WO2025214764A1

WO2025214764A1 - A low-power time-domain reflectometry system

Info

Publication number: WO2025214764A1
Application number: PCT/EP2025/058272
Authority: WO
Inventors: Farshad MORADI; Milad ZAMANI; Yasser REZAEIYAN; Yarallah KOOLIVAND; Alireza MOSALMANI; Elham HATAMZADEH; Hossein ESMAILBEYGI
Original assignee: Aarhus Universitet
Current assignee: Aarhus Universitet
Priority date: 2024-04-11
Filing date: 2025-03-26
Publication date: 2025-10-16
Anticipated expiration: 2026-10-11

Abstract

The disclosure regards an electronic time-domain reflectometer configured to conduct time-domain reflectometry measurements and collect time-domain reflectometry data, said time-domain reflectometry circuit comprising a line driver configured for stimulating a transmission line sensor, such as an elongated 2-wire sensor, with an electric stimulation signal, a comparator circuit configured for detecting any change in the amplitude of a reflected signal received from the transmission line sensor in response to the stimulation signal, and a timer circuit configured for measuring the time passed from the stimulation signal is applied to the transmission line sensor until the comparator circuit indicates a change of the amplitude of the reflected signal, wherein the timer circuit comprise an integrator circuit, or a high-speed start-stop counter. The disclosure further relates to a sensor unit and to a system for detecting and localizing leaks in a pipeline.

Description

A low-power time-domain reflectometry system

The present disclosure relates to a novel time-domain reflectometry system and a system for detecting leaks using the same.

Background

Time domain reflectometry (TDR) is a technique used in electronic applications and telecommunications to analyse the characteristics of transmission lines. It operates by sending short pulses to a transmission line and measuring the reflection signals which can indicate impedance mismatches or discontinuities along the transmission line. By analysing the time it takes for these reflection signals to return to the source, TDR can determine the location and nature of faults or irregularities in the line.

The state of the art of TDR tools relates to high-power consumption systems comprising high-speed analog-to-digital converters (DAC), and demand a robust digital setup, resulting in power demanding and expensive instruments. Such TDR tools may continuously conduct measurements on an object, e.g., a transmission line, and they can determine the location of possible damage. Due to their high-energy consumption, TDR systems require to be powered via an external power supply. However, in various applications, it can be challenging or even not possible to continuously power a TDR tool via an external power supply, due to the nature of the application.

For instance, in the task of maintenance of underground pipes, the state of the art involves monitoring of the pipes using TDR systems, which are powered by an external power source. However, maintaining a power cable on each TDR system in an underground pipeline can be a highly costly process.

Summary

One objective of the present disclosure is to provide a solution to the problem of high- energy consuming TDR units for various applications, such as monitoring of underground pipelines. Specifically, the present disclosure relates to an electronic timedomain reflectometer configured to conduct time-domain reflectometry measurements and collect time-domain reflectometry data. The time-domain reflectometry circuit comprises a line driver configured for stimulating a transmission line sensor, such as an elongated 2-wire sensor, with an electric stimulation signal. The time-domain reflectometry circuit further comprises a comparator circuit configured for detecting any change in the amplitude of a reflected signal received from the transmission line sensor in response to the stimulation signal, and a timer circuit configured for measuring the time passed from the stimulation signal is applied to the transmission line sensor until the comparator circuit indicates a change of the amplitude of the reflected signal. The comparator circuit is also written as a window comparator circuit herein. The timer circuit may comprise an integrator circuit or a high-speed start-stop counter.

The integrator circuit may comprise a capacitor and a constant current source, such as a current DAC, wherein the capacitor is configured for being charged by the current source from the point in time when the stimulation signal is applied to the transmission line sensor until the comparator circuit indicates a change of the amplitude of the reflected signal, so that the resulting voltage across the capacitor is a measure of the period of time, during which the capacitor has been charged. The above approach may also be considered as an analogue approach, due to the nature of the components used. For example, the analogue approach could function by linearly charging a depleted capacitor with a fixed current. The charging of the capacitor can occur when the stimulating signal is sent to the transmission line, and the charging of the capacitor can be stopped when the reflected signal is received by the TDR system. Therefore, the ToF, and consequently the position of damage in the transmission line can be obtained by measuring the voltage of the integrator circuit, by knowing the current that was flowing in the integrator circuit, and by knowing the propagation velocity in the transmission line.

In an embodiment, another approach can be utilized to estimate the ToF by utilizing the high-speed start-stop counter. Specifically, the high-speed start-stop counter can be configured for being started at the point in time when the stimulation signal is applied to the transmission line sensor and stopped again when the comparator circuit indicates a change of the amplitude of the reflected signal, so that the resulting number to which the counter has counted is a measure of the period of time, during which the counter has been active. Such an approach can be considered as a digital approach, as it relates to a digital integrator to estimate the ToF. The digital approach can be used complementary with the analogue approach described in the previous paragraph, or it may be exclusively used to estimate the ToF, depending on the type of TDR application. The advantages of using such approaches to estimate the ToF are that the power used to conduct such TDR measurements and locate the position of a leak can be minimized. That is the result of integrating low-power DAC instruments with the TDR measurements. One of the reasons for the lower power consumption of the digital design is that it can also can be operated at lower voltages. Therefore, such a circuit allows the reflectometer to be self-powered, e.g. by the use of thermoelectric devices. The line driver may be an electronic amplifier circuit, configured to drive a load with an adjustable gain. For example, an electric stimulation signal can be generated by the liner driver with the purpose of stimulating a transmission line sensor. The comparator circuit may be used to detect the reflected signal from the transmission line in response to the stimulation signal. When the transmission line is stimulated and the reflection signal is observed, the localized impedance discontinuity can be detected. The observed signal amplitude with respect to the applied signal amplitude will vary depending on whether there is an impedance discontinuity or not. For example, in the presence of an open or short in the transmission line, the signal amplitude may either double or drop to zero.

