WO2014177883A1

WO2014177883A1 - Improved rf detection system

Info

Publication number: WO2014177883A1
Application number: PCT/GB2014/051369
Authority: WO
Inventors: Guy Tipton; Tom GOODERHAM
Original assignee: Intertek Group Plc.
Priority date: 2013-05-02
Filing date: 2014-05-02
Publication date: 2014-11-06
Also published as: GB201307977D0; GB2513640A

Abstract

The invention resides in a system configured to monitor the level of a radio frequency (RF) in oil gas and mining operations using explosive devices. A device, removably mountable on a vehicle, has a plurality of antennae, wherein each antenna is configured to receive a range, or band, of RF signals, wherein each antenna corresponds to a different band of RF signals to be monitored. A detector is configured to receive the output from the antennae, and a controller is connected to the detector for scanning and monitoring the output from the antenna. An interface provides an indication of the RF level of the or each RF antenna in each RF band. A control panel, connected to the device, is configured to receive via a communication cable connected to the interface, signals for providing an alarm if the device detects an RF signal that exceeds a predetermined threshold. The invention also resides in a method of monitoring the level of radio frequency (RF) in areas where explosive devices or detonators are being used using the device and system.

Description

IMPROVED RF DETECTION SYSTEM

The invention relates to an improved radio frequency (RF) detection device for determining the presence of hazardous RF signals that could erroneously trigger an explosive device, such as a detonator or some other incendiary product. The invention further relates to a system having such a device, and a method for detecting and/or monitoring RF signals . More specifically, the invention relates to a RF detector for u se in oil, gas or mining applications , such as those involving blasting operations .

RF detectors are often required to have a minimum performance level to detect RF power levels according to a criteria determined by an industrial standard . In oil or gas extraction applications reference is made to document SPE 20635 (Society of Petroleum Engineers 20635 , titled "S afe Perforating Unaffected by Radio and Electric Power, by K.B . Huber) , which includes a formula for determining induced RF power. It is important, however, to have a high degree of accuracy in the region close to the transmitter, or near field.

Known RF detectors in this field provide a basic level of detection, typically monitoring RF signals in a single wide frequency band, and providing an indication of the peak RF power in said band. A problem as sociated with known RF detectors is the limited range of RF detection, and an inability to distinguish and/or measure power received accurately. Current RF modules work over a small frequency range and have limited and un-repeatable functionality. Continual improvements in RF detection seek to increase the safety of operations involving blasting caps . Research papers include: SPE0036637, published 1996 (Unique Electrical Detonator Safety in Explo sive Operations) ; and SPE74718 , published 2002 (S afety Strategies for operating devices in Radio-Frequency Environments) . These papers provide details on the issues of Radio Frequencies and the use of explosives . Information on the safe operating distances for portable devices is known from SLP 20: S afety Guide for the Prevention of Radio Frequency Radiation Hazards in the Use of Commercial Electric Detonators (Blasting Caps) , published in December 201 1 by the Institute of Makers of Explosives .

The last few decades have seen a dramatic increase in the use of RF communications throughout the world; these technologies have found their way into everyday life and into the work site. Typical applications of wireless RF transmitters include: CB radio (used between supply truck and work site users) ; Ham radio (non-commercial amateur radio) ; Marine Radio (Ship to shore) ; AirB and or AirCraft (aviation. Air traffic control) ; Pagers ; and Cellular devices (personal and work use) . The increase of personal RF devices , communications and the supporting infrastructure has increased the likely hood of potentially hazardous RF signals being exposed to products and components such as blasting caps , leading to an increase in the number of accidental detonations .

Known products currently in use in oil, gas and mining applications use a single antenna, meaning that the products is specifically tuned for one area of frequency. Further, the detector itself has no way of determining what frequency caused the alarm. Poor information leads to operator confusion and frustration and, in some cases , to the detector and/or system being turned off, which results in a dangerous working environment.

Another problem is as sociated with the operation of known RF detectors . The average user cannot be expected to understand measurement values and parameters such as logarithm scales , decibels (dB s), frequency (Hz) and a basic power received formula (see the above mentioned SPE 20635 standard) to analyse the potential risk.

Yet another problem as sociated with RF signals is that they can be intermittent - appearing and disappearing quickly. This is exacerbated by the increase in traffic around a work site as sociated with increasingly complex excavation of oil and gas etc .

It is therefore an aim of the present invention to provide an improved RF device, system and method which attempts to negate the abovementioned problems .

