GB2527095A

GB2527095A - Location-aware thickness gauge

Info

Publication number: GB2527095A
Application number: GB1410428.5A
Authority: GB
Inventors: David George
Original assignee: CYGNUS INSTR Ltd
Current assignee: CYGNUS INSTR Ltd
Priority date: 2014-06-11
Filing date: 2014-06-11
Publication date: 2015-12-16
Also published as: GB201410428D0

Abstract

A thickness gauge 10 comprising a thickness measurement section including means for measuring and outputting the thickness of a substrate (eg wall, 14) in the vicinity of the instrument. The gauge also includes an ultra-high-frequency RFID reader (100, fig 4) adapted to determine and output the location of the instrument by reading an ultra-high-frequency RFID tag in the vicinity of the instrument, and a storage section (70) adapted to store thickness data indicating the thickness of the substrate output from the thickness measurement section in association with RFID location data indicating the corresponding location of the instrument output from the ultra-high-frequency RFID reader. A method for measuring and storing the thickness of a substrate is also disclosed.

Description

LOCATION-AWARE THICKNESS GAUGE

The present invention relates to a thickness gauge able to determine and store the location of a thickness measurement. The invention also relates to a method of measuring the thickness of a substrate and storing the measurement in association with its location.

Thickness gauges are employed in various industries. In oil and gas drilling for example, it is often necessary to check the thickness of the walls of a structure such as a drilling platform on a regular basis to ensure the integrity of the structure. These thickness measurements can be time-consuming, particularly as it is necessary to measure thicknesses at various locations around the structure and to record the location of each thickness measurement for later comparison.

According to a first aspect of the invention, there is provided a thickness gauge comprising: a thickness measurement section including means for measuring and outputting the thickness of a substrate in the vicinity of the instrument; an ultra-high-frequency RFID reader adapted to determine and output the location of the instrument by reading an ultra-high-frequency RFID tag in the vicinity of the instrument; and a storage section adapted to store thickness data indicating the thickness of the substrate output from the thickness measurement section in association with RFID location data indicating the corresponding location of the instrument output from the ultra-high-frequency RFID reader.

Using the thickness gauge of the present invention, thickness measurements are automatically associated with the location at which the measurement was taken. This saves the user the time that would be required to manually enter the location of the measurement and avoids human error in recording the measurement locations. Since an ultra-high-frequency (UHF) RFID tag reader is used in the present invention, reading of the RFID tag identifying the location is more reliable than when using a high-frequency (HF) reader. By using a UHF reader to read an RFID tag at the location, the location can be determined more accurately and reliably than would be possible using a global positioning system (GPS) receiver.

According to a second aspect of the invention, there is provided a method for measuring and storing the thickness of a substrate, the method comprising: measuring the thickness of the substrate at a first location to produce first thickness data; reading a first ultra-high-frequency RFID tag to produce first RFID location data representing the first location; and storing the first thickness data in association with the first RFID location data.

Embodiments of the present invention will now be described by way of further example only and with reference to the accompanying drawings, in which: Fig. 1 is a sectional side view of a thickness gauge according to an embodiment of the invention in contact with a wall to be measured; Fig. 2(a) is a representative waveform of a driving pulse as used in an embodiment of a thickness gauge in accordance with the present invention; Fig. 2(b) is a representative waveform of the response of an ultrasonic transducer to the driving pulse of Fig. 2(a); Fig. 3 is an output waveform of a detector employed in an embodiment of the present invention; and Fig. 4 is a schematic illustration of a thickness gauge according to the present invention.

As shown in Fig. 1, the thickness gauge 10 is placed preferably in direct contact with an outer surface 12 of a front wall 14 of a structure 16, which may be, for example, a leg of an offshore drilling platform. The apparatus 10 comprises a piezoelectric or other ultrasonic transducer 50, which generates mechanical vibrations in response to an incoming electrical driving signal and is preferably placed in mechanical contact with or close to the surface l2so that its vibrating face is parallel with the outer surface 12. Since it is assumed that the structure 16 is underwater, the water itself will fill any interstices between the outer face of the piezoelectric transducer and the surface 12, thereby creating a sufficiently good conduction path between the transducer and the surface 12.

Thus, there is no need to apply a couplant gel between the two surfaces, which would be the case if the conduction medium were air.

