Door position sensing system with reduction of noise generated by dynamic ferromagnetic components

An electronic lock device according to one embodiment includes a first magnetometer, a second magnetometer, a dynamic ferromagnetic component positioned between the first magnetometer and the second magnetometer, a processor, and a memory comprising a plurality of instructions stored thereon that, in response to execution by the processor, causes the electronic lock device to read sensor data from the first magnetometer and the second magnetometer, modify the sensor data to generate compensated sensor data that compensates for magnetic noise generated by the dynamic ferromagnetic component, and determine whether the door is in a closed state or an open state based on the compensated sensor data.

BACKGROUND

Security systems can monitor the position of a door, gate, panel, or other access barrier (e.g., collectively “doors”) relative to an associated entryway or structure. Such positional information may provide an indication as to whether the door is positioned to prohibit or allow ingress or egress into/from the associated entryway and/or structure. Certain types of monitoring systems use a reed switch and magnet, such that the reed switch changes between open and closed positions based on the location of the magnet. In some circumstances, a magnet may be mounted or otherwise embedded in a door, while the reed switch is mounted in a door frame, or vice versa. When the door, and thus the magnet embedded therein, comes within close proximity to the reed switch, the reed switch can be actuated. Conversely, the reed switch may be de-activated when the door, and thus the magnet, is positioned/moved away from the reed switch. The activation and de-activation of the reed switch may be monitored by an access control device.

SUMMARY

One embodiment is directed to a unique system, components, and methods for door position sensing with reduction of noise generated by dynamic ferromagnetic components. Other embodiments are directed to apparatuses, systems, devices, hardware, methods, and combinations thereof for door position sensing with reduction of noise generated by dynamic ferromagnetic components.

According to an embodiment, an electronic lock device adapted to be secured to a door may include a first magnetometer, a second magnetometer, a dynamic ferromagnetic component positioned between the first magnetometer and the second magnetometer, a processor, a memory comprising a plurality of instructions stored thereon that, in response to execution by the processor, causes the electronic lock device to read sensor data from the first magnetometer and the second magnetometer, modify the sensor data to generate compensated sensor data that compensates for magnetic noise generated by the dynamic ferromagnetic component, and determine whether the door is in a closed state or an open state based on the compensated sensor data.

In some embodiments, the dynamic ferromagnetic component may be positioned between the first magnetometer and the second magnetometer in a first dimension, and the first magnetometer may be adapted to be positioned between a permanent magnet secured to a door frame and the dynamic ferromagnetic component.

In some embodiments, the dynamic ferromagnetic component may be adapted to rotate relative to the first dimension.

In some embodiments, the dynamic ferromagnetic component may be positioned between the first magnetometer and the second magnetometer along an axis.

In some embodiments, the dynamic ferromagnetic component may include at least one component of a spring cage.

In some embodiments, the plurality of instructions may further cause the electronic lock device to determine calibrated sensor data values based on reference data and the sensor data read from the first magnetometer and the second magnetometer, and to modify the sensor data to generate the compensated sensor data may include to generate the compensated sensor data based on the calibrated sensor data values.

In some embodiments, to determine the calibrated sensor data values may include to determine a difference between the reference data and the corresponding sensor data read from the first magnetometer and the second magnetometer.

In some embodiments, to generate the compensated sensor data may include to determine a difference between the calibrated sensor data values.

In some embodiments, to determine whether the door is in the closed state or the open state may include to determine whether the door is in the closed state or the open stated based on the compensated sensor data and at least one system threshold.

In some embodiments, the at least one system threshold may be based on electromagnetic properties of at least one component of the electronic lock device.

In some embodiments, the plurality of instructions may further cause the electronic lock device to generate an alert message in response to a determination that the door is in the open state.

According to another embodiment, an access control system includes a permanent magnet positioned at a door frame and structured to generate a first magnetic field, and an access control device configured to determine whether the door is in an open state or a closed state based on the first magnetic field sensed by the access control device, wherein the access control device includes a mechanical component having dynamic motion and adapted to generate a second magnetic field as a result of the dynamic motion, a first sensor configured to sense magnetic fields within a vicinity of the first sensor and positioned between the permanent magnet and the mechanical component in a first dimension, and a second sensor configured to sense magnetic fields within a vicinity of the second sensor, and the mechanical component is positioned between the first sensor and the second sensor in the first dimension.

In some embodiments, the first sensor may be a first distance from the permanent magnet in the first dimension, the mechanical component may be a second distance from the permanent magnet in the first dimension, the second sensor may be a third distance from the permanent magnet in the first dimension, the second distance may be greater than the first distance, and the third distance may be greater than the second distance.

