Patent Description:
Sensors for measuring parameters of vehicles are known. , <CIT> discloses a tire measurement system. The tire pressure is continuously measured by a device located inside the tire. As a power supply, it comprises a rechargeable battery or a replaceable battery having an estimated life time of over <NUM> years. A device for watching revolutions of a shaft in a vehicle is disclosed in <CIT>. In order to reduce power consumption while ignition is off, yet a movement of the watched shaft shall still be detected, it is proposed to add a further sensitive device in combination with trigger circuitry. The sensitive device is sensible to a movement of the magnet which serves as well for measuring the movement of the shaft. If a movement is detected, the sensor proper is activated.

Other approaches for reducing power consumption have been conceived where low power consumption is required. <CIT> and <CIT> propose to switch the device on, i.e. connect the power supply (a battery of limited capacity), manually if required. A switch device in parallel to the manually operated switch and controlled by the electronic circuitry allows the electronic circuitry to remain powered until the current activity is completed. Accordingly, the entire electronic circuitry is disconnected from power in the off state.

Traditionally, measuring a parameter on an aircraft like tire pressure is performed by some equipment fitted to the aircraft. It is either permanently fitted to the aircraft (such as the pressure sensor of a tire pressure measurement system [TPMS]) or temporarily fitted to the aircraft for the duration of the measurement (such as a pressure gauge used for tire pressure checks). All parameters used in the processing are either pre-set constants or measurements from devices present permanently or temporarily on the aircraft.

Some existing products already use a device external to the aircraft for measuring vehicle parameters. One example is described in patent <CIT>. However these products use a bespoke, application-specific piece of a kit (often called "hand-held device"). This device is an integral part of the product. It is provided by the product manufacturer. The product cannot be used without this device and the device has no other use than the one of the product. This extra piece is a burden to users. It may get lost or damaged, thus preventing the entire product from being used.

Known aircraft tire pressure measurement systems comprise pressure sensor devices (PSD) which are either installed on a dedicated port on the wheel ("pressure port" different from the "inflation port"), or installed on the "inflation port" (i.e. inflation valve) hence preventing the tire from being re-inflated (the equipment must be removed in order to connect an inflation means).

In the aerospace industry, equipment may be stored several years before being installed on aircraft. Minimizing the power consumption of the PSD during the storage period is critical to ensure that the contractual service life of the PSD is ensured once installed on an aircraft.

In the prior art, powering-up battery-powered device requires specific equipment and conditions. For example in patents <CIT> or <CIT>, the device is activated when subjected to a certain pressure or by reception of an activation signal.

Activation by pressure is constraining because checking the proper operation of the device requires subjecting it to pressure, which is not convenient for goods-in control (i.e. quick check of the device at delivery). Moreover it means that a specific stimulus is required to activate the device, whereas in the present invention the absence of a stimulus activates the device. This makes the present invention more robust.

Activation by reception of an activation signal requires specific equipment. This is not desirable because this specific equipment may not be available.

Therefore, it is an object of the present invention to propose a sensor of a physical property of a vehicle, in particular the tire pressure of an aircraft, wherein the power source of the sensor can be safely and easily switched on at least in order to increase shelf life.

Further objects aimed at by preferred embodiments are:.

The first object is attained by the sensor assembly defined in claim <NUM>. The further claims present preferred embodiments of the sensor assembly.

Accordingly, the sensor is equipped with a primary switch which can be operated by a magnetic field. More specifically, the primary switch is arranged to be open, i.e. the electric circuit is interrupted, when the magnetic field strength is above the switching threshold. Furthermore, the primary switch is connected in parallel to a locking circuitry comprising a secondary switch which is initially open, yet closes once at least the primary switch has closed and the locking conditions are met. Once the primary switch closes due to a change in a magnetic field applied to the primary switch, the locking circuitry is powered on. Once the locking arrangement is active, possibly depending on further conditions, it switches on the second switch. As the second switch is effectively connected in parallel to the first switch so the latter is shortcut. As a consequence, the switched-on state is maintained independently of if the primary switch changes its state, f. if the magnetic field raises above the switching threshold again.

