Validating Operation of an Electronic Marker Locator

A locator for locating a buried electromagnetic marker is operable to generate a test signal in order to validate that the locator is operating in accordance with calibration data. The locator comprises a transmission antenna and a first reception antenna. The transmission antenna is configured to generate a first oscillatory magnetic field to couple with an electromagnetic marker and the first reception antenna is configured to receive an oscillatory magnetic field emitted by the electromagnetic marker. In order to validate the operation of the locator, the transmission antenna is configured to generate a test oscillatory magnetic field, and the first reception antenna is configured to receive the test oscillatory magnetic field and thereby generate a first detected test signal.

FIELD OF THE INVENTION

Embodiments of the present invention relate to locators for locating buried electronic markers. In particular, embodiments of the present invention relate to the validation of the operation of locators for locating electronic markers.

BACKGROUND

Buried electronic markers are used to indicate the location of a buried structure or utility. A buried marker is made from a circular coil that is arranged in a resonant circuit and designed to resonate at a specific frequency. An oscillatory electric current may be induced in this circuit by an externally applied pulse or pulses of magnetic flux linking the coil. The oscillatory current in the coil gives rise to an oscillatory magnetic field around the coil. The presence of this oscillatory magnetic field may be detected, allowing the position of the marker to be determined. The axis of the coil in the buried electronic marker is arranged to be oriented vertically so that the location of the buried marker may be found directly beneath the position where the magnitude of the oscillatory magnetic field is detected to be at a maximum. The depth of the electronic marker may be estimated by detecting the signals transmitted from the marker.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention a locator for locating a buried electromagnetic marker has a validation mode in which the operation of a transmission antenna of the locator can be validated against calibration data. The locator comprises: a transmission antenna for generating a first oscillatory magnetic field to couple with an electromagnetic marker; and a first reception antenna for receiving an oscillatory magnetic field emitted by the electromagnetic marker. In order to validate the operation of the transmission antenna, the transmission antenna is configured to generate a test oscillatory magnetic field, and the first reception antenna is configured to receive the test oscillatory magnetic field and thereby generate a first detected test signal. The locator further comprises a first analogue to digital converter configured to generate a first digitised test signal from the first detected test signal, the first digitised test signal is indicative of the test oscillatory magnetic field received by the first reception antenna.

In an embodiment the locator further comprises a memory storing calibration data; and a processor configured to calculate a validation value from the first digitised test signal and determine if the validation value is within predetermined limits of the calibration data. In this embodiment the validation of the locator is carried out on the locator itself.

In an embodiment the locator further comprises a second reception antenna for receiving an oscillatory magnetic field emitted by the electromagnetic marker, the second reception antenna being configured to receive the test oscillatory magnetic field and thereby generate a second detected test signal, and a second analogue to digital converter configured to generate a second digitised test signal from the second detected test signal, the second digitised test signal being indicative of the test oscillatory magnetic field received by the second reception antenna. In this embodiment the signals detected by both of the reception antenna may be used in the validation process.

In an embodiment the locator further comprises: a memory storing calibration data; and a processor configured to calculate a validation value from the first digitised test signal and the second digitised test signal and determine if the validation value is within predetermined limits of the calibration data.

In an embodiment the first oscillatory magnetic field comprises a plurality of pulses having a first pulse width, and the test oscillatory magnetic field comprises a plurality of pulses having a second pulse width, the second pulse width being shorter than the first pulse width.

In an embodiment the first oscillatory magnetic field comprises a plurality of pulses having a first amplitude, and the test oscillatory magnetic field comprises a plurality of pulses having a second amplitude, the second amplitude being smaller than the first amplitude.

In embodiments, the power of the test oscillatory magnetic field is reduced compared to the power of the first oscillatory magnetic field. This avoids the reception antenna becoming saturated by the test oscillatory magnetic field.