In some embodiments, the first sensor, the second sensor, and the mechanical component may be positioned along an axis.

In some embodiments, each of the first sensor and the second sensor may include a magnetometer.

In some embodiments, the mechanical component may be adapted to rotate relative to the first dimension.

In some embodiments, the access control device may include an electronic lock device, and the mechanical component may include a spring cage of the electronic lock device.

In some embodiments, to determine whether the door is in the open state or the closed state based on the first magnetic field sensed by the access control device may include to compensate for the second magnetic field generated by the mechanical component.

In some embodiments, the access control device may include a printed circuit board assembly, and each of the first sensor and the second sensor may be secured to the printed circuit board assembly.

In some embodiments, the access control system may further include a strike plate, and the permanent magnet may be one of secured to or integrally formed with the strike plate.

This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. Further embodiments, forms, features, and aspects of the present application shall become apparent from the description and figures provided herewith.

DETAILED DESCRIPTION

References in the specification to “one embodiment,” “an embodiment,” “an illustrative embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may or may not necessarily include that particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. It should further be appreciated that although reference to a “preferred” component or feature may indicate the desirability of a particular component or feature with respect to an embodiment, the disclosure is not so limiting with respect to other embodiments, which may omit such a component or feature. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. Additionally, it should be appreciated that items included in a list in the form of “at least one of A, B, and C” can mean (A); (B); (C); (A and B); (B and C); (A and C); or (A, B, and C). Similarly, items listed in the form of “at least one of A, B, or C” can mean (A); (B); (C); (A and B); (B and C); (A and C); or (A, B, and C). Further, with respect to the claims, the use of words and phrases such as “a,” “an,” “at least one,” and/or “at least one portion” should not be interpreted so as to be limiting to only one such element unless specifically stated to the contrary, and the use of phrases such as “at least a portion” and/or “a portion” should be interpreted as encompassing both embodiments including only a portion of such element and embodiments including the entirety of such element unless specifically stated to the contrary.

The terms longitudinal, lateral, and transverse may be used to denote motion or spacing along three mutually perpendicular axes, wherein each of the axes defines two opposite directions. The directions defined by each axis may also be referred to as positive and negative directions. Additionally, the descriptions that follow may refer to the directions defined by the axes with specific reference to the orientations illustrated in the figures. For example, the directions may be referred to as distal/proximal, left/right, and/or up/down. It should be appreciated that such terms may be used simply for ease and convenience of description and, therefore, used without limiting the orientation of the system with respect to the environment unless stated expressly to the contrary. For example, descriptions that reference a longitudinal direction may be equally applicable to a vertical direction, a horizontal direction, or an off-axis orientation with respect to the environment. Furthermore, motion or spacing along a direction defined by one of the axes need not preclude motion or spacing along a direction defined by another of the axes. For example, elements described as being “laterally offset” from one another may also be offset in the longitudinal and/or transverse directions, or may be aligned in the longitudinal and/or transverse directions. The terms are therefore not to be construed as further limiting the scope of the subject matter described herein.

It should be appreciated that the use of magnetic sensors in electro-mechanical access control devices (e.g., lock devices), can create a potential environment in which magnetic noise can interfere with a magnetometer's reading (e.g., of a rare earth magnet or other type of permanent magnet positioned in a door frame). For example, the existence of ferromagnetic components in the mechanical subsystems of the access control device (e.g., mechanical subsystems configured to rotate or otherwise have dynamic movements) may induce stray magnetic fields (magnetic noise) due to material properties and manufacturing processes. In turn, these stray field, can render a single magnetometer door position sensing (DPS) system inoperable, which may cause the system to report inaccurate readings and alerts with respect to door position. The techniques described herein allow for the cancellation of such noise within the sensing system.

Referring now toFIG.1, in the illustrative embodiment, a door position sensing system100with reduction of noise generated, for example, by dynamic ferromagnetic components is shown. The illustrative system100depicts an access control device102secured to a door104and a strike plate106secured to a door frame108while the door104is in a closed position such that a latch110of the access control device102extends through an aperture defined in the strike plate106. It should be appreciated that the access control device102is configured to move away from the strike plate106as door104is opened.