According to one aspect, the invention resides in a portable device configured to monitor the level of a radio frequency (RF) for monitoring RF signals in areas where explosive devices are being used, the device having: a plurality of antennae, wherein each antenna is configured to receive a range, or band, of RF signals ; a detector configured to receive the output from the antennae; a controller, connected to the detector for monitoring ; and an interface for providing an indication of the RF level of the or each RF antenna in each RF band.

The device can trigger an alarm if an RF signal that could detonate an explosive device is detected or the power of an RF signal exceeds a threshold limit. The device can be modular, such that the device can be quickly and readily adapted and configured with more or fewer antennae and associated detectors so that the range can be adj usted according to different problems/environments , such as whether local power lines or other activity is a risk.

The antennae can be configured to monitor three frequency bands . The device can have an antennae corresponding to each band of RF signals to be monitored. Three antennae can be provided to cover three frequency bands .

The RF signals received by the or each antenna can be pas sed through filters , wherein each filter is configured to output a different frequency to the detector. A filter can be provided for each antenna. The device can have three filters .

The device can have a detector corresponding to each band of RF signals to be monitored. The detector can output RF signals to an analogue to digital converter (ADC) . The ADC can output to a controller. The controller can measure the power output, peak power, average power and standard deviation of the power over a given time. The output of the or each detectors can be configured to feed in to peak hold amplifiers . The output of each detector can be calibrated .

The output of the or each antenna can be fed directly to an Analogue to Digital Converter (ADC) , and subsequent calibration and/or detection of the signal can be proces sed digitally in the controller.

The device can be configured to scan for RF signals generated by mobile communication devices , such as a cellular or mobile phones . The device can be powered and configured to communicate to another device over a two-wire cable. The devices can be configured in a daisy-chain manner. The plurality of devices can be connected to the control panel, or similar u ser interface. The cable can be a coaxial cable .

The or each antennae can be mounted on a ground plane that is configured to extend horizontally, when placed on a flat area of ground. The or each antennae can be configured to extend perpendicularly from the ground plane . The ground plane can define a footprint of the enclosure of the device .

The device can incorporate a self-leveling device, such as a gimbal, for keeping the ground plane level . The device can be mounted upon a stand. The stand can be up to l m in height. The stand can be adju stable to enable the RF detector to be placed at a height where optimum performance is achieved.

The antennae, detector, controller and interface can be packaged in an enclosure having a sub stantially cylindrical form. Alternatively, the enclosure can be a cuboid, a pyramid or a cone. The maximum height of the enclosure is preferably less than 30cm. The maximum diameter of the enclosure is preferably les s than 20cm.

The enclosure can be configured to store a cable thereon. The cable can be wrapped around the enclosure.

Overall, the invention provides a more accurate, range-specific level of RF detection and/or cellular phone activity. RF signals and their characteristics are distinguishable and the detection accuracy is improved. An operator of a user interface, such as a control panel, connected to the RF device can identify a specific hazardous frequency and, therefore, remove it or deactivate it more quickly, efficiently and safely . The power levels of RF signals in a band can be detected more accurately such that information, such as the maximum power level, as sociated with a specific frequency, or narrow frequency band, can be presented to a user operating a system having the device according to the invention .

Additionally or alternatively to splitting frequencies into bands and monitoring said bands, the device of the invention can operate a Cellular search mode for identifying, for example, mobile phone use. This enables an engineer monitoring the site using the device to search for cellular devices in the working area to ensure that all devices are switched off prior to explosive devices (ED ' s) being used. The detection of cellular devices can include detecting the transmis sion of data, such as digital data or data packets from a device.

The device is contained in a single portable unit such that it is capable of being remotely installed, and configurable, to send data back to an operator located nearby in, for example, a wireline truck operating a drilling operation. The functionality of the device can be implemented on a controller such as an embedded controller. Additionally or alternatively, the device can be provided with a user interface to enable it to function as a stand-alone unit.

Another aspect of the invention relates to a system configured to monitor the level of radio frequency (RF) signals for monitoring RF signals in areas where explosive devices are being used, the system having : a device according to any preceding claim; and a control panel connected to the device and configured to provide an alarm if the device detects an RF signal that exceeds a predetermined threshold . The device can be configured to detect RF signals within a 15m radius of the device. The system and/or device can be adjusted to detect RF signals within 100m of the device .

The control panel can be located in a vehicle, and the device can be located remotely from the vehicle . The device can connect with the control panel via a two-wire cable that carries both power and communication signals . The control panel, or similar u ser interface, can connect with the controller or embedded controller of the RF device.

