阅读说明：本技术 监测温度传感器的状态 (Monitoring the state of a temperature sensor ) 是由 克里斯蒂安·普克 迈克尔·科恩 帕沃·弗尔多利亚克 于 2018-11-14 设计创作，主要内容包括：本发明涉及一种用于确定和/或监测温度的装置(1),该装置(1)包括第一温度传感器(17)、第二温度传感器(18)和电子器件(14),该电子器件(14)被配置为将电流形式的至少一个电发送信号(I<Sub>S</Sub>)施加到第一温度传感器(17)和/或第二温度传感器(18),并从第一温度传感器(17)和/或第二温度传感器(18)中分接出电压形式的至少一个第一电接收信号和/或第二电接收信号(U<Sub>E1</Sub>、U<Sub>E2</Sub>)。装置(1)还包括至少六个连接线(19a-19f),用于与第一温度传感器(17)和第二温度传感器(18)进行接触,特别是电接触,其中,连接线(19a-19f)被布置和配置为使得第一温度传感器(17)和第二温度传感器(18)串联连接,并且可以向其施加发送信号(I<Sub>S</Sub>),并且使得可以从第一温度传感器(17)分接出第一接收信号(U<Sub>E1</Sub>)和/或可以从第二温度传感器(18)分接出第二接收信号(U<Sub>E2</Sub>)。(The invention relates to a device (1) for determining and/or monitoring a temperature, the device (1) comprising a first temperature sensor (17), a second temperature sensor (18) and an electronic device (14), the electronic device (14) being configured to transmit at least one electrical transmission signal (I) in the form of an electrical current S ) Is applied to the first temperature sensor (17) and/or the second temperature sensor (18) and at least one first electrical receiving signal and/or second electrical receiving signal (U) in the form of a voltage is tapped off from the first temperature sensor (17) and/or the second temperature sensor (18) E1 、U E2 ). The device (1) further comprises at least six connection lines (19a-19f) for making contact, in particular electrically, with the first temperature sensor (17) and the second temperature sensor (18)A contact, wherein the connection lines (19a-19f) are arranged and configured such that the first temperature sensor (17) and the second temperature sensor (18) are connected in series and to which a transmission signal (I) can be applied S ) And makes it possible to tap off a first received signal (U) from the first temperature sensor (17) E1 ) And/or a second received signal (U) can be tapped off from the second temperature sensor (18) E2 )。)

1. Device (1) for determining and/or monitoring a temperature, comprising

A first temperature sensor (17),

a second temperature sensor (18),

an electronic device (14), the electronic device (14) configured to:

transmitting at least one electrical signal (I) in the form of an electrical current_S) Is applied to the first temperature sensor (17) and/or the second temperature sensor (18), and

at least one first and/or second electrical reception signal (U) in the form of a voltage is tapped off from the first and/or second temperature sensor (17, 18)_E1、U_E2) And an

At least six connection lines (19a-19f) for making contact, in particular electrical contact, with the first temperature sensor (17) and the second temperature sensor (18);

wherein the connection lines (19a-19f) are arranged and configured such that:

the first temperature sensor (17) and the second temperature sensor (18) are connected in series and the transmission signal (I) can be applied to the first temperature sensor (17) and the second temperature sensor (18)_S) And is and

the first receiving signal (U) can be tapped from the first temperature sensor (17)_E1) And/or the second reception signal (U) can be tapped off from the second temperature sensor (18)_E2)。

2. The device (1) according to claim 1,

wherein a first connection line (19a) extends from the electronic device (14) to the first temperature sensor (17), a second connection line (19b) extends from the first temperature sensor (17) to the second temperature sensor (18), and a third connection line (19c) extends from the second temperature sensor (18) to the electronic device (18).

3. Device (1) according to claim 1 or 2,

wherein a fourth connection line (19d) extends from the first temperature sensor (17) to the electronic device (14) and a fifth connection line (19e) extends from the second temperature sensor (18) to the electronic device (14).

4. Device (1) according to at least one of the preceding claims,

wherein a sixth connection line (19f) connects the electronic device (14) to the second connection line (19 b).

