WO2015050489A1

WO2015050489A1 - Wireless sensor for measuring a hydraulic pressure

Info

Publication number: WO2015050489A1
Application number: PCT/SE2014/051085
Authority: WO
Inventors: Fredrik Sebelius; Jonas Tilly
Original assignee: Novosense AB
Current assignee: Novosense AB
Priority date: 2013-10-02
Filing date: 2014-09-23
Publication date: 2015-04-09
Anticipated expiration: 2016-04-02
Also published as: SE1351160A1; SE537096C2

Abstract

The present invention relates to a sensor (100) for measuring a hydraulic pressure in a hydraulic chamber, the sensor (100) comprising a housing (102) having an end section (124) being penetrable to radio signals, a circuitry (106, 300) housed within the housing (102), the circuitry (106, 300) comprising a pressure gauge (104) for measuring the hydraulic pressure in the hydraulic chamber, a wireless communication unit (1 10) arranged to communicate data pertaining to the hydraulic pressure in the hydraulic chamber, a battery (108, 306), arranged to power the sensor (100), a plurality of contacts (114, 302) arranged to make galvanic contact with outside circuitry (500, 600), wherein the circuitry (106, 300) is arranged to be switchable between a first state and a second state, wherein in the first state the circuitry (106, 300) is arranged such that the plurality of contacts (1 14, 302) are set to have the same electrical potential and in the second state the circuitry (106, 300) is arranged such that at least a first one of the plurality of contacts (1 14, 302) is set to have a different electrical potential relative to a second one of the plurality of contacts (1 14, 302).

Description

WIRELESS SENSOR FOR MEASURING A HYDRAULIC PRESSU E

FIELD OF THE INVENTION

The present invention relates to a sensor for measuring a hydraulic pressure in a hydraulic chamber.

BACKGROUND OF THE INVENTION

Hydraulics is frequently used for the generation, control, and transmission of power by the use of pressurized liquids in hydraulic chambers. Hydraulic systems comprise one or more hydraulic chambers for suspension and accurate positioning of system parts in relation to each other, i.e. as hydromounts, hydro bushings, or bearing components. An example of such a system is attachment of a chuck to a drive spindle of a revolving machine tool such as a cutting tool, drill, or tool holder. The position of the chuck parallel to and/or perpendicular to the rotational axis of the revolving machine tool is adjusted by the forces transmitted by the chuck, which in turn is set by the amount of hydraulic pressure in one or several hydraulic chambers within the chuck.

To ensure proper function of hydraulic systems it is of importance to measure the pressure within the hydraulic chambers. Sensors comprising pressure gauges are therefore at least partly arranged inside the pressure chambers in order to measure the hydraulic pressure. It is however problematic to access data pertaining to the hydraulic pressure as the sensor in many situations is arranged in heavy machinery or inside a machine tool. As the sensors often are hidden from view the powering and/or

communication of data pertaining to the hydraulic pressure in the hydraulic chambers is advantageously obtained via electric cables that via sliding contacts are in contact with the sensor. For hydraulic systems comprising for instance high speed rotational parts this is, however, not an optimal solution. For these systems it is difficult to maintain an effective electrical contact. Moreover heat generation at or in the vicinity of the contacts may reduce the performance of the sensor and/or the reliability of the data communication with the sensor. To this end, the environment surrounding the sensors may contain oil leakage, electrically conducting residues and/or liquids that may disturb the performance of the contacts, induce chemical reactions in the vicinity of the sensor or even short circuit the sensor.

It is therefore desirable to remotely access the data pertaining to the hydraulic pressure in the hydraulic chamber. This may be accomplished by using wireless communication. Such a solution, however, requires an internal power source such as a battery within the sensor which limits the lifetime of the sensor.

SUMMARY OF THE INVENTION

An object of the present invention is to solve or at least to reduce the problems discussed above.

In particular according to a first aspect of the invention, a sensor for measuring a hydraulic pressure in a hydraulic chamber, the sensor

comprising a housing having an end section being penetrable to radio signals, a circuitry housed within the housing, the circuitry comprising a pressure gauge for measuring the hydraulic pressure in the hydraulic chamber, a wireless communication unit arranged to communicate data pertaining to the hydraulic pressure in the hydraulic chamber, a battery, arranged to power the sensor, a plurality of contacts arranged to make galvanic contact with outside circuitry, wherein the circuitry is arranged to be switchable between a first state and a second state, wherein in the first state the circuitry is arranged such that the plurality of contacts are set to have the same electrical potential and in the second state the circuitry is arranged such that at least a first one of the plurality of contacts is set to have a different electrical potential relative to a second one of the plurality of contacts.

