HK1124748B - System for in-vivo measurement of an analyte concentration - Google Patents

Description

System for in vivo measurement of analyte concentration

Technical Field

The present invention relates to a system for in vivo measurement of analyte concentrations in a human or animal body.

Background

The present invention is based on the in vivo measurement of analyte concentrations in the human or animal body, for example as known from US 2004/0133164 a 1.

Systems of this type for in vivo measurement of analyte concentrations typically include an exchangeable sensor as an exchangeable or consumable and a long-life base station to which the exchangeable sensor is connected.

Disclosure of Invention

The object of the present invention is to propose a way in which the reliability of a system of the above-mentioned type can be improved and the user operation can be simplified.

The present invention achieves the above objects by a system having the features of the first aspect of the invention. Subject matter of its dependent aspects relates to other improvements.

The measurement of the invention involves the analytical unit of the base station, make the sensor connected to it pass statistical analysis as the measured signal that the raw data provide in operation, and produce the compressed measured data from the raw data, in order to be sent to the display device by the sender; and a display device comprising an electronic analysis unit, in operation, for determining an analytical concentration value by analyzing the compressed measurement data, allowing the amount of data to be transmitted, and thus the energy consumption, to be advantageously kept low, while still taking advantage of the high measurement rate.

In order to keep the weight of the body-worn system components as low as possible, it is advantageous to keep the energy consumption of the base station as low as possible, since a small and light battery suffices to provide sufficient long-term energy for powering the system components.

The measurement or sensor signal provided by the sensor is preferably recorded as raw data at a first time interval of, for example, a duration of from 0.5 seconds to 5 seconds. The raw data are used to generate compressed measurement data for a second time interval of, for example, 10 to 1000 seconds, so that the second time interval is at least 10 times longer, preferably at least 50 times longer, than the first time interval. Preferably, both the first time interval and the second time interval are constant.

Thus, for a first time interval, exactly one measurement signal value which is correlated with the analyte concentration to be determined is stored in the base station. In order to reduce the energy consumption associated with transmitting data, compressed measurement data values are preferably generated from signal values stored as raw data, each of at least 10, in particular at least 50, corresponding to larger time intervals.

The measurement signal can be generated by using an implantable sensor in a very short time interval of, for example, 1 second, so that a very large amount of raw data can be obtained while the measurement is continued. Another aspect of the invention that is independently significant relates to a method for compressing raw data determined with an implanted sensor, the method comprising: the method comprises forming pairs of measured signal values from raw data generated for a time interval, then determining for each pair of measured signal values the slope of the line connecting the two values of a pair of values and calculating the median of the slopes thus determined, then calculating for the time interval the compressed data value from the median of the slopes and the compressed data value of the preceding time interval.

Since initially no compressed data value is available for the first time interval, a median value or e.g. an arithmetic mean value of the raw data determined for the first time interval may be used as the compressed data value for the first time interval. Raw data values that appear unrealistic, e.g., due to abnormally large deviations from the rest of the raw data values of the time interval, may be discarded when determining compressed data values, e.g., because they are not used to form value pairs (calls of values).

Preferably, in a first step of the analysis, the measurement signals provided by the sensors are compressed in the base station as raw data into measurement data, the compressed measurement data are transmitted to the display device, and in a further step of the analysis, the measurement data are used by an analysis unit of the display device to calculate an analyte concentration value. A two-step analysis of this type, with a first step comprising an analysis in the base station and a second step comprising an analysis in the display device, allows the advantages of continuous or quasi-continuous measurement in terms of currency and accuracy to be exploited, while still keeping the amount of data to be transmitted by the base station small. In particular, a relatively simple, and thus cost-effective, microprocessor in the base station is sufficient for compressing the raw data, for example by forming an average value or by using a repeated median process. For final analysis of the compressed measurement data, powerful and expensive microprocessors are available for the display device and may be used therein for other tasks, such as for graphical representation of the analyte concentration so determined, and linked to other data that has been generated and stored by the display device or originated from other sources. Thus, in a further aspect of the invention, which may independently be of interest, a system for in vivo measurement of analyte concentrations in the human or animal body comprises: at least one implantable sensor for generating a measurement signal related to the concentration of an analyte to be measured; a base station connectable to the sensor and comprising an electronic analysis unit for analyzing a measurement signal of the sensor connected thereto and a transmitter for wirelessly transmitting an analysis result; and a display device comprising a receiver for receiving the analysis signal transmitted by the base station and a display means for displaying the analyte concentration value, whereby the analysis unit of the base station, in operation, subjects the raw data provided by the sensor connected thereto to statistical analysis and generates from the raw data compressed measurement data which is transmitted by the transmitter to the display device, and the display device contains an electronic analysis unit which, in operation, determines the analyte concentration value by analyzing the measurement data.

Thus, another aspect of the invention which may independently be of interest relates to a system for in vivo measurement of analyte concentrations in the human or animal body, comprising: at least one implantable sensor for generating a measurement signal related to the concentration of an analyte to be measured; a base station connectable to the sensor and comprising a voltage regulator for providing a voltage to the sensor of this type and a receiver and a transmitter for wirelessly transmitting data, whereby the base station is adapted such that the transmission of data is initiated by receiving a control signal transmitted by the wireless part. To prevent erroneous communication with devices that are not part of the system, the control signal may contain a characteristic identifier that is used by the sampling device to indicate an identity to the base station. Likewise, the base station may transmit a characteristic identifier signal to indicate its identity when communicating.

In particular, the data may be compressed measurement data which has been determined by an analysis unit comprised in the base station from raw data obtained as measurement signals of connected sensors. The control signal initiating the transfer of measurement data may be sent by a display device, for example.

In systems where analyte concentrations (e.g., glucose) are measured in vivo, it is often necessary to replace the sensor every few days. The operation of replacing sensors and connecting the new sensors correctly to the base station is cumbersome for many users, particularly for patients with age or disease that are not hands-flexible. By having the sensor as an integral part of a replaceable sensor carrier comprising a closed housing in which the sensor is arranged and having the housing of the sensor carrier latched to the base station for connecting the sensor to the base station, handling of the system, in particular replacement of the sensor, can be significantly simplified, so that the system according to the invention is also particularly suitable for use by non-medical personnel.