5. Device (1) according to at least one of the preceding claims,

wherein the electronic device (14) comprises a circuit for tapping off the first reception signal (U) from the first temperature sensor (17)_E1) And a first voltage determination unit (21a) for tapping off the second reception signal (U) from the second temperature sensor (18)_E2) And a second voltage determining unit (21 b).

6. The device (1) according to claim 5,

wherein the first voltage determination unit is configured to tap the first reception signal between the fourth connection line and the sixth connection line, and wherein the second voltage determination unit is configured to tap the second reception signal between the fifth connection line and the sixth connection line.

7. Device (1) according to at least one of the preceding claims,

wherein the electronic device comprises means for generating the transmission signal (I)_S) And at least one switching element (22, 22a, 22 b).

8. The device (1) according to claim 7 and 2-4,

wherein the at least one switching element (22, 22a, 22b) is arranged and configured such that an electrical connection can be established between the first connection line (19a) and the sixth connection line (19f) and/or between the third connection line (19c) and the sixth connection line (19f) by means of the switching element (22, 22a, 22 b).

9. The device (1) according to at least one of claims 1 to 6,

wherein the electronic device (14) comprises means for generating the transmission signal (I)_S) A first current generating unit (21a) and a second current generating unit (21 b).

10. The device (1) according to claim 9,

wherein the first current generating unit (21a) and the second current generating unit (21b) are connected in series and to each other by means of a seventh connecting line (19 g).

11. The device (1) according to claim 10,

wherein the sixth connecting line (19f) connects the second connecting line (19b) and the seventh connecting line (19g) to each other.

12. The device (1) according to any one of claims 9-11,

wherein the first current generating unit (20a) and the first voltage determining unit (21a) are arranged in a first electronics unit (14a), and wherein the second current generating unit (20b) and the second voltage determining unit (21b) are arranged in a second electronics unit (14 b).

13. The device (1) according to any one of claims 9-11,

wherein the first and second current generating units (20a, 20b) and the first and second voltage determining units (21b ) are arranged together in the same electronic device (14).

14. Device (1) according to at least one of the preceding claims,

an eighth connection line (19h) is included, the eighth connection line (19h) extending from the second connection line (19b) to the electronic device (14).

15. Device (1) according to claim 14

Wherein the first voltage determination unit (21a) is configured to tap off the first reception signal (U) between the fourth connection line (19d) and the eighth connection line (19h)_E1) And wherein the second voltage determination unit (21b) is configured to tap off the second reception signal (U) between the fifth connection line (19e) and the eighth connection line (19h)_E2)。

Technical Field

The invention relates to a device for determining and/or monitoring the temperature of a medium, comprising two sensor elements and electronics. The medium is located in a container, e.g. a tank or a pipe, and the device may for example be introduced into or attached to the container.

Background

In many embodiments, thermometers are known from the prior art. Some thermometers use the expansion of a liquid, gas or solid with a known coefficient of expansion to measure temperature, while others measure temperature by relating the conductivity of a material to temperature using, for example, a resistive element or thermocouple. In contrast, in a pyrometer, the temperature of a substance is determined using its thermal radiation. The underlying measurement techniques have been described in various publications in each case.

Thermometers with resistive elements typically comprise so-called thin film sensor elements or Resistance Temperature Detectors (RTDs). Typically, such sensor elements have a carrier substrate provided with connection leads and a metal-coated front surface. The back side may also have a metal coating. For example, commercially available platinum elements named PT10, PT100 and PT1000 are used as sensor elements.

In many cases, the sensor element is preferably encapsulated or embedded in a pure ceramic powder, and the connection wires are led in a conduit to an electronic device, such as a temperature transmitter.