Actual sensor elements are mostly not capable to switch on and off considerable load like the sensor device's circuitry. Furthermore, real life sensors may have a switching characteristic inverse or different to the one required. Hence, according to preferred aspect, primary as well as secondary switch may be understood to comprise the actual sensor/input element and further components for switching higher powers (most importantly: currents) and to inverse and/or to improve the switching characteristic. As a consequence, in a preferred variant, the power portion, e.g. the switch means actually connecting and disconnecting the power supply from the sensor device's circuitry, of primary and secondary switch may be a common part of primary and secondary switch. In other terms, according to this variant, primary and secondary switch comprise each a control portion and a power portion, the power portion (e.g. a power transistor) being common to both switches, and the two control portion being connected to the common power portion the way that the required overall behaviour is achieved. The logical equivalent is in part an OR-link of the outputs of the control portions, with the output of the OR link being the control input of the (common) power portion. The condition that the secondary switch can only inhibit switching off, yet is not able to switch on the power supply, may be achieved by the fact, that the control portion of the second switch is only powered-on once the primary switch has closed. In contrast, the primary switch is permanently active and as required connected to the power source, preferably only its parts actually necessary to be able to respond to the externally applied field or other stimulus. In the powerless state, the secondary switch is unable to produce a logical true level to the OR link, hence is not capable to incite the power portion to connect the power supply to the sensor device's circuitry.

Regarding a preferably targeted property of an aircraft: the relative tire pressure, the sensor may therefore have a sealed layout, i.e. only a sensing access for the tire pressure. Therefore, it is highly insensitive to detrimental or irritating environmental influences, in particular dirt and fluids.

Preferably, the present invention relates to a wireless, battery-powered device used as a sensor on an aircraft. In order to be robust to the environment, the device, once installed on aircraft, is fully hermetic. Any opening, buttons, connectors or any of the like through the housing would compromise the robustness of the device. Therefore the device housing does not feature any mechanical means to power the device on or off.

However, it is useful to turn the device off when not in use (e.g. during storage prior to installation on aircraft) in order or increase its service life (the device being powered by a battery). The present invention describes a novel means to put the device in an ultra-low-power mode, typically for storage, without compromising the robustness of the device housing and without requiring a bespoke tool to power on the device.

The present invention does not require any specific equipment to activate or de-activate the device. This is important because the first application of the present invention is in business aviation. Business aircraft can land in remote airfields where very little equipment is available. The same applies to commercial aviation as logistics to have a bespoke device at each location is complex and expensive.

A simple, small, light, inexpensive and commonly available magnet is sufficient to de-activate the device if located and oriented reasonable precisely. Such a magnet may be included in the packaging of the device. Moreover, the magnet is used to de-activate the device. The absence of a magnet leads to the device being activated, therefore no equipment at all is required to activate the device. This makes usage convenient even in a remote location where specific equipment is not available.

Another aspect of use of the sensor is the existence of PEDs as evaluation device which are provided with at least the capability to wirelessly communicate with sensors of a vehicle, preferably also via a network (e.g. the internet) with remote databases or sensors, and computing capabilities so that the PED can question a sensor for its value and compute a property of the vehicle based on a 1st parameter which is the value measured by the sensor, and one or more 2nd parameters obtained from another source, be it a sensor of the vehicle, a built-in sensor of the PED, some other sensor with which the PED can communicate, a parameter measured in a remote location, or a value retrieved from a remote data source like a data base or a data provider. the actual relative tire pressure may be determined based on the absolute pressure value provided by a tire pressure sensor and the local atmospheric pressure. The latter may be determined by a sensor integrated in the PED (or a sensor attached to it), a sensor provided by the aircraft, or a meteorological service provider.

Generally, "communicating", in particular with a remote data furnishing installation like a remote server, is intended to mean any transmission, even unidirectional, of information. It includes even obtaining data which need further processing by the PED, like data obtained from satellites of a GNSS.

A benefit is to use preferably a PED (portable electronic device, preferably one in common use as a daily personal accessory, e.g. a smartphone) provided by the user. The user already owns and carries the PED with him. Therefore there is no extra piece of kit required. Moreover, there are no development and manufacturing costs associated with an extra piece of kit, hence reducing the price of the system.

The invention will be explained more in detail by means of preferred exemplary embodiments example with reference to the Figures:.