In an embodiment the locator further comprises an interface configured to transfer the first digitised test signal to a coupled computing device. In this embodiment the validation is carried out on the coupled computing device.

According to a second aspect of the present invention a method of validating the operation of a locator for locating a buried electromagnetic marker comprises:

controlling a transmission antenna of the locator to generate a test oscillatory magnetic field; controlling a reception antenna of the locator to receive the test oscillatory magnetic field and thereby generate a first detected test signal; calculating a validation value from the first detected test signal; and determining if the validation value is within predetermined limits of calibration data.

In an embodiment the method further comprises generating a certificate if the validation value is within the predetermined limits of the calibration data.

In an embodiment the method further comprises determining an identifier of locator and retrieving the calibration data from a remote database using the identifier of the locator.

In an embodiment the transmission antenna of the locator is configured to generate a first oscillatory magnetic field to couple with an electromagnetic marker and the test oscillatory magnetic field comprises a plurality of pulses having a second pulse width, the second pulse width being shorter than a first pulse width.

In an embodiment the transmission antenna of the locator is configured to generate a first oscillatory magnetic field to couple with an electromagnetic marker and the test oscillatory magnetic field comprises a plurality of pulses having a second amplitude, the second amplitude being smaller than the first amplitude.

According to a third aspect of the present invention a computer readable carrier medium carrying computer readable instructions is provided.

According to a fourth aspect of the present invention a method of validating the operation of a locator for locating a buried electromagnetic marker, the method comprises: generating a test oscillatory magnetic field in a transmission antenna of the locator; receiving the test oscillatory magnetic field in a reception antenna of the locator and thereby generating a first detected test signal; calculating a validation value from the first detected test signal; and determining if the validation value is within predetermined limits of calibration data.

In an embodiment the method further comprises disabling the locator if the validation value is not within the predetermined limits of the calibration data.

DETAILED DESCRIPTION

FIG. 1shows an electronic marker locator100. An electronic marker20is buried below ground level10. The electronic marker20comprises a resonant circuit formed from a coil22and a capacitor. The electronic marker20has a resonant frequency, the value of which is dependent on the capacitance of the capacitor and the inductance of the coil22.

The locator100comprises a transmission antenna110, a first reception antenna120and a second reception antenna130. The locator100has control and processing module140which controls the antennas and processes the signals received from the antennas. The control and processing module140is described in more detail with reference toFIG. 2below.

The locator100has a major axis160. The transmission antenna110, the first reception antenna120and the second reception antenna130are arranged such that their magnetic axes are parallel to the major axis160. As shown inFIG. 1, the locator is used with the major axis160perpendicular to the ground plane10.

The second reception antenna130is separated from the first reception antenna120by a distance s along the major axis160.

In use, the transmission antenna110transmits energy to the electronic marker20as an oscillating magnetic field. The frequency of the oscillating magnetic field is selected to match the resonant frequency of the resonant circuit in the electronic marker20. After the transmission antenna110stops transmitting, the first reception antenna120and the second reception antenna130detect signals received from the electronic marker20. From the ratio R of the signal strengths and the known value s of the separation of the first reception antenna120and the second antenna130the depth d of the electronic marker20is calculated according to the following formula:

The derivation of the above formula is described in United Kingdom Patent Application number 1308550.1, the content of which is incorporated herein by reference.

The depth at which a marker can be located depends on the strength of the transmitted signal. If the transmission antenna does not function within the factory calibration then the depth at which markers can be located may be reduced.

Embodiments of the present invention provide methods of performing a validation test on a locator to check that the transmission antenna is operating within predetermined limits of factory calibration data.

FIG. 2shows the control and processing module140of the electronic marker locator100in more detail. The control and processing module140comprises a controller142, a first analogue to digital converter (ADC)144, a second analogue to digital converter146, a processor150, an output module152, an input module154, and storage156.