Various measuring principles for determining the temperature by means of a resistance element are known from the prior art. For example, detailed information about industrial platinum resistance thermometers can be found in european standard EN 60751. A transmit signal, typically in the form of a current, is applied to the sensor element, and a receive signal, typically in the form of a voltage drop across the sensor element, is detected and evaluated with respect to temperature. In the simplest case, the temperature is determined by means of a temperature-dependent resistance using the so-called two-wire measuring technique, in which the sensor element is contacted via two connecting wires. The disadvantage of this solution is that the resistance of the connecting leads is determined as an error into the temperature. In the three-wire measuring technique, the sensor element is contacted by three connecting wires. If it can be assumed that the resistances of the three connecting wires are the same, the resistance of the connecting wire or connecting line can be largely compensated by pair-wise tapping of the voltage drop between each two of the three connecting wires.

The highest measurement accuracy can be achieved by means of the so-called four-wire measurement technique. The sensor elements are contacted via four connecting wires, wherein the transmit signals are applied to the sensor elements via a first pair of connecting wires, and wherein the receive signals are received via a second pair of connecting wires. Any potential asymmetry in the line resistances of the various connecting wires may also be compensated for when using the four-wire measurement technique.

Redundant designs of thermometers are known from the prior art for increasing the reliability and/or the measurement accuracy. One possibility is that multiple thermometers may be used simultaneously. However, thermometers with at least two temperature sensors are also known, which may be arranged, for example, in a single sensor head or measuring insert. If one of the two temperature sensors fails, the temperature can still be determined by means of the same thermometer via the second temperature sensor. Such thermometers are called, for example, "double pt 100" or "double pt 1000", depending on the type of sensor element used.

In thermometers with a plurality of temperature sensors, in particular in the form of resistance elements, it can be problematic that each individual temperature sensor has to be contacted individually by means of a connecting line. As the number of temperature sensors in a thermometer increases, the number of required connecting wires increases accordingly, both the size of the thermometer and the complexity of the electronics increase.

Depending on the measuring technique used, the number of connecting lines to be guided also increases to a different extent. In view of the usual dimensions of an industrial thermometer measuring insert, in particular the dimensions of the conduits for conducting the connecting wires to the electronics, it is difficult to implement a four-wire measuring technique even in the case of one measuring insert with only two temperature sensors, since in this case eight connecting wires have to be conducted to the electronics. Electrical insulation must be provided between the various connecting wires and from the conduits throughout the distance from each temperature sensor to the electronics.

In order to be able to achieve a good compromise between the typical requirements on the dimensions of the individual thermometers and the achievable measurement accuracy, thermometers with at least two temperature sensors are usually designed according to the three-wire measurement technique. In this case, for example, for a thermometer with two temperature sensors, six connecting lines have to be routed to the respective electronics.

In order to reduce the size of a device with two temperature sensors, it is alternatively known from DE102011084320a1 to apply a high-frequency electrical signal to each sensor element for a predetermined frequency of the particular sensor element. The impedance as a function of temperature can then be determined from the reflected measurement signal. In this way, two measuring elements with a pair of connecting lines can be used. However, such electronic devices are delicate and complex.

Disclosure of Invention

The object of the invention is to disclose a possibility for increasing the measurement accuracy of a thermometer with at least two temperature sensors and the most compact design in the simplest possible manner.

This object is achieved by a device for determining and/or monitoring a temperature, comprising a first temperature sensor, a second temperature sensor and electronics. The electronics are configured to apply at least one electrical transmit signal in the form of a current to the first temperature sensor and/or the second temperature sensor and to tap at least one electrical receive signal in the form of a voltage from the first temperature sensor and/or the second temperature sensor. The device according to the invention further comprises at least six connecting lines for making contact, in particular electrical contact, with the first temperature sensor and the second temperature sensor, wherein the connecting lines are arranged and configured such that the first temperature sensor and the second temperature sensor are connected in series and can have a transmit signal applied thereto, and a first receive signal can be tapped off from the first temperature sensor and/or a second receive signal can be tapped off from the second temperature sensor.

At least one temperature sensor, in particular two temperature sensors, is preferably a resistive element, for example a platinum element. For example, the electronics are also temperature transmitters.

The thermometer according to the invention can be used, for example, as a temperature measuring insert, wherein the connecting line is guided in a conduit which can in turn be brought into direct contact with a corresponding medium. The conduit may be at least partially filled with an insulating material, e.g., a ceramic powder.