In the presence of a short circuit or for example leakage in a transmission line, which can cause an impedance discontinuity, a falling edge reflection can be observed. Comparators can effectively detect such rising and falling edges, by employing threshold voltages that trigger when the reflected voltage is larger or lower compared to the threshold voltage. Further details regarding comparators are provided in the detailed description of the present disclosure.

To estimate the exact location of a damage in the transmission line, such as a leak on a waterpipe, a timer circuit is utilized, which is capable of measuring the time passed from when the stimulation signal was generated until the comparator circuit detects the reflected signal. As the velocity of the signal through the transmission line can be known, the exact position of the damage in the transmission line can be estimated.

As known by the person skilled in the art, TDR operates by sending a short electrical pulse into a transmission line, and then by measuring the reflections that occur due to impedance mismatches, faults or other discontinuities along the line, it is possible to pin-point damages in a transmission line. The time difference between sending a stimulation signal and receiving a reflection signal is known as time of flight (ToF). Considering the propagation velocity of the wave through the transmission line, the ToF can be linked a length, where said length can pin-point the position of a damage in the transmission line, e.g. a leak in a water pipe.

The present disclosure further relates to a unit that is integrating the TDR system with a communication unit, with the purpose of transferring data e.g. TDR data to another device, and with the possibility of alerting a user of possible damage in a transmission line. Specifically, the present disclosure relates to a sensor unit comprising a timedomain reflectometer, such as a time-domain reflectometer described in the above sections of the summary, and a communication unit configured to wirelessly receive and transmit data and to communicate with other units external to the sensor unit, such as communication units of similar sensor units and/or a data collection centre. The sensor unit may be powered exclusively by energy harvested by one or more thermoelectric generators, said thermoelectric generators are positioned between two adjacent pipes. Such a communication unit can beneficial, as it can allow the transmission of valuable data from the TDR system to a database center, allowing a user to evaluate the data collected from the TDR unit. For example, if the sensor unit collects reflectometry data that indicate a leak in an underground pipe, such data may be transmitted to the communication unit, which may be then transmitted to another server or database. A user may access that data and determine whether the pipe would need to be serviced, and what would be the optimal timeframe to operate on the pipe. The communication unit may also collect data from a plurality of sensor units, as for example it may be an unmanned aerial vehicle (UAV) which can fly over the sensor units and collect data. Further details regarding the sensor unit are provided in the detailed description of the present disclosure.

The present disclosure can be applied in any kind of transmission lines that may require maintenance. Such transmission lines may be water pipes that carry e.g. cold or warm water in cities, such as district heating pipes. Therefore, the present disclosure relates to a system for detecting and localising leaks in a pipeline comprising at least two pipes, such as an underground pipeline, in particular a district heating pipeline. The system can comprise one or more thermoelectric generators each configured to harvest energy based on the thermoelectric effect from the temperature gradient between two pipes having different temperature or between a pipe and the surroundings, and a plurality of sensor units distributed along the at least two pipes, wherein each sensor unit is powered exclusively by energy harvested by the one or more thermoelectric generators, and wherein each sensor unit is configured to collect time-domain reflectometry data from the pipes.

The sensor units can be the sensor units described in the previous sections. For example, it can be a TDR sensor, which can generate stimulation signals to the transmission lines, and monitor the reflected signals. In the case of a district heating pipeline, or any pipeline, the transmission line may be the pipeline itself. For example, a pipe can be surrounded by an electrical insulating material, such as polyurethane. If a leak occurs, then that electrical insulator can become wet, resulting in a change of the dielectric constant, leading to a change in the characteristic impedance of the transmission line. In an embodiment, the transmission line can be a bi-wire sensor transmission line, where two wires along a pipeline can act as a transmission line sensor.

The thermoelectric generators operate based on the Seebeck effect. For example, a thermoelectric generator can be positioned to be in contact with two pipes, where said pipes have different temperatures. Therefore, by the temperature gradient, it is possible to generate electricity which can be used to power the system for detecting and localising leaks in the pipeline.

In summary, the present disclosure provides an efficient novel solution in time-domain reflectometry measurements, which can consume less power due to its design, and it can be applied in combination with communication units to provide maintenance of various applications, such as underground pipelines.

Description of Drawings

Various embodiments are described hereinafter with reference to the drawings. The drawings are examples of embodiments and are intended to illustrate some of the features of the presently disclosed low-power time-domain reflectometry system, and are not limiting to the presently disclosed systems and devices.

Fig. 1 shows a schematic of an electronic time-domain reflectometer.

Fig. 2 shows a schematic of a number of parallel-coupled sub-drivers.

Fig. 3 shows a schematic of a comparator circuit.

Fig. 4 shows measurements of reflected signal amplitude as a function of time. Fig. 5 shows a band gap reference circuit to generate current references.

Fig. 6 shows an analog implementation of an integrator circuit for estimating the ToF. Fig. 7 shows a schematic of an electronic time-domain reflectometer having a digital implementation of an integrator comprising a start-stop counter for estimating the ToF. Fig. 8 shows a time-domain reflectometer and additional electronics mounted on a printed circuit board.

Figs. 9A and 9B show an example of a thermoelectric device applied in a twin-pipe system with a hot pipe and a cold return pipe.

Fig. 10 A, B shows a schematic of a system comprising an analogue time-domain reflectometer, an energy harvesting device from two pipes, a processing unit, a communication unit, and a hub (in the form of a drone) to collect the data from each sensor node.

Fig. 11 shows an example of implementing a time-domain reflectometer on a twin-pipe system.

