Tamper detection system

Abstract

A tamper detection system (510) for a utility meter (500) is disclosed. The system includes at least one sensor (515, 520) configured to sense a magnetic field. The system includes a processing circuit (525) coupled to the at least one sensor and configured to generate a pulse for incrementing the pulse counter in response to a level of the at least one signal from the at least one sensor being outside a first threshold range. When the processing circuit determines that the pulse counter is not incremented within the tamper detection interval, the processing circuit determines whether the magnetic field sensed by the at least one sensor has changed beyond a second threshold range based on the level of the at least one signal.

Description

Technical Field

[0001] This disclosure relates to a tamper detection system for utility meters, particularly for utility meters such as gas meters that include a dial-wheel. This disclosure also relates to a method for tamper detection. Background Technology

[0002] Flow-based metering devices can be used to measure the consumption of resources such as gas or water. Such metering devices (which may generally be referred to in the art as utility meters) can be installed in residential, commercial, and / or industrial buildings to measure resource consumption so that utility providers can charge consumers based on the level of resource consumption.

[0003] Such known utility meters may include, for example, rotary or turbine meters, in which measurable rotation of one or more mechanical components can be caused by the flow of fluid through the meter. In some known examples, one or more magnetic field sensors can be implemented to sense the rotation of one or more mechanical components, thereby enabling the deduction of the fluid volume consumed. In some examples, such utility meters may locally store data corresponding to the fluid volume consumed, or such data may be transmitted to a remote system.

[0004] For accurate measurement, any such measurement of the volume of fluid flowing through the meter is essential. Furthermore, since such utility meters can be installed in a large number of buildings (e.g., residential applications), it is also essential that such utility meters be relatively inexpensive to implement and exhibit a high level of reliability.

[0005] It is also desirable to prevent and (where possible) detect any tampering with utility meters. In one example, a consumer might tamper with the meter to reduce and / or disable the measurement of gas or water consumption at their home.

[0006] In some cases, consumers may directly tamper with one or more sensors within a utility meter. In some cases, known steps can be taken to prevent such tampering, such as by making the utility meter's casing difficult to open, and / or by providing components that detect when the casing is opened.

[0007] In some cases, consumers can indirectly tamper with one or more sensors within a utility meter, such as by interfering with signals sensed by one or more sensors. Such tampering may be more difficult to detect and / or prevent.

[0008] Therefore, there is a need for a system to detect any tampering with utility meters that may affect resource consumption. In particular, it is desirable that any such system be relatively inexpensive to implement and highly reliable and accurate.

[0009] In addition, it is essential that any such system exhibits relatively low power consumption, because in some cases the metering portion of such a utility meter may be battery powered.

[0010] Therefore, the purpose of at least one embodiment of at least one aspect of this disclosure is to eliminate or at least mitigate at least one of the aforementioned disadvantages of the prior art. Summary of the Invention

[0011] This disclosure relates to a tamper detection system for utility meters, particularly for gas meters including a rotary dial wheel. This disclosure also relates to a method for tamper detection. According to a first aspect of this disclosure, a tamper detection system for utility meters is provided. The tamper detection system includes at least one sensor configured to sense a magnetic field. The tamper detection system includes processing circuitry coupled to the at least one sensor and configured to generate pulses for incrementing a pulse counter in response to a level of at least one signal from the at least one sensor outside a first threshold range. When the processing circuitry determines that the pulse counter has not incremented within a tamper detection interval, the processing circuitry determines, based on the level of the at least one signal, whether the magnetic field sensed by the at least one sensor has changed beyond a second threshold range.

[0012] Advantageously, further determining whether the magnetic field sensed by at least one sensor has changed beyond a second threshold range can effectively detect tampering caused by a weak external magnet, which might otherwise go undetected.

[0013] Furthermore, the disclosed tamper detection system can help avoid unnecessary tamper detection, thereby helping to reduce the overall power consumption of the tamper detection system.