However, a protective tube can additionally be provided, which can be brought into contact with the medium and in which at least two temperature sensors and at least a part of the connecting lines are arranged.

The device according to the invention achieves a space-saving compact design by reducing the number of connection lines that are led to the electronic component. The two temperature sensors are connected by means of at least one of the at least six connecting lines, so that of the at least six connecting lines only at least five connecting lines are led to the electronic device. Due to the series connection of the two temperature sensors and due to the fact that the received signal can be tapped off individually from each temperature sensor, a high measuring accuracy can be achieved in a simple manner using the device according to the invention despite its compact design. At the same time, the reliability of the device can be ensured. If one of the two temperature sensors fails, the temperature may continue to be determined and/or monitored by the other, functioning properly, using three-wire measurement techniques.

It is advantageous if the first connection line extends from the electronic device to the first temperature sensor, the second connection line extends from the first temperature sensor to the second temperature sensor, and the third connection line extends from the second temperature sensor to the electronic device. In this way, a series connection of two temperature sensors can be realized in a simple manner.

It is also advantageous if the fourth connection line extends from the first temperature sensor to the electronic device and the fifth connection line extends from the second temperature sensor to the electronic device.

It is also advantageous if the sixth connection line connects the electronic device to the second connection line.

In this embodiment, even if only five connection lines are wired to the electronics, two temperature sensors can be advantageously operated according to the four-wire measurement technique. In case of a failure of one of the two temperature sensors, the remaining properly functioning temperature sensors can still be operated according to the three-wire measurement technique. For example, a first receive signal may be tapped from the first temperature sensor between the fourth connection line and the sixth connection line, and a second receive signal may be tapped from the second temperature sensor between the fifth connection line and the sixth connection line.

A preferred embodiment of the device according to the invention comprises an electronic device with a first voltage determination unit for tapping a first received signal from a first temperature sensor and a second voltage determination unit for tapping a second received signal from a second temperature sensor.

In this case, it is advantageous if the first voltage determination unit is configured to tap the first receive signal between the fourth connection line and the sixth connection line, wherein the second voltage determination unit is configured to tap the second receive signal between the fifth connection line and the sixth connection line.

A preferred embodiment of the device according to the invention comprises an electronic device with a single current generating unit for generating the transmit signal and at least one switching element.

Then, for example, in a first switching position of the switching element, the transmission signal can be applied to the first temperature sensor, while in a second switching position of the switching element, the transmission signal can be applied to the second temperature sensor. Furthermore, a third switching position of the switching element is preferably provided, in which the transmission signal can be applied to both temperature sensors.

Within the scope of the invention, both a single switching element with at least two, preferably three, switching positions and at least two switching elements with at least two switching positions each are conceivable.

It is advantageous if the at least one switching element is arranged and configured such that an electrical connection can be established between the first connection line and the sixth connection line and/or between the third connection line and the sixth connection line by means of the switching element.

The electronics can be configured, for example, such that it can detect whether one of the two temperature sensors is defective on the basis of the received signals received in each of the different switch positions. The electronics and/or the at least one switching element may also be configured such that the switching element may be activated by means of the electronics, i.e. various switching positions may be adjusted by means of the electronics.

In the event of a failure of one of the two temperature sensors, the determination and/or monitoring of the temperature can be continued with the respective normally operating sensor by suitable activation of the switching element. In this case it can be ensured that the temperature can be found at least according to the three-wire measurement technique. For example, if the received signal is no longer received in one of the switching positions, it can be concluded that the respectively activated temperature sensor is malfunctioning.

In an alternative preferred embodiment of the device according to the invention, the electronic device has a first and a second current generating unit. Both current generating units are used to generate at least one transmit signal.

In this case, it is advantageous if the first current generating unit and the second current generating unit are connected in series and to each other by means of a seventh connecting line.

It is also advantageous if the sixth connecting line connects the second connecting line and the seventh connecting line to each other. In this case, the two current generation units are located at opposite sides of the junction of the sixth connection line and the seventh connection line.

In the case of normal operation of both temperature sensors, the sixth connecting line in this embodiment advantageously remains currentless if substantially the same current is generated by means of both current generating units, respectively.