Detailed description

In a first aspect, the present disclosure relates to an electronic time-domain reflectometer configured to conduct time-domain reflectometry measurements and collect time-domain reflectometry data, said time-domain reflectometry circuit comprising a line driver configured for stimulating a transmission line sensor, such as an elongated 2-wire sensor, with an electric stimulation signal. The electronic timedomain reflectometer can further comprise a comparator circuit configured for detecting any change in the amplitude of a reflected signal received from the transmission line sensor in response to the stimulation signal, and a timer circuit configured for measuring the time passed from the stimulation signal is applied to the transmission line sensor until the comparator circuit indicates a change of the amplitude of the reflected signal. The timer circuit may comprise an integrator circuit, or a high-speed start-stop counter.

The integrator circuit may comprise a capacitor and a constant current source, such as a current DAC, wherein the capacitor is configured for being charged by the current source from the point in time when the stimulation signal is applied to the transmission line sensor until the comparator circuit indicates a change of the amplitude of the reflected signal, so that the resulting voltage across the capacitor is a measure of the period of time, during which the capacitor has been charged. The high-speed start-stop counter can be configured for being started at the point in time when the stimulation signal is applied to the transmission line sensor and stopped again when the comparator circuit indicates a change of the amplitude of the reflected signal, so that the resulting number to which the counter has counted is a measure of the period of time, during which the counter has been active. In an embodiment, the high-speed counter is clocked by an output signal of a phase locked loop.

One of the advantages provided when using an integrator circuit or a high-speed startstop counter is their energy efficiency in conducting time-domain reflectometry (TDR) measurements. Unlike traditional timer circuits that may require continuous high- frequency clock signals or complex processing, these circuits operate in a more powerefficient manner. The integrator circuit, for instance, relies on a capacitor being charged by a low-power constant current source, such as a current DAC, only during the measurement period, thereby minimizing energy consumption. Similarly, the highspeed start-stop counter remains active only for the duration of the signal propagation and reflection detection, reducing unnecessary power usage. This efficiency can be particularly beneficial for applications requiring low-power operation, enabling the TDR system to function effectively even when powered by energy-harvesting sources, such as thermoelectric generators. Consequently, these circuit implementations open up possibilities for deploying TDR technology in remote or resource-constrained environments where power availability is limited.

Further details regarding the integrator circuit and the high-speed stat-stop counter are disclosed in the sections below.

The time-domain reflectometer can further comprise a band gap reference circuit configured for generating current sources required for other parts of the time-domain reflectometer. For example, the band gap reference circuit can provide current to the timer circuit of the reflectometer, or to other components which can be included. For example, a band gap reference circuit can have a band gap of 605 mV, and it can generate current sources using an external resistor of 605 kohm. In the example shown in Fig. 5, the bang gap reference circuit 500 can draw 15 pA from a 1.2 V power supply. For example, as seen in Fig. 1 , a schematic of an example of an electronic timedomain reflectometer 100 is shown, comprising a line driver 101 and a comparator circuit 102. The line driver may stimulate the transmission line 103 with a source resistance 104, said source resistance can be adjusted to be equal to the impedance Zo of each transmission line that is tested. The stimulation signal generated by the line driver results in a reflection signal from the transmission line, said reflection signal can be detected by the comparator circuit 102. The electronic time-domain reflectometer may also comprise a band gap reference circuit 105 for generating bias current sources, and a test signal generator 106, which can be utilized to mimic a short or open transmission line signal for testing or calibration purposes. For example, it is possible to generate an artificial stimulation signal from the test signal generator, which can be processed by the comparator to verify whether the comparator operates as it should.

The electronic time-domain reflectometer can also comprise a timer circuit, having the purpose of estimating the ToF between a stimulation signal generated and a measured reflected signal, said ToF can be linked to the location of the impedance mismatch in the transmission line. The timer circuit may comprise an integrator circuit, or a highspeed start-stop counter to determine the ToF, where both the integrator circuit and the high-speed start-stop counter are described in the following sections of the detailed description. Note, that the timer circuit or an integrator circuit is not shown in Fig. 1. Further details regarding the timer circuit, the integrator circuits that can be used and the estimation of the ToF are provided in the later sections of the present disclosure.

Line driver

Moreover, the time-domain reflectometer can be configured, such that a source resistance of the line driver is adjustable so that it can be adjusted to be equal to the line impedance Zo of the transmission line. As described above, such a feature can be beneficial as it can allow the reflectometer to be used in different transmission lines having different impedance Zo. In certain application, the impedance of a transmission line may be affected by external parameters, such as humidity or temperature of the environment, and it can therefore be useful to have a source resistance to calibrate the impedance match between the line driver and the transmission line.

In an embodiment the time-domain reflectometer can be configured, such that the line driver comprises a number of parallel-coupled sub-drivers each having a well-specified output conductance, so that the resulting source conductance, and thereby the resulting source resistance, of the line driver can be adjusted by activating different numbers of these parallel sub-drivers. Such a feature can be important, as having a variable source resistance may induce large parasitic capacitance that can increase the rise time of the stimulating signal of the reflectometer. Therefore, using a number of parallel-coupled sub-drivers can be useful, as each sub-driver can have a fixed source conductance. A number of control signals can be used to determine how many subdrivers should be activated to have impedance match with a transmission line. For example, when applying the reflectometer to a first transmission line, a first number of sub-drivers can be activated, while when moving the reflectometer to a second transmission line with a different impedance, a second number of sub-drivers can be activated in order to have impedance match. Moreover, the time-domain reflectometer can be configured such that the line driver comprises a between 8 and 128 sub-drivers, preferably between 16 and 64 sub-drivers, such as 32 sub-drivers. An example of a number of parallel-coupled sub-drivers can be seen in Fig. 2, where 32 sub-drivers 200 are connected in parallel.