In the context of the present invention the term radio is construed as an electromagnetic wave having a frequency in the radio frequency range, i.e. from about 30 kHz to 300 GHz. Examples of common standards for wireless communication utilizing radio waves are ZigBee and Bluetooth. ZigBee is a low-power, wireless mesh network standard operating in the industrial, scientific and medical (ISM) radio bands; 868 MHz in Europe, 915 MHz in the USA and Australia and 2.4 GHz in other jurisdictions worldwide. Bluetooth also uses short-wavelength radio transmissions in the ISM band. A person skilled in the art realizes that other standards for wireless communication can also be used according to the present invention.

The wording an end section being penetrable to radio signals should be understood as that the material of the end section may be chosen such that it allows for radio waves to propagate through the material without full attenuation of the amplitudes of the radio waves. Radio waves containing information may therefore continue to propagate after passing the end section such that the information may be transferred through the end section.

Outside circuitry should be understood as a charger, an initiation key, test equipment or other electronic devices that are capable of communicating with the circuitry of the sensor via one or more of the plurality of contacts.

By arranging the sensor such that it is switchable between the first state and the second state it will be possible to for example charge the battery of the sensor or switching the sensor on or off using the plurality of contacts. However, for charging the battery and for some implementations of switching the sensor on or off contacts of the sensor must have different electrical potentials. But if the plurality of contact of the sensor is set to different potentials during operation in hydraulic systems problems may occur due to oil leakage, electrically conducting residues and/or liquids that may short circuitry the sensor. Hence, due to ability to switch the circuitry between the first state and the second state an efficient sensor that has an improved lifetime is obtained. It is therefore advantageous that the sensor is switchable to the second state which provides efficient charging, initiation or electrical communication with the sensor that requires at least one potential difference among the plurality of contacts.

The battery may be chargeable and the plurality of contacts may be arranged to make galvanic contact with the outside circuitry such that charging of the battery is made possible. It is favorable that the battery of a sensor is chargeable as this extends the lifetime of the sensor. This further reduces the number of parts of the sensor as the arrangement does not require that the battery is removably attached to or removable fastened inside the housing of the sensor.

As the contacts of the sensor per se needs to be in electrical contact with the chargeable battery, the associated potential difference between the plurality of contacts increases the risk of short circuit of the circuitry within the sensor and chemical reactions, such as for instance oxidation occurs at these contacts.

The common potential for ail of the contacts, in the first state, mitigates these and other problems associated with the environment surrounding the sensor, i.e. the minimized potential difference within the plurality of contacts reduces problems associated with leakage currents, short circuiting, oxidation, or chemical reactions causing wear of or destruction to the contacts or the sensor. Hence the sensor can be exposed to liquids such as water or detergents during for instance cleaning of the sensor, or oil, chemicals substances and even conducting materials such as metal residues during the usage of the sensor, which could be inside a machine tool.

The circuitry may be flexible such that the circuitry is foldable around the battery. This reduces the amount of empty space in the housing of the sensor which in turn leads to a reduced the size of the sensor.

The wireless communication unit may further comprise a flexible antenna for transmitting and/or receiving radio signals. This is advantageous in terms of size and allows for optimization of the position of the antenna within the sensor assembly.

By further arranging the antenna in close proximity to the end section of the housing an improved transmission of radio signals to and from the sensor is achieved.

The end section of the housing may be made of a glass, a ceramic or a plastic material as this improves transmission of radio signals to and from the sensor. The housing may comprise a threaded portion for fastening the sensor in the hydraulic chamber. This allows the sensor to be screw-fastened in a treaded recess in a hydraulic chamber, whereby the sensor is removeably attached to the hydraulic chamber.

The housing may further comprise a plurality of recesses arranged such that the housing may be positioned in a predetermined relation with the outside circuitry and/or such that an adapter used for fastening the sensor in the hydraulic chamber is removably engageable to the housing. This arrangement reduces the amount of material in the vicinity of the end section of the sensor.

The housing may at least partly be made of a metal, which provides a strong and robust housing that mechanically protects the interior parts of the sensor.

The switching of the circuitry may be initiated by the outside circuitry. This is advantageous as the circuitry can be set to be in the first state or the second depending on the configuration of the outside circuitry.