[0014] The processing circuit can be configured to determine that the magnetic field sensed by at least one sensor has changed beyond a second threshold range by determining the difference between the maximum and minimum levels of at least one signal.

[0015] The processing circuit can be configured to increment an iterative counter when it determines that the magnetic field change sensed by at least one sensor does not exceed a second threshold range.

[0016] The processing circuit can be configured to increase the sampling time when it determines that the magnetic field change sensed by at least one sensor does not exceed a second threshold range. The processing circuit can be configured to increment an iterative counter.

[0017] The processing circuit can be configured to sample at least one signal from at least one sensor after a sampling time when the processing circuit determines that the magnetic field change sensed by at least one sensor does not exceed a second threshold range, and the processing circuit can be configured to increment an iterative counter.

[0018] The processing circuit can be configured to further determine whether the magnetic field sensed by at least one sensor has changed beyond a second threshold range. When the processing circuit determines that the change in the magnetic field sensed by at least one sensor has not exceeded the second threshold range, the processing circuit can be configured to increment an iterative counter.

[0019] The processing circuit can be configured to determine that no tampering event has occurred when the iteration counter reaches a predetermined maximum iteration value.

[0020] The processing circuit can be further configured to increase the sampling time when the processing circuit increments the iteration counter and when the value of the iteration counter has not reached a predetermined maximum iteration value.

[0021] Increasing the sampling time can include doubling the sampling time.

[0022] Advantageously, increasing the sampling time (e.g., the time between samples) can reduce the overall power consumption of the system.

[0023] Between sampling at least one signal level from at least one sensor and determining whether the magnetic field has changed beyond a second threshold range, the processing circuit may be further configured to determine that a tampering event has occurred if the level of the sampled signal is outside a tampering threshold range greater than the second threshold range.

[0024] The processing circuit can be configured such that when the processing circuit has determined that the magnetic field sensed by at least one sensor has changed beyond a second threshold range, the processing circuit is further configured to: set the tampering state to suspicious if the tampering state is not set to suspicious; or increment the suspicious tampering counter if the tampering state is set to suspicious.

[0025] The processing circuitry can be configured to determine that a tampering event has occurred when the suspected tampering counter reaches a predetermined maximum value.

[0026] At least one sensor may include a first sensor and a second sensor. At least one signal may include a first signal from the first sensor and a second signal from the second sensor.

[0027] The processing circuit can be configured to use the first signal to generate pulses for incrementing the pulse counter.

[0028] If the processing circuitry determines that the second signal is outside the tampering threshold range, the second sensor and / or processing circuitry can be configured to generate an interrupt.

[0029] At least one sensor may include at least one of the following: a Hall effect sensor; a tunnel magnetoresistive (TMR) sensor; a giant magnetoresistive (GMR) sensor; an anisotropic magnetoresistive (AMR) sensor; a microelectromechanical system (MEMS) magnetic sensor; and an induction coil.

[0030] According to a second aspect of this disclosure, a utility meter is provided, comprising: a tamper detection system according to any one of the preceding claims; and a dial wheel configured such that rotation of the dial wheel senses a changing magnetic field at at least one sensor.

[0031] Utility meters can be configured to measure the flow of fluids, where the flow of fluids causes the rotation of a dial wheel.

[0032] According to a second aspect of this disclosure, a method for tamper detection is provided. The method includes: configuring processing circuitry coupled to at least one magnetic field sensor to generate pulses when at least one signal from the at least one sensor is outside the first threshold range. The method includes counting the generated pulses.

[0033] The method includes determining that no pulses are counted within the tamper detection interval.

[0034] The method may include sampling at least one signal from at least one sensor. The method includes determining, based on the level of the at least one signal, whether the magnetic field sensed by the at least one sensor has changed beyond a second threshold range.