The controller142is coupled to the transmit antenna110, the first reception antenna120and the second reception antenna130. The controller142is configured to control the transmit antenna110, the first reception antenna120and the second reception antenna130. The controller142controls the antennas to operate in one of two modes: a marker locate mode and a validation mode.

In the marker locate mode, the controller142controls the transmit antenna110to transmit signals to a buried marker.

In the validation mode, the controller142controls the transmit antenna110to transmit signals directly to the first reception antenna120and the second reception antenna130in order to validate that the transmit antenna110is operating within predetermined limits of factory calibration data.

The storage156stores calibration data158. The calibration data158is generated in the factory when the locator is calibrated.

In a marker locate mode, the controller142is configured to cause the transmit antenna110to transmit an oscillating signal to the electronic marker. When the locator is in the marker locate mode, the controller142is also configured to switch the first reception antenna120and the second reception antenna130to a mode in which they do not produce an output signal in response to a magnetic field. The reception antennas are switched to this mode when the transmission antenna110is transmitting to the electronic marker so that the reception antennas do not directly detect the signal transmitted by the transmission antenna110.

U.S Pat. No. 6,617,856, the content of which is incorporated herein by reference, describes electronic marker locator system and method with one receive antenna. The processing associated with the signals from each of the reception antennas in the electronic marker locator100shown inFIG. 2may be implemented as described in U.S. Pat. No. 6,617,856.

In the marker locate mode, the controller142may be configured to cause the transmission antenna110to transmit a sequence of pulses. While the transmission antenna110transmits the sequence of pulses, the reception antennas are switched to a mode in which they do not detect the pulses transmitted by the transmission antenna110. After the sequence of pulses has been transmitted by the transmission antenna, the controller142switches the first reception antenna120and the second reception antenna130into a mode in which they are sensitive to magnetic signals transmitted from the electronic marker.

The first reception antenna120is connected to the first ADC144. The first reception antenna120is configured to produce a first analogue signal in response to an oscillating magnetic field. The first ADC144is configured to digitise the first analogue signal and produce a first digital signal.

The second reception antenna130is connected to the second ADC146. The second reception antenna120is configured to produce a second analogue signal in response to an oscillating magnetic field. The second ADC146is configured to digitise the second analogue signal and produce a second digital signal.

The processor150is configured to receive the first and second digital signals and to calculate an estimate of the depth of the electronic marker using the ratio of the magnitudes of the magnetic field detected by the first reception antenna120and the second reception antenna130.

The output module152is coupled to a display which provides an indication of the calculated depth as a numeric value.

The input module154allows a user to input a selection of the type of marker to be located. The table below shows the resonant frequencies for markers associated with different types of utility.

The input module154is configured to allow a user to select the frequency of the electronic markers being located.

In an embodiment, the processor and the controller are implemented as a single module.

FIG. 3is a flowchart showing a method carried out by a locator in a marker locate mode.

In step S302a user input indicating the type of electronic markers to be located is received. In step S304, the controller causes the transmission antenna to transmit a pulse or a series of pulses having a frequency corresponding to the selected type of electronic markers. While the transmission antenna is transmitting, the reception antennas are switched to a mode in which they to do not output a signal. During step S304, if there is an electronic marker of the selected type below the locator, an oscillatory current at the resonant frequency of the marker will be induced in the marker.

In step S306, the controller causes the transmission antenna to stop transmitting. In step S308the reception antennas are switched by the controller into a mode in which they can detect magnetic fields. The oscillatory current in the electronic marker decays and the electronic marker produces an oscillating magnetic field at its resonant frequency. The reception antennas detect the magnetic field produced by the electronic marker.

In step S310the ADCs convert the analogue signals produced by the reception antennas into digital signals.

In step S312the processor calculates the depth of the electronic marker from the ratio of the field strength detected by the first receive antenna and the field strength detected by the second receive antenna.

In step S314the output module outputs an indication of the calculated depth.

