing force of the pressing body  8   e  is essentially determined by the spring  8   f  which has the consequence that the membrane  4  is connected to the sensor  2  preferably independently or hardly dependently on the force acting on the movable housing part  5   c . The force brought about by the spring  8   f  is reproducible, which permits a uniform covering of the sensor  2  with the membrane  4 . The sensor  2  has in particular a uniform reproducible layer thickness of electrolyte  3 . 
     The apparatus shown in  FIG. 2  could have the means  6 ,  7 ,  8  shown in the  FIGS. 3 ,  4  and  5  in that the means  6  is arranged in the lower part  5   b  of the housing and the means  7  and  8  are arranged in the upper part  5   a  of the housing. 
       FIG. 6  shows a longitudinal section through a means  9  for the cleaning of the sensor head  2   a . The means  9  includes a holding part  9   a  in which a rotary piston  9   b  with a cleaning cloth  9   d  is displaceably mounted. The rotary piston  9   b  is moreover coupled via a spring  9   c  to the holding part  9   a . A pressure exerted downwardly onto the actuating means  5   c  is transmitted via the cylinder-like projection  5   d , which is guided in the housing upper part  5   a , onto the means  9  so that the latter is moved downwardly. During this movement the cleaning cloth  9   d  contacts the sensor head  2   a  at some time so that the rotary piston  9   b  is thrust into the holding part  9   a  as a result of the further movement. The relative movement of the rotary piston  9   b  with respect to the holding part  9   a  causes, as can be seen in  FIG. 7 , a rotary movement of the rotary piston  9   b .  FIG. 7  shows in the side view the means  9  for the cleaning of the sensor head  2   a . The holding part  9   a  has a slit  9   e  extending obliquely in which a cam  9   f , which is fixedly connected to the rotary piston  9   b , is displaceably mounted. If the cleaning cloth  9   d  now lies on the sensor head  2   a  and the holding part  9   a  is then moved further downwardly, then the rotary piston  9   b  will be thrust into the holding part  9   a  and the slit  9   e  and the cam  9   f  bring about a rotary movement of the rotary piston  9   b  and thus in particular of the cleaning cloth  9   d , so that the sensor head  2   a  is particularly intensively cleaned. 
       FIG. 8  shows a longitudinal section through a means  10  for the removal of the membrane  4  secured to a sensor  2 . The means  10  includes a holding means  10   a , a guide part  10   b  and also a lateral holding means  10   c . The means  10  can be connected via a resilient connection means  11   a  to a common carrier  11 . The sensor  2  with a membrane  4  is introduced into the means  10  with the membrane  4  aligned upwardly so that the holding ring  4   a  of the membrane  4  is held in the lateral holding means  10   c . Thereafter, a force is exerted onto the membrane  4  via the actuating means  5   c  which is guided via the cylinder-like projection  5   d  in the housing upper part  5   a  and also by the guide part  5   e . Through this force exerted by the projection  5   d  the holding ring  4   a  is separated from the sensor  2 . During this separation the holding means  6  shown in  FIG. 3  is preferably arranged beneath the means  10  so that the sensor  2  is held in the holding means  6  directly after the release of the holding ring  4   a.    
     The means  6 ,  7 ,  8 ,  9 ,  10  shown in the  FIGS. 3 to 8  all serve for the preparation of an electrochemical sensor  2 . Preferably at least the means  6 ,  7  and  8  are arranged in one apparatus  1  for the preparation of the electrochemical sensor  2  as shown in  FIG. 2 . it can also prove advantageous to provide further means, such as the means  9  and  10 . All these means  6 ,  7 ,  8 ,  9 ,  10  can be arranged in the most diverse manner in an apparatus  1  in order to enable a preparation of the sensor  2 . 
       FIG. 9  shows a top view of a common carrier  11  on which the means  10  for the removal of the membrane  4 , the means  9  for the cleaning of the sensor head  2   a , the means  7  for the dispensing of the electrolyte  3  and also the means  8  for the dispensing of the membrane  4  are arranged distributed in the peripheral direction. Of the means  8  only the holding part  8   c  is shown. 