The electric driving signal is normally a single very short, high voltage pulse. When the pulse is applied to a piezoelectric transducer, it causes the piezoelectric material to vibrate (or ring) at ultrasonic frequencies and hence emit ultrasound. Fig. 2(a) shows such a short, high voltage pulse and Fig. 2(b) shows the response of an ultrasonic transducer, for example a 2.25 MHz ultrasonic transducer, to the same waveform. In particular, the waveform in Fig. 2(b) may be characterised as a burst of 4 or 5 cycles with a frequency of 2.25 MHz.

Application of the short, high voltage pulse to the transducer causes mechanical vibrations having a waveform as shown in Fig. 2(b) to be conducted through the thickness d of the wall 14 and, when they reach the inner surface 18 of the wall, a proportion of these vibrations carry on into the space beyond the wall. The rest of the burst incident on the inner surface 18 is reflected back toward the outer surface 12. In Fig. 1 the incident burst is shown by the large black arrow 22, the reflected burst is shown by the smaller black arrow 24 and the further propagated burst is shown by the white arrow 28. When the reflected burst 24 reaches the outer surface 12 it, in turn, is reflected back toward the surface 18, and this second reflected burst is itself reflected back toward the surface 12, and so on for a number of reflections, giving rise to a series of oscillations of decreasing amplitude.

Preferably, each burst (see Fig. 2(b)) should be shorter than the propagation time through the wall 14, otherwise reflections back from the surface 18 will start to occur while the original burst 22 is still propagating toward the surface 18. Using short bursts allows the same piezoelectric transducer 50 to be used as the transmitter of the driving pulse and the receiver of the subsequent reflections.

If it is assumed that the material of the wall is steel, the thickness of the wall is 1.5cm and the speed of the ultrasound through steel is approximately 5,920 m/s, then the burst width should be < 2.55 ps (1.5/592000). Hence, assuming 5 cycles per burst, each cycle should be <0.51 r.ls in width. This corresponds to a driving frequency of> 1.96 MHz.

In practice, it has been found that a frequency of around 2.2 MHz gives good results. Note that, if too high a frequency is used, then the attenuation in steel (and in any paint applied to the structure) increases to the point where it may be difficult to reliably measure the peak amplitudes of reflections greater than a certain number; on the other hand, too low a frequency will result in a loss of resolution.

As shown in Fig. 4, in addition to the ultrasonic piezoelectric transducer 50, the thickness gauge preferably comprises a microprocessor (controller) 60, a memory 70, a power supply 80 and an interface 90. The power supply 80 is preferably a battery.

The processor 60 controls the operation of the thickness gauge 10, based on a program stored in the memory 70. The memory 70 may also provide a working memory for the processor 60. In particular, the processor 60 controls the transducer 50 to emit bursts of ultrasonic energy as described above. It should be noted that the driving signal for driving the transducer 50 need not be a sine wave and that a square, ramp and other suitable waveforms may be used.

The processor 60 may comprise any number of active and passive components, including signal generators, filters, op-amps etc as required to carry out its required functions.

S

The processor 60 receives the return signals from the transducer 50 and processes them, as described below, to determine the thickness of the wall. The processor may then communicate the result of the determination via the interface 90.

The interface 90 may also be used to communicate the result of determination via cabling, sonar, radio or any other suitable means, for example to the surface where the apparatus is being used underwater. In addition, the interface 90 can be used to reprogram the apparatus 10 and to retrieve historical information, such as the return signals and/or the results of processing of the return signals and/or the results of previous determinations.

These may all be stored in the memory 70 by the processor 60, and are preferably associated with one another. The interface 90 may also comprise a control panel or at least one operation button or trigger.

It should be noted that separate transducers may be used to generate ultrasound signals and to detect the reflections. However, as discussed above, it is preferable to provide a single piezoelectric transducer 50 to carry out both functions.

The apparatus 10 is first calibrated by positioning it at a location where the thickness of the wall is known. Assuming that a single pulse is used as the driving signal, the apparatus receives the detected signal at the surface 12 and the processor 60 determines the respective timings of the peaks Pi in the detected signal along the time axis in Fig. 3.

In practice, the apparatus 10 is small and lightweight and may be provided with a watertight casing. It may be hand-held by a user. To use the apparatus 10, the user simply places it against the substrate and presses the operation button or trigger. This causes the apparatus 10 to emit one or several bursts of ultrasound energy, depending on how the apparatus 10 has been pre-programmed.