In an embodiment of the device according to the invention, the first current generating unit and the first voltage determining unit are arranged in a first electronics unit, wherein the second current generating unit and the second voltage determining unit are arranged in a second electronics unit.

In an alternative embodiment of the apparatus according to the invention, the first and second current generating units and the first and second voltage determining units are arranged together in the same electronic device.

In a particularly preferred embodiment, the device according to the invention comprises an eighth connection line which extends from the second connection line to the electronic component. In this embodiment, a total of at least six connection lines are led to the electronic device. However, with the embodiment with the eighth connecting line, it can advantageously be ensured that in the event of a failure of one of the two temperature sensors, the device can always be operated according to the four-wire measuring technique, resulting in a further increase in the measurement accuracy achievable by the device. This also applies if one of the two temperature sensors fails.

For this embodiment, it is advantageous if the first voltage determination unit is configured to tap the first receive signal between the fourth connection line and the eighth connection line, wherein the second voltage determination unit is configured to tap the second receive signal between the fifth connection line and the eighth connection line. In case both temperature sensors are functioning properly, the seventh connection line remains currentless as in the previously described exemplary embodiment.

Drawings

The invention is explained in more detail with reference to the following figures. The figures show:

FIG. 1 illustrates a two wire measurement technique according to (a), according to the prior art; (b) three-wire measurement technology; and (c) a schematic of a thermometer with two temperature sensors for a four wire measurement technique,

figure 2 shows a schematic view of a thermometer according to the invention with five connection lines leading to the electronics,

figure 3 shows a schematic view of a thermometer according to the invention with five connection lines leading to the electronics and a single current generating unit,

fig. 4 shows a schematic diagram of a thermometer according to the invention with five connection lines leading to the electronics and (a) two current generating units arranged in a common electronics unit and (b) in two electronics units, and

fig. 5 shows a schematic view of a thermometer according to the invention with six connection lines leading to the electronics.

In the following description, like elements have like reference numerals.

Detailed Description

Fig. 1 shows various schematic views of a thermometer 1 according to the prior art. Fig. 1a shows a thermometer 1, in particular a temperature transmitter, with a protective tube 2 and electronics 4. The partial region of the protective tube 2 facing the medium 5 is also referred to as the sensor head 3 in each case. The inner space of the sensor head 3 is filled with a filler, in particular an electrically insulating filler 6, in particular cement.

Furthermore, a first temperature sensor 7 and a second temperature sensor 8 are arranged inside the sensor head 3, and each temperature sensor is electrically contacted via two connection lines 9a, 9b and 9c, 9d, respectively, which are led to the electronics 4. Other embodiments may comprise, for example, a catheter for guiding the connecting wires 9a-9 d. The temperature sensors 7 and 8 are, for example, resistance elements, in particular resistance elements that are identical in structure.

The thermometer shown in fig. 1a operates according to the two-wire measurement technique, which has been mentioned in the introductory part of the description and is well known in the art. However, in order to compensate for the influence of the, in particular ohmic, line resistance of the connection lines 9a-9d, it is proposed to use a three-wire or four-wire measuring technique as shown in fig. 1b and 1 c. If the three-wire measurement technique shown in fig. 1b is used, six connection wires are already required if the thermometer 1 has two temperature sensors 7 and 8; even eight connection lines are required if the four-wire measurement technique shown in fig. 1c is used. This puts high demands on the geometric design of the thermometer. For example, it must be ensured that the connection lines 9a-9f are always insulated from each other and from the catheter. In addition, commercially available protective tubes and/or catheters usually have a diameter of only maximally 3 mm.

The invention solves this problem by providing a thermometer which has at least two temperature sensors and the most compact design possible and which can simultaneously achieve a high measurement accuracy. In particular, the influence of the line resistance of the connecting line on the temperature determination and/or monitoring may be taken into account or compensated.