To be clear, the detection and monitoring functions of the RF detector device can reside in a controller, such as an embedded controller. S aid controller can reside in the RF device . B y performing detection and monitoring calculations within the device the accuracy of the monitoring can be improved because there is no attenuation of the signals and corruption of the data is avoided.

S aid controller may alternatively reside in the control unit of a system. The functions provided by the RF device, such as the monitoring functions or the alarm functions, can be divided between the RF device and the control unit of the system.

The system can have at least three devices such that the system can use a triangulation technique to determine the location of a source of an RF signal. The triangulation can use three or more antennae to determine the location of a source of an RF signal and/or cellular activity. The antennae preferably are the same type or model of antenna such that they have the same performance characteristics .

The invention also relates to a method of monitoring the level of radio frequency (RF) in areas where explosive devices are being used, the method including : receiving RF signals using a plurality of antennae, wherein each antenna is configured to receive a range, or band, of RF signals ; providing the output of the or each antenna to a detector; monitoring the output of the detector against predetermined threshold levels of RF signals ; and indicating on an interface an indication of the RF level of the or each RF antenna in each band. The method can be implemented on a computer. The computer can have a controller configured to run the method. The controller can be an embedded controller.

The invention can reside in the method of proces sing the output of the ADC . Processing the output of the ADC can be performed on the controller, or embedded controller of the RF device . Additionally or alternatively, proces sing of the ADC output can be performed by a control unit of the system. A user interface of the system can be configured to monitor and/or adju st at least one of the accuracy, sensitivity or alarm threshold .

The received RF signals can be filtered and/or calibrated before being monitored to generate an alarm to indicate when an RF signal that could detonate an explosive device is detected or the power of an RF signal exceeds a threshold limit. The invention enables more accurate RF detection . The RF signal being detected can be measured in step s . The steps can be broken down into sections . Each section can cover, logarithmically, a range power levels .

In another aspect, the invention resides in a system configured to monitor the level of a radio frequency (RF) for monitoring RF signals in oil gas and mining operations using explosive devices , the system having :

a device, removably mountable on a vehicle, having : a plurality of antennae, wherein each antenna is configured to receive a range, or band, of RF signals, wherein each antenna corresponds to a different band of RF signals to be monitored; a detector configured to receive the output from the antennae; a controller, connected to the detector for scanning and monitoring the output from the antenna; and an interface for providing an indication of the RF level of the or each RF antenna in each RF band; and a control panel, connected to the device, configured to receive via a communication cable connected to the interface, signals for providing an alarm if the device detects an RF signal that exceeds a predetermined threshold .

The controller can be located on a vehicle, such as a truck having a substantially rectangular footprint, wherein at least four devices are removably attached to the vehicle and wherein a device is located at each of the corner regions of the vehicle. In this way, the system to able to have visibility of high-frequency, such as cellular activity, all around the vehicle thus avoiding any shadow s or blind- spots . It is therefore able to detect the movement of an RF signal from one side of the vehicle to the other with respect to the position of the wellhead, or similar sensitive location.

The system can be configured with two or more devices wherein each device is adapted for detecting different frequency bands . By way of example, a single device with three antennas (for detecting low, medium and high RF bands) can be located at one corner of a vehicle, while three further devices configured for detecting high frequency RF signals (which are susceptible to blind- spots die to line-of- sight transmis sion) are located at each of the other corners of a vehicle.

The controller can be located on a vehicle, such as a truck, and is configured to selectively monitor (i) RF emissions only or (ii) each of the RF emissions , the potential difference between the truck and the wellhead and the impedance of the ground between the truck and the well-head.

The system can be configured such that a record of alarms or warnings can be maintained together with the associated back ground readings leading to the event.

It will be appreciated by tho se skilled in the art that the improved RF device can be used in a wide number of applications in which RF signals can be hazardous . Although the following description refers to RF detection where explosive devices are used, the inventive concept herein can be used for a wide variety of applications in hazardous areas where a RF signal can trigger an explo sion or cau se an electronic device to malfunction.

In another aspect, the invention resides in a method of monitoring the level of radio frequency (RF) in areas where explosive devices or detonators are being used, the method including : providing a system according to any proceeding claim; scanning and monitoring for RF signals , and if an RF signal is detected by the detector communicating the RF level of the or each RF antenna in each RF band to a control panel and providing an alarm if the device detects an RF signal that exceeds a predetermined threshold.