In practice, where several bursts are emitted, the user will need to hold the apparatus against the substrate for less than a second to achieve accurate results.

In the present invention, advantage is taken of the fact that the time interval between successive peaks in the reflected signal detected by the apparatus lOis a measure of the thickness of the wall of the structure. More precisely, and referring again to Fig. 1, the wall thickness d is given by: d = v.At/2 where v is the velocity of the ultrasound through the wall and at is the time between peaks Pi in Fig. 3. Thus, the processor 60 of the present invention calculates the thickness of the wall based on the respective timings of the peaks Pi in the detected signal.

In other words, the thickness gauge works on the pulse-echo principle. The transducer transmits a very short pulse of ultrasound which enters the test piece to be measured.

The transducer then acts as a receiver listening for return echoes, converting them into electrical signals which are processed to produce timing information that can be used to determine the material thickness. There are three distinct modes of operation/measurement that can be used in the invention as follows.

Single Echo Mode uses the time to the first return echo signal to determine thickness.

Echo -Echo Mode uses the time between the first and second return echo signals to determine thickness. This method will ignore any surface coatings.

Multiple Echo Mode: uses the time between at least 3 successive return echo signals to determine thickness and verify the measurement. This method will ignore any surface coatings.

In practice, the minimum thickness that can be measured is double the wave period.

Assuming a 2.25 MHz ultrasound probe is used, this distance can be calculated using d = vt/2, so the maximum thickness of steel is 2 x 440 ns = 880 ns at 5,920 mIs, or 2.6 mm.

Thinning of the wall can occur due to metal corrosion. Consequently, if a structure is monitored on a continuous basis then the onset of corrosion can be detected and remedial action can be taken as a result. The thickness gauge can be applied to the structure by the user for a spot check and the result compared with a result obtained some time before.

The thickness gauge also includes an ultra-high-frequency (UHF) radio-frequency identification (RFID) tag reader 100 having an ultra-high-frequency radio antenna. The tag reader 100 operates by reading an ultra-high-frequency RFID tag attached to the wall or substrate of which the thickness is being measured. The RFID tag contains location data specifying the location of the tag, which is read by the reader 100. Since the reader is only able to read the tag when the reader and hence the thickness gauge are within a small radius of the tag, the location data acquired by the reader from the tag indicates the location of the thickness gauge itself.

Preferably, the thickness gauge includes an active reader 100, which transmits an encoded UHF signal to interrogate the tag. The tag is typically also active. The tag receives the signal from the reader and responds with authentication information for the tag and the location data. The location data is stored in non-volatile memory within the tag.

The reader 100 of the invention communicates with the tag using a radio frequency around 433 MHz or higher. This contrasts with high-frequency (HF) RFID readers for example, which typically use a frequency around 13.5 MHz. The inventors have found that the cost penalty of using a UHF RFID reader in the invention is outweighed by the benefits of higher data speed and range, which allows location data to be recorded more quickly and reliably than by using a HF REID reader.

The REID reader of the invention uses a proprietary UHE reader module that is embedded into the thickness gauge. A custom designed antenna within the module is designed and selected to suit the REID tag size and reading range required for the particular application in which the gauge is used.

At approximately the same time as the UHE RFID tag reader acquires the location data from the tag, the thickness gauge measures the thickness of the wall or substrate. The tag reader outputs the acquired REID location data to the processor and the processor generates a thickness measurement from the signal detected by the transducer 50 as described above. The thickness measurement generated by the processor is stored by the processor in association with the RFID location data output from the tag reader. Eor example, the processor may store a table consisting of thickness measurements and RFID location data, each thickness measurement being associated with a corresponding piece of location data identifying the location at which the measurement was taken. In this way, a record of all thickness measurements taken along with their locations can be kept in the apparatus for later retrieval.

The thickness gauge may also include a global positioning system (GPS) receiver. The GPS receiver is activated at approximately the same time that a thickness measurement is taken and generates a set of coordinates indicating the global location of the thickness gauge, i.e. GPS location data. The GPS location data can be stored in association with the corresponding thickness measurement and RFID location data, so that the table stored in the memory of the thickness gauge contains two indications of the location of each measurement. By using both GPS and the REID tags to provide location data, it can be ensured that the locations of the measurements are reliable and accurate.