FIGS. 4ato4cshow the timing of the signals transmitted and received by the transmission antenna and the first and second receive antennas in the marker locate mode.

FIG. 4ashows the signals output by the transmission antenna. The controller controls the transmission antenna to transmit a first series412of pulses at the selected marker frequency. The first series412of pulses includes 22 pulses.

FIG. 4bshows the signals received by the first and second reception antennas. A settling time422is allowed to elapse before the first and second antennas are switched into a receive mode by the controller. Once the settling time422has elapsed, the first and second antennas receive antenna signals424. The received signals are sampled at 1 Msps by the first and second ADCs.

The sampling rate of the ADC may be varied. The sampling rate of the ADC must be sufficient to meet the Nyquist sampling criterion but there is no upper limit other than the sample rate capability of the ADC and the processing capability and power consumption of the DSP versus the system power budget.

FIG. 4cshows the timing of the control of the reception antennas by the controller. The controller switches the antennas into a mode where signals are not detected for a first antenna blanking interval432. The first antenna blanking interval comprises the time that the transmit antenna is transmitting the first series of pulses412and the settling time422. Once the settling time has elapsed, the reception antenna channels are enabled for a first reception time period434.

As can be seen fromFIG. 4c, the first reception time period434extends beyond the time that the first and second antennas receive signals424. During the additional time, the processing of the received signals may take place, and/or signals emitted from buried conductors may be detected and processed as discussed below.

At the end of the first reception time period434, the next cycle begins. The controller causes the transmission antenna to transmit a second series of pulses414. Then after a settling time has elapsed, the reception antennas receive the signals426transmitted by the electronic marker. The controller switches the reception antennas into a blanked mode during a second antenna blanking interval436while the transmission antenna is transmitting and during the settling period. Following the second antenna blanking interval436, the receive antennas are enabled for a second reception time period438.

The repetition rate of the transmit bursts is a parameter that is a trade-off between power consumption from the battery and the signal-to-noise ratio of the detected signal. Given the need to provide “real-time” operation to enable the user to sweep the Locator over an area of interest in search of buried markers, the optimum burst rate is typically between 100 and 1000 per second.

In the embodiment described above in relation toFIGS. 4a-c, the first and second series of pulses each include 22 pulses. The number of pulses in the series may be varied. The preferred range of numbers of pulses is related to the exponential time constant of the build-up of signal current in the marker in response to an applied magnetic field that is alternating at the resonant frequency of the marker. Too few pulses results in a weak return signal from the marker. Beyond a certain number of pulses there is little additional signal to be gained by adding more pulses. Adding more pulses is wasteful of battery power. The optimum number of pulses usually lies in the range from approximately 16 to 36 pulses.

FIG. 5shows a method carried out by the marker in a validation mode. In step S502, an input is received initiating the validation procedure. In step S504, the transmission antenna generates a test signal. The test signal is an oscillatory magnetic field. In step S506, the test signal is received by the reception antennas. Here it is noted that in the validation mode, the test signal is received directly by the reception antennas from the transmission antenna. This means that the antenna blanking described above in relation toFIG. 4cis not required in the validation mode. In embodiments, the power of the test signal transmitted by the transmission antenna may be reduced to avoid saturation of the reception antennas. This is described in more detail with reference toFIGS. 6 and 7below.

In step S508the processor calculates a validation value from the strengths of the detected signals. In step S510the processor determines whether the validation value is within predetermined limits of the calibration data158stored in the storage156.

The results of the validation test are conveyed to the user via the output module152. If the locator fails the validation test a warning may be displayed to the user. Alternatively, or additionally, the locator may be locked to prevent its use until the locator is recalibrated and the validation test is passed.