The enclosed housing of the sensor carrier protects the sensitive sensor from the harsh environment. For this reason, the sensor carrier can also be handled by unskilled personnel without the risk of damaging or contaminating the sensor. The operation of attaching the sensor carrier to the base station is facilitated by the latch. The sensor can be exposed for insertion after connection, for example by means of a predetermined sensor breaking point provided on the housing of the sensor carrier.

For example, where an electrochemical sensor is employed, the sensor may be electrically connected to a base station via a data line. If an optical sensor is used, such as the one known from US 6584335, the sensor may also be connected to the base station by means of an optical data line.

However, it is also feasible to let the sensor vehicle communicate with the base station in a wireless manner, for example by inductance or by RFID. The advantage of wireless communication between the sensor carrier and the base station is that the problem of sealing of the sensor carrier and the base station worn by the patient's body is largely prevented. In particular, the risk of leakage currents disturbing the measurement results may also be reduced. Wireless communication over very short distances between the sensor carrier and the base station latched to the sensor carrier can be achieved in a cost-effective manner, for example by inductive coupling. Only in the base station is a costly transmitter with a large communication range of, for example, 1 meter required for communication with the display device.

The sensor carrier preferably contains a data carrier with calibration data for the sensor. This has the advantage that it reliably ensures that the data determined by the sensor are always analyzed using adapted calibration data. In particular, in the case of a sensor carrier which communicates wirelessly with a base station, a data carrier which can be written with calibration data by means of a closed housing of the sensor carrier, for example an electronic memory which can also be read and/or written with RFID, can advantageously be provided in the housing of the sensor carrier. In this way it is possible to sterilize the entire sensor carrier by exposure to radiation, to determine the required calibration data using a random sampling of a production batch after the sterilization process, and then to write the calibration data to the data carrier of the sensor carrier. However, it is also possible to provide the sensor in a first chamber of the sensor carrier and the data carrier in a second chamber. In this way, the sensor can be sterilized in the sealed chamber, and the data carrier with the calibration data can then be inserted into the second chamber.

The sensor carrier preferably comprises a battery. In particular, the battery may also be used to power the base station, so that the consumables of the system of the invention may be advantageously assembled in the sensor carrier. In particular, it is preferred that the battery is surrounded by the housing of the sensor carrier. This has the advantage that the battery is well protected and made less accessible to the user.

In the system of the present invention, the base station preferably includes: a housing adapted to fit the sensor carrier; and an interface adapted to the interface of the sensor carrier, the sensor being electrically connected to the base station by placing the housing of the base station against the housing of the sensor carrier. The reversible, i.e. subsequently releasable, connection of the sensor carrier to the base station can be realized, for example, by form-fitting or non-positive connections (non-positive). In this context, it is highly advantageous to have the sensor vehicle latched to the base station, since this can be perceived by the user, which can signal to him that the sensor vehicle has been properly connected to the base station.

For example, the sensor may be a amperometric sensor that is powered by a voltage regulator included in the base station. However, electrochemical sensors that do not require a potentiostat may also be used in the system, such as coulometric sensors or optical sensors.

Drawings

Further details and advantages of the invention are illustrated by means of exemplary embodiments and with reference to the accompanying drawings. Like and corresponding parts are identified with the same reference numerals. The features described hereinafter may form the subject of the invention either individually or in combination. The drawings comprise:

FIG. 1 is a schematic diagram illustrating one exemplary embodiment of a system for in vivo measurement of analyte concentrations in a human or animal body in accordance with the present invention;

FIG. 2 is a schematic diagram illustrating the interaction of system components of the exemplary embodiment shown in FIG. 1;

FIG. 3 illustrates an exemplary embodiment of a base station and a sensor vehicle coupled thereto of the system of FIG. 1;

FIG. 4 shows a cross-sectional view associated with FIG. 3;

FIG. 5 illustrates the sensor housing of the exemplary embodiment shown in FIGS. 3 and 4;

FIG. 6 illustrates components of another exemplary embodiment;

FIG. 7 shows a longitudinal cross-section of the components shown in FIG. 6 in an assembled state;

FIG. 8 illustrates the base plate of the exemplary embodiment shown in FIG. 7 with an insertion aid for inserting the sensor into the patient;

FIG. 9 shows a longitudinal section through the base plate shown in FIG. 8 with an insertion aid provided thereon prior to insertion of the sensor; and

fig. 10 shows a longitudinal section through the base plate shown in fig. 8 with an insertion aid provided thereon after insertion of the sensor.

Detailed Description

Fig. 1 is a schematic diagram showing a system 1 for in vivo measurement of analyte concentration in a human or animal body. The system 1 comprises a sensor carrier 10 as a consumable or replaceable component, in which at least one implantable sensor 3 is provided for generating a measurement signal related to the analyte concentration to be measured. The sensor carrier 10 has a housing 12, which is shown in fig. 3 as having a bottom 27, which bottom 27 extends along the surface of the human body when the sensor carrier 10 is attached to the body of a patient for its purpose. The sensor carrier 10 contains a battery 5 and a data carrier 11 with calibration data of the sensor 3. The battery 5 and the data carrier 11 are arranged in the housing 12 of the sensor carrier 10 so that they cannot be touched by the user, in order to exclude erroneous results or damage to the extent possible due to improper operation.

The sensor carrier 10 may be connected to the base station 2 by a snap-in mechanism. The base station 2 is a multipurpose component of the system 1. The used sensor carrier 10 can be separated from the base station 2 and replaced by a new sensor carrier 10. The base station 2 includes: a voltage regulator 48 for supplying a voltage to the sensor 3 of the sensor carrier 10 connected thereto; an electronic evaluation unit 47 for evaluating the measurement signals of the sensor 3 connected thereto; and a communication unit 31 in which a transmitter for wirelessly transmitting the analysis result is provided. The base station 2 also comprises an electronic intermediate memory 60 for storing measured values or data derived therefrom. In the exemplary embodiment shown, the base station 2 comprises: memory for intermediate storage of raw data, such as RAM memory; and a memory, such as an EEPROM or flash memory, for storing compressed measurement data until such data is transmitted and/or for storing data transferred by the display device 4 to the base station 2.