[0035] The above description of the invention is intended to be exemplary only and not restrictive. This disclosure includes one or more corresponding aspects, embodiments, or features, individually or in various combinations, whether specifically stated (including claimed) in such combination or individually. It should be understood that features defined above according to any aspect of this disclosure or features hereinafter relating to any particular embodiment of this disclosure may be used alone or in combination with any other defined features for any other aspect or embodiment or to form another aspect or embodiment of this disclosure. Attached Figure Description

[0036] These and other aspects of this disclosure will now be described by way of example only with reference to the accompanying drawings, which are as follows:

[0037] Figure 1 An example is depicted of a magnetic field sensor signal from a prior art tamper detection system during normal operation;

[0038] Figure 2An example is depicted of the signal from a magnetic field sensor in a prior art tamper detection system during exposure to a relatively strong external magnet;

[0039] Figure 3a A first example of a signal from a magnetic field sensor in a prior art tamper detection system during exposure to a relatively weak external magnet is depicted;

[0040] Figure 3b A second example is depicted of the signal from a magnetic field sensor in a prior art tamper detection system during exposure to a relatively weak external magnet;

[0041] Figure 4 A flowchart illustrating the operation of a tamper detection system according to embodiments of the present disclosure is provided.

[0042] Figure 5 A utility meter including a tamper detection system is depicted according to embodiments of the present disclosure; and

[0043] Figure 6 A method for tamper detection according to embodiments of the present disclosure. Detailed Implementation

[0044] Figure 1 An example of a signal from a magnetic field sensor in a prior art tamper detection system during normal operation is depicted. The prior art tamper detection system includes a first magnetic field sensor and a second magnetic field sensor. Each sensor may be a Hall effect magnetic field sensor. The signal from the first magnetic field sensor is denoted as HEMS-U1, and the signal from the second magnetic field sensor is denoted as HEMS-U2.

[0045] In a practical implementation of a utility meter, a first sensor and a second sensor may be positioned relatively close to a dial wheel configured to rotate in response to the flow of the metered fluid. The dial wheel may include magnetic components, such as permanent magnets, or neodymium magnets.

[0046] The rotation of the dial wheel relative to the first and second sensors can sense a changing magnetic field, which can be detected by the first and second sensors, such as... Figure 1 As shown.

[0047] In the example, the signal HEMS-U1 from the first sensor can be used to generate pulses. These pulses can be counted to provide an indication of the amount of fluid consumed. In the depicted example, it can be seen that a first threshold range of approximately + / - 3.2 mT defines the pulse signal, denoted as PULSE_CT. That is, when the signal HEMS-U1 exceeds +3.2 mT, the signal HEMS-U1 transitions from low to high, and when the signal HEMS-U1 falls below -3.2 mT, the signal HEMS-U1 transitions from high to low.

[0048] Due to the rotation of the dial wheel relative to the first and second sensors, the magnetic field detected around the first and second sensors can periodically switch from positive to negative, such as from... Figure 1 As can be seen, the change signal HEMS-U1 from the first sensor generates a series of pulses indicated by the signal PULSE_CT, where the amount of pulses indicates the amount of fluid consumed.

[0049] In other words, in some examples, the first sensor (or the processing circuitry coupled to the first sensor) can operate in a "latch mode." In this latch mode, a defined threshold range (e.g., two thresholds) can exist to switch the logic level of the digital output signal. This threshold range can be centered on the zero axis. Once the sensed magnetic field value exceeds the positive threshold of the threshold range, the digital output state (e.g., the signal PULSE_CT) will remain in a specific state until the magnetic field value drops below the negative threshold point. Therefore, this latch requires both a positive and a negative magnetic field to operate. Figure 1 As described, this cycle repeats and can generate digital pulses corresponding to the rotation of the dial wheel. These pulses can then be counted by the controller, indicating the amount of fluid consumed.

[0050] In the example, the signal HEMS-U2 from the second sensor can typically correspond to the signal HEMS-U1 from the first sensor during normal operation, such as... Figure 1 As shown, the time offset between the signal HEMS-U1 from the first sensor and the signal HEMS-U2 from the second sensor may be due to the physical distance between the first and second sensors.