The contacts may be arranged such that a portion of each contact is extending through the end section of the housing. This provides easy access to the plurality of contacts and further allows for efficient galvanic contacting of the sensor and outside circuitry.

Other advantages and novel features of the invention will be apparent from the following detailed description of examples of embodiments of the invention when considered in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION_, OF THE DRAWINGS

The above and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiments of the invention. The figures should not be considered limiting to the invention to the specific embodiment; instead they are used for explaining and understanding the invention. As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.

FIG. 1 is a schematic diagram of a sensor for measuring the hydraulic pressure in a hydraulic chamber according to an embodiment of the invention.

FIG. 2 is a perspective side view, showing a sensor in an assembled condition according to an embodiment of the present invention.

FIG. 3 is a perspective side view, showing an adaptor for fixation of the sensor of Fig. 2.

FIG. 4 is a schematic circuit diagram of an embodiment of a circuitry within a sensor according to the present invention.

FIG. 5 is a schematic circuit diagram of an embodiment of an outside circuitry according to the present invention.

FIG. 6 is a schematic circuit diagram of an embodiment of an outside circuitry according to the present invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

The basic idea of this invention is to provide a sensor arranged such that its electrical contacts may be switched between a first state where the contacts are set to have the same electrical potential and a second state where at least a first one of the plurality of contacts is set to have a different electrical potential relative to a second one of the plurality of contacts.

The common potential for all of the contacts, in the first state, mitigates problems associated with the often harsh environment that may surround the sensor, i.e. the sensor provides reduced risks of performance problems associated with leakage currents, shout circuiting, oxidation, or other chemical reactions causing wear on the contacts or damage to the sensor. Hence the sensor can be exposed to water or detergents during for instance cleaning of the sensor. Oil, chemical substances or even conducting materials such as metal residues may also be present during usage of the sensor. By switching the sensor to the first state problems arising from being in these environments are reduced.

By further providing a sensor that is switchable to the second state a potential difference within the plurality of contacts can be obtained which is advantageous when for example charging, initiating, or shutting off the sensor.

Referring now to the drawings and to Fig. 1 in particular. Fig. 1 shows a schematic diagram of one embodiment of the sensor 100. The sensor 100 comprises a housing 102 and a pressure gauge 104 for measuring the hydraulic pressure in a hydraulic chamber. Further the sensor 100 comprises circuitry 106, a battery 108, a wireless communication unit 1 10 having an antenna 1 12; and a plurality of contacts 1 14. The sensor 100 may also be equipped with a processing unit 1 16 and a memory 1 18. The battery 108, the wireless communication unit 1 10, the plurality of contacts and the processor may be regarded as being part of the circuitry 06.

Fig. 2 illustrates an embodiment of the sensor 100 in an assembled condition. The sensor is housed in a housing 102. The housing 102

comprises an attachment portion 120, a body 122, and an end section 124. The attachment portion 120 has a threaded portion 126 arranged to be screw- fastened in a treaded recess in a hydraulic chamber, whereby the sensor 100 is removeably attached to the hydraulic chamber.

The body 22 comprises a plurality of recesses 128 in which an adapter 200, see Fig. 3, for fixation of the sensor is removeably attachable such that a sufficient rotational force is obtained during the attachment of the sensor 100 in a hydraulic chamber. Moreover, the plurality of recesses 128 are arranged such that the housing 102 may be positioned in a predetermined relation with the outside circuitry and/or such that the adapter 200 used for fastening the sensor 100 in the hydraulic chamber is removably engageable to the housing 102.

A person skilled in the art realizes that other geometries or means for fixation of the sensor 100 is also possible.

The body 122 of the sensor 100 is advantageously made of a metal such as stainless steel to provide a strong and robust housing 102 that mechanically protects the interior parts of the sensor 100. Such a design is also favorable when fastening the sensor 100 in the hydraulic chamber. The housing 102 is advantageously sealed in order to prevent liquids and other media to enter the interior volume of the sensor 100. To fixate and/or protect the parts within the sensor 100 from vibration, moisture and corrosive agents the interior volume of the housing 102 is preferably filled with electrical potting compounds and encapsulation materials such as epoxy, silicone or polymer systems.

A person skilled in the art realizes that other materials may be used for the housing 102 of the sensor 100 as well as for the encapsulation. Non limiting examples of material that may be used are a ceramic or a plastic.