The sensor carrier 10 comprises a housing 12 in which an interface for electronic connection of the sensor 3 to the base station 2 is provided. Accordingly, the base station 2 includes: a housing adapted to mate with the sensor carrier 10; and an interface adapted to the interface of the sensor carrier 10, the sensor 3 being electrically connectable to the voltage regulator 48 by placing the housing of the base station 2 against the housing 12 of the sensor carrier 10 so that the sensor contacts 3a, 3b and 3c are connected to the base stations 6a, 6b and 6 c. In the process, the battery 5 and the data carrier 11 are also connected to the contacts 7a, 7b and 8a, 8b, respectively, of the interface of the base station 2. The manual mating interfaces of the sensor carrier 10 and the base station 2 may form a plug-in connection, wherein a male part of the plug-in connection may be provided on the base station 2 and a female part on the sensor carrier 10, or vice versa.

The sensor carrier 10 is activated by connecting it to the base station 2, in particular the measuring process of the sensor 3 is initiated in this way. Thus, the sensor 3 is activated by connecting the sensor 3 to the base station 2, causing it to start providing a measurement signal. Reset and initialization commands for this aspect may be implemented in the processor forming the analysis unit 47 when connecting the sensor carrier 10 to the base station 2. This has the advantage that no switches are required to turn the system on and that the start-up of the system is achieved by a user-specified action, i.e. by connecting the sensor carrier 10 to the base station 2. Once the voltage is applied by connecting the battery to the potentiostat 48, the charge carriers automatically leave the working electrode immediately, minimizing the risk of charge accumulation.

Another long-life component belonging to the system is a display device 4, which comprises: a receiver 30 for receiving data transmitted by the base station 2; and a display device 29, such as a liquid crystal display, for displaying the analyte concentration value. The receiver 30 of the display device 4 preferably also comprises a transmitter and the transmitter 31 of the base station also comprises a receiver, so that a two-way communication between the base station 2 and the display device 4 is possible. The transmissions of the base station 2 and the display device 4 may be characterized by an identifier, such as a bit sequence. In order to exclude erroneous communication with other patient's devices, signals without the intended identifier may be omitted by the base station 2 and the display device 4.

The functions of the system components, the sensor carrier 10, the base station 2, the display device 4 and the distribution of the components enable optimum results to be obtained in terms of weight, cost and user convenience of the system components worn by the human body. The system's consumables, such as the sensor 3 and the battery 5, are part of the sensor carrier 10 that need to be replaced periodically, such as every 5 days, so that all of the consumables can be replaced as conveniently as possible. In order to generate the measurement data with the sensors 3 of the sensor carrier 10, long-life system components, such as the potentiostat 48 and the analysis unit, are required in addition to the consumables. The distribution of these long-lived system components over the base station 2 and the display device 4, which are also worn by the human body, is implemented to be able to provide the most possible user convenience, so that a base station 2 that is as small and light as possible can be implemented. For this purpose, the base station 2 includes: a voltage regulator 48 for supplying power to the sensor 3 connected thereto; a transmitter for transmitting data to the display device 4; and an analysis unit 47 for preliminarily analyzing the measurement data provided by the sensors connected thereto. The base station 2 does not need to have its own display means since this function is taken over by the display device 4. Combining the preliminary analysis in the base station 2 with the final analysis in the display device 4 enables the amount of data to be transmitted to be kept low. The base station 2 therefore requires only a small memory and a simple analysis unit and consumes very little energy, making the patient wear as little mass as possible.

The display device 4 can be equipped with a large memory and complex analysis electronics, in particular a powerful microprocessor, so that a greater range of mathematical analyses can be carried out on the data over a longer period of time. In particular, the display device 4 may test for a newly implanted sensor whether the new sensor is functioning correctly by comparison with data or defined levels and/or gradient values and form factors or samples of previous sensors. Furthermore, the display device 4 allows its user to conveniently enter patient data, such as various thresholds, whereby the display device 4 may generate an alarm signal when these values are exceeded or not reached. In addition to the analysis, display and alarm functions, the display device 4 may also assume the functions of a data and communication center for other components of the system, such as the injection device.

For its purpose, the base station 2 and the sensor carrier 10 are worn by the body of the patient during in-vivo measurements. In the process, the electrochemical sensor 3 is inserted into the patient's body and is powered by a potentiostat 48 contained in the base unit. During measurement, a current flows between the working electrode and the counter electrode of the sensor 3, the amplitude of which is related to, for example, in an ideal case proportional to the analyte concentration to be measured. In this process, the potentiostat 48 changes the potential applied to the counter electrode so that the potential of the reference electrode of the sensor 3 remains constant.

The system 1 described above may be used to monitor the concentration of an analyte in a patient in a continuous or quasi-continuous manner. This means that the sensor 3 can be used to perform measurements in short time intervals of less than 5 minutes, in particular less than 1 minute or less than 10 seconds. In this context, the measurement may be achieved by digitizing a raw signal, such as a current, to generate a measurement signal. Other data, such as temperature and/or electrode voltage, may be collected concurrently with these measurements, which may be used for plausibility checks and/or error compensation.

Measurements made in the system 1 described herein at intervals of approximately 1 second, e.g., between 0.5 and 2 seconds, result in an extremely large amount of raw data. The measurement signal provided by the sensor 3 during such time intervals may be the value of a continuous signal which is amplified and/or filtered, for example with a low pass filter, to filter out electrical disturbances which may be generated, for example, by the frequency of the public power network (50Hz or 60Hz), noise or radio communication. The cut-off frequency of a low-pass filter of this type is preferably between 3Hz and 50Hz, in particular between 5Hz and 20 Hz. In this context and according to the general use case, the cut-off frequency is understood to mean the frequency at which the low-pass filter produces a 3dB attenuation.

By means of a filtering algorithm, for example by means of a repeated median process as described in the present application, low-frequency interferences in the measurement signal, which may arise, for example, from electrochemical interferences at the interface between the sensor and the surrounding human tissue, can be eliminated.

The measurement signals provided by the operating sensors 3 are subjected to a preliminary analysis by an analysis unit 47 comprised in the base station 2. In this process, the measurement signal is statistically analyzed as raw data and, as a result, compressed measurement data is generated from the raw data. The compressed measurement data is generated by the base station 2 for a constant continuous time interval of, for example, one minute, so that there is an unambiguous allocation of time of the measurement data, which results from the sequence and size of the time interval. The compressed measurement data is then transmitted wirelessly to the display device 4 and further analyzed therein by an analysis unit, such as a microprocessor, to determine the analyte concentration value.