[0051] In this example, the HEMS-U2 signal from the second sensor can be used to detect the presence of any external magnetic field that might interfere with the accuracy of the count. In this example, the HEMS-U2 signal from the second sensor can also be used, additionally or alternatively, to detect the removal or opening of the utility meter's housing. Reference Figures 2 to 3b The use of the HEMS-U2 signal is described in more detail.

[0052] Figure 2 An example is depicted of the signal from a magnetic field sensor in a prior art tamper detection system during exposure to a relatively strong external magnet.

[0053] In the example, due to the proximity of a relatively strong external magnet to the second sensor, the signal HEMS-U2 from the second sensor saturates at approximately -21 mT.

[0054] In the example use, a task to check for tampering can be performed at "tamper check" intervals (e.g., by a processor coupled to the sensor). In the example, such an interval could be in the range of fifteen minutes, although this can be optional.

[0055] At each tampering check interval, the magnetic field values ​​of both signals HEMS-U1 and HEMS-U2 can be checked to determine whether either magnetic field value exceeds or is equal to a magnetic tampering threshold range of ±20mT (e.g., indicating saturation conditions).

[0056] If any signal meets or exceeds the magnetic tampering threshold, further checks can be scheduled in some cases (such as after a time period of 500ms) to confirm whether the signal remains at or above the magnetic tampering threshold. If any signal remains saturated, a magnetic tampering event can be indicated.

[0057] However, under conditions of a relatively weak external magnet (or more generally, a relatively weak external magnetic field), one or both of the signals HEMS-U1 and HEMS-U2 may be unsaturated, or may not be fully saturated. This is explained in the reference below. Figure 3a and 3b Describe, Figure 3a and 3b First and second examples of signals from a magnetic field sensor in a prior art tamper detection system are depicted during exposure to a relatively weak external magnet.

[0058] exist Figure 3a and Figure 3b In both cases, the externally applied magnetic field, caused by the weak external magnet, is only strong enough to partially saturate both the offset signals HEMS-U1 and HEMS-U. Therefore, pulse counting is disabled because, in both examples, signal HEMS-U1 fails to repeatedly cross the first threshold range of approximately + / - 3.2 mT. In this scenario, magnetic tampering is only detected when examining the saturated portion of the magnetic curve; otherwise, it may be undetectable, for example, when exceeding the magnetic tampering threshold range of +- 20 mT.

[0059] Figure 4 A flowchart illustrating the operation of a tamper detection system according to embodiments of the present disclosure is provided. Figure 4 The described tamper detection system can be used in utility meters, such as gas meters or water meters. The tamper detection system may include at least one sensor configured to sense a magnetic field. In some embodiments, the tamper detection system may include two magnetic field sensors, for example, as referenced above. Figures 1 to 3b As stated above.

[0060] One or more sensors may be coupled to processing circuitry (e.g., one or more processors, microcontrollers, etc.), wherein the processing circuitry may be configured to determine whether a pulse counter has not incremented within the tamper detection interval. That is, in operation, at a first determination point 405, it can be determined whether the pulse counter has incremented within the tamper detection interval. In the depicted non-limiting example, the tamper detection interval is set to 1 hour; however, it should be understood that other times may be chosen alternatively.

[0061] If it is determined at the first decision point 405 that the pulse counter has incremented within the tampering detection interval, it can be assumed that no tampering occurred during the tampering detection interval. In this case, the magnetic tampering current state parameter can be reset, and the suspected tampering count parameter can also be reset. The use of the tampering state parameter and the suspected tampering count parameter is described in more detail below. Such parameters can be stored in memory (such as local memory), which can be volatile or non-volatile.

[0062] If it is determined at the first determination point 405 that the pulse counter has not incremented within the tamper detection interval, then the magnetic field value sensed by one or more sensors can be read (e.g., sampled).