The end section 124 is further penetrable to radio signals as will be discussed below. The plurality of contacts 1 14 are preferably arranged (not shown) such that a portion of each of the contacts is extending through the end section 124 of the housing 102 such that the plurality of contacts 1 14 may be brought in galvanic contact with outside circuitry. In this embodiment the end section 124 is made of epoxy which is penetrable to radio signals and visually transparent. The usage of a visually transparent epoxy provides visual indication means, for example via a light emitting diode, giving efficient access to information pertaining to the status of the sensor 100. The visual indication may provide the charge level of the battery. It should be noted that the end section 124 could in another embodiment consist of a glass, a ceramic or a plastic material, being penetrable to radio signals. The end section 124 may comprise a visually opaque material as long as the material of the end section 124 is penetrable to radio signals. In order to efficiently use the volume within the housing 102 the circuitry 106 is preferentially made flexible such that the circuitry 106 is foldable around the battery 108.

It is further advantageous if the wireless communication unit 1 10 comprises a flexible antenna 1 12 for transmitting and/or receiving radio signals.

According to one embodiment the antenna 1 12 is integrated in a flex- rigid printed circuit board (PCB) which is arranged such that the antenna 1 12 is brought in close proximity of the end section 124 of the housing 102. This improves the efficiency of the antenna 112. For example, the antenna 1 12 may be glued to the end section 124.

In an alternative embodiment is the antenna 1 2 is a wire antenna. The adapter 200 for fixation is schematically illustrated in Fig. 3. In the disclosed embodiment an end portion of the adapter 200 for fixation is shaped as a hexagonal nut 202. It should be noted that the end portion of the adapter 200 for fixation may be of any shape, such as comprising a notch, a knurled nut, or a T-nut, as long as an efficient attachment of the sensor 100 in the hydraulic chamber is provided. The adapter 200 for fixation further comprises edge portions 204 arranged such that they fit into the plurality of recesses 128 on the housing 102 of the sensor 100. An advantage of having the plurality of recesses 128 on the housing 102 of the sensor 100 is that the amount of housing material close to the end section 124 is reduced. The material reduction reduces the shielding of signals to and/or from the antenna 1 12 and the wireless communication unit 1 10 of the sensor 100. Hence, an improved efficiency of the wireless communication unit 1 10 in communicating data to and/or from the sensor 100 is obtained during the usage of the sensor 100. It should however be noted that in another embodiment the body 122 may comprise edge portions and the adaptor 200 for fixation may comprise corresponding recesses.

With reference to Fig. 4 an embodiment of the circuitry 300 of the sensor 100 according to the present invention is described. The circuitry 300 comprises a plurality of contacts 302 denoted C1 - C5, a switch 304, a battery 306, and a plurality of resistors R1 - R2. The switch 304 is arranged to switch between a first state and a second state. In the first state the switch 304 is in a position A such that the potential of contact C1 is set to ground via the resistor R1. A potential V on contact C2, preferable between 3 - 5V, switches the switch 304 to a position B, such that the circuitry 300 is in the second state. It should be noted that if no potential is applied to contact C2, the potential of contact C2 is set to ground via the resistor R2. The contacts C3 - C5 are set to ground. Hence this circuitry 300 is, depending on the input potential on C2, switched between the first state and the second state. In the first state the plurality of contacts 302 are set to have the same electrical potential. In the second state the circuitry 300 is arranged such that contact C1 is set to have a different electrical potential relative to the contacts C2 - C5. The second state is therefore arranged such that the battery 306 and the contact C1 are in electrical connection, which provides efficient charging of the battery 306.

It should be noted that the switch 304 further connects the circuitry 300 via Vp_0Wer in order to power the sensor 100. By this arrangement the power for the sensor 100 is turned off during charging, during which the battery 306 is connected to the contact C1. This is advantageous as better control of the charging of the battery 306 is obtained and that the energy consumption of the sensor is minimized when the charging of the sensor 100 is terminated. The sensor 100 may be reset as the sensor 100 is removed from a charger, i.e. a hardware reset. The processing unit 310 may before or after the reset read data from and/or write data to the memory 1 18. The sensor 100 may further be arranged such that it is powered after being removed from the charger such that it is in a low power mode that requires initiation (WAKE UP) by the key circuitry 500. The WAKE UP procedure reduces the power consumption of the sensor 100.