FIG. 6shows the control of the transmission antenna in an embodiment. A power supply610has a positive terminal (+) and a negative terminal (−). Four switches620630640and650in an H-bridge formation connect the power supply610to the transmission antenna110. The controller controls the switches so that two switches are open and two are closed so that a current flows through the transmission antenna in one direction. As shown inFIG. 6, a first switch620is open and a second switch630is closed so the one connection to the transmission antenna110is connected to the negative terminal of the power supply610. A third switch640is closed and a fourth switch650is open so the second connection to the transmission antenna is connected to the positive terminal of the power supply610. The controller142controls the direction which current flows through the transmission antenna110by selectively opening and closing pairs of the switches.

In one embodiment the switches are MOSFETs, though other transistors or switching devices can be used.

The controller controls the switching of the MOSFETs to provide the required output signal on the transmission antenna. The control signals can be altered to narrow the pulses. This is done by a software change in the controller. The narrowing of the pulse reduces the power transmitted by the transmission antenna.

Another method of reducing the power is by reducing the power supply level.

The control signal can be altered to change the transmit frequency to any marker ball frequency or to other non-marker ball frequencies. In one embodiment only one marker ball frequency will be used.

The required signal can be generated by other means like a half-bridge or a linear amplifier circuit.

FIG. 7ashows the test signal in an embodiment.FIG. 7ashows the pulses710of the test signal and also the pulses720of the locate mode for comparison. The pulses710of the test signal are shown as solid lines and the pulses720of the locate mode are shown in broken lines. As shown inFIG. 7a, the controller controls the transmission antenna to transmit the test signal as a series of pulses710having a narrower pulse width compared to the pulses720in the locate mode. The pulses710of the test signal have an equal height to the pulses720of the locate mode.

FIG. 7bshows the test signal in an alternative embodiment. As shown inFIG. 7b, the controller controls the transmission antenna to transmit pulses730with a lower height than the pulses720in the locate mode. This may be achieved by reducing the level of the power supply.

FIG. 7cshows the signal received by the reception antennas in for either of the signals shown inFIG. 7aandFIG. 7b. As shown inFIG. 7c, the received power740is lower the antenna saturation level750. This means that the reception antennas are not saturated and the power of the transmitted signals can be determined.

In the embodiment described above, the validation test is carried out on the locator. In an alternative embodiment, parts of the validation test are carried out by a computing device such as a personal computer, tablet or smartphone.

FIG. 8shows a locator according to an embodiment in which the validation test is carried out when the locator is coupled to a computing device. The locator800comprises a control and processing module140, a transmission antenna110, a first reception antenna120and a second reception antenna130. The transmission antenna110, the first reception antenna and the second reception antenna are as described above in relation toFIGS. 1 and 2.

The control and processing module140comprises a controller142, a first analogue to digital converter (ADC)144, a second analogue to digital converter146, a processor150, an output module152, an input module154, and an interface module860.

The controller142, the first ADC144, the second ADC146, the output module152and the input module152are as described above in relation toFIG. 2. The processor150processes signals in the locate mode as described above in relation toFIGS. 3 and 4.

The interface module860is a wired or wireless interface which allows the locator800to communicate with a computing device. For example the interface module may be a wired interface such as universal serial bus (USB) interface, or a wireless interface such as a bluetooth or wi-fi interface.

FIG. 9shows a system for validating the operation of the locator ofFIG. 8. The locator800communicates with a personal computer33, or a smartphone35using the interface module860. In this embodiment the locator800communicates over a wireless connection with the personal computer33or the smartphone35, however in other embodiments the connection may be a wired connection.

The personal computer33and the smartphone35are connected via a network37such as the internet to a server39. The server39is coupled to a storage device41which stores calibration data for the locator800. The storage device41may store calibration data for a plurality of locators. The calibration data may be searchable using an identifier, for example a serial number, of the locator. A printer43is coupled to the personal computer33.

FIG. 10shows a method carried out on a computing device such as the personal computer33, or the smartphone35to validate the operation of the locator800.