Depending on the application and the specifics of each transmission line, a different output conductance for each sub-driver can be used. Hence, the time-domain reflectometer can be configured, such that the output conductance of each of the subdrivers is between 1 mS and 25 mS, preferably between 2 mS and 10 mS, such as 5 mS. In certain situations, it can be advantageous that the output conductance of a subdriver is as low as possible, as that can increase the resolution of the total output conductance. It can also be advantageous that a first number of sub-drivers have a larger number of output conductance compared to a second number of sub-drivers, such that the first number of sub-drivers can be used as a coarse estimate of the total output conductance, and the second number of sub-drivers can be used to fine-tune the total output conductance.

Comparator circuit

The comparator circuit is the core of the TDR process, and it is therefore important that it can measure the reflected signal with accuracy, such that the timer circuit can correctly assess the location of a damage in a transmission line, such as a leak in a pipeline. In an embodiment, the time-domain reflectometer can be configured, such that the window comparator circuit comprises one or more comparators configured for detecting a drop in the amplitude of the reflected signal from an expected amplitude, and the window comparator circuit further comprises one or more comparators configured for detecting a raise in the amplitude of the reflected signal from the expected amplitude. Monitoring such drops or raises in the amplitude of the reflected signal can be important, as it is an indication of impedance mismatch in the transmission line. As seen in Fig. 1 , the window comparator circuit comprises two comparators 107, 108, wherein each of the comparators may be used to detect a drop or a raise in the amplitude of the reflected signal.

For example, Fig. 3 shows a window comparator circuit comprising two comparators 310, 311. Each of the comparators are configured to compare the reflected signal coming either from the transmission line or from a test signal generator. In this example, the two comparators are named as CP1 and CP2 respectively. The input voltage V1 300 can serve as the reference voltage for short circuit detection, set at e.g. 0.45 x VSTM where VSTM is the voltage of the stimulation signal. V2 301 can be set at a voltage larger than V1, such as 50 mV above V1. Initially, before stimulating the transmission line, the reflected signal is zero, which leads to the CP1 and CP2 outputs, said outputs are the S 302 and R 303 inputs of the SR latch 304 being one and zero respectively. The SR latch is also known as Set-Reset latch and it can form the basic building block of all other types of flip-flop circuits. Consequently, the output Q 305 of the SR latch is one, and the output STOP 306 of the D-FF 307 is zero. D-FF, also known as Data Flip-Flop, is an electronic circuit which can store single bits of data, such as zero and one in this example. When the transmission line is stimulated, the transmission line signal reaches STM/2, which is higher than V1 and V2, causing the S and R inputs of the SR latch to become zero and one respectively. Despite the change in the output Q of the SR latch to zero, the STOP output remains zero. However, when the transmission line experiences a short, the reflected signal decreases in amplitude. If the reflected signal lies between V1 and V2, the S and R inputs of the latch maintain the previous state of the latch output. Once the reflected signal drops below V1, the Q output of the latch changes to one, creating a rising edge transition on the clock of the D-FF, thus changing the STOP output to one, which can send a signal to the timer circuit to terminate the ToF measurement. As a result, using the above example it is possible to detect the total time between a stimulation signal is sent to a transmission line, and the reflected signal detected by the comparator circuit which corresponds to a short in the transmission line. The specific circuits for estimating the ToF are described in the later sections of the detailed description. The time-domain reflectometer can be configured, such that the comparator circuit can detect when the amplitude of the reflected signal deviates from an expected amplitude by a first predefined deviation voltage and when the amplitude of the reflected signal deviates from the expected amplitude by a second predefined deviation voltage, the second predefined deviation voltage preferably being twice the first predefined deviation voltage. For example, as seen in Fig. 4, when the transmission line is stimulated and the reflection signal is observed, the localized impedance discontinuity can be detected. Figure 4 shows the amplitude of the reflected signal as a function of time. The observed signal amplitude with respect to the applied signal amplitude will vary depending on the impedance discontinuity. In the presence of an open or short in the transmission line, the signal amplitude may either double 400 or drop to zero 401 respectively. For an open transmission line, a reflection signal will develop an increasing amplitude 402. However, in the presence of a short circuit caused by e.g. a leakage in a pipeline, a decreasing amplitude of the reflection signal amplitude can be recorded 403. The increasing or decreasing amplitude is also known as rising or falling edge respectively. The comparator circuit can detect such amplitude changes, by employing level-triggered comparators. Due to possible signal noise, the reference levels for the comparators can be to at a value ±A V different from VSTM/2, where VSTM represents the amplitude of the stimulator output driving the transmission line matched to the impedance. The value of A can vary depending on the type of application. For example, reference levels of 0.45XVSTM 404 and 0.55XVSTM 405 can be used for detection. As a result, to identify the open and short conditions, two comparators can be utilized, by measuring whether the reflected signal has either increased above a threshold value or decreased below a threshold value respectively. However, as it is important to determine the position of a leak that can cause a short, additional comparators can be utilized.

To identify the open and short conditions, such as the position of a leak that causes a short, two additional comparators can be utilized. As shown in Fig. 4, while the change in amplitude of the stimulation signal occurs at a time instance T 406, the comparators measure a time instance T1 407 instead, resulting in a position error of (T1-T)Vj_ns/2, where Vj_ns denotes the electromagnetic wave’s propagation velocity in the insulating substance. Depending on the parasitic capacitance and line driver characteristics, the signal slope may be faint, leading to significant errors in location estimation. To address this, two additional comparators with reference levels that have ±2AV difference from VSTM 12 can be used, for example, 0.4XVSTM 409 and 0.6XVSTM 410, allowing the determination of time instance T2 408. Taking into account the linear slope of the reflected signal at the transition, the exact instant of the edge, T, can be calculated as follows: T = T1 - (T2 - T1). Effectively, the systematic errors of the TDR system can be disregarded by taking multiple measurements along the slope of the decreasing or increasing reflected signal. Due to the repetitive nature of the phenomena, it is possible to program the reference levels of the comparators, which eliminates the need for extra comparators. As a result, the exact time instance of when the reflection signal changes amplitude can be calculated after two consecutive stimulations.