According to this embodiment of the sensor 100, the circuitry 300 further comprises a thermistor 308 which is electrically connected to the contact C3 and becomes biased during the charging of the battery 306. The resistance of the thermistor 308 varies substantially with temperature. By placing the thermisor 308 in vicinity of the battery 306 variations in the temperature of the battery 306 is detected. If for example the temperature of the battery 306 is outside a predetermined temperature interval the charging of the battery 306 is terminated. This improves the efficiency of the charging of the battery 306 and reduces the risks of the battery 306 being overheated. A longer lifetime of the battery is thereby obtained.

The circuitry 300 comprises a processing unit 310 and a filter 312, both being in electrical connection with contacts C4 and C5. The processing unit 310 is arranged such that a potential applied on C4 initiates the processor unit 310, in a so called "WAKE UP" procedure. The filter 312 together with a voltage dependent resistor (VDR) 314 is provided to filter out spurious signals such as electrostatic discharges that for instance may initiate the processing unit 310. The circuitry 300 is thereby also arranged to short circuit high voltages to ground in order to protect the processing unit 310. The processing unit 310 may comprise a CC2530 chip.

Contact C5 is connected to ground and thereby to the battery 306. The outside circuitry according to the present invention may for instance comprise key circuitry 500 or charger circuitry 600 as will be described in the following.

Fig. 5 shows key circuitry 500 arranged to, via the processing unit 310, initiate the sensor 100 in an excitation/initiation procedure often referred to as a "WAKE UP" procedure. The key circuitry 500 comprises a battery 502, a resistor 504, and the contacts C4' and C5'. The battery 502 is preferably a silver oxide battery which provides a long lifetime of the key circuitry 500. The resistor 504 is matched to the processing unit 310 and arranged such that it is connected in series with a digital input of the processing unit 310. This is advantageous as the key circuitry 500 may initiate or "WAKE UP" the sensor 100 even if the potential of the battery is substantially reduced from its fully charged level. The resistor 504 also reduces the short circuit current occurring in the circuitry 500 in case of a short circuit, which protects the circuitry 500 from damage. The contacts C4' and C5' are arranged such that they may be brought in galvanic contact with the contacts C4 and C5 of the circuitry 300, respectively. Hence efficient electrical contacts between the circuitry 300 and the key circuitry 500 are achieved.

Fig. 6 shows charger circuitry 600 of a charger arranged to charge the circuitry 300 of the sensor 100. The charger circuitry 600 comprises a power source 602, a micro switch 604, a processing unit 606, a plurality of indicators 608, and a plurality of contacts 610 (C1 ", C2", C3", C5"). The power source 602 is arranged to power the charger circuitry 600 and the charging of the battery 306. The power source 602 may comprise a battery, a chargeable battery, a USB connection providing the desirable voltage for operating the charger or some other suitable power source. The micro switch 604 is switchable between a conducting and a non-conducting state. The micro switch 604 is arranged such that the charger circuitry 600 is powered when the micro switch 604 is set to a conducting state. This could for instance occur when at least a part of the sensor 100 is brought in contact with the charger. The contact is preferable a galvanic contact.

The processing unit 606 comprises logics and circuitry arranged to charge a chargeable battery such as a lithium battery. The potentials used for initiating the charging (switching the switch 304) and the charging of the battery 306 are provided by the processing unit 606 and applied via the contacts C1 " and C2". The processing unit 606 is further arranged to via contact C3" and the thermistor 308 access the temperature of the battery 306 during charging. This provides as discussed above efficient charging of the battery.

The processing unit 606 may be a BQ24040DSQT.

The plurality of indicators 608 are connected to the processing unit

606, and are arranged such that they indicate the status of the charger circuitry 600. It is thereby easy to visually determine for example if the power from the power source 602 is sufficient for charging the battery 306, if the charging of the battery is ongoing or finished etc.

The plurality of contacts 610 (C1 ", C2", C3", C5") are arranged such that they may be brought in galvanic contact with the contacts C1 , C2, C3 and C5 of the circuitry 300, respectively. Hence, efficient electrical contacts between the circuitry 300 and the charger circuitry 600 are achieved.

The charger circuitry 600 may further comprise a plurality of resistors 612, the resistance of which determines the currents used during charging of the battery 306. It is thereby possible to for example set the maximum current and the minimum current used during the charging, which reduces risks of overheating the battery 306 or other damages to the battery 306 or the circuitry 300 that may occur as a consequence of too large currents flowing in the circuitry 300. This arrangement also improves the lifetime of the battery 306.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the applied claims.

For example, the person skilled in the art realizes that the sensor may be used for measuring pressures other than a hydraulic pressure.