In the exemplary embodiment shown, the base station 2 comprises a memory in which compressed measurement data can be stored, so that these measurement data do not need to be transmitted immediately after generation. The stored data set may be provided with a check code that allows the compressed measurement data to be checked for data corruption and erroneous measurement data to be identified in subsequent steps of the analysis. Status information of the base station 2, such as battery charge status, internal functional test results and the like, may also be stored in the memory together with the measurement data. This status information may be stored as a status code, such as a byte, and considered in the analysis.

In particular, by storing only the deviation from the previous measurement data value as a measurement data value, an efficient storage of compressed measurement data can be obtained. This means that it is sufficient if the first measurement data value is stored completely in the memory. All subsequent values can then be unambiguously characterized by their difference from the previous measured data value, so it is sufficient to store this difference.

The measurement signals to be compressed are temporarily stored as raw data in the base station only before the compressed measurement data are generated. The base station 2 therefore comprises a raw data memory, the content of which is overwritten after the compressed measurement data values have been determined for a measurement signal of a certain time interval, and the measurement signal is no longer required. For some applications it is advantageous to provide the option of accessing the original data later. This can be achieved by sending the original data before it is overwritten, for example. This transfer may be performed unidirectionally, i.e. the receiving device storing the original data does not acknowledge the reception of such data by receiving a signal. The base station 2 may comprise an additional transmitter for unidirectional transmission.

FIG. 2 shows a schematic diagram of the interaction of various system components. The left side of the dashed line shows the sensor 3 of the base station 2 and the components connected thereto, while the components of the display device 4 are shown on the right side of the dashed line.

The base station 2 supplies, in operation, a voltage 49 to the sensor 3, the magnitude of which may depend on calibration data 50 stored in the data carrier 11 shown in fig. 11. The sensor 3 provides a measurement signal 32, which is digitized by an analog-to-digital converter 33 and then statistically analyzed by an analysis unit 47, preferably a microprocessor, as digital raw data 51. In this process, compressed measurement data 36 is generated from raw data 51. The compressed measurement data 36 is put into a memory 35, which memory 35 is accessible by an analysis unit 47 and a communication unit 31 comprising a transmitter and a receiver. In order to prevent access conflicts, the analysis unit 47 and the communication unit 31 are connected to the memory 35 via the changeover switch 34, the changeover switch 34 providing the analysis unit 47 or the communication unit 31 with access to the memory 35 depending on its switching state.

The communication unit 31 of the base station 2 reads out the compressed measurement data 36 from the memory 35 and transmits it to the communication unit 30 of the display device 4. In the exemplary embodiment shown, the communication unit 30 comprises a transmitter and a receiver, which makes a bidirectional data exchange possible. However, it is also feasible that the compressed measurement data 36 is transmitted unidirectionally by the communication unit 31 of the base station 2. In particular, it is possible to equip the evaluation unit 47 with a transmitter 61 for the unidirectional transmission of the raw data.

The compressed measurement data 36 is analyzed in the analysis device 4 by an analysis unit 52, such as a microprocessor, contained therein to determine an analyte concentration value 53, which can be displayed by the display device 29 and stored in a memory 54, as is the compressed measurement data 36. During the analysis of the compressed measurement data 36, the analysis unit 52 of the display device 4 also performs a calibration taking into account the measurement results of the measurement means 56 integrated into the display device 4 and determines the analyte concentration of the body fluid sample, for example, obtained from a small puncture wound.

During the analysis of the compressed measurement data 36, the analysis unit 52 of the display device 4 can add the time of day and date to the analyte concentration values determined from this time and the compressed measurement data 36 with the real-time clock 55, since the compressed measurement data applies to time intervals of constant duration.

The statistical analysis of the measurement signals in the base station 2 can in the simplest case be the formation of a mean value. However, the statistical analysis may equally comprise filtering and/or correction algorithms to exclude or correct values containing errors from further analysis by filtering. For example, a kalman filtering process is suitable for this purpose.

The iterative median process can be used as a method of filtering and compressing the original data. In such a process, the median of the slopes between pairs of measured signal values for a certain time interval is formed. Extreme (and thus incredible) raw data values may be discarded in this median formation, e.g. values deviating from the average of all remaining raw data values of the time interval by more than some given threshold. However, it is also possible to actually take into account all pairs of values that can be formed with the original data values of the time interval during the median formation of the slopes.

Then, a measurement data value is calculated for the current time interval from the median of the slopes and the compressed measurement data value of the previous time interval. To this end, the product of the median value of the slope multiplied by the duration of the time interval may be added to the measured data value of the preceding time interval. For a true first time interval, for example, the median of the raw data values contained in the time interval may be used as the compressed measurement data value.

In the above-described repeated median process, it is preferred to select time intervals for which the compressed measurement data calculated from the median value of the slope and the previous measurement data value overlap. In particular, it is also possible to apply a repeated median process multiple times, for example to generate compressed (condensed or compressed) measurement data values from the original data values in a first step and to further compress the compressed measurement data values by repeatedly applying the repeated median process in a further step.

Having a two-stage analysis, in which a first stage analysis is performed in the base station 2 and a second stage analysis is performed in the display device 4, allows to process a larger amount of raw data, thus allowing to obtain fully continuous or quasi-continuous measurements in terms of correlation in real time and accuracy. Nevertheless, only a small amount of data needs to be transmitted from the base station 2 to the display device 4. Thus, the energy consumption of the body worn base station 2 is low, so that a small, lightweight and cost-effective battery 5 is sufficient to meet the energy requirements of the base station 2 and the sensor carrier 10. Thus, the two-stage analysis process helps to reduce the weight worn by the patient's body as much as possible, thereby improving user convenience.

In order to minimize the data traffic between the base station 2 and the display device 4, a complete analysis of the raw data can be carried out in the base station 2, so that only the analyte concentration values need to be transmitted to the display device 4. However, in the two-stage analysis described above, only very little processor power is required in the base station 2, so that a particularly cost-effective microprocessor can be used as the analysis unit 47. A further advantage of the two-stage analysis process described above is that the calibration of the measurement data can be performed in the display device 4 by controlling the measurement within the scope of the second analysis step. For this purpose, the display device 4 contains a measuring device for determining the analyte concentration of the body fluid sample. Such a measuring device can be constructed, for example, as a commercially available blood glucose measuring device, and the glucose concentration of the body fluid sample applied to the test strip 28 can be determined photometrically or electrochemically. Since the analysis unit of the display device 4 is connected to the measuring apparatus, the analyte concentration value which has been determined for the body fluid sample can be used for calibration during the analysis of the measurement data which have been sent to the base station 2.