       FIG. 13  shows in a three-dimensional elevation a further embodiment of a common carrier  11  with means  10 ,  9 ,  7  and  8  arranged distributed in the peripheral direction. The transparent membrane  4  with the holding ring  4   a  is mounted in the means  8  for the dispensing of the membrane. The carrier  11  showing in  FIG. 13  includes all consumed parts which are required for the preparation of the electrochemical sensor  2 . The carrier  11  is preferably designed as a disposable part, i.e. as a throw-away part.  FIG. 14  shows the carrier  11  shown in  FIG. 13  in a view from below. The carrier  11  includes resilient connection means  11   a  with which the means  8  and  10  are connected together and also a rigid connection means  11   b  with which the means  7  and  9  are connected. The carrier  11  further includes a first connection part  11   d , cams  11   c , a second connection part  11   e  and also a locking part  11   f.    
       FIG. 10  shows, in a cross-section, a particularly advantageously designed apparatus  1  for the preparation of an electrochemical sensor  2 . The same apparatus  1  is shown in  FIG. 11  in a side view and in  FIG. 12  in the plan view. As is shown in  FIG. 11  the housing  5  includes a housing upper part  5   a  and also a housing lower part  5   b  which form two half shells within which the common carrier  11  and further components are arranged. The housing upper part  5   a  has a plurality of holding means  51  arranged distributed in the peripheral direction which engage into the housing lower part  5   b  in such a way that a bayonet connection is formed thanks to which the two housing parts  5   a ,  5   b  can be mutually connected and also released again. The bayonet connection is moreover designed in such a way, and the holding means  51  are distributed in the peripheral direction in such a way, that the two housing parts  5   a ,  5   b  are mutually rotatably mounted. The housing  5  also includes a movable housing upper part  5   c  also termed actuating means which is displaceably mounted with respect to the housing upper part  5   a  and also with respect to the housing lower part  5   b  in the direction of movement s. A part of the sensor  2  projects into the opening  5   m  and is located within the interior of the housing  5 . The plan view of  FIG. 12  likewise shows a housing  5  with the housing upper part  5   a  and also with the actuating means  5   c  which is displaceably mounted relative to the latter. The housing upper part  5   a  is moreover rotatably mounted, together with the actuating means  5   c  in the direction of rotation D, with respect to the housing lower part  5   b . The actuating means  5   c  has markings A, B and C at the surface. If the marking A is in the opening  5   m , then the sensor  2  can, as shown, be introduced into the apparatus  1 . Thereafter the actuating means  5   c  is pressed downwardly in the direction of the movement s and thereafter relaxed upwardly again. Thereupon the housing upper part  5   a  with the actuating means  5   c  is turned in the direction of rotation D and the actuating means  5   c  is pressed downwardly again in the direction of movement s and relaxed upwardly again. This process is repeated until the marking B is located at the opening  5   m . In this position of the actuating means  5   c  the preparation of the sensor  2  is completed and it can be removed from the apparatus  1 . Through a further rotation of the actuating means  5   c  in the direction D the marking C reaches the opening  5   m . In this position the bayonet connection is unlatched and the housing  5  can be opened. Thereafter the common carrier can be removed from the housing  5  and replaced by a new common carrier  11 . The housing is put together again and the bayonet connection is latched so that the apparatus  1  is available for the preparation of a further sensor  2 . 