Furthermore, The time-domain reflectometer can be configured, such that the detection of the deviation of the amplitude of the reflected signal from the expected amplitude by the first deviation voltage and by the second deviation voltage, respectively, is performed using different sets of comparators. As described in the previous paragraph, such a setup is possible, and it can allow the precise estimation of the location of a leak in a transmission line. In addition, the time-domain reflectometer can be configured, such that the detection of the deviation of the amplitude of the reflected signal from the expected amplitude by the first deviation voltage and by the second deviation voltage, respectively, is performed using the same set of comparators in two consecutive stimulations of the transmission line sensor, between which two stimulations the reference levels of the comparators have been adjusted appropriately.

Timer circuits

As described in the previous sections of the present disclosure, different types of timer circuits can be combined with the comparator circuit in order to determine the ToF, and link the ToF to the location of the transmission line that creates a short.

Specifically, the time-domain reflectometer can be configured, such that the timer circuit comprises an integrator circuit, which integrator circuit comprises a capacitor and a constant current source, such as a current DAC, wherein the capacitor is configured for being charged by the current source from the point in time when the stimulation signal is applied to the transmission line sensor until the comparator circuit indicates a change of the amplitude of the reflected signal, so that the resulting voltage across the capacitor is a measure of the period of time, during which the capacitor has been charged.

An example of an integrator circuit is shown in Fig. 6 600. In this example, the integrator circuit comprises a metal-insulator-metal (MIM) capacitor 601 and a current DAC 602 that can output a current between 0.5 pA to 64 pA, with binary weighted steps with 3 control bits. The band gap reference circuit described earlier can be used to set the reference of the DAC on a fixed current value 603. Alternatively, a compensated l/C current source 604 can be used from a calibration circuit. When the stimulation signal is sent to the transmission line, the integration begins its operation by linearly charging a depleted capacitor with a fixed current. The integration stops, when a reflection signal is received. Therefore, the ToF and consequently the position of a possible leak are obtained by measuring the voltage of the integrator and knowing the amount of integrating capacitor/current and propagation velocity.

Moreover, the time-domain reflectometer can be configured, such that the capacitance of the capacitor is between 2 pF and 50 pF, preferably between 5 pF and 25 pF, such as 8 pF. The value of the capacitance can be important, and it can depend on the length of the transmission line. For example, if a transmission line is very long, then a larger capacitance may be preferred, as the integrator circuit may integrate for a longer period of time without being saturated, until the reflected signal is detected by the reflectometer. In addition, the time-domain reflectometer can be configured, such that the constant current from the current source can be adjusted to be between 0.1 pA and 100 pA, preferably between 0.5 pA and 64 pA. Thus, another way of supporting a longer transmission line is to make the output current of the DAC smaller.

Depending on the type of experiment that is conducted, different current values can be used. In an embodiment, the constant current source can be a current DAC with binary weighted steps, wherein the constant current source is a current DAC with between 1 and 5 control bits, such as 3 control bits, for setting the current DAC value.

Furthermore, the integrator may also comprise a thermistor unit comprising a plurality of thermistor temperature sensors. A thermistor is a resistor where its resistance depends on the temperature, making it suitable to measure the temperature of an object. To measure the resistance, it is possible to inject a current through a resistor and measure its voltage, estimating the resistor which can be linked to a temperature. The current source that is used for the integrator can also be used for the thermistor unit.

The present disclosure relates to an additional timer circuit approach which includes a digital integrator. Specifically, the time-domain reflectometer can be configured, such that the timer circuit comprises a high-speed start-stop counter, which is configured for being started at the point in time when the stimulation signal is applied to the transmission line sensor and stopped again when the comparator circuit indicates a change of the amplitude of the reflected signal, so that the resulting number to which the counter has counted is a measure of the period of time, during which the counter has been active. In an embodiment, the high-speed counter is clocked by an output signal of a phase locked loop.

Effectively, the above start-stop counter has the same concept as the integrator described in the previous paragraphs, but the process of starting and stopping the timer is fundamentally different. Fig. 7 shows a time-domain reflectometer comprising a comparator circuit 700 a band gap reference circuit 701 a line driver 702, and a startstop counter 703 comprising a phase locked loop 704 and a digital integrator 705, where the digital integrator comprises a high-speed counter unit 706. The phase locked loop has the function of generating a high speed clock for the high-speed counter. When the stimulation signal is sent from the liner driver to the transmission line, the high-speed counter unit starts to operate, and it stops when the reflection signal is received. Therefore, the ToF can be estimated, and the location of a possible short can be pinpointed in the transmission line.

The time-domain reflectometer can be configured, such that the electronic circuits comprised by the time-domain reflectometer are implemented using discrete electronic components mounted on a printed circuit board or the like. An example of such a printed board where various electronic circuits are printed can be seen in Fig. 8, where a printed circuit comprises a time-domain reflectometer sensor 800, a temperature sensor 801 , a switching regulator 802, and energy harvester circuit 803, a storage device 804 and a microcontroller unit (MCU) 805. Depending on the type of application that the time-domain reflectometer is used, different electronic circuits may be used, such as a thermistor or a communication unit. Moreover, the time-domain reflectometer can be configured, such that the electronic circuits comprised by the time-domain reflectometer are implemented as one or more integrated circuits, for instance using CMOS technology, such as TSMC 65 nm chips.

The time-domain reflectometer can be configured, such that it conducts TDR measurements to locate possible damages, such as a short, in a transmission line periodically, preferably every 6 hours, more preferably every 3 hours, even more preferably every 1 hour, most preferably every 30 minutes.