The illustrative access control device102is depicted with an outer escutcheon removed, which exposes various circuitry and components within the access control device102. For example, in the illustrative embodiment, the access control device102includes two magnetometers112,114, which are secured to a printed circuit board assembly116of the access control device102(e.g., along with a processor, memory, and/or other circuitry). In the illustrative embodiment, the magnetometers112,114are positioned on either side of a spring cage118along an axis. It should be appreciated that the spring cage118is designed to mechanically couple to a knob, lever, or other adjustment mechanism and also mechanically coupled (e.g., via a linkage) to the latch110, such that when the knob or lever is turned, the spring cage118rotates and causes the latch110to be retracted (e.g., from the aperture in the strike plate106).

As shown, the system100also includes two permanent magnets120,122positioned at the door frame108, which, as magnets, are designed to generate corresponding magnetic fields. In various embodiments, the magnets120,122may be secured to the strike plate106, integrally formed with the strike plate106, or otherwise positioned at or nearby the strike plate106. In the illustrative embodiment, the magnets120,122are equally spaced (e.g., along a y-dimension) relative to the center of the aperture of the strike plate106such that a midpoint between the magnets120,122coincides with the center of the aperture of the strike plate106and the latch110(i.e., when the door104is in the closed position with the latch110extended). As shown, the net magnetic flux124due to the magnets120,122may be represented as a vector positioned in line with the latch110and/or the magnetometers112,114and directed toward the magnetometers112,114(e.g., along an x-axis).

Depending on the particular embodiment, the magnets120,122may or may not be identical in material, shape, size, and/or electromagnetic properties. In some embodiments, one or both the magnets120,122may be embodied as a rare earth magnet or other type of magnet with a magnetic field stronger than Earth's magnetic field. Although the illustrative embodiment includes two permanent magnets120,122, it should be appreciated that a different number of magnets may be used in different embodiments. Further, although the magnetometers112,114are described herein as magnetometers specifically, it should be appreciated that one or both of the magnetometers112,114may be embodied as another type of sensor configured to sense magnetic fields within the vicinity of the respective sensor in other embodiments.

It should be appreciated that the spring cage118may be formed of ferrous material, which can become magnetized during the manufacturing process. Accordingly, when the spring cage118is rotated to retract the latch110(without changing the position of the door104itself), the motion of the magnetized component can alter the magnetic field sensed by the magnetometers112,114(e.g., changing the coordinates characterized as “home” or reference coordinates during calibration). When unaccounted for, the altered “coordinates” from the magnetized parts mimic that of the door104opening, which makes it difficult to distinguish between the door104opening and simply rotation of the spring cage118(and spindle), and the access control device102becomes vulnerable to false reporting of door position. Accordingly, the techniques described herein allow for the access control device102to cancel stray magnetism or magnetic fields from the spring case118(or other dynamic ferromagnetic parts).

It should be appreciated that the access control device102may be embodied as any type of device capable of controlling access through a passageway. For example, in some embodiments, the access control device102may be embodied as an electronic lock device (e.g., a mortise lock, a cylindrical lock, or a tubular lock), gate opener, exit device, or auto-operator of a passageway. Depending on the particular embodiment, the access control device102may include a credential reader or be electrically/communicatively coupled to a credential reader configured to receive access credentials. In some embodiments, the access control device102may be configured to manage access credentials that may be used to gain access through the passageway secured by the access control device102. For example, the access control device102may store updated authorized credentials, whitelists, blacklists, device parameters, and/or other suitable data.

It should be appreciated that the access control device102may be embodied as and/or include components similar to a computing device/system similar to the computing system300described below in reference toFIG.3. For example, in the illustrative embodiment, the access control device102may include a processing device302and a memory306having stored thereon operating logic308for execution by the processing device302for operation of the access control device102(e.g., to receive sensor data from the magnetometers112,114and perform the various functions described herein).

Referring now toFIG.2, in the illustrative embodiment, a system200for sensing a magnetic field with reduction of noise generated by dynamic ferromagnetic components is shown. It should be appreciated that, in some embodiments, the system200ofFIG.2is embodied as a generalized system of the system100ofFIG.1. Accordingly, in some embodiments, the system100ofFIG.1may be at least one embodiment of the system200ofFIG.2. As such, the descriptions of the various components of the system100ofFIG.1may be equally applicable to various embodiments of the system200ofFIG.2, and the descriptions of those components have not been repeated herein in full for brevity of the disclosure.

The illustrative system200depicts an access control device202and a permanent magnet204. Further, the access control device202includes magnetometers206,208and at least one dynamic ferromagnetic component210. The permanent magnet204is structured to generate a magnet signal/field212similar to that described above with respect to the system100ofFIG.1. In some embodiments, the permanent magnet204may be embodied as a rare earth magnet or other type of magnet with a magnetic field stronger than Earth's magnetic field. Although depicted and described in the singular, it should be appreciated that the system200may include multiple permanent magnets204in some embodiments.