[0063] At the second determination point 410, it can be determined whether the sampled signal is outside the magnetic tampering threshold range. The magnetic tampering threshold range can be greater than the second threshold range, which is described in more detail below. Figure 4 In a non-limiting example, and as described in the example above, the magnetic tampering threshold range is ±20 mT. Similarly, it should be understood that in other embodiments, the magnetic tampering threshold range may be greater than or less than ±20 mT.

[0064] If it is determined at the second determination point 410 that the sampled signal is outside the magnetic tampering threshold range, a magnetic tampering event can be indicated. This can indicate the presence of a strong external magnet.

[0065] If it is determined at the second determination point 410 that the sampled signal is not outside the magnetic tampering threshold range, then at the third determination point 415, it can be determined whether the magnetic field sensed by at least one sensor has changed beyond the second threshold range. Figure 4In this context, the second threshold range is referred to as "MF_ChangeThreshold," and for the purposes of non-limiting example, the second threshold range is + / - 2mT. In some examples, it can be determined that the magnetic field sensed by at least one sensor has changed beyond the second threshold range by determining the difference between the maximum and minimum levels of at least one signal.

[0066] If it is determined at the third decision point 415 that the change in the magnetic field sensed by at least one sensor has not exceeded the second threshold range, then at the fourth decision point 420, the iteration counter (denoted as "itercount") can be incremented, and it can be determined whether the value of the iteration counter has reached a predetermined maximum iteration value. Figure 4 In the unrestricted example, the maximum predetermined iteration value is 10.

[0067] If it is determined at the fourth decision point 420 that the value of the iteration counter has reached the predetermined maximum iteration value, it can be indicated that no magnetic tampering event has occurred. In this case, the tampering interval (initially set to 1 hour in this non-limiting example) can be increased, such as to 6 hours.

[0068] If it is determined at the fourth decision point 420 that the value of the iteration counter has not reached the predetermined maximum iteration value, the sampling time can be increased.

[0069] The sampling time can correspond to the time between samples of one or more signals.

[0070] exist Figure 4 In the example, if it is determined at the fourth decision point 420 that the value of the iteration counter has not reached the predetermined maximum iteration value, the sampling time can be doubled.

[0071] In a non-limiting example embodiment, the predetermined maximum iteration value is 12, and the time interval between samples can be 2n seconds, where n is the nth reading, for example, 0, 1, 2...9, 10, 11. Following this method, the magnetic field value can be sampled at seconds 0, 1, 3, 7, 15, 31, 63, 127, 255, 511, 1023, and 2047.

[0072] If it is determined at the third decision point 415 whether the magnetic field sensed by at least one sensor has changed beyond the second threshold range, then it is determined at the fifth decision point 425 whether the aforementioned magnetic tampering current state parameter has been set.

[0073] If it is determined at the fifth decision point 425 that the magnetic tampering current state parameter is not set, then the magnetic tampering current state parameter is set. The set magnetic tampering current state parameter can indicate suspicious tampering. After the tampering interval, the process restarts. Figure 4The process described. That is, after the tampering interval (1 hour in this non-restrictive example), a determination is made at the first decision point 405.

[0074] If it is determined at the fifth decision point 425 that the current state parameter has been magnetically altered, then at the sixth decision point 430, it is determined whether the aforementioned suspected alteration count parameter has reached a predetermined maximum value. Figure 4 In the non-restricted examples, the predetermined maximum value of the suspected tampering count parameter is 3, although in other examples the value may be greater than three or as little as 2.

[0075] If, at the sixth determination point 430, it is determined that the suspected tampering count parameter has not reached the predetermined maximum value, the suspected tampering count parameter is incremented. After the tampering interval, the count restarts. Figure 4 The described process. That is, after the tampering interval (1 hour in this non-restrictive example), the determination at the first decision point 405 can be made again.

[0076] If it is determined at the sixth decision point 430 that the suspected tampering count parameter has reached the predetermined maximum value, a magnetic tampering event can be indicated.