In addition to the measuring device for determining the analyte concentration of the body fluid sample, the display device 4 can also comprise an input option for inputting patient data. The patient data may be, for example, information about meals that have been taken or thresholds of measurement data, which when exceeded or not reached generate an alarm signal. Further, the display device 4 may be adapted to communicate with other system components, such as with an infusion set or advanced HOST system such as a physician, nurse or clinician's personal computer.

The display device 4 is provided with a transmitter 30 for transmitting control signals and the base station 2 is provided with a receiver 31 for receiving control signals and with an electronic memory for storing compressed measurement data. The transmission of the compressed measurement data is triggered by a control signal issued by the display device 4. The display device 4 acknowledges the reception of the measurement data by sending an acknowledgement signal.

The display device 4 contains a clock for determining the actual time. When the display device 4 receives the compressed measurement data from the base station 2, the current measurement data value may be marked with a current time stamp (in which the current time and date are encoded) and stored. The time stamp of the measurement data value of the forward run may be calculated from the time stamp. For example, if compressed measurement data values are generated for successive time intervals of one minute each, the time of day of the measurement data values can be determined for all measurement data values by incrementally reducing the time by one minute at a time.

The display device 4 comprises a memory which is large enough to store measurement data determined for a plurality of sensor wearing periods, i.e. for a number of days using different sensor carriers 10. In this process, each measurement data from different sensors 3 may be provided with a sensor identifier, so that information such as the measurement time may be calculated for each measurement data value, from the sensor identifier and the moment of time the measurement data was received.

In the exemplary embodiment shown, when the display device 4 makes repeated visits to the base station 2, only the measurement data newly generated during this period is transmitted so that the transmission time and the transmission energy are minimized. The Time of the last access may be stored in a data header (data header) within the display device 4, as may other general data, such as an identifier of the sensor vehicle and a Time format, such as a Universal Time Convention.

The memory of the base station 2 storing the compressed measurement data may be provided with a lock so that overwriting of the measurement data is allowed only after the measurement data has been sent to the display device 4 and receipt of the data has been confirmed when a new sensor carrier 10 is connected. For example, the start-up of the base station 2 by connecting a new sensor vehicle 10 may initially be performed before new measurement data is recorded. However, it is also feasible to select the memory of the base station 2 to be sufficiently large so that more measurement data can be stored in the memory of the base station 2 before the sensor carrier 10 needs to be replaced than the data generated with one sensor carrier 10 within, for example, 5 days. The operation of automatically sending measurement data before replacing the sensor carrier 10 can ensure that the time stamp can be determined by the display device 4 for all measurement data stored in the base station 2. Unless the measurement data is generated continuously, there is a risk of data loss for the assignment of unambiguous time stamps.

During the replacement of the sensor, no measurement data is usually generated for an indeterminate time period. To ensure that an absolute time can be unambiguously assigned to each measured value, the sensor start date and time of each sensor is stored in the memory of the base station 2. If any old data generated with the previous sensor needs to be sent to the display device 4 before the new sensor is connected, the sensor start date and time can be made available by the display device 4 without any difficulty. The sensor start date may be stored in the base station 2 and may be stored in a data header transmitted together with the compressed measurement data. However, it is also possible to store the sensor start date and time in the display device and use it for determining the time of the respective measurement data value. If measured values at constant successive time intervals are determined, the time at which they are measured can be determined for each measured value even when the sensor is replaced.

Fig. 1 shows connection contacts 6a, 6b, 6c in the base station 2 for connecting the sensor 3 and connection contacts 7a, 7b in the base station 2 for connecting the battery 5. The base station 2 furthermore has at least one data input 8a, 8b for connecting and reading a data carrier 11 with calibration data. These calibration data identify the sensitivity of the sensor 3, the sensor 3 being an electrochemical sensor, for example comprising an enzyme that generates charge carriers by catalytic conversion of the analyte, which can be measured in the form of a current flowing between electrodes of the sensor. For example, if the analyte is glucose, the enzyme may be glucose oxidase.

Sensors for measuring the concentration of an analyte in a body fluid, such as blood or interstitial fluid, often cannot be manufactured with an accurately predetermined measurement sensitivity. There is usually a considerable variation in the sensitivity of the sensor between production batches, which can be reflected by the calibration data in the analysis of the measurement signal of the sensor. Calibration data is typically determined by the manufacturer by random sampling of each relevant sensor itself or by other sensors of the corresponding production lot. This type of calibration data generally describes the difference between the ideal sensor sensitivity and the determined sensor sensitivity.

The data input terminals 8a, 8b are connected to a spring element 9, the spring force making it easier for the data carrier to be connected. The data carrier 11 is preferably a memory chip, so that the data input is formed by electrically connecting contacts. The data carrier 11 can likewise be an RFID or magnetic data carrier, for example, and the data inputs 8a, 8b can therefore comprise read heads. In the exemplary embodiment described, the calibration data read by the data carrier 11 are transmitted from the base station 2 to the display device 4, in which arrangement the measurement data are analyzed. It is also possible that the calibration data have been processed in the base station 2 and taken into account to generate compressed measurement data. This prevents the risk of a user mixing up data carriers 11 with calibration data of different sensors 3.

The base station 2 comprises a test circuit 26 which is connected to the voltage regulator 48 and which during system testing provides a response signal or response signals to the analysis unit 47 of the base station 2, which response signal(s) is/are analyzed by the analysis unit 47, whereby the analysis unit 47 compares the value of at least one response signal with a predicted value and generates an error signal when the value of at least one response signal deviates from the predicted value by more than a predetermined tolerance value. The error signal may be sent to the display device 4, for example via the transmitter 31, which in turn indicates the error to the user. The test circuit simulates that the sensor 3 is connected to the voltage regulator 48 so that the analysis unit 47 can check the correct function of the voltage regulator 48 and the charge state of the battery 5 with the test circuit 26. In the simplest case, test circuit 26 may take the form of a switchable fixed-value resistor.

The housing of the sensor carrier 10 has at least two compartments 13, 14, 15, the sensor 3 being provided in a first compartment 13 under sterile conditions, and the data carrier 11 with calibration data of the sensor 3 and, if applicable, the battery being provided in a second compartment 14. In the exemplary embodiment shown, the battery 5 is provided in the third chamber 15.