The dynamic ferromagnetic component210is configured to generate a magnetic signal/field214in a manner similar to that described above with respect to the system100ofFIG.1. It should be appreciated that the dynamic ferromagnetic component210may be embodied as any type of mechanical component having dynamic motion and adapted to generate a magnetic signal/field214as a result of the dynamic motion (e.g., due to the mechanical component being magnetized). For example, in some embodiments, the dynamic ferromagnetic component210may be embodied as a spring cage or spindle of an electronic lock device.

Although the magnetometers206,208are described herein as magnetometers specifically, it should be appreciated that one or both of the magnetometers206,208may be embodied as another type of sensor configured to sense magnetic fields within the vicinity of the respective sensor in other embodiments.

As shown, in the illustrative embodiment ofFIG.2, the magnetometer206is positioned between the permanent magnet204and the dynamic ferromagnetic component210in a first dimension/direction230, and the dynamic ferromagnetic component210is positioned between the magnetometer206and the magnetometer208in the same dimension/direction230. More specifically, in the illustrative embodiment, the magnetometer206is a distance220from the permanent magnet204(e.g., along an axis), the dynamic ferromagnetic component210is a distance222from the magnetometer206(e.g., along the same axis), and the magnetometer208is a distance224from the dynamic ferromagnetic component210(e.g., along the same axis). Accordingly, it should be appreciated that the magnetometer206is a first distance from the permanent magnet204, the dynamic ferromagnetic component210is a second distance from the permanent magnet204greater than the first distance, and the magnetometer208is a third distance from the permanent magnet204greater than the second distance. It should be further appreciated that, in some embodiments, the dynamic ferromagnetic component210may be configured to rotate or otherwise move transversely relative to the first dimension/direction230(e.g., relative to the above-referenced axis).

Although the permanent magnet204, the magnetometer206, the dynamic ferromagnetic component210, and the magnetometer208are depicted as being along the same axis inFIG.2, it should be appreciated that one or more of the permanent magnet204, the magnetometer206, the dynamic ferromagnetic component210, and the magnetometer208may be offset relative to such an axis in some embodiments.

It should be appreciated that the access control device202may be embodied as and/or include components similar to a computing device/system similar to the computing system300described below in reference toFIG.3. For example, in the illustrative embodiment, the access control device202may include a processing device302and a memory306having stored thereon operating logic308for execution by the processing device302for operation of the access control device202(e.g., to receive sensor data from the magnetometers206,208and perform the various functions described herein).

Referring now toFIG.3, a simplified block diagram of at least one embodiment of a computing system300is shown. The illustrative computing system300depicts at least one embodiment of a computing device/system that may be utilized in connection with the access control device102illustrated inFIG.1and/or the access control device202illustrated inFIG.2. Depending on the particular embodiment, the computing system300may be embodied as an access control device and/or any other computing, processing, and/or communication device capable of performing the functions described herein.

The computing system300includes a processing device302that executes algorithms and/or processes data in accordance with operating logic308, an input/output device304that enables communication between the computing system300and one or more external devices310, and memory306which stores, for example, data received from the external device310via the input/output device304.

The input/output device304allows the computing system300to communicate with the external device310. For example, the input/output device304may include a transceiver, a network adapter, a network card, an interface, one or more communication ports (e.g., a USB port, serial port, parallel port, an analog port, a digital port, VGA, DVI, HDMI, FireWire, CAT 5, or any other type of communication port or interface), and/or other communication circuitry. Communication circuitry may be configured to use any one or more communication technologies (e.g., wireless or wired communications) and associated protocols (e.g., Ethernet, Bluetooth®, Wi-Fi®, WiMAX, Ultra-Wide Band, etc.) to effect such communication depending on the particular computing device300. The input/output device304may include hardware, software, and/or firmware suitable for performing the techniques described herein.

The external device310may be any type of device that allows data to be inputted or outputted from the computing system300. In some embodiments, the external device310may be embodied as a computing device, switch, diagnostic tool, controller, printer, display, alarm, peripheral device (e.g., keyboard, mouse, touch screen display, etc.), and/or any other computing, processing, and/or communication device capable of performing the functions described herein. Furthermore, in some embodiments, it should be appreciated that the external device310may be integrated into the computing system300.