A good example of the present invention is an aircraft tire pressure measurement system (TPMS) as shown in <FIG>. A sensor <NUM> fitted on an aircraft wheel <NUM> measures the tire pressure and wirelessly <NUM> transmits the result to a PED <NUM>. System users typically want to read the relative pressure of a tire (i.e. difference between the tire pressure and the surrounding atmospheric pressure) rather than the absolute pressure (i.e. difference between the tire pressure and the vacuum) because this is what is mentioned in the aircraft maintenance documents. This means that the system has to measure both the tire pressure and the surrounding atmospheric pressure. The variations of the surrounding atmospheric pressure (due to the temperature and altitude) have a non-negligible impact on the relative tire pressure.

The atmospheric pressure can be measured in several ways:.

A preferred tire pressure measurement device (wireless tire pressure gauge, WTPG) comprises a pressure sensor device (PSD) <NUM> and a pressure sensor holder (PSH) <NUM>. The PSD <NUM> contains a pressure transducer <NUM> and some electronics <NUM>. The PSH <NUM> is a mechanical interface allowing installing the PSH <NUM> on an aircraft wheel <NUM>.

The PSH <NUM> fulfils the following functions:.

The combination of these four functions allows installing the PSD <NUM> on the tire inflation valve in a convenient way.

The present invention allows fitting the pressure measurement device on the inflation port of the aircraft wheel <NUM> whilst providing a standard interface for inflating the tire. This allows equipping aircraft whose wheels do not have a separate "pressure port", without impairing maintenance. It also allows replacing the PSD <NUM> without deflating the tire. This is required because the PSD <NUM> is a battery-powered device that needs to be replaced periodically.

The PSD <NUM> being a battery-powered device, it needs to minimize its power consumption. It must do so in service but also during storage. In the aerospace industry, equipment can be stored for several years before being installed on aircraft. Minimizing the PSD <NUM> power consumption during the storage period is critical to ensure that the contractual service life of the PSD <NUM> once installed on aircraft is ensured.

Due to the very harsh environment the PSD <NUM> is subjected to once installed on an aircraft (mounted on a landing gear wheel, subjected to shocks, water, mud, dust, insects, corrosive fluids, centrifugal accelerations, etc.), it is not convenient to have an on/off switch on the PSD external enclosure <NUM>. The enclosure <NUM> must remain perfectly hermetic. Therefore a contactless switch has been developed. It uses a reed switch <NUM> that opens or closes (depending whether it is normally closed or normally open) when subjected to an appropriate magnetic field (e.g. by approaching a magnet). This allows activating the PSD <NUM> through the PSD enclosure <NUM> without compromising the hermeticity and the robustness of the enclosure <NUM>. A novelty resides in the "lock-on" function once the PSD <NUM> is turned on. In order to prevent spurious switch-offs in service due to reed switch malfunction (caused by vibrations, shocks, high centrifugal accelerations, etc.), the PSD <NUM> can be locked in the on state by software.

This solution contains <NUM> valves <NUM>, <NUM> in series. Inner valve <NUM> is located between the tire <NUM> and the PSD <NUM>. Outer valve <NUM> is located between the PSD <NUM> and the inflation interface <NUM>. Inner valve <NUM> allows removing the PSD <NUM> without deflating the tire <NUM>. Outer valve <NUM> allows plugging the usual inflation means. Inner valve <NUM> is contained into the first element of the PSH <NUM>, called Wheel-Sensor Interface (WSI) <NUM>. Outer valve <NUM> is contained in the second element of the PSH <NUM>, called retaining nut <NUM>. Both valves <NUM>, <NUM> contain a standard aircraft wheel valve core. They are normally closed (and maintained as such by a spring <NUM>, <NUM>). They open when the stem <NUM>, <NUM> is pushed.

In <FIG> (and <FIG> as well relating to the alternative embodiment set forth below), the dotted areas are the areas connected to the tire pressure <NUM>. Regarding interfaces between detachable parts like the PSD <NUM>, the usual means for sealing against pressure loss are applied, like O-rings <NUM> (cf. <FIG>), even if not explicitly mentioned.