[0077] Figure 5 A utility meter 500 including a tamper detection system 510 is depicted according to an embodiment of the present disclosure. The example tamper detection system includes a first sensor 515 and a second sensor 520. The first sensor 515 and the second sensor 520 are magnetic field sensors. Each of the first sensor 515 and the second sensor 520 may be a Hall effect sensor, a tunneling magnetoresistive (TMR) sensor, a giant magnetoresistive (GMR) sensor, an anisotropic magnetoresistive (AMR) sensor, a microelectromechanical system (MEMS) magnetic sensor, an induction coil, etc.

[0078] Each of the first sensor 515 and the second sensor 520 is coupled to processing circuitry 525. Processing circuitry 525 may include at least one processor, microcontroller, etc. In some other exemplary embodiments, at least a portion of processing circuitry 525 may be physically remote from utility meter 500, for example, coupled to utility meter 500 via a network.

[0079] The first sensor 515 and the second sensor 520 and / or processing circuitry 525 may include an analog front end (e.g., one or more analog-to-digital converters, etc.) for sampling the signals provided by the first sensor 515 and the second sensor 520.

[0080] The processing circuit 525, together with the first sensor 515 and the second sensor 520, can be configured as the reference mentioned above. Figure 4The described tamper detection system operates accordingly. In some other example embodiments, the processing circuitry 525 and / or the second sensor 525 may be configured to generate an interrupt if it is determined that the second signal is outside the tamper threshold range.

[0081] A dial wheel 530 is also depicted. The dial wheel can be configured such that rotation of the dial wheel senses a changing magnetic field at a first sensor 515 and a second sensor 520. For example, the first sensor 515 and the second sensor 520 can be positioned relatively close to the dial wheel 530, wherein the dial wheel 530 is configured to rotate by the flow of a metered fluid. An exemplary dial wheel 530 includes a magnetic component 535, such as a permanent magnet, for sensing a measurable signal at the first sensor 515 and the second sensor 520.

[0082] For illustrative purposes only, the example utility meter 500 also includes a communication module 540. The communication module 540 is communicatively coupled to the processing circuitry 525 and is configured to communicate data to a remote system (e.g., wirelessly or via a wired network). In this example, the communication module 540 may be configured to transmit data corresponding to a tamper detection status.

[0083] at last, Figure 6 A method for tamper detection according to embodiments of the present disclosure is described. In the example, Figure 6 The method can be found in Figure 5 This is implemented on a utility meter 500. In the first step 605, a processing circuit 525 coupled to at least one magnetic field sensor 515, 520 can be configured to generate a pulse when at least one signal from at least one sensor 515, 520 is outside a first threshold range, and to count the generated pulses.

[0084] In the second step, the processing circuit 525 can determine that no pulses are counted within the tamper detection interval.

[0085] In the third step, the processing circuit 525 can determine, based on the level of at least one signal, whether the magnetic field sensed by at least one sensor 515, 520 has changed beyond a second threshold range (e.g., “MF_ChangeThreshold” mentioned above).

[0086] Although this disclosure has been described with reference to specific embodiments as described above, it should be understood that these embodiments are merely illustrative and the claims are not limited to those embodiments. In view of this disclosure, those skilled in the art will be able to make modifications and substitutions, which are considered to fall within the scope of the appended claims. Each feature disclosed or shown in this specification may be incorporated into any embodiment, either alone or in any suitable combination with any other feature disclosed or shown herein.

[0087] List of reference numerals

[0088] 405 First Judgment Point

[0089] 410 Second Judgment Point

[0090] 415 Third Judgment Point

[0091] 420 Fourth Judgment Point

[0092] 425 Fifth Judgment Point

[0093] 430 Sixth Judgment Point

[0094] 500 utility meters

[0095] 510 Tamper Detection System

[0096] 515 First Sensor

[0097] 520 Second Sensor

[0098] 525 processing circuit

[0099] 530 dial wheel

[0100] 535 magnetic components

[0101] 540 communication module

Claims

1. A tamper detection system (510) for a utility meter (500), the system comprising: At least one sensor (515, 520) is configured to sense a magnetic field; as well as A processing circuit (525), coupled to the at least one sensor and configured to generate pulses for incrementing a pulse counter in response to a level of at least one signal from the at least one sensor being outside a first threshold range, When the processing circuit determines that the pulse counter has not incremented within the tamper detection interval, the processing circuit determines, based on the level of the at least one signal, whether the magnetic field sensed by the at least one sensor has changed beyond a second threshold range.