Sensor unit

The time-domain reflectometer described above can be combined with a communication unit, in order to collect TDR data and transfer such data to another device, with the purpose of analysing the data and/or alerting a user of possible shorts in a transmission line. Specifically the present disclosure relates to a sensor unit comprising a time-domain reflectometer, such as a time-domain reflectometer according to any of the specifications described in the previous sections of the present disclosure, and a communication unit configured to wirelessly receive and transmit data and to communicate with other units external to the sensor unit, such as communication units of similar sensor units and/or a data collection centre. The sensor unit can be powered exclusively by energy harvested by one or more thermoelectric generators, said thermoelectric generators (TEG) are positioned between two adjacent pipes. Since various application may involve areas that are hard to be approached, such as underground pipelines, a wireless communication can be beneficial, allowing the TDR data to be transferred to an external device, where the data can be analyzed and possible maintenance actions can be scheduled.

A thermoelectric generator is a device that converts heat to electricity by using the Seebeck effect. A TEG can be placed in contact to two pipes having different temperature, thereby producing electricity that can power all the functions of the sensor unit, such as the time-domain reflectometer or the communication unit. An example of how a TEG can be positioned is shown in Figs. 9A and 9B where a sensor unit 900 is positioned between a hot pipe 901 and a cold pipe 902. The temperature gradient can be used in order to generate electricity to power e.g. the time-domain reflectometer 903. In an embodiment, the TEG comprises a hot thermal conductor 904 and a cold thermal conductor 905. In this embodiment, the two pipes are surrounded by an insulating Polyvinyl chloride (PVC) jacket 906. The use of a TEG is enabled due to the advantageous design of the time-domain reflectometer, which utilizes an integrator or a high-speed start-stop counter in order to consume as less energy as possible in order to perform TDR measurements.

For example, for a time-domain reflectometer applied on an underground pipeline, when the TDR measurements indicate a short in the pipeline, the data can be transferred using the communication unit to an external unit such as a data collection center. Such data can be interpreted and analysed by a computer and/or a user, who can determine whether the pipeline needs to be serviced. TDR data can also be transmitted in a regular basis, in order to keep record of a pipeline, and monitor its impedance over time. Such a feature can be used in order to predict certain damages in a pipeline, and therefore prevent a short from occurring.

In addition, the sensor unit can be configured, such that the sensor unit further comprises one or more sensor devices configured to collect humidity and/or temperature data. Depending on where a sensor unit is applied, different types of measurements may be relevant. For example, monitoring the temperature and/or the humidity of water pipes can be important, as a change in temperature or humidity may indicate a possible leak of a pipe.

Furthermore, the sensor unit can further comprise one or more capacitors configured to store energy, which is harvested by the one or more thermoelectric generators. Such a feature can be advantageous, as the capacitors can continuously store energy, and that energy can be used when the sensor unit performs a task such as conducting TDR measurements or transmitting data using the communication unit. Such process do not occur continuously, therefore it can be beneficial to store energy using the capacitors in order to use it for these operations on demand.

In an embodiment, the sensor unit can be dimensioned to use less than 500 mW, preferably less than 200 mW, most preferred less than 100 mW during active operation. In addition, the sensor unit can be dimensioned to use less than 1 mW, preferably less than 500 pW, most preferred less than 200 pW in a stand-by mode when no time-domain reflectometry data is collected and no data are received or transmitted. Depending on the type of application, the power consumed by the sensor unit can vary during active operation and during stand-by mode, however the power used is able to be provided by the thermoelectric generator.

The time-domain reflectometer of the sensor unit may be configured according to any one of the embodiments described herein.

System for detecting and localising leaks in a pipeline

The present disclosure further relates to a system for detecting and localising leaks in a pipeline comprising at least two pipes, such as an underground pipeline, in particular a district heating pipeline. The system comprises one or more thermoelectric generators each configured to harvest energy based on the thermoelectric effect from the temperature gradient between two pipes having different temperature or between a pipe and the surroundings, and a plurality of sensor units distributed along the at least two pipes, wherein each sensor unit is powered exclusively by energy harvested by the one or more thermoelectric generators, and wherein each sensor unit is configured to collect time-domain reflectometry data from the pipes. Each of the sensors can be configured according to any of the specifications of the present disclosure.

The system can be configured, such that the at least two pipes are arranged adjacent to one another. Such a configuration enables the installation of an energy harvesting device, such as a thermoelectric generator, which can be placed between the two pipes such that the energy harvesting device is contacting both pipes. As a result, if there is a temperature gradient between the pipes, the thermoelectric generator can generate electricity, which can then be used for various tasks, such as performing timedomain reflectometry measurements.

Furthermore, the system can be further configured, such that the time-domain reflectometry data are collected by a given sensor unit using an elongated 2-wire transmission line sensor, which sensor is arranged along the pipes of the pipeline in one or both longitudinal directions thereof from the respective sensor unit, preferably within an insulation material, in which the pipes are also enclosed. For example, instead of using the pipes as the transmission lines, it is also possible to use elongated wires that are in contact with the pipes, and transmit signals through the elongated wires. If leak occurs in a pipe, then the elongated wires would also become wet, changing their impedance and therefore allowing the system to locate the position of the leak. Moreover, the system can be configured, such that the insulating material preferably has a relative permittivity (er) close to 1 , such as less than 1.5, preferably less than 1.2. The relative permittivity is linked to the impedance of the transmission line, and when the transmission line comes in contact with a liquid e.g. water, the impedance is affected. Therefore it can be important that the insulating material has a relative permittivity close to 1 , which is much lower than the relative permittivity of water which is 80. Therefore, if water comes in contact with the transmission line, the impedance will be significantly modified, resulting in a reflection signal of modified amplitude.