When the WSI <NUM> only is fitted on a wheel <NUM>, inner valve <NUM> is closed. The tire pressure <NUM> is maintained. The WSI <NUM> is screwed into the wheel <NUM> rim in place of the original inflation valve. It features the same thread.

When the PSD <NUM> is slid onto the WSI <NUM> (<FIG>), nothing happens. The PSD <NUM> is in place but is not connected to the tire pressure <NUM>. When the retaining nut <NUM> is screwed on the WSI <NUM>, a design feature of the retaining nut <NUM> pushes on the inner valve <NUM> and opens it. Tire pressure <NUM> flows through inner valve <NUM>. Outer valve <NUM> remains closed. Outer valve <NUM> would open if an inflation means was connected to the retaining nut <NUM>. The thread <NUM> on the free end of the retaining nut <NUM> features the exactly same interface (thread and thread length) as the original inflation valve. The PSD <NUM> is free to rotate around the PSH <NUM> until the retaining nut <NUM> is tightened. The orientation of the PSD <NUM> around the PSH <NUM> does not matter. A circumferential groove <NUM> in either the PSH <NUM> or the PSD <NUM> (or both) allows the PSD <NUM> to be subjected to tire pressure <NUM> whatever its orientation may be. By this means, the PSD <NUM> may be fixed in any rotational position on PSH <NUM> with maintaining a fluidic connection between the gas under pressure <NUM> and the PSD <NUM>, in particular its pressure transducer <NUM>.

A standard valve cap <NUM>, same as the one of the original inflation valve, screws onto the thread <NUM> of the free end of the retaining nut <NUM>. It protects the valves <NUM>, <NUM> from contamination (e.g. water, dust, etc.). Therefore, the thread <NUM> is exactly the same as that of the original inflation valve, or is at last compatible therewith so that accessories like the cap <NUM> can be attached to the free end of the retaining nut <NUM> as to the original inflation valve.

The previously described solution with two valves in series meets all expectations, although it is fairly complex and costly to manufacture. A second variant has been designed and tested that achieves the same functions with a simpler design: An inner valve is omitted, and the retaining nut <NUM> becomes simpler. This results in a PSH <NUM> that is cheaper, lighter, more compact and more reliable (because it contains less parts).

The function fulfilled by inner valve <NUM> (retaining tire pressure during PSD <NUM> replacement) is fulfilled by the very small size of the hole <NUM> that directs the pressure from the inside of the WSI <NUM> to the PSD <NUM>. When the PSD <NUM> is removed, the tire gas flows freely to the atmosphere and the tire deflates. However, since the hole <NUM> in the WSI <NUM> is very small, the gas flow is also small. Hence the operator has ample time to remove and re-install a PSD <NUM> before the tire deflation becomes problematic. A novelty resides in the combination with outer valve <NUM> that allows connecting an inflation means and inflating the tire.

Conservative calculations show that a hole diameter of <NUM> to <NUM> achieves the required performance. Such a hole size leads to a decrease of tire pressure of only <NUM> PSI (<NUM> hPa, i.e. about <NUM> hPa) after more than <NUM>. This is in line with maintenance procedures and tire limitations and leaves enough time for the operator to replace the PSD <NUM>. More generally, a value of at most <NUM> hPa, preferably at most <NUM> hPa, or more preferably at most <NUM> hPa loss of gas pressure within <NUM> may be acceptable.

The WSI <NUM> is screwed into the wheel <NUM> rim in place of the original inflation valve. It features the same thread. When the PSD <NUM> is slid onto the WSI <NUM>, the PSD <NUM> is subjected to tire pressure <NUM> and the tire gas no more leaks into the atmosphere. The tire does not deflate anymore.

The retaining nut <NUM> is screwed on the WSI <NUM> for securing the PSD <NUM> in its position. In this single-valve design solution, the retaining nut <NUM> actually is a simple nut. (Outer) valve <NUM> remains closed. Valve <NUM> would open if an inflation means was connected to the retaining nut <NUM>. The thread <NUM> on the free end of the PSH <NUM> features exactly the same interface (thread and thread length) as the original inflation valve. The general considerations for thread <NUM> set forth above in the preceding embodiment apply as well. The PSD <NUM> is free to rotate around the PSH <NUM> until the retaining nut <NUM> is tightened. The orientation of the PSD <NUM> on the PSH <NUM> does not matter. A circumferential groove <NUM> in either the PSH <NUM> or the PSD <NUM> or both allows the PSD <NUM> to be subjected to tire pressure <NUM> whatever its orientation is.