The processing device302may be embodied as any type of processor(s) capable of performing the functions described herein. In particular, the processing device302may be embodied as one or more single or multi-core processors, microcontrollers, or other processor or processing/controlling circuits. For example, in some embodiments, the processing device302may include or be embodied as an arithmetic logic unit (ALU), central processing unit (CPU), digital signal processor (DSP), and/or another suitable processor(s). The processing device302may be a programmable type, a dedicated hardwired state machine, or a combination thereof. Processing devices302with multiple processing units may utilize distributed, pipelined, and/or parallel processing in various embodiments. Further, the processing device302may be dedicated to performance of just the operations described herein, or may be utilized in one or more additional applications. In the illustrative embodiment, the processing device302is of a programmable variety that executes algorithms and/or processes data in accordance with operating logic308as defined by programming instructions (such as software or firmware) stored in memory306. Additionally or alternatively, the operating logic308for processing device302may be at least partially defined by hardwired logic or other hardware. Further, the processing device302may include one or more components of any type suitable to process the signals received from input/output device304or from other components or devices and to provide desired output signals. Such components may include digital circuitry, analog circuitry, or a combination thereof.

The memory306may be of one or more types of non-transitory computer-readable media, such as a solid-state memory, electromagnetic memory, optical memory, or a combination thereof. Furthermore, the memory306may be volatile and/or nonvolatile and, in some embodiments, some or all of the memory306may be of a portable variety, such as a disk, tape, memory stick, cartridge, and/or other suitable portable memory. In operation, the memory306may store various data and software used during operation of the computing device300such as operating systems, applications, programs, libraries, and drivers. It should be appreciated that the memory306may store data that is manipulated by the operating logic308of processing device302, such as, for example, data representative of signals received from and/or sent to the input/output device304in addition to or in lieu of storing programming instructions defining operating logic308. As shown inFIG.3, the memory306may be included with the processing device302and/or coupled to the processing device302depending on the particular embodiment. For example, in some embodiments, the processing device302, the memory306, and/or other components of the computing system300may form a portion of a system-on-a-chip (SoC) and be incorporated on a single integrated circuit chip.

In some embodiments, various components of the computing system300(e.g., the processing device302and the memory306) may be communicatively coupled via an input/output subsystem, which may be embodied as circuitry and/or components to facilitate input/output operations with the processing device302, the memory306, and other components of the computing system300. For example, the input/output subsystem may be embodied as, or otherwise include, memory controller hubs, input/output control hubs, firmware devices, communication links (i.e., point-to-point links, bus links, wires, cables, light guides, printed circuit board traces, etc.) and/or other components and subsystems to facilitate the input/output operations.

The computing system300may include other or additional components, such as those commonly found in a typical computing device (e.g., various input/output devices and/or other components), in other embodiments. It should be further appreciated that one or more of the components of the computing system300described herein may be distributed across multiple computing devices. In other words, the techniques described herein may be employed by a computing system that includes one or more computing devices. Additionally, although only a single processing device302, I/O device304, and memory306are illustratively shown inFIG.3, it should be appreciated that a particular computing system300may include multiple processing devices302, I/O devices304, and/or memories306in other embodiments. Further, in some embodiments, more than one external device310may be in communication with the computing system300.

Referring now toFIG.4, in use, the system100and/or the system200may execute a method400for calibrating a door position sensing system. It should be appreciated that the particular blocks of the method400are illustrated by way of example, and such blocks may be combined or divided, added or removed, and/or reordered in whole or in part depending on the particular embodiment, unless stated to the contrary. Additionally, although the method400may be executed by either the system100or the system200, for simplicity and without loss of generality, the method400is described herein as being executed by the system200. It should be appreciated that the method400may be executed upon new installation of one or more components of the system200(e.g., the access control device202, the permanent magnet204, etc.) and/or may be executed periodically during typical use to update the calibration.

The illustrative method400begins with block402in which the access control device202determines whether the door is in a closed/secure state (e.g., closed with a latch extended into a strike plate). If so, the method400advances to block404in which the access control device202selects one of the magnetometers206,208and reads sensor data from the selected magnetometer206,208(e.g., the magnetometer206, without loss of generality). In block406, the access control device202determines whether a sufficient amount of sensor data has been read from the magnetometer206. For example, in the illustrative embodiment, the access control device202reads/records a sample of ten data points from the magnetometer206. It should be appreciated that the access control device202may sample a different number of data point in other embodiments. The method400returns to block404until a sufficient number of data points has been read/recorded.