2. The tamper detection system (510) according to claim 1, wherein, The processing circuit (525) is configured to determine, by determining the difference between the maximum and minimum levels of the at least one signal, that the magnetic field sensed by the at least one sensor (515, 520) has changed beyond a second threshold range.

3. The tamper detection system (510) according to claim 1 or 2, wherein, When the processing circuit (525) determines that the change in magnetic field sensed by the at least one sensor (515, 520) does not exceed the second threshold range, the processing circuit is configured to: Incrementing iterative counter; Increase sampling time; The at least one signal from the at least one sensor is sampled after the sampling time; as well as Further determine whether the magnetic field sensed by the at least one sensor has changed beyond the second threshold range.

4. The tamper detection system (510) according to claim 3, wherein, The processing circuit (525) is configured to determine that no tampering event has occurred when the iteration counter reaches a predetermined maximum iteration value.

5. The tamper detection system (510) according to claim 4, wherein, The processing circuit (525) is configured to increase the sampling time when the iteration counter is incremented to a value less than the predetermined maximum iteration value.

6. The tamper detection system (510) according to claim 3, 4 or 5, wherein, Increasing the sampling time includes doubling the sampling time.

7. The tamper detection system (510) according to any one of the preceding claims, wherein, Between sampling at least one signal level from the at least one sensor (515, 520) and determining whether the magnetic field has changed beyond a second threshold range, the processing circuit (525) is further configured to: If the level of the sampled signal is outside the tampering threshold range, a tampering event is determined to have occurred, wherein the tampering threshold range is greater than the second threshold range.

8. The tamper detection system (510) according to any one of the preceding claims, wherein, When the processing circuit (525) has determined that the magnetic field sensed by the at least one sensor (515, 520) has changed beyond a second threshold range, the processing circuit is further configured to: If the tampering status is not set to suspicious, then set the tampering status to suspicious, or If the tampering status is set to suspicious, the suspicious tampering counter is incremented.

9. The tamper detection system (510) according to claim 8, wherein, The processing circuit (525) is configured to determine that a tampering event has occurred when the suspected tampering counter reaches a predetermined maximum value.

10. The tamper detection system (510) according to any one of the preceding claims, wherein: The at least one sensor (515, 520) includes a first sensor (515) and a second sensor (520); and The at least one signal includes a first signal from the first sensor and a second signal from the second sensor.

11. The tamper detection system (510) according to claim 10, when subordinate to claim 7, wherein: The processing circuit (525) is configured to use the first signal to generate pulses for incrementing the pulse counter; as well as The second sensor (525) and / or the processing circuit are configured to generate an interrupt if the processing circuit determines that the second signal is outside the tampering threshold range.

12. The tamper detection system (510) according to any one of the preceding claims, wherein, The at least one sensor (515, 520) includes a Hall effect sensor.

13. A utility meter (500), comprising: The tamper detection system (510) according to any one of the preceding claims; as well as A dial wheel (530) is configured such that rotation of the dial wheel senses a changing magnetic field at at least one sensor (515, 520).

14. The utility meter (500) according to claim 13, configured for measuring the flow of fluid, wherein, The flow of the fluid causes the dial wheel (535) to rotate.

15. A method for tamper detection, the method comprising: A processing circuit (525) coupled to at least one magnetic field sensor (515, 520) is configured to generate pulses when at least one signal from at least one sensor is outside a first threshold range, and to count the generated pulses. It was determined that no pulses were counted within the tamper detection interval; as well as The level of the at least one signal is used to determine whether the magnetic field sensed by the at least one sensor has changed beyond a second threshold range.

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