A standard valve cap <NUM>, same as the one of the original inflation valve, screws onto thread <NUM> of the free end of the retaining nut <NUM>. It protects the valve <NUM> from contamination (e.g. water, dust, etc.).

Both designs (two valves in series or one single valve) fulfil the four main functions:.

The means to put the PSD <NUM> in low-power mode is based on a magnetic switch circuitry <NUM> containing a reed switch <NUM> and lock-on circuit <NUM> for locking the entire circuit in the powered-on-state.

The purpose of the magnetic switch circuitry <NUM> is to change state when a magnetic field is applied or removed, in order to switch off the device and increase the life of battery <NUM>. The presence of a magnetic field can only be ensured during the storage (controlled environment) and not during the operation, hence the storage mode occurs when the magnetic field is applied. Consequently the normal operating mode occurs when the magnetic field is removed.

The most convenient way to apply a magnetic field is a magnet <NUM>. A magnet <NUM> is included in the device shipping package, at a precise location and orientation, in order to maintain it in storage mode. Once the device is removed from its package, it automatically turns on. If it is put back into its package, it turns back off.

The magnetic switch <NUM> is located just underneath the device housing <NUM>, so that the magnetic field generated by the magnet <NUM> located close to the device operate the magnetic switch <NUM>. The housing is transparent to magnetic fields, or is at least sufficient permeable for a magnetic field that the magnetic switch can be operated by a magnet located adjacent to the housing <NUM>.

<FIG> shows the state with the device removed from its package so that the magnet <NUM> is removed. Therefore the magnetic switch circuitry <NUM> is closed and hence the device is powered on. The magnetic switch circuitry locking means <NUM> is still open, which means that the device is not locked in operating mode. If the device went to encounter an unwanted magnetic field or if the magnetic switch <NUM> had a mechanical failure, the device could revert back to ultra-low-power mode.

When the device is installed on an aircraft, it is configured by the user via an app (software) running on a PED <NUM>. Once this configuration is entered, the device knows that it is installed on a wheel <NUM>. When the configuration is entered, the software residing in the electronics <NUM> of the device commands a transistor (or another switching component, e.g. an electronic switch). This transistor closes a circuit <NUM> that locks the device in power-on state. When this lock-on circuit <NUM> is closed, the state of the reed switch <NUM> (open or closed) does not matter. The device remains powered even if the reed switch <NUM> changes state. This feature protects the device operation from failures of the reed switch <NUM>. It also prevents the device from being disturbed by unwanted magnetic fields that may be present in the environment.

<FIG> illustrates this locked-on status: The device is in operating mode and the magnetic switch circuitry locking means <NUM> is closed. The magnetic switch circuitry locking means <NUM> is closed because the software hosted in the electronics <NUM> commanded an electronic switch (e.g. a transistor) to close. The software commanded this electronic switch to close because it received a configuration command from a user, hence it knows it is installed on aircraft. Since the magnetic switch circuitry locking means <NUM> is closed, the device is locked in operating mode whatever the state of the magnetic switch circuitry <NUM>. This makes the design robust because the device will not exit operating mode even if it encounters an unwanted magnetic field or if the magnetic switch <NUM> fails.

If the device configuration is deleted by the user, i.e. the software is put in a state that the device is no more installed on an aircraft, the software stops commanding the transistor and the lock-on circuit <NUM> opens. Then the magnetic switch circuitry <NUM> is no more bypassed. This function allows the device to be put back into storage in ultra-low-power mode after a period of operation.

The entire circuitry is designed to minimize leakage currents. In battery-powered devices, small leakage currents can have a significant detrimental impact on the service life. The described embodiment minimizes the leakage currents down to a few nano-Ampere (at most <NUM> nA, preferably at most <NUM>, <NUM><NUM>, <NUM> or even <NUM> nA with increasing preference).

<FIG> shows the states of the device and the transitions between states:.