If and when the access control device202determines that a sufficient number of data points has been read/recorded, the method400advances to block408in which the access control device202averages the sensor data points. Further, in block410, the access control device202sets the average sensor values as reference data (e.g., “home coordinates”). For example, in some embodiments, the magnetometer206sensor data points <xiMa, yiMa, ziMa>, for i=1 . . . 10, may be averaged and set as reference data according to:

In block412, the access control device202determines whether to calibrate another magnetometer206,208. If so, the method400returns to block402in which the access control device202confirms that the door is still in a closed and secured state and executes the method400as described above. For example, the access control device202may also execute the method400with respect to the magnetometer208. Accordingly, in some embodiments, the magnetometer208sensor data points <xiMb, yiMb, ziMb>, for i=1 . . . 10, may be averaged and set as reference data according to:

〈xrefMb,yrefMb,zrefMb〉=〈11⁢0⁢∑i=11⁢0⁢xiMb,11⁢0⁢∑i=11⁢0⁢yiMb,11⁢0⁢∑i=11⁢0⁢ziMb〉
where Mb references the magnetometer208and xiMb, yiMb, and ziMbare the respective sensor values read from the magnetometer208.

Although the blocks402-412are described in a relatively serial manner, it should be appreciated that various blocks of the method400may be performed in parallel in some embodiments. For example, in some embodiments, the data associated with both of the magnetometers206,208may be calibrated in parallel.

Referring now toFIG.5, in use, the system100and/or the system200may execute a method500for reducing noise generated in a door position sensing system. It should be appreciated that the particular blocks of the method500are illustrated by way of example, and such blocks may be combined or divided, added or removed, and/or reordered in whole or in part depending on the particular embodiment, unless stated to the contrary. Additionally, although the method500may be executed by either the system100or the system200, for simplicity and without loss of generality, the method500is described herein as being executed by the system200. After calibration, it should be appreciated that the access control device202may periodically (or otherwise) execute the method500to determine whether the door has changed from a closed state to an open state (or otherwise determined a change of state).

The illustrative method500begins with block502in which the access control device202reads/samples sensor data from the magnetometers206,208. For example, in some embodiments, the sampled data may be denoted as <xnewMa, ynewMa, znewMa> for data sampled from the magnetometer206and as <xnewMb, ynewMb, znewMb> for data sampled from the magnetometer208.

In block504, the access control device202determines calibrated sensor values for each magnetometer206,208based on the sampled data and the reference data determined during calibration (see, for example, the method400ofFIG.4). In doing so, in block506, the access control device202may determine calibrated sensor values as a difference between the reference data and the sampled data. For example, in some embodiments, the calibrated sensor values (xcalMaand xcalMb) may be determined according to xcalMa=xrefMa−xnewMaand xcalMb=xrefMb−xnewMb.

In block508, the access control device202compensates for noise generated by the dynamic ferromagnetic component210. In doing so, in block510, the access control device202may determine the difference between the calibrated sensor values. For example, in some embodiments, the difference δxmay be determined according to δx=xcalMa−xcalMband may be treated as noise-compensated sensor data.

In block512, the access control device202determines whether the door is in a closed state or an open state based on the noise-compensated sensor data (δx) and a system threshold (γsystem). For example, in some embodiments, the access control device202evaluates whether the expression −τsystem<δx<τsystemis true based on the particular noise-compensated sensor data (δx) and system threshold (τsystem) values. If the noise-compensated sensor data falls within the thresholds, the access control device202determines the door to be in a closed state. Otherwise, the door is determined to be in an open state. In the illustrative embodiment, the system threshold (τsystem) may be determined (e.g., experimentally) based on electromagnetic properties of one or more components of the access control device202and predefined (e.g., in firmware) before execution of the method500.

In block514, the access control device202may record the determined door state. Further, in some embodiments, if the access control device202determines that the door is in an open state, the access control device202may generate an open door alert message in block516. The alert message may take various forms depending on the particular embodiment. For example, in some embodiments, the alert message may be an audible and/or visual message transmitted by the access control device202. In other embodiments, the alert message may be transmitted by the access control device202to one or more remote devices (e.g., via a wireless communication connection).

In block518, the method500is delayed for the sample period (e.g., three seconds or another suitable period of time). If the access control device202determines, in block520, that the sample period has elapsed, the method500returns to block502in which the access control device202samples new sensor data from the magnetometers206,208to again evaluate the state of the door.

Although the blocks502-520are described in a relatively serial manner, it should be appreciated that various blocks of the method500may be performed in parallel in some embodiments.