Received RF signals can be filtered and/or calibrated before being monitored to generate an alarm to indicate when an RF signal that could detonate an explosive device is detected or the power of an RF signal exceeds a threshold limit.

In yet another aspect, the invention resides in a wireline vehicle or trailer having a system as according to claim 1 . In yet another aspect, the invention resides in a device, or system having a device, as hereinbefore described and as shown in the Figures .

In order that the invention can be more readily understood, reference will now be made, by way of example, to the drawings in which:

Figure 1 is a schematic diagram of controller having components configured to implement a method according to the invention ;

Figure 2 is a schematic diagram of a device in accordance with the invention;

Figure 3 is a schematic diagram of the components of the device of Figure 2;

Figure 4 is a schematic view of a known RF detection system installed on a wireline trailer close to a wellhead; Figure 5 is a schematic view of the device of Figure 2 located remotely from, and connected to, a wireline trailer close to a wellhead;

Figure 6 is a schematic view of the device of Figure 2 located on a stand and positioned remotely from, and connected to, a wireline trailer close to a wellhead;

Figure 7 is a schematic view of the device of Figure 2 located at a point on a wireline trailer closest to the ground and in the line of sight with wellhead;

Figure 8 is a schematic view of the device of Figure 2 located in a corner region of a wireline truck;

Figure 9 is a schematic view of the device of Figure 2 located in a corner area of a wireline truck, wherein RF detection regions are indicated; and

Figure 10 is a schematic view of the device of Figure 2 located in a corner area of a wireline truck and integrated with a controller to monitor a number of safety thresholds in the region of a derrick.

Referring to Figure 1 , by way of example, a schematic diagram of a controller of a device according to the invention, or of a system comprising the functions of the controller, upon which the invention can be implemented and the general method described herein can be implemented using, at least in part, software operating on a computer system.

The invention can reside in a computer implemented method running on a controller. The controller can be an embedded controller. The embedded controller can be dedicated to monitoring signals received by an RF unit. By way of example, the controller can have the components in Figure 1 , which is an example of a computer system having a device 100. The device 100 includes a bus 102, at least one proces sor 104 , at least one communication port 106, a main memory 108 , a removable storage media 1 10, a read only memory 1 12 and a random acces s memory 1 14. The components of device 100 can be configured acros s two (2) or more controllers , or the components can reside in a single controller. The device can also include a battery 1 16. The port 106 can be complimented by input means 1 1 8 and output connection 120.

The processor 104 can be any such device such as (but not limited to) an Intel(R), AMD(R) or ARM proces sor. The proces sor may be specifically dedicated to the device . The port 106 can be a wired connection, such as an RS -232 connection, or a Bluetooth connection or any such wireles s connection. The port can be configured to communicate on a network such a Local Area Network (LAN) , Wide Area Network (WAN), or any network to which the device 100 connects . The read only memory 1 12 can store instructions for the proces sor 104.

The controller can, be way of example, be configured to communicate via a two-wire power and communication line, wherein the power supply to the device and/or controller and the communications are provided via a two wire connection.

The bus 102 communicably couples the processor 104 with the other memory 1 10, 1 12, 1 14, 108 and port 106, as well as the input and output connections 1 18 , 120. The bus can be a PCI /PCI-X or SCSI based system bus depending on the storage devices used, for example. The removable memory 110 can be any kind of external hard-drives, floppy drives, flash drives, for example. The device and components therein is provided by way of example and does not limit the scope of the invention. The processor 104 can implement the methods described herein.

The processor 104 can be configured to retrieve and/or receive information from a remote server or device. The device can be an input means 14 that is in addition to, or is an alternative, to the input means of the functional area 18.

The device 100 also includes a programmable interface 122, to receive instructions via the bus 102 which may have been input via, for example but not limited to, a touch sensitive device, keyboard, a joystick or transducers These devices can be operable to control a touch-sensitive display module 124.

Components 126, 128, 130, 132 can store instructions and notify the processor which instruction it has received (so that for example, feedback can be given to the user) and enables a user to control or adjust the sensitivity of the RF detection or reset alarms.

Figure 2 shows an RF unit 200 having a base 202 that incorporates a ground plane 204. Mounted upon the ground plane are antennae 206, 208, 210 extending perpendicularly from the ground plane. An electronic module 212, which includes a detector 212 located in the base unit 200. The module 212 is shown located upon the ground plane, and in this configuration the module will be shielded using, by way of example, a Faraday cage, to inhibit any electromagnetic signals from the module being received by the antennae. The module can, additionally or alternatively, be located beneath the ground plane such that it is shielded.