The circuit is implemented using a simple electronic switch <NUM> (e.g. a transistor) being controlled by an OR'ed command <NUM> of the magnetic switch <NUM> and a signal <NUM> coming from the microcontroller (software-driven, not shown). The "microcontroller" represents the sensor's circuitry designed for measuring the physical property or properties (according to this embodiment, the interior pressure of a tire) and auxiliary functions, like the interface to the PED, and the section deriving the signal <NUM> from the state of the device. Notably, signal <NUM> is off or false if the sensor device has not yet been configured, and switches to on or true once the sensor device is configured. The output <NUM> of the electronic switch <NUM> is the power supply of the microcontroller. The input <NUM> of the electronic switch <NUM> is connected to the power source of the sensor device, in particular a battery. In contrast to <FIG>, the magnetic switch does not directly switch the power, but is connected to the signal of the lock-on logic by means of the OR'd command <NUM>, which supplies the control signal to the electronic power switch <NUM>. Accordingly, the magnetic switch <NUM> may be optimized in view of sensitivity, but needs not be designed to carry significant current.

The magnetic switch <NUM> hat its contact open in stand-by condition, i.e. absent a magnet field or exposed to a magnetic field below its switching level (e. a normal-open Reed switch). When the magnet is present, i.e. located sufficiently near to the magnetic switch <NUM> so to create a magnetic field of a strength above switching level of the magnetic switch <NUM> through it, the magnetic switch <NUM> is maintained in closed position by the magnetic field. This keeps the electronic switch <NUM> in open-circuit position.

When the magnet is removed (put further away) the magnetic switch <NUM> opens, the Or'd command <NUM> changes the logical level at the control input of the electronic switch <NUM> from open (interrupt) to closed level and consequently the electronic switch <NUM> connects the battery to the device electronics, i.e. input <NUM> with output <NUM>.

The electronic switch <NUM> is also controlled by a signal <NUM> coming from the microcontroller on which runs the software for controlling the sensor device, determining the measured value, furnishing the retrieved data to a receiver device, etc..

<FIG> shows the electronic circuitry more on detail. The magnetic switch is connected to the input <NUM> and the middle connection of a voltage divider constituted by resistors <NUM> and <NUM>. The other terminal of resistor <NUM> is connected to the gate of FET transistor <NUM> which is the electronic switch, the 2nd terminal of resistor <NUM> to ground. Capacitor <NUM> in parallel to resistor <NUM> suppresses the effect of contact bouncing.

In low-power mode, i.e. with a magnet close to magnetic switch <NUM> and, therefore, magnetic switch <NUM> closed, the gate of transistor <NUM> is connected to its source via resistor230. Transistor <NUM> is of the type which constitutes a high resistance, i.e. represents a switch in off state, when its gate is connected to the source, i.e. gate and source are at about the same voltage level.

The current via magnetic switch <NUM> and resistor <NUM> is an important factor of the power consumption in low-power state. Given a power supply of some volts, resistor has to be at least <NUM> (<NUM> = <NUM><NUM> Ω), preferably at least <NUM>, <NUM>, <NUM>, <NUM>, or even <NUM> with increasing preference.

The "microcontroller" <NUM> is disconnected form the power source at input <NUM>, hence its output <NUM> is inactive and mostly at ground potential <NUM>. The gate of transistor <NUM> would be on ground, too, yet as usual resistor <NUM> is provided to safely keep the gate at ground potential <NUM>. Transistor <NUM> is as well a type which is off if its gate is on the same potential as its source.

In order to minimize power consumption, particularly in this switched-off mode, most importantly transistor <NUM> is a (MOS-)FET, and transistor <NUM> is a (MOS-)FET as well. Thereby, it is possible to choose high resistance values for resistor <NUM> through which current flows if magnetic switch <NUM> is closed.

Once the magnet is removed, switch <NUM> opens, and the gate of transistor <NUM> is drawn toward ground potential <NUM> by resistors <NUM> and <NUM> as fast as capacitor <NUM> is discharged, transistor <NUM> turns to low resistance equivalent to closing a switch, and microcontroller <NUM> is powered on. Now, the device is in state <NUM> (<FIG>), i.e. active, yet unconfigured. In particular, an automatic reset is preferred which secures a predefined, unconfigured state after power-on.