According to the present invention, as will be explained in detail with reference to fig. 2 to 5, the number of connection lines 19 led to the electronic device 14 is reduced while ensuring high measurement accuracy. For this purpose, two temperature sensors 17, 18 are connected in series. Nevertheless, it is ensured that the reception signal can be tapped off separately from each temperature sensor 17, 18. As a result, each of the two temperature sensors 17, 18 can be operated individually, in particular in the event of a failure of one of the two temperature sensors 17, 18.

Fig. 2 shows a first possible design according to an embodiment of the invention. A first connection line 19a extends from the electronic device 14 to the first temperature sensor 17, a second connection line 19b extends from the first temperature sensor 17 to the second temperature sensor 18, and a third connection line 19c extends from the second temperature sensor 18 back to the electronic device 14. In this way, a series connection of the two temperature sensors 17, 18 is achieved by means of three connection lines 19a-19 c. The electronic device 14 is designed to produceTransmission signal I applicable to both temperature sensors 17, 18_S. For this purpose, it has, for example, at least one current generating unit [ not shown in FIG. 2 ]]。

Further, a fourth connection line 19d extends from the first temperature sensor 17 to the electronic device 14, a fifth connection line 19e extends from the second temperature sensor 18 to the electronic device 14, and a sixth connection line 19f extends from the second connection line 19b to the electronic device 14. The electronic device 14 is further configured to tap the first reception signal U between the fourth connection line 19d and the sixth connection line 19f_E1And a second reception signal U is tapped between the sixth connection line 19f and the fifth connection line 19e_E2. For this purpose, the electronic component 14 has, for example, at least one voltage determination unit [ not shown in fig. 2 ]]。

If one of the two temperature sensors 17 or 18 fails, the thermometer 1 can still determine and/or monitor the temperature via the respective remaining, normally operating temperature sensor 17 or 18. The thermometer according to the invention is therefore fail-safe. At the same time, it is ensured in any case that at least a three-wire measuring technique is used for the determination and/or monitoring, so that in any case the potential influence of the line resistances of the connecting lines 19a to 19f can be taken into account. At the same time, in contrast to the arrangements known from the prior art, according to the embodiment of fig. 2 only five connection lines 19a and 19c-19f are led to the electronic device 14 according to the invention.

Fig. 3 shows another embodiment of the present invention. The reference numerals explained in connection with fig. 2 are not discussed here. The electronic device 14 has a circuit for generating a transmission signal I_SAnd for tapping off a first received signal U from the first temperature sensor 17_E1And a first voltage determining unit 21a for tapping a second receiving signal U from the second temperature sensor 18_E2The second voltage determining unit 21 b.

The electronic device 14 further comprises a switching element 22 having a first switch 22a and a second switch 22 b. The electronic device 14 may alternatively also have a single switching element 22 or at least two switching elements 22. The switching element 22 has at least two switching positions. In fig. 2, an electrical connection can be established or broken between the first connection line 19a and the sixth connection line 19f by means of the first switch 22a based on the current switch position of the first switch 22 a. Similarly, an electrical connection can be established or broken between the third connection line 19c and the sixth connection line 19f by means of the second switch 22b based on the current switch position of the second switch 22 b.

The electronics 14 are preferably configured to be able to be based on the received signal U received in each of the different switch positions of the two switches 22a and 22b_E1And U_E2To detect whether one of the two temperature sensors 17, 18 is faulty. The electronics 14 and/or the two switches 22a, 22b can also be designed such that the switches 22a and 22b can be actuated by means of the electronics 14, i.e. the switch positions (here: open or closed) of the two switches 22a and 22b can be adjusted by means of the electronics 14. In the arrangement shown in fig. 3, it can be ensured that the temperature of the medium can be determined and/or monitored at least in accordance with the three-wire measuring technique even if one of the two temperature sensors 17 or 18 fails. For example, the two switches can be closed regularly or, if appropriate, alternately at predefinable points in time in order to check whether one of the two temperature sensors 17 or 18 has failed. If, for example, the received signal U can no longer be tapped off from the respective temperature sensor 17 or 18 being examined_E1Or U_E2It can be concluded that the respective temperature sensor 17 or 18 has failed. However, faults may also be detected in many other ways. For example, the received signals U measured at different times when the respective switch 22a or 22b is closed may be compared with each other_E1Or U_E2. In this case, if there is a deviation above a predefinable threshold value, it can be concluded that a fault has occurred in one of the two temperature sensors 17 or 18. In this way, a deterioration in the measurement accuracy of the two temperature sensors 17 or 18 can also be detected.