In step S1002, the computing device controls the locator800to generate the test signal in the transmission antenna110and to receive the test signal in the first reception antenna120and the second reception antenna130. The signals are generated and received as described above in relation toFIGS. 5,6,7a,7band7c. The detected test signals are then digitised by the ADCs in the locator800. The interface unit860of the locator800then sends the digitised detected test signals to the computing device.

The computing device receives the digitised detected test signals in step S1004.

In step S1006, the computing device calculates a validation value from the digitised detected test signals.

In step S1008, the computing device determines whether the validation value is within predetermined limits of the calibration data.

In an embodiment, the computing device retrieves the calibration data from the storage device41coupled to server39using an identifier of the locator800. The computing device may determine the identifier of the locator800from data stored on the locator800.

In an alternative embodiment, the computing device may determine the calibration data from data stored on the locator.

In an embodiment, if the validation data is within the predetermined limits of the calibration data, the personal computer33generates a certificate to show that the locator has passed the validation test. The certificate may be printed by the printer43coupled to the personal computer33.

FIGS. 11aand11bshow a locator1100according to an embodiment. The locator1100is contained within a housing1102. The housing1102comprises a handle1104which is held by a user during use. Adjacent to the handle is a display1106which displays indications to a user, for example the results of the validation test. The housing1102has a section which extends from the handle towards the ground during use. The transmission antenna1108is located at the opposite end of the housing from the handle1104and is foldable away from the housing.

FIG. 11ashows the transmission antenna1108in a folded position andFIG. 11bshows the transmission antenna1108in an unfolded position.

In an embodiment, the validation test described above is carried out in the folded position. It is noted that in the folded position, the transmission antenna will have its axis substantially perpendicular to the axes of the reception antennas which are within the housing, this means that the received power of the test signal will be reduced. As discussed above, this may be advantageous as it avoids saturation of the reception antennas.

In an alternative embodiment, the validation test described above is carried out with the transmission antenna in the unfolded position. In use in the marker locate mode, the transmission antenna is positioned in the unfolded position.

In an embodiment the locator is also operable to locate buried conductors such as cables or pipes by detecting magnetic fields emitted by the buried conductor. The locator may have a dual locate mode in which information on the location of buried electronic markers and information on the location of buried conductors is provided to the user at the same time.

While inFIGS. 11aand11bthe transmission antenna is shown as being foldable, in an alternative embodiment, the transmission antenna may be fixed in position. Such alternative embodiments could use a transmit coil wound around a core of magnetically permeable material, such as a ferrite rod. The core acts to concentrate the magnetic flux, enabling the coil to be made smaller than an air cored antenna of equivalent capability. Such a transmit coil could be concealed inside the locator.

In addition to the validation of the locator as described above, the operation of the reception antennas may be validated using windings around each of the transmission antennas as described in United Kingdom Patent application 0803873.9, the content of which is incorporated herein by reference.

The digital domain signal processing described above may be implemented in FPGA, DSP or microcontroller devices, or split across some combination of the aforementioned devices.

Aspects of the present invention can be implemented in any convenient form, for example using dedicated hardware, or a mixture of dedicated hardware and software for the processing of the signals. The computing devices and processing apparatuses can comprise any suitably programmed apparatuses such as a general purpose computer, personal digital assistant, mobile telephone (such as a WAP or 3G-compliant phone) and so on. Since the processing of the present invention can be implemented as software, each and every aspect of the present invention thus encompasses computer software implementable on a programmable device. The computer software can be provided to the programmable device using any conventional carrier medium. The carrier medium can comprise a transient carrier medium such as an electrical, optical, microwave, acoustic or radio frequency signal carrying the computer code. An example of such a transient medium is a TCP/IP signal carrying computer code over an IP network, such as the Internet. The carrier medium can also comprise a storage medium for storing processor readable code such as a floppy disk, hard disk, CD ROM, magnetic tape device or solid state memory device.

The present invention has been described above purely by way of example. Modifications in detail may be made to the embodiments within the scope of the claims appended hereto.