Configuring (transition <NUM>) entails that microcontroller <NUM> activates its output <NUM>, hence a high potential is applied to the gate of transistor <NUM>. Transistor <NUM> gets low resistance and shortcuts resistors <NUM>, <NUM>, corresponding to state <NUM>. In this state, activating magnetic switch <NUM> by a magnetic field will not have any effect on the state of transistor <NUM>, hence the sensor device is locked in the on-state or powered state.

Configuration may be any useful entry, starting with only entering a datum meaning that the device has to remain on. Other useful data are status indication that the sensor is attached to a plane, indications to which tire of which wheel of a plane it is attached, and other data. These date may be permanently stored in a memory comprised in the sensor (not shown), more particularly in the microcontroller, so that the microcontroller can access it.

Removing these data, i.e. resetting the microcontroller <NUM> substantially to the configuration it has immediately after powering-on, is detected by the microcontroller <NUM> and causes the inactivation of its output <NUM> (transition <NUM>). The gate of transistor <NUM> is drawn to ground potential <NUM> again, transistor <NUM> gets non-conductive, and the system is back in state <NUM> where it is no more locked in the on-state. By approaching a magnet, e.g. by putting the sensor back in its packaging provided with a magnet in the proper place, the sensor can be deactivated one again, i.e. switched back into (ultra-)low power mode (state <NUM>).

The main advantage of the described embodiment is that no specific equipment is required to activate or de-activate the device. This is important because the first field of application of the invention is aviation. Aircrafts, and in particular business aircrafts, may land in remote airfields where very few equipment is available. Furthermore, commercial aircraft operators cannot manage the burden of having a bespoke equipment to generate a signal to activate this pressure sensing device. Commercial aircrafts are flying all around the world and it is not practical and not economical (and not environmentally friendly either) to make such bespoke equipment available in hundreds of airports. Not requiring specific equipment to activate or de-activate the device is a significant improvement over the prior art. A simple, small, light, inexpensive and commonly available magnet is sufficient to de-activate the device if located and oriented reasonable precisely. Such a magnet may be included in the packaging of the device. Moreover, the magnet is used to de-activate the device. The absence of a magnet leading to the device being activated, no equipment at all is required to activate the device. This makes usage convenient even in a remote location where specific equipment is not available.

Claim 1:
A sensor assembly providing values of a physical property of a vehicle, preferably pressure values of a gas-inflated tire of a wheel (<NUM>), more preferably of a tire (<NUM>) of an aircraft, the sensor assembly comprising an electronic circuitry (<NUM>) comprising a sensor suited to sense the physical property and a locking arrangement, and further an exhaustable power source (<NUM>), in particular a battery, and a first (<NUM>, <NUM>; <NUM>,<NUM>,<NUM>; <NUM>,<NUM>,<NUM>,<NUM>) switch means functionally arranged between the circuitry and the power source, wherein the first switch means is controllable from outside the sensor assembly, preferably by means of a field, more preferably a magnetic field, characterized in
- that the sensor assembly comprises a second (<NUM>; <NUM>, <NUM>, <NUM>; <NUM>,<NUM>, <NUM>) switch means functionally arranged in parallel to the first switch means and between the circuitry and the power source,
- that the second switch means is controllable by the locking arrangement, so that starting with a storage mode where both switch means are open, the first switch can be closed from outside the sensor assembly, and the locking arrangement powered-on thereby is capable to activate the second switch means so that reopening the first switch means is no more capable to interrupt the connection between power source and circuitry, and
- that first (<NUM>, <NUM>; <NUM>,<NUM>,<NUM>; <NUM>,<NUM>,<NUM>,<NUM>) and second (<NUM>; <NUM>, <NUM>, <NUM>; <NUM>,<NUM>, <NUM>) switch means comprise in common a third switch element (<NUM>) and a logical OR unit (<NUM>) having at least two inputs and an output, one input is assigned to the first switch means and the other input being assigned to the second switch means, and the output is functionally connected to a control input of the third switch element (<NUM>), wherein the third switch element is arranged that by closing the third switch element the power supply is connected to the electronic circuitry of the sensor assembly.