Any electronic circuit preferably has a continuous ground plane on one side with a minimal dielectric thickness. For an FR4 board, this means having four layers to maintain rigidity. Preferably, SMA (SubMiniature version A) connectors are used to connect to the circuit. The unit 200 is enclosed in a housing 214 having a handle 216 for carrying the device by hand. The height 'x' and the width 'y' are typically, respectively, between 25 and 30cm and between 15 and 20cm. By way of example, the housing is cylindrical. The housing can also be shaped to allow a communication cable to be wrapped around the unit for storage purposes. The housing material can be a plastic type material, such as ABS, polypropylene, Nylon, high density polyurethane. The material of the housing is selected and configured to minimise any attenuation of RF signals to be detected.

Figure 3 shows, schematically, the signal path between antennae 206, 208 and 210 and the controller 100. The antennae can be configured to detect one or more of the following bands of RF frequencies: HF band broadcast services 2 - 30 MHz; Low band VHF, 30 MHz to 88 MHz; Broadcast band 88 to 108 MHz; High band VHF 117 -137, 160 MHz maritime to 430 MHz UHF PMR; UHF TV 430 to 860 MHz; and 860 to 2100 MHz cellular/UMTS.

The various bands can be split into 3 main band widths, and Figure 3 shows three antennae by way of example. The output of each antenna is passed through a filter 218. Three filters are shown: a high pass filter 218a configured to allow frequencies over 500MHz to pass; a band-pass filter 218b configured to allow frequencies between 50MHz and 500MHz to pass therethrough; and a low-pass filter 218c, configured to allow frequencies up to 50MHz to pass. These filters determine the frequency bands to be monitored.

The frequency range of each band is described here by way of example, and filter 218c, 218b and 218a may, by way of example, provide for monitoring of a first band of frequencies from 5MHz to 50MHz, a second band of frequencies from 50MHz to 500MHz and a third band of frequencies of 500MHz to roll-off, respectively. Each filter 218 can be configured to correspond to an antenna. In the example shown in Figure 3 antenna 208 is a GSM UMTS type antenna for receiving radio frequencies in the ranges 824 to 960 MHz, and 1710 to 2170MHz, and the filter 218a is configured to allow radio frequencies between 825MHz and 2.2GHz to pass. Antenna 210 is a UHF band antenna for receiving radio frequencies in the range 460MHz to 860MHz, and up to 1.1 GHz and the filter 218b is configured to allow radio frequencies between 460MHz and 1.1GHz to pass. Antenna 212 is a quarter-wavelength citizen-band (CB) antenna (EXL25TNX, unity gain) for receiving radio frequencies in the range 25MHz to 30MHzand the filter 218c is configured to allow radio frequencies between lMHz and 400MHz to pass.

Further frequency band coverage can be provided in accordance with the sensitivity of the environment to uncontrolled detonation of an explosive device, or an electrical discharge generated by RF signals. HF, VHF, UHF communications, base stations for GSM900, DCS 1800 and UMTS at 2.1 GHz can all be considered a threat.

Accordingly, the RF unit can be configured with antennae for detecting RF levels in bands including: MF and HF (15 MHz and below) where there is a threat from high powered SSB/AM HF radio installations;

The output of the filter 218 passes to a detector 220. Three detectors 220a, 220b and 220c are shown corresponding to filters 218a, 218b and 218c, respectively. A detector can be provided for each filter as shown to optimise the performance of a detector for a given frequency band.

The or each detector may have a peak detector 222, although only one peak detector is shown. Peak detectors can be provided to assess a 'pulse' response, wherein the peak detector integrates pulses of all widths, gradually charging up the detector until a threshold is crossed. The peak detector mimics the integration effect of an electro- explosive device, which can occur as heat builds up over time.

Each of the output signals from the detectors can be fed through a calibration circuit 224. The calibration can be integral with the controller 100. The detector can be calibrated based on a practical real-life operating scenario e.g. SLP20 indicates a safe operating distance of 14.3m (47ft) at lwatt for CB radio, hand-held. The detector can be configured to emit an alarm when it detects a signal within a specific band, in this case low band, and the thresholds are based on the distances give in the SLP 20. The user can then interpreted the alarm too mean that within 47ft of the RF detector a CB radio is being operated. The device can be similarly calibrated for the mid and high bands. To be clear, the system is configured to indicate whether there is an RF source within a predetermined range. This can be achieved through calibration.