       FIG. 10  shows the actuating means  5   c  which is displaceably mounted with respect to the housing upper part  5   a  in the direction of movement s, with a resetting spring  5   h  being located at the center in order to always bring the actuating means  5   c  back into the illustrated basic position again after a movement downwardly. The actuating means  5   c  includes a plurality of plungers  5   d  which are formed as cylindrical projections and which act on the means  7 ,  8 ,  9  or  10 . The holding means  6  shown in  FIG. 3 , in which the sensor  2  can be firmly held, is arranged in the housing lower part  5   b . The housing lower part  5   b  also includes a pivot bearing  5   g  in which a spigot  5   f  of the housing upper part  5   a  is rotatably mounted so that the housing upper part  5   a  is rotatably mounted with respect to the housing lower part  5   b  in the direction of rotation D. The common carrier  11  is arranged in the internal space of the housing  5 . The common carrier  11  is connected via a first connecting part  11   d  with the rotatable bearing  12 . The rotatable bearing  12  is pressed upwardly by a spring  5   i . The carrier  11  is rotatably mounted with respect to the housing lower part  5   b . The carrier  11  is moreover connected via a second eccentric connecting part  11   e  to the housing upper part  5   a  and coupled to the housing upper part  5   a  with respect to a rotation in the direction D. The pivot bearing  5   g  has at the outer side grooves  5   k  extending in the direction s into which the cams  11   c  engage during the movement in the direction s, so that the common carrier  11  and also the housing upper part  5   a  is blocked during this movement with respect to rotation in the direction D. 
     All the components illustrated in the  FIGS. 3 to 8  are arranged in the apparatus  1  of  FIG. 10 , with only the apparatus  7  and  9  being explicitly shown for the sake of simplicity of the illustration in  FIG. 10 , whereas the apparatuses  8  and  10  are not shown. The carrier  11  arranged in  FIG. 10  is however in principle identical to the carrier  11  shown in  FIGS. 13 and 14  and thus includes the apparatuses  7 ,  8 ,  9  and  10 . 
     The preparation of a electrochemical sensor  2  with the apparatus  1  partly shown in  FIG. 10  includes the following steps:
         The bayonet connection of the two housing halves  5   a ,  5   b  is opened, the common carrier  11  is removed, a new common carrier  11 , such as is shown in the  FIGS. 13 and 14  is inserted, the bayonet connection of the two housing halves  5   a ,  5   b  is closed again and the marking A of the actuating means  5   c  turned to the opening  5   m.      The sensor  2  shown in  FIG. 1   b  comprising a membrane  4  is introduced into the inlet opening  5   m  of the housing  5 , with the means  10  shown in  FIG. 8  for the removal of the membrane  4  being located behind the inlet opening  5   m . As soon as the sensor  2  is introduced into the means  10  the actuating means  5   c  is pressed downwardly so that the cylinder-like projection  5   d  releases the sensor  2  from the holding ring  4   a  and the sensor  2  is supplied to the holding means  6  as shown in  FIG. 10 . The holding ring  4   a  with the membrane  4  remains in the means  10 . Thereupon the pressure on the actuating means  5   c  is reduced or the actuating means  5   c  is fully released so that the actuating means  5   c  moves upwardly again into the base position shown in  FIG. 10 .   Thereupon the housing cover  5   a  is rotated in the direction D until the means  9  for the cleaning of the sensor head  2   a  is located above the sensor  2 . The actuating means  5   c  is then pressed downwardly and the sensor head  2   a  is cleaned, as already described with respect to  FIGS. 6 and 7 , so that any electrolyte eventually present on the sensor head  2   a  is removed. The actuating means  5   c  is thereupon released again so that it moves upwardly.   Thereupon the housing cover  5   a  is turned in the direction D until the means  7  for the dispensing of the electrolyte is located over the sensor  2 . The actuating means  5   c  is then pressed downwardly and the sensor head  2   a  is provided with electrolyte  3  as already described with respect to  FIG. 4 . Thereafter the actuating means  5   c  is released again so that it moves upwardly.   Thereupon the housing cover  5   a  is turned in the direction D until the means  8  for the dispensing of the membrane  4  is located above the sensor  2 . The actuating means  5   c  is then pressed downwardly and the membrane  4  is connected to the sensor  2  as already described with the  FIG. 5 . Thereafter the actuating means  5   c  is released again so that it moves upwardly.   Thereupon the housing cover  5   a  is turned in the direction D until the marking B is located in front of the opening  5   m  so that the now completely prepared sensor  2  can be removed from the apparatus  1  by renewed pressing and releasing of the housing cover  5   a.      The housing cover  5   a  is then turned further, until the marking C is located in front of the opening  5   m . The bayonet connection of the two housing halves  5   a ,  5   b  is thus unlocked, the common carrier  11  can be removed, a new common carrier  11 , as is shown in  FIGS. 13 and 14  can be inserted and the bayonet connection of the two housing halves  5   a ,  5   b  can be closed again.   The apparatus  1  is now ready to prepare a further electrochemical sensor  2 .       