The thickness gauge optionally features a wireless transceiver such as a Bluetooth transceiver coupled to the processor. The processor transmits the stored thickness measurements and associated location data to an external device such as a smartphone via the wireless transceiver. The data from the thickness gauge may be exported to an external database in a common delimited file format via Bluetooth, USB link or removable memory card.

The foregoing description has been given by way of example only and it will be appreciated by a person skilled in the art that modifications can be made without departing from the scope of the present invention.

For example, the present invention has been described as using a single processor 60 and a single memory 70. However, it is apparent that processing operations can be split and distributed by multiple processors, which may also be termed controllers. Thus, the device 10 may have a controller for controlling the transducer 50 and a further processor for processing the signal returned from the transducer to determine the thickness.

Where a separate controller and processor are referred to in this specification, including the claims, they may be embodied by a single controller/processor.

Similarly, more than one memory and more than one type of memory can be used.

Preferably, the apparatus 10 comprises a ROM for storing program coding and an EEPROM for storing historical data detected by the apparatus in a non-volatile manner. The memory 70 may also comprise a RAM acting as a working memory for the processor.

Fig. 6 shows the apparatus 10 comprising a power source 80. Preferably power source 80 comprises a battery (which may be rechargeable or replaceable, or may be neither) but the device may also be externally powered. In short, any suitable power supply may be used.

Claims

CLAIMS1. A thickness gauge comprising: a thickness measurement section including means for measuring and outputting the thickness of a substrate in the vicinity of the instrument; an ultra-high-frequency REID reader adapted to determine and output the location of the instrument by reading an ultra-high-frequency REID tag in the vicinity of the instrument; and a storage section adapted to store thickness data indicating the thickness of the substrate output from the thickness measurement section in association with RFID location data indicating the corresponding location of the instrument output from the ultra-high-frequency REID reader.
2. A thickness gauge according to claim 1, wherein the thickness measurement section comprises a piezoelectric transducer.
3. A thickness gauge according to claim 2, wherein the piezoelectric transducer is adapted to generate mechanical vibrations in response to a driving waveform from the thickness gauge and to generate a detection electrical signal in response to mechanical vibrations reflected from the substrate.
4. A thickness gauge according to claim 3, wherein the thickness gauge is adapted to calculate the thickness of the substrate based on the time interval between peaks in the detection electrical signal generated by the piezoelectric transducer.
5. A thickness gauge according to any preceding claim, wherein the thickness measurement section is adapted to measure the thickness using a single-echo technique. ii
6. A thickness gauge according to any of claims ito 4, wherein the thickness measurement section is adapted to measure the thickness using a multiple-echo technique.
7. A thickness gauge according to any of claims ito 4, wherein the thickness measurement section is adapted to measure the thickness using an echo-to-echo technique.
8. A thickness gauge according to any preceding claim, wherein the storage section stores a plurality of thickness data and a plurality of RFID location data, each thickness represented by the thickness data being associated with a corresponding location represented by the RFID location data.
9. A thickness gauge according to any preceding claim, further comprising a global positioning system (GPS) receiver adapted to determine a GPS location of the thickness gauge, wherein the storage section is adapted to store GPS location data indicating the location of the instrument output from the GPS receiver in association with the corresponding thickness data and RFID location data.
10. A thickness gauge according to any preceding claim, wherein the storage section comprises a removable memory card containing the thickness data and the RFID location data.
11. A thickness gauge according to any preceding claim, further comprising a wireless transmitter adapted to transmit the thickness data to an external device in association with the corresponding RFID location data.
12. A method for measuring and storing the thickness of a substrate, the method comprising: measuring the thickness of the substrate at a first location to produce first thickness data; reading a first ultra-high-frequency RFID tag to produce first REID location data representing the first location; and storing the first thickness data in association with the first REID location data.
13. A method according to claim 12, further comprising: measuring the thickness of the substrate at a second location to produce second thickness data; reading a second ultra-high-frequency REID tag to produce second RFID location data representing the second location; and storing the second thickness data in association with the second REID location data.
14. A method according to claim 12 or claim 13, further comprising: determining first GPS location data representing the first location using a GPS receiver; and storing the first GPS location data in association with the first thickness data and the first REID location data.