Moreover, the system can further comprise a pipeline data collection centre and, potentially, one or more auxiliary devices, and wherein each of the sensor units comprises a communication unit configured to wirelessly transmit data to the pipeline data collection centre directly and/or via the one or more auxiliary devices and/or via one or more other sensor units of the system. In an embodiment, the one or more auxiliary devices comprise one or more unmanned aerial vehicles (UAV). For example, the system can use a plurality of UAVs which can fly over the sensors at predetermined points during each day, collecting the data that the sensor unit has collected. Then, the UAVs can return to the pipeline data collection centre, transmitting the data to the collection centre. A user and/or a computer software may interpret the data collected, and determine the status of the pipeline, as well as determine whether service is required, in order to repair a leak or to prevent a leak from occurring.

In addition, the system can further comprise one or more data processing units configured to determine, at least partly on the basis of the collected time-domain reflectometry data, any presence and location of a leak in the pipeline, the one or more data processing units being located in the plurality of sensor units, in the one or more auxiliary devices and/or in the pipeline data collection centre. For example, the determination of whether a pipeline has a leak, or it may require service to prevent a leak, can either be performed in the sensor unit itself, or it can be performed in the UAV that transmits the data, or on the pipeline data collection centre. Depending on the type of the application, and the power that is consumed by the sensor unit, the presence and location of a leak in the pipeline can be determined by an auxiliary device or by the pipeline data collection centre, in order to minimize the energy consumption of the sensor unit.

Fig. 10 shows an example of a system comprising a time-domain reflectometer 1000 harvesting energy from a TEG 1001 which is applied on two pipes 1002. The system comprises a communication unit 1003 which is capable of communication with an auxiliary device 1004 such as a UAV, to transmit the data collected by the sensor unit.

In an embodiment, the one or more data processing units are configured to detect any leakages from the collected time-domain reflectometry data using artificial intelligence and to compress data by pre-processing and cutting away useless information. For example, a spiking neural network may be employed in order to determine the position of a leak or to predict based on the data collected if a leak is about to occur in the pipeline.

In addition, the system can be configured, such that the pipeline data collection centre is configured to alert a user of the presence and position of the leak detected in the pipeline.

In an embodiment, the distance between two neighbouring sensor units positioned along the pipeline is between 2 and 50 meters, preferably between 5 meters and 25 meters, most preferred between 10 meters and 15 meters, such as 12 meters. The distance between two neighbouring sensor units cannot be too large, as that would require more energy to transmit a wave along the transmission line, and it could reduce the accuracy of the leak-location determination. Therefore, a reduced distance can be chosen, wherein each sensor unit can conduct time-domain reflectometry measurements along both longitudinal directions of a pipe.

Furthermore, the system can be configured such that the time-domain reflectometry data are collected periodically, such as once per hour, once every two hours, or once per day, and data is transmitted to the pipeline data collection centre periodically, such as once per day.

Fig. 11 shows an example of implementing a time-domain reflectometer 1100 on a district heating pipeline 1101 comprising two pipes. A typical district heating pipeline has an insulating material 1102 and it is has areas without insulation 1103 every 12 meters. A sensor unit comprising a time-domain reflectometer can be positioned on the pipeline on every 12 meters, conducting TDR measurements using TDR sensor wires 1104.

Claims

1. An electronic time-domain reflectometer configured to conduct time-domain reflectometry measurements and collect time-domain reflectometry data, said time-domain reflectometry circuit comprising: a line driver configured for stimulating a transmission line sensor, such as an elongated 2-wire sensor, with an electric stimulation signal, a comparator circuit configured for detecting any change in the amplitude of a reflected signal received from the transmission line sensor in response to the stimulation signal, and a timer circuit configured for measuring the time passed from the stimulation signal is applied to the transmission line sensor until the comparator circuit indicates a change of the amplitude of the reflected signal, wherein the timer circuit comprises an integrator circuit or a high-speed start-stop counter.

2. The time-domain reflectometer according to claim 1, wherein the integrator circuit comprises a capacitor and a constant current source, such as a current DAC, wherein the capacitor is configured for being charged by the current source from the point in time when the stimulation signal is applied to the transmission line sensor until the comparator circuit indicates a change of the amplitude of the reflected signal, so that the resulting voltage across the capacitor is a measure of the period of time, during which the capacitor has been charged.

3. The time-domain reflectometer according to claim 1 , wherein the timer circuit comprises a high-speed start-stop counter, which is configured for being started at the point in time when the stimulation signal is applied to the transmission line sensor and stopped again when the comparator circuit indicates a change of the amplitude of the reflected signal, so that the resulting number to which the counter has counted is a measure of the period of time, during which the counter has been active.

4. The time-domain reflectometer according to any one of the claims 1-3, wherein a source resistance of the line driver is adjustable so that it can be adjusted to be equal to the line impedance Zo of the transmission line.

5. The time-domain reflectometer according to claim 4, wherein the line driver comprises a number of parallel-coupled sub-drivers each having a well- specified output conductance, so that the resulting source conductance, and thereby the resulting source resistance, of the line driver can be adjusted by activating different numbers of these parallel sub-drivers.

6. The time-domain reflectometer according to claim 5, wherein the line driver comprises a between 8 and 128 sub-drivers, preferably between 16 and 64 sub-drivers, such as 32 sub-drivers.

7. The time-domain reflectometer according to any one of the claims 5-6, wherein the output conductance of each of the sub-drivers is between 1 mS and 25 mS, preferably between 2 mS and 10 mS, such as 5 mS.

8. The time-domain reflectometer according to any of the preceding claims, wherein the comparator circuit comprises one or more comparators configured for detecting a drop in the amplitude of the reflected signal from an expected amplitude, and the comparator circuit further comprises one or more comparators configured for detecting a raise in the amplitude of the reflected signal from the expected amplitude.

9. The time-domain reflectometer according to any of the preceding claims, wherein the comparator circuit is configured to detect when the amplitude of the reflected signal deviates from an expected amplitude by a first predefined deviation voltage and when the amplitude of the reflected signal deviates from the expected amplitude by a second predefined deviation voltage, the second predefined deviation voltage preferably being twice the first predefined deviation voltage.