An alternative embodiment of the electronic device 14 is shown in fig. 4. The electronic device 14 comprises two current generating units 20a and 20b, which are electrically connected in series and connected to each other by means of a seventh connecting line 19 g. In this case, the sixth connection line 19f extends between the second connection line 19b and the seventh connection line 19g, and the two current generating units 20a and 20b are located at opposite sides of the junction between the sixth connection line 19f and the seventh connection line 19 g. On the one hand, the electronic device 14 may comprise two units 14a and 14b, each having a current generating unit 20a and 20b and a voltage determining unit 21a and 21b, respectively, as shown in fig. 4 a. However, it is also conceivable that both the two current generating units 20a and 20b and both the voltage determining units 21a and 21b are arranged in a single or the same electronic device 14, as shown in fig. 4 b. In the scope of the explanation of fig. 4, reference numerals which have already been explained in connection with other figures are not discussed in detail again.

In the two variants shown in fig. 4, the two current generating units 20a and 20b and the two temperature sensors 17 and 18 are connected in series by means of a first connecting line 19a, a second connecting line 19b, a third connecting line 19c and a seventh connecting line 19 g. If both temperature sensors 17 and 18 are functioning properly, the sixth connection 19f remains currentless in both configurations shown in fig. 4. On the other hand, if one of the two temperature sensors 17 or 18 fails, current flows through the sixth connecting line 19f and the determination and/or monitoring of the temperature can be continued by means of the respective remaining, normally operating temperature sensor 17 or 18 according to the at least three-wire measuring technique. In the configuration shown, it is advantageous to automatically detect a malfunction of one of the two temperature sensors 17 or 18 from a special circuit arrangement.

Finally, fig. 5 shows a further possible embodiment of the invention. Here, the electronic device 14 also includes two current generating units 20a and 20b and two voltage determining units 21a and 21 b. It should be noted that the embodiment in fig. 5 may also be combined with the exemplary embodiments previously shown in fig. 2-4. As in the previous figures, the already explained reference numerals are not discussed in detail with respect to fig. 5.

In addition to the embodiments shown so far, the embodiment in fig. 5 has an eighth connecting line 19h, which, like the sixth connecting line 19f, extends from the second connecting line 19b to the electronic component 14. In this embodiment, the first voltage determination unit 21a is designed to tap off the first reception between the fourth connection line 19d and the eighth connection line 19hSignal U_E1. Similarly, the second voltage determining unit 21b is configured to tap the second reception signal U between the fifth connecting line 19e and the eighth connecting line 19h_E2。

As shown in fig. 4, if both the temperature sensors 17 and 18 are fully functioning normally, the sixth connection line 19f remains currentless. However, if one of the two temperature sensors 17 or 18 fails, a current flows along the sixth connection line 19 f.

The eighth connection 19h allows the signal I to be transmitted_SIs applied to the temperature sensor 17 and/or 18 and receives the signal U accordingly_E1And/or U_E2Are completely separated from each other with respect to the connecting lines used in each case. This means that if both temperature sensors 17 and 18 are functioning properly and if only one of the two temperature sensors 17 or 18 is functioning properly, the temperature can advantageously be determined and/or monitored by means of a four-wire measuring technique.

List of reference numerals

1 thermometer

2 protective tube

3 sensor head

4 electronic device

5 media

6 Filler

7 temperature sensor

8 temperature sensor

9a-9f connecting line

10 thermometer according to the invention

14, 14a, 14b electronic device or electronic device unit

17 first temperature sensor

18 second temperature sensor

19a-19 h connecting line

20. 20a, 20b current generating unit

21. 21a, 21b voltage determination unit

22. 22a, 22b switching element, switch

I_STransmitting a signal

U_E1First received signal

U_E2Second received signal