The output of the detectors is passed through an analogue to digital converter to interface with a controller. The detector resolution can be modelled, by way of example, in Table 1, using a Linear Technology LT5504 RF Log detector. This RF Log detector has a dynamic range of 60dB, although a dynamic range of 40db in the region of -55dB to -15dB (0.6V to 1.4V) is preferable. A 10-bit programmable integral controller (PIC) can provide 1096 resolution steps, which inn provides roughly 27 steps per dB (dB are used as the logarithmic scale yields linear results, rather that measuring power in Watts because it provides non-linear results).

By way of example, the resolution is determined by splitting the 1096 steps into four sections, each section covering a range of the logarithmic scale. Table 1 shows that each section (Spans 1, 2, 3 and 4) has 256 steps of resolution. Span 1 through to Span 4 covers a lmW to 10W range. 256 256 256 256

Span 1 Span 2 Span 3 Span 4 lmW lOmW lOmW lOOmW lOOmW 1W 1W 10W

-55dB -45dB -45dB -35dB -35dB -25dB -25dB -15dB

OdB lOdB lOdB 20dB 20dB 30dB 30dB 40dB

0.5v 0.725V 0.725V 0.950V 0.950V 1.175V 1.175V 1.4v

Table 1

The controller 100 has a main control unit 226, a clean power supply 228 adequately filtered to prevent electromagnetic interference propagating to the power supply of the controller, calibration circuitry 230 and interface modules 232.

The control unit 226 is configured receive the output from each detector. The unit 226 stores threshold limits of the RF power that can be detected before an alarm is triggered. The threshold can be selected by a user, and can include predetermined threshold values.

The functionality of the unit 226 can be adjusted to output a signal, for a display, the measured value in watts for each band being monitored The output to a display can provide the threshold level at which an alarm will be triggered for each band. An over-ride facility is provided to silence and/or reset an alarm.

The threshold level can be adjusted for specific applications. By way of example, a user can select threshold levels required to safely handle lohm or 50ohm blasting caps. The sensitivity and/or threshold of the unit 200 can be set according to the proximity of the unit to the well head, and have predetermined threshold levels for distances of 10m to 15m, 15m to 50m and up to 100m.

Figure 4 illustrates a drilling operation site 300, in which a wireline truck 302 is parked on the ground in the vicinity of a derrick and is connected to a derrick 304 via clamps 306, wherein the derrick is mounted over a wellhead 308. The truck 302 is connected to the derrick via cables 310a and 310b. An interface 312 is located within the truck 302 to enable an operator to monitor and control drilling operations, and to monitor hazards such as RF signals.

In known systems a single antenna 314 is provided and located on the roof of the truck 302. The position of the antenna establishes, with respect to the antenna, an effective ground plane 316. The effective ground plane is determined by the electromagnetic characteristics of the truck that interfere with RF signals received by the antenna, and the height of the truck. The area beneath the ground plane 316 is, effectively, a 'blind-spot' or an area where the antenna 316 cannot detect RF signals, or measure RF signal strength accurately.

Figure 5 is a similar installation to that shown in Figure 4, but alternatively shows an improved RF detection system 400 wherein an improved control unit 402 is located in a truck 302 and connected to a RF unit 200 via a communication cable 404. The communication cable is, by way of example, a two-wire power and communication cable. The cable 404 can be co-axial cable.

By being portably connected to the truck 302, the RF unit 200 can be optimally placed relative to the derrick 304, and enable line-of-sight reception. To be clear, an RF unit located away from the truck 302 serves to inhibit interference and/or attenuation of an RF signal to be detected by the unit 200. Signal reflections and cancellations, created by constructive and deconstructive interference of RF waves are minimised. Moreover, the RF unit 200 is on a similar plane to RF sensitive cables and, therefore, can provide a more representative measurement of the RF signals the cables are subjected to.

A system 400 with an RF unit 200 located directly on the ground may experience signal attenuation due to ground absorption of the RF signal. To overcome this issue a stand 406 can be provided as shown in Figure 6, which can be considered an optimal system 400 configuration. The RF unit 200 can be located upon the stand 406 to reduce the potential effects of ground absorption and the potential effects of signal reflections and any constructive and deconstructive interference of RF waves.