The switch 304 may also be a single-pole/double-throw monolithic CMOS analog switch or a MOSFET.

The sensor 100 may comprise a first temperature gauge arranged to sense the temperature in the hydraulic chamber. A second temperature gauge is preferable arranged outside the pressure chamber. This

arrangement allows for measurements of the relative temperature pertaining to the temperature measured with the first and the second temperature gauges, respectively. An advantage being that a more reliable and efficient temperature measurement may be obtained.

The wireless communication unit 1 0 is further arranged to via the antenna 1 12 transmit and/or receive radio signals. This allows for instance for communication between individual sensors, with a receiver unit and or a control unit. The receiver may comprise a processing unit and a

communication unit for transferring data to and from the sensors 100. The receiver may be understood as a repeater or an amplifier of the radio signals in order to improve the data transfer to and from the sensor 100. It is favorable to arrange a receiver in the vicinity of a sensor 100 in environments such as a machine tool comprising metals and other materials that may interfere or shield the radio signals to and from the sensor. There may be a receiver assigned to each of the sensors or a receiver assigned to a plurality of sensors 100. The control unit may comprise a display for displaying data pertaining to the hydraulic pressure in the hydraulic chamber as sensed by the sensor. The control unit may further be arranged to communicate with the processing unit 1 16, 300 of the sensor.

The battery 306 may be a chargeable lithium battery.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person practicing the claimed invention, from study of the drawings, the disclosure, and the appended claims. Moreover, in the drawings and specifications, there have been disclosed preferred embodiments and examples of the invention and, although specific term are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being set forth in the following claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Claims

1 . A sensor (100) for measuring a hydraulic pressure in a hydraulic chamber, the sensor (100) comprising:

a housing (102) having an end section (124) being penetrable to radio signals,

a circuitry (106, 300) housed within the housing (102), the circuitry

(106, 300) comprising:

a pressure gauge (104) for measuring the hydraulic pressure in the hydraulic chamber,

a wireless communication unit (1 0) arranged to communicate data pertaining to the hydraulic pressure in the hydraulic chamber, a battery (108, 306), arranged to power the sensor (100), a plurality of contacts ( 14, 302) arranged to make galvanic contact with outside circuitry (500, 600),

wherein the circuitry (106, 300) is arranged to be switchable between a first state and a second state, wherein in the first state the circuitry (106, 300) is arranged such that the plurality of contacts (1 14, 302) are set to have the same electrical potential and in the second state the circuitry (106, 300) is arranged such that at least a first one of the plurality of contacts (1 14, 302) is set to have a different electrical potential relative to a second one of the plurality of contacts (1 14, 302).

2. A sensor (100) according to claim 1 , wherein the battery (108, 306) is chargeable and wherein the plurality of contacts (1 14, 302) are arranged to make galvanic contact with the outside circuitry (500, 600) such that charging of the battery (108, 306) is made possible.

3. A sensor according to claim 1 or 2, wherein the circuitry (106, 300) is flexible such that the circuitry (106, 300) is foldable around the battery (108, 306).

4. A sensor (100) according to claims 1 - 3, wherein the wireless

communication unit (1 10) further comprises a flexible antenna (112) for transmitting and/or receiving radio signals.

5. A sensor (100) according to claim 4, wherein the antenna (1 12) is arranged in close proximity to the end section (124) of the housing (102).

6. A sensor (100) according to claims 1 - 5, wherein the end section (124) of the housing (102) is made of a glass, a ceramic or a plastic material.

7. A sensor (100) according to claim 1 - 6, wherein the housing (102) comprises a threaded portion (126) for fastening the sensor (100) in the hydraulic chamber.

8. A sensor (100) according to claim 1 - 7, wherein the housing (102) comprises a plurality of recesses (128) arranged such that the housing (102) may be positioned in a predetermined relation with the outside circuitry (500, 600) and/or such that an adapter (202) used for fastening the sensor (100) in the hydraulic chamber is removably engageable to the housing (102).

9. A sensor (100) according to claims 1 - 8, wherein the housing (102) is at least partly made of a metal.

10. A sensor (100) according to claim 1 - 9, wherein the switching of the circuitry (106, 300) is initiated by the outside circuitry (500, 600).

1 1 . A sensor (100) according to claim 1 - 10, wherein the contacts (1 14, 302) are arranged such that a portion of each contact (1 14, 302) is extending through the end section (124) of the housing (102).