The housing 12 is adapted to the interface of the base station 2, and the sensor 3 and the corresponding data carrier 11 contained in the housing 12 can be connected to the base station 2 by placing the housing 12 against the interface. The connection of the sensor carrier 10 to the base station 2 automatically initializes the measuring system 1 and starts the measuring process.

The housing 12 contains a spring member 20 which supports the connection of the battery 5 when the housing 12 is placed against the interface of the base station 2. Spring members may also be provided in the first compartment 13 and the second compartment 14, respectively, to support the connection of the sensor 3 and/or the data carrier to the base station.

In the exemplary embodiment shown, the interfaces of the housing 12 and the base station 2 are adapted to each other such that, when the housing 12 is placed against the interface, the battery 5 and the data carrier 11 are first connected to the base station 2, after which the sensor 3 is connected to the base station 2 via the specially provided contacts 6a, 6b, 6 c. In the exemplary embodiment shown, the sensor 3 is flat in structure and is connected to the base station 2 by a zero-insertion-force connector 3 a. The sensor 3 may also have a sandwich structure or be formed in the shape of a rod, i.e. rotationally symmetrical, and the contacts 6a, 6b, 6c may be arranged to cooperate therewith.

In this context, the seal 21 of the base station 2, which in the exemplary embodiment shown is provided in the form of a gasket, enables a watertight connection of the sensor 3 to the base station 2, so that no moisture can penetrate into the inner space of the base station 2. Thus, the base station 2 can be worn, for example, by the abdomen of a patient without being damaged by body fluids. The seal 21 achieves a high resistance seal of the base station and the connected sensor 3. In this way, the sensor 3 provided in the form of an electrochemical sensor can be supplied with voltage by means of the potentiostat 48 provided in the base station 2 without any disturbance caused by leakage currents.

Fig. 3 shows an oblique view of an exemplary embodiment of a base station 2 with a sensor carrier 10 connected to the base station. Fig. 4 shows a sectional view in relation to fig. 3, in which the sterile housing chamber 13 and the sensor 3 and the second housing chamber 14 of the sensor provided therein and the battery 5 and the data carrier 11 provided therein are shown. The base station 2 is also shown to comprise: a voltage regulator 48 for supplying current and voltage to the sensor 3; an analysis unit 47 provided in the form of a microprocessor; and a transmitter and receiver 31 for performing wireless communication with the display device 4, an antenna for performing wireless communication with the display device 4 being surrounded by the housing of the base station 2.

The housing of the sensor carrier 10 is made of a rigid plastic material, similar to the housing of the base station 2. In the exemplary embodiment shown, the interface of the base station 2 and the interface of the sensor vehicle 10 provide a form-fitting connection. The housing 12 comprises snap studs 40 which engage in recesses in the base station 2 adapted thereto. These grooves are provided on the outside of the two springs 41 so that the catch is pressed into the grooves by the spring force. The latching studs 40 of the sensor carrier 10 can be released from their mating recesses by pressing the spring 41 and the sensor carrier 10 can be removed from the base station 2. By pressing the spring 41, the sensor carrier 10 can be placed correspondingly against the base station 2.

As an alternative or in addition to the form-fitting connection, a sensor carrier 10 can also be provided which is connected to the base station 2 in a friction-locked manner.

The cross-sectional view shown in fig. 4 shows that the sensor carrier 10 comprises two compartments 13, 14, so that the sensor 3 is provided in the first compartment 13 under sterile conditions, and that the data carrier 11 with the calibration data of the sensor 3 and the battery 5 for supplying power to the base station 2 are provided in the second compartment 14. The connection lines of the sensor 3 are led out from the first chamber 13 into the second chamber 14 to a printed board 45 which is in contact with the data carrier 11 provided in the form of a memory chip. In the exemplary embodiment shown, the printed board 45 is connected to the base station 2 by a multipolar plug-in connection 46.

The sterilization chamber 13 in which the sensor 3 is stored is closed by two septa 42, so that an insertion needle 43 for inserting the sensor 3 into a human or animal body is guided through the septa 42. The forward end of the insertion needle protruding from the housing chamber 13 is surrounded by a sterile shield which is removed only when the sensor 3 is inserted into the human or animal body through the insertion needle 43. A sterile shield 44 contactlessly encloses the insertion needle and is connected to the remaining housing 12 by a predetermined breaking point 16.

For ease of wearing, it is advantageous to have the sensor carrier 10 with a sensor opening, through which the sensor 3 or its connecting line 39 is guided, and which is arranged as far away as possible from the edge of the bottom 27 of the sensor carrier 10, in order to minimize tilting moments. In the exemplary embodiment shown, the sensor opening is disposed more than 1cm from the edge of the bottom 27. In particular, it is also possible to provide the sensor opening in the center of the substrate 27 or at a position which is offset from the center by less than 20% of the length of the substrate, in particular by less than 10% of the length of the substrate.

For the insertion of the sensor 3, the sensor carrier 10 is for example placed in the abdomen of the patient and the insertion needle 43 penetrates into the patient. Subsequently, the insertion needle 43, which may be provided, for example, in the form of a recess with the sensor 3, may be withdrawn from the patient, leaving the sensor 3 in the patient. In order to obtain a particularly good germ-proof seal, the front region of the insertion needle 43 in the penetration direction can be provided in the form of an open groove, while the region adjoining the open groove is provided in a tubular form. The tubular region may be guided by a septum closing the housing to be sealed against bacteria.

In principle, insertion can be performed through any angle between the direction of penetration and the skin surface. It is particularly advantageous to insert subcutaneous adipose tissue at an angle of between 30 ° and 60 °. The sensor 3 has a sensor head 38 designed for implantation and an electronic connection line 39 connected to the sensor head 38, which is therefore guided in an arc of preferably 30 ° to 150 ° in the housing 12 of the sensor carrier 10. The sensor carrier 10 shown is provided so that the user can actually see the puncture location during insertion of the sensor 3.

The sensor carrier 10 has a base plate 27 which is adhesively attached to the patient for its purpose. The base station 2 is provided on the sensor carrier 10, more precisely on the substrate 27. The housing of the base station 2 laterally contacts the housing 12 of the sensor carrier 10. The substrate 27 has an adhesive surface protected by a film which can be peeled off and divided into portions which each cover a different area of the adhesive surface and which are separated from each other when the film is peeled off. The adhesive surface may for example be provided in the form of a double-sided adhesive film or pad which is adhesive on both sides, so that one adhesive surface can be adhered to the underside of the sensor carrier 10, while the other adhesive surface can be adhered to the skin of the patient for its purpose. The film for protecting the adhesive surface may be a commercially available adhesive plaster. The film can be removed more easily from the adhesive side if the adhesive side is protected by several parts of the film. This makes it possible to apply the sensor carrier 10 only after insertion of the sensor, since the individual parts of the film protecting the adhesive surface can be torn off from underneath the sensor carrier 10 from different directions.