10. The time-domain reflectometer according to claim 9, wherein the detection of the deviation of the amplitude of the reflected signal from the expected amplitude by the first deviation voltage and by the second deviation voltage, respectively, is performed using different sets of comparators.

11. The time-domain reflectometer according to claim 9, wherein the detection of the deviation of the amplitude of the reflected signal from the expected amplitude by the first deviation voltage and by the second deviation voltage, respectively, is performed using the same set of comparators in two consecutive stimulations of the transmission line sensor, between which two stimulations the reference levels of the comparators have been adjusted appropriately.

12. The time-domain reflectometer according to any of the preceding claims, further comprising a band gap reference circuit configured for generating current sources required for other parts of the time-domain reflectometer.

13. The time-domain reflectometer according to any one of the claims 1 -2 or 4-

12, wherein the capacitance of the capacitor is between 2 pF and 50 pF, preferably between 5 pF and 25 pF, such as 8 pF.

14. The time-domain reflectometer according to any one of the claims 1-2 or 4-

13, wherein the constant current from the current source can be adjusted to be between 0.1 pA and 100 pA, preferably between 0.5 pA and 64 pA.

15. The time-domain reflectometer according to any one of claims 1-2 or 4-14, wherein the constant current source is a current DAC with binary weighted steps.

16. The time-domain reflectometer according to any one of the claims 1-2 or 4- 15, wherein the constant current source is a current DAC with between 1 and 5 control bits, such as 3 control bits.

17. The time-domain reflectometer according to any one of the claims 1 or 3-12, wherein the high-speed counter is clocked by an output signal of a phase locked loop.

18. The time-domain reflectometer according to any of the preceding claims, wherein the electronic circuits comprised by the time-domain reflectometer are implemented using discrete electronic components mounted on a printed circuit board or the like.

19. The time-domain reflectometer according to any one of the preceding claims, wherein the electronic circuits comprised by the time-domain reflectometer are implemented as one or more integrated circuits, for instance using CMOS technology.

20. A sensor unit comprising

• a time-domain reflectometer, such as a time-domain reflectometer according to any of the preceding claims, and

• a communication unit configured to wirelessly receive and transmit data and to communicate with other units external to the sensor unit, such as communication units of similar sensor units and/or a data collection centre, wherein the sensor unit is powered exclusively by energy harvested by one or more thermoelectric generators, said thermoelectric generators are positioned between two adjacent pipes.

21. The sensor unit according to claim 20, wherein the sensor unit further comprises one or more sensor devices configured to collect humidity and/or temperature data.

22. The sensor unit according to claim 21 further comprising one or more capacitors configured to store energy, which is harvested by the one or more thermoelectric generators.

23. The sensor unit according to any of claims 20-22, wherein the sensor unit is dimensioned to use less than 500 mW, preferably less than 200 mW, most preferred less than 100 mW during active operation.

24. The sensor unit according to any of claims 20-23, wherein the sensor unit is dimensioned to use less than 1 mW, preferably less than 500 pW, most preferred less than 200 pW in a stand-by mode when no time-domain reflectometry data is collected and no data are received or transmitted.

25. The sensor unit according to any one of the claims 20-24, wherein the timedomain reflectometer is the time-domain reflectometer according to any one of the claims 1-19.

26. A system for detecting and localising leaks in a pipeline comprising at least two pipes, such as an underground pipeline, in particular a district heating pipeline, the system comprising:

• one or more thermoelectric generators each configured to harvest energy based on the thermoelectric effect from the temperature gradient between two pipes having different temperature or between a pipe and the surroundings, and

• a plurality of sensor units distributed along the at least two pipes, wherein each sensor unit is powered exclusively by energy harvested by the one or more thermoelectric generators, and wherein each sensor unit is configured to collect time-domain reflectometry data from the pipes.

27. The system according to claim 26, wherein the time-domain reflectometry data are collected by a given sensor unit using an elongated 2-wire transmission line sensor, which sensor is arranged along the pipes of the pipeline in one or both longitudinal directions thereof from the respective sensor unit, preferably within an insulation material, in which the pipes are also enclosed.

28. The system according to claim 27, wherein the insulating material preferably has a relative permittivity (e_r) close to 1 , such as less than 1 .5, preferably less than 1.2.

29. The system according to any of claims 26-28, wherein the plurality of sensor units are sensor units according to any of claims 20-25.

30. The system according to any of claims 26-29, wherein the system further comprises a pipeline data collection centre and, potentially, one or more auxiliary devices, and wherein each of the sensor units comprises a communication unit configured to wirelessly transmit data to the pipeline data collection centre directly and/or via the one or more auxiliary devices and/or via one or more other sensor units of the system.

31. The system according to claim 30, wherein the one or more auxiliary devices comprise one or more unmanned aerial vehicles.

32. The system according to any of the claims 26-31, further comprising one or more data processing units configured to determine, at least partly on the basis of the collected time-domain reflectometry data, any presence and location of a leak in the pipeline, the one or more data processing units being located in the plurality of sensor units, in the one or more auxiliary devices and/or in the pipeline data collection centre.

33. The system according to claim 32, wherein the one or more data processing units are configured to detect any leakages from the collected time-domain reflectometry data using artificial intelligence and to compress data by preprocessing and cutting away useless information.

34. The system according to any of claims 30-33, wherein the pipeline data collection centre is configured to alert a user of the presence and position of the leak detected in the pipeline.

35. The system according to any of claims 26-34, where the distance between two neighbouring sensor units positioned along the pipeline is between 2 and 50 meters, preferably between 5 meters and 25 meters, most preferred between 10 meters and 15 meters, such as 12 meters.

36. The system according to any of claims 26-35, wherein the time-domain reflectometry data are collected periodically, such as once per hour, once every two hours, or once