     In order to position the respective means  7 ,  8 ,  9 ,  10  precisely with respect to the sensor  2  held in the holding means  6  during rotation of the housing cover  5   a  the housing lower part  5   b  has, as illustrated in  FIG. 15  in a section A-A along the  FIG. 11 , inwardly projecting cams  5   n  on which the locking part  11   f  of the common carrier  11  respectively abuts with its tongue  11   g . The cams  5   n  are arranged distributed in the peripheral direction so that, on abutment of the locking part  11   f , the respective means  7 ,  8 ,  9 ,  10  is arranged precisely with respect to the sensor  2  so that the function corresponding to means  7 ,  8 ,  9 ,  10  can be executed at the sensor  2  by a downward pressing the actuating means  5   c . The tongue  11   g  of the locking part  11   f  is designed in such a way that it comes to lie directly after the cam  5   n  while the common carrier  11 , after completely moving downwardly, moves upwardly again and is thus no longer in engagement with the cam  5   n . Thus the housing cover  5   a  is again freely rotatably in the direction of rotation D until the locking part  11   f  engages into the next projecting cam  5   n . This design causes the actuation of the apparatus  1  to be compulsorily guided in that the operation which has to take place for each step is preset. The housing cover  5   a  is rotated in the direction of rotation D up to an abutment. Thereafter a movement of the actuating means  5   c , and associated with it a movement of common carrier  11  must necessarily take place in the direction s. After the housing  5  is again located in the basic position shown in  FIG. 10  the cover  5   a  can again be turned in the direction of rotation D up to the next following abutment This compulsory guidance ensures that during the preparation of the sensor  2  no operation is forgotten. The apparatus  1  is thus particularly suited for use in an environment with high stress, for example at an intensive care station or for a patient at home who hardly has experience with the preparation of an electrochemical sensor  2 . 
     The embodiments of apparatuses for preparing an electrochemical sensor  2  shown in the Figures represent embodiments from a plurality of design possibilities in order to satisfy the required function of the preparation of the sensor  2 . 
     The apparatus  1  shown in  FIG. 10  is also suitable to cover a sensor  2  with a membrane  4  for the first time. The sensor  2  without membrane  4  and holding ring  4   a  is introduced for this purpose in the housing position shown in  FIG. 12  into the inlet opening  5   m  of the housing  5  and, by pressing the actuating means  5   c  downwardly secured in the holding means  6  with the aid of the means  10 . Thereafter, the apparatus is actuated further, as described in  FIG. 10 , so that the sensor  2  is provided with electrolyte and membrane. As soon as the housing upper part  5   a  and also the actuating means  5   c  have been turned sufficiently far that the marking B is located at the inlet opening  5   m  the sensor  2  is fully prepared. 
     The means  7 ,  8 ,  9 ,  10  may not all be arranged at the common carrier  11  but can rather also be connected individually or in groups directly to the housing  5 . 
     In the above it has been described several times that the actuating means  5   c  is pressed in the direction downwardly with respect to the illustrated arrangement of the apparatus  1 . The apparatus  1  can also be fully held in the hand so that the actuating means  5   c  is pressed downwardly with respect to the housing lower part  5   b . The term downwardly not only means a vertical direction with respect to the surface of the earth, but also a movement towards the housing lower part  5   b .