Preferably, the adhesive side, the carrier, such as a film or a pad, is stretchable, so that the carrier can later be removed from the patient's body by pulling it apart with a pulling force applied parallel to the adhesive side. Stickers with corresponding resilience are commercially available, for example stickers for poster posting under the trade name tesa powerstrips.

The carrier suitable for attaching the adhesive surface of the sensor carrier 10 can be made of foam, in particular polyurethane foam (polyurethane foam), for example. An additional advantage of a carrier made of foam is that it can reduce the relative movement of the body with respect to the sensor carrier 10.

During the manufacture of the sensor carrier 10, the sensor 3 is initially provided in the first housing chamber 13, which is then sealed. In order to make the exemplary embodiment shown in fig. 4, in this assembly step a sterile shield 44 is also provided around the end of the sensor 3, which projects from the first housing chamber 13 and surrounds the insertion needle 43 with the sensor 3, and the sterile shield 44 is connected to the housing chamber 13. Subsequently, the housing chamber 13 is exposed to strong radiation, such as electron radiation, so that the sensor 3 and the insertion needle are sterilized. Fig. 4 shows a detailed view of the first housing chamber 13, wherein a sterile hood 44 is attached to the first housing chamber 13 and jointly sterilizes them by radiation exposure after insertion of the sensor 3

In a next assembly step, the first housing chamber 13 is connected with the second housing chamber 14 to form the sensor carrier 10. In this process, an insertion aid 37 can be attached to the sensor carrier 10, which makes it easier for the sensor 3 and/or the insertion sleeve with the sensor to penetrate into the patient. The insertion aid may comprise a spring, which may be pretensioned when the sensor carrier is delivered, or may be tensioned by the user by means of a pretension rod (not shown). The user may trigger the stretched insertion spring by activating the trigger button, thus effecting penetration of the sensor or the insertion cannula 43 with the sensor.

In the foregoing exemplary embodiment, the sensor carrier 10 communicates with the base station 2 via an electric wire. Thus, the sensor carrier 10 comprises an interface with electrical contacts 3a, 3b, 3c, the electrical contacts 3a, 3b, 3c being in contact with electrical contacts 6a, 6b, 6c of the interface of the base station 2 to connect the sensor carrier 10 to the base station 2. However, the foregoing exemplary embodiments may also be modified such that the sensor vehicle 10 communicates with the base station 2 in a wireless manner. Data exchange may be performed, for example, by inductive coupling or RFID. This means that the sealing of the base station 2 and the sensor carrier 10 is made easier. A further advantage of this measure is that the risk of distortion of the measurement signal due to leakage currents can be significantly reduced.

The sensor carrier 10, which is arranged for wireless communication with the base station 2, comprises a voltage regulator 48, for example a voltage regulator arranged in the base station 2 of the aforementioned exemplary embodiment. The sensor carrier 10 preferably also includes a preamplifier for amplifying the sensor signal.

The advantage of providing power to the base station 2 by the battery 5 provided in the sensor carrier 10 is also applicable to the case of wireless communication between the sensor carrier 10 and the base station 2. For example, electrical energy may be transferred from the sensor vehicle 10 to the base station 2 via inductive coupling. In order to generate the alternating voltage required for the inductive coupling, a chopper can be provided in the sensor carrier 10 in addition to the battery 5.

Fig. 6 shows parts of another exemplary embodiment which differ from the preceding exemplary embodiment only in mechanical structure. The base station 2 is constructed in the form of an electronic device having contacts 6a, 6b, 6c for connection to the sensor 3 and, like the base station 2 of the preceding exemplary embodiment, also contains an analysis unit, a voltage regulator, a test circuit and a transmitter and a receiver for communication with a display device. Unlike the previous exemplary embodiments, the base station 2 is protected in use by a movable housing formed by the base plate 27 and a housing cover 64 that can be provided thereon.

In order to protect the electronic components of the base station 2 when it is handled by a user, the base station 2 has a separate housing which is preferably immovable. The housing may also provide electrical shielding and insulation. For example, it may be constructed from an epoxy cast composite or injection molded part.

In the exemplary embodiment shown in fig. 6, a body-worn substrate 27 forms the sensor carrier 10. The base plate 27 has an aperture through which the sensor 3 can be inserted into the body tissue of a patient during insertion. For this purpose, a housing cover 64 is provided on the base plate 27. The base plate 27 has snap or latch features to latch the housing cover 64 in place. In addition, the base plate 27 is provided with a seal 63, such as an O-ring or sealing flange, for closing an inner space which is then enclosed by the base plate 27 and the housing cover 64. Alternatively or additionally, a sealing element 63 and a snap-in element can also be provided on the housing cover 64.

Fig. 7 illustrates a longitudinal cross-sectional view of the system components in an assembled state when the unit is worn on the patient's body, as shown in fig. 6. In the process, the seal 63 seals the sensor shafts in front of the contacts 6a, 6b, 6c of the base station 2, so that they are protected in a gas-tight interior.

The housing cover 64 has a transparent viewing window 65 through which the sensor penetration site, and thus the aperture provided in the base plate 27 of the sensor 3, can be viewed. The viewing window 65 makes it possible to visually check the sensor penetration position, so that problems such as infection can be detected early.

Fig. 6 shows that the battery 5 is provided in the housing cover 64. However, the battery 5 may be provided in the substrate 27. The battery 5 is preferably easily removable by the user after removal of the housing cover 64 so that the battery can be disposed of separately.

The base plate 27, the housing cover 64, the battery 5 and the sensor 3 are consumables designed for one-time use, whereas the base station 2 can be used many times. The consumable is closed during manufacture with the insertion aid 66 shown in fig. 8-10 and sterilized by exposure to radiation. Sterilization of the battery 5 is not absolutely necessary.