If it is unsuitable to position the RF unit 200 remote from the truck 302 because of the local environment, such as the ground conditions or the risk of the unit being damaged, then the unit can be located on the truck in a position where the effective ground plane 316, determined by the relative height of the base 202 of the unit 200 to the ground, is as low as practical. By way of example, the unit can be mounted on a shelf at approximately the height of the axle of the truck 302, as shown in Figure 7. The RF unit is also located to the rear of the truck and in line-of- sight with the derrick.

For practical reasons, the unit 200 may be located on the corner of a truck 302 or trailer, to inhibit damage to the cable 404, as shown in Figure 8. The system 400 provides a complete monitoring system having a unit 200 with integral detector 220 configured to receive the output from the antennae. The output is scanned and monitored before being communicated to the control unit 402 in the cabin of the truck to provide an indication of the RF level of the or each RF antenna in each RF band. The control panel can provide an alarm if the device detects an RF signal that exceeds a predetermined threshold.

Although not shown, the truck 302 can be configured with a unit 200 at each corner to improve the sensitivity of the detection to improve the ability to locate the source of RF. The system 400 can be configured to operate in numerous modes. Figure 9 illustrates the system 400 configured to monitor for RF signals only. The monitor reel and ground reel are not connected to earth or the derrick. A single unit is shown and configured to detect low and mid-band RF signals within a first region 500 around the unit 200. The controller 402 makes calculations based on free space propagation. A second region 502 is provided indication a zone for high-band RF detection i.e. for cellular detection.

Figure 10 illustrates the system configured for full well-head monitoring between the truck 302 and the derrick 304. The controller 402 is configured to monitor the potential difference between the truck and the wellhead, the impedance of the ground between the truck and the well-head and the RF emissions in the area. By way of example, the thresholds can be configured as: wellhead potential - 0.25V; ground integrity - 25 ohms; low band RF - 1W within 15m or 4W within 25m (omnidirectional); mid band RF - 1W within 15m or 4W within 25m (omnidirectional); and high band RF - 4W within 8 meters (directional). Although not shown, the system of Figure 10 can additionally incorporate atmospheric sensors to determine the risk of a lightning strike occurring in the vicinity of the derrick.

The interface 402 located within the truck 302 can provide a number of support functions to an operator, such as an interface for providing an indication of the RF level of the or each RF antenna in each RF band. A control panel, which can also be located in the truck, and connected to the interface and the unit, is configured to receive via the two-wire cable signals for providing an alarm if the device detects an RF signal that exceeds a predetermined threshold. The control panel is connected to one or more units 200 and can recording back ground levels of RF using an on board or separate data capture device enables RF activity during operations to be analysed and potential near misses can be retrospectively assessed and the effectiveness of mitigation procedures evaluated. The RF unit 200 and the system 400 can have integral self-check functionality to enable an engineer to generate a test signal that triggers an alarm state in the or each band. By way of example, a signal generator generates a known test signal within the controller and injects the signal into the detectors to simulate an alarm state signal. This can be controlled by putting the system/RF unit in a test mode. Additionally or alternatively, a signal generator or known test signal can be attached over the top of the RF unit to simulate an alarm state.

The controller 100 is operable to take into account a number of variables when calculating the RF power level. Variables include: losses associated with antenna; the performance characteristics of each antenna; safe working distances; for each band the lowest matched frequency is used as a constant to calculate the RF power; and information on ADC sample rates and data/signal analysis/conditioning. These variable parameters can be reviewed by a user operating the system.

The system 400 and/or RF unit 200 can incorporate a cellular phone detection mode. In this mode the controller processes the RF signal passes through high pass filter 218a and detector 220a. By way of example, a threshold value will be set by detecting the back ground noise for around 20 seconds by sampling at over 1 KHz and determining a suitable threshold setting. Determining the setting can include averaging and statistical analysis such as measuring the standard deviation. The background noise can be stored and/or displayed to an operator. Once the threshold has been calculated a display will indicate a countdown of, for example, 2 minutes and 20 seconds. If the threshold is not breached then the display will indicate "no cell phones detected". A graphical representation of the noise and threshold level can be displayed to an operator. This test can be repeated continuously to constantly monitor for cell phone use. Testing the background noise enables detection of 3G and 4G activity from the higher bands. The controller 100 of the RF unit can detect page request and the random access burst signals generated by a cell phone - within the Time Division Multiple Access (TDMA) protocol the bursts are around 4.7ms in length for GSM, and longer for 2G to 4G. Preferably, the RF unit has antennae for receiving omnidirectional circular polarisation (so that both linear and horizontal polarized waves are detected). A wideband and omnidirectional discone antenna can be used. Additionally or alternatively, a set of planar spirals can be used, offering broad band, circular polarization.