Fig. 8 to 10 show the various steps involved in inserting the sensor 3 in the patient. In a first step, the base plate 27 is adhered to the patient's body. Then, the insertion aid 66 is provided on the base plate 27, and the insertion aid 66 is preferably snapped onto the base plate 27. Fig. 9 shows a longitudinal sectional view of the insertion aid 66 with the adapter base plate 27. The insertion aid 66 comprises an injection needle 43 which can be inserted into the patient through the opening of the base plate. In this process, the sensor 3, which has been provided in the injection needle 43 by the manufacturer, is inserted into the patient.

The sensor 3 is advanced by the user together with the insertion needle 43 by a linear movement guided at a predetermined angle of the insertion aid 66. This linear movement can likewise be effected by a rotational or shearing movement, but preferably no transverse movement relative to the puncturing position should occur. The insertion movement can also be achieved using an automatic mechanism. For example, the penetration of the insertion needle 43 may be supported by a spring.

After the penetration, the insertion needle is withdrawn, leaving the sensor 3 in the patient. Subsequently, the insertion aid 66 can be removed from the base plate 27. Finally, a case cover 64 is placed on the base plate 27, the case cover 64 having the base station 2 in contact with the battery 5 provided therein. Thus, the base station 2 is in contact with the sensor 3. The system then automatically starts working. Thus, once the housing cover 64 with the base station 2 is placed on the base plate 27, the measurement signal is generated and subjected to statistical analysis and compressed by the analysis unit comprised by the base station 2. The compressed raw data generated by this means is transmitted by the transmitter of the base station 2 to the display device 4, as shown in fig. 1.

Preferably, a data carrier 11 (not shown) with calibration data of the sensor 3 is provided on the housing cover 64 or the base plate 27, as described with reference to fig. 1, the data carrier 11 being in contact with the base station 2 and being read by it in the operating state as shown in fig. 7.

List of reference numerals

System for in vivo measurement of analyte concentration

2 base station

3 sensor

3a, 3b, 3c sensor contact

4 display device

5 Battery

6a, 6b, 6c connecting contact

7a, 7b connecting contact

Data input terminal of 8a, 8b base station

9 spring element

10 sensor carrier

11 data carrier

12 casing

13 housing chamber

14 housing chamber

15 housing chamber

16 predetermined breaking point

17 cover part

20 spring element

21 sealing element

26 test circuit

27 base plate

28 test piece

29 display device

30 transmitter/receiver

31 transmitter/receiver

32 measurement signal

33 analog-to-digital converter

34 change-over switch

35 memory

36 compressing the measurement data

37 insertion aid

38 sensor head

39 connecting wire

40 clamping column

41 spring of base station 2

42 spacer

43 insertion needle

44 sterile hood

45 printing plate

46 insertion connection part

47 analysis unit

48 voltage stabilizer

49 voltage

50 calibration data

51 raw data

52 analysis unit

53 analyte concentration value

54 memory

55 real-time clock

56 measuring device

60 intermediate storage

61 transmitter

62 clamping piece

63 shim

64 casing cover

65 view window

66 insertion aid

Claims (15)

1. A system for in vivo measurement of analyte concentration in a human or animal body, comprising:

at least one implantable sensor (3) for generating a measurement signal related to the concentration of the analyte to be measured;

-a base station (2) connectable to said sensor (3), comprising: an electronic evaluation unit (47) for evaluating measurement signals of a sensor (3) connected thereto; and a transmitter (31) for wirelessly transmitting the analysis results; and

display device (4), comprising: a receiver for receiving the analysis results transmitted by the base station (2); and display means (29) for displaying the analyte concentration value, characterized in that,

in operation, the analysis unit (47) of the base station (2) subjects the measurement signals provided by the sensors (3) as raw data to statistical analysis and generates compressed measurement data from the raw data, which is transmitted by the transmitter (31) to the display device (4), and

the display device (4) comprises a second electronic analysis unit which, in operation, determines an analyte concentration value by analyzing the compressed measurement data;

wherein exactly one measurement signal value is determined for each first time interval and compressed measurement data is generated for a second time interval from the measurement signal values of a plurality of first time intervals such that one compressed measurement data value is available for each of the second time intervals.

2. The system according to claim 1, characterized in that the compressed measurement data (36) is determined continuously for a constant time interval and that a time stamp containing the date and time of day is calculated in the display device (4) for the compressed measurement data (36) on the basis of the transmission time of the compressed measurement data from the base station (2) to the display device, the duration of the constant time interval and its sequence, wherein the constant time interval is the second time interval.

3. The system of any of the preceding claims, wherein the second time interval is at least 10 times the first time interval.

4. A system as claimed in claim 1, characterised in that the display device (4) records the date and time of insertion of the new sensor (3).

5. A system as claimed in claim 1, characterized in that the analysis unit (47) of the base station performs a procedure in the statistical analysis for generating the compressed measurement data (36), in which procedure pairs of measurement signal values are formed from the measurement signals (32) generated in a second time interval, then for each pair of measurement signal values the slope of the line connecting the two values of the pair is determined and the median value of the slope thus determined is calculated, and then compressed measurement data for the second time interval is calculated from the median value of the slope and the compressed measurement data of the preceding second time interval.

6. The system according to claim 1, characterized in that the sensor (3) is activated by connecting to the base station (2).

7. The system according to claim 1, characterized in that the sensor (3) is an integral part of a replaceable sensor carrier (10) which snaps onto the base station (2) to connect the sensor (3) to the base station (2).

8. The system according to claim 7, characterized in that the sensor carrier (10) has a closed housing (12) inside which the sensor (3) is arranged.

9. The system according to claim 7, wherein the sensor carrier (10) comprises a battery (5).

10. The system according to claim 8, characterized in that the housing (12) of the sensor carrier (10) has a predetermined breaking location (16) for removing a hood (44) closing a chamber (13) containing the sensor (3).

11. The system according to claim 7, characterized in that the sensor carrier (10) contains a data carrier (11) with calibration data of the sensor (3).

12. The system of claim 7, wherein the sensor vehicle (10) communicates wirelessly with the base station (2).

13. The system of claim 7, wherein the sensor carrier (10) comprises an interface with electrical contacts (3a, 3b, 3c), the electrical contacts (3a, 3b, 3c) being in contact with electrical contacts (6a, 6b, 6c) of the interface of the base station (2) to connect the sensor carrier (10) to the base station (2).

14. The system of claim 7, wherein the sensor carrier (10) comprises a preamplifier for amplifying a sensor signal.

15. The system according to claim 8, wherein the housing (12) of the sensor carrier (10) comprises a transparent wall portion (65) for visually controlling the penetration position of the sensor (3).