In practice, the configuration and calibration of the system 400 uses the SLP20 standard as a guide based on the distance of the derrick or wellhead to the receiver. Calibration is not limited to equations based on received power levels. Using the unit 200, including multiple tuned antennas or an antenna array, together with independent detector circuits to detect RF signals within specific bands, provides a low cost means for RF detection. The formula for power received is: Pr = Gr * ERP (24 / (r * Fm)) wherein:

Pr = power received

Gr = gain

ERP = transmitter power

24 = propagation factor

r = distance from transmitter

Fm = frequency

There are a number of factors to consider to calculate the power received, including the distance from the RF transmitter, its frequency and the power. The most important factor, however, is the distance between the RF source and the detonator. With known single antenna solutions it is difficult to accurately apply the power received equation because it will resonate over a specific frequency band that may not match the RF transmitter, thus making subsequent power and distance calculations inaccurate. The unit 200 provides different antenna to more accurately detect band areas and the device 100 is configured to provide accurate detections for a broad range of RF devices.

Implementation and calibration involves selecting appropriate antenna for each RF band to be monitored. Filters are configured and matched to the antenna to provide signals to the module 212. The module can have peak hold detector operational amplifiers. The unit 200 is calibrated for each frequency band by setting the frequency for each band to higher than expected frequency, which is effectively a weaker than expected RF signal for any given band ensuing detection of lower frequencies in each band. The unit is then tested against the SLP 20 (mentioned above).

The present invention has been described above purely by way of example, and modifications can be made within the spirit and scope of the invention, which extends to equivalents of the features described and combinations of one or more features described herein. The invention also consists in any individual features described or implicit herein.

Claims

1 . A system configured to monitor the level of a radio frequency (RF) for monitoring RF signals in oil gas and mining operations using explo sive devices , the system having:

a device, removably mountable on a vehicle, having :

a plurality of antennae, wherein each antenna is configured to receive a range, or band, of RF signals , wherein each antenna corresponds to a different band of RF signals to be monitored;

a detector configured to receive the output from the antennae;

a controller, connected to the detector for scanning and monitoring the output from the antenna; and

an interface for providing an indication of the RF level of the or each

RF antenna in each RF band; and

a control panel, connected to the device, configured to receive via a communication cable connected to the interface, signals for providing an alarm if the device detects an RF signal that exceeds a predetermined threshold .

2. A device according to claim 1 , wherein the antennae are configured to monitor three frequency bands .

3. A device according to any preceding claim, wherein the device has a detector corresponding to each band of RF signals to be monitored.

4. A device according to any preceding claim, wherein the device is powered and configured to communicate to another device and/or the control panel over a two-wire cable.

5. A device according to any preceding claim, wherein the or each antennae are mounted on a ground plane that is configured to extend horizontally, when placed on a flat area of ground .

6. A device according to claim 5 , wherein the or each antennae are configured to extend vertically or perpendicularly from the ground plane.

7. A system according to any preceding claims , wherein the control panel is located in a vehicle or trailer, and the device is located remotely from the vehicle.

8. A system according to any preceding claim, wherein at least three devices are provided such that the system can use a triangulation technique to determine the location of a source of an RF signal.

9. A system according to any preceding claim, wherein the controller is located on a vehicle, such as a truck having a substantially rectangular footprint, and at least four devices are removably attached to the vehicle and wherein a device is located at each of the corner regions of the vehicle.

10. A system according to any preceding claim, wherein the output of the or each detector is connected to a peak hold amplifiers .

1 1. A system according to any preceding claim, wherein the controller is located on a vehicle, such as a truck, and is configured to selectively monitor (i) RF emis sions or (ii) each of the RF emis sions , the potential difference between the truck and the wellhead and the impedance of the ground between the truck and the well-head.

12. A method of monitoring the level of radio frequency (RF) in areas where explosive devices or detonators are being u sed, the method including : providing a system according to any proceeding claim; scanning and monitoring for RF signals , and if an RF signal is detected by the detector communicating the RF level of the or each RF antenna in each RF band to a control panel and providing an alarm if the device detects an RF signal that exceeds a predetermined threshold.

13. A method according to claim 12, wherein received RF signals are filtered and/or calibrated before being monitored to generate an alarm to indicate when an RF signal that could detonate an explosive device is detected or the power of an RF signal exceeds a threshold limit.

14. A wireline vehicle or trailer having a system according to any of claims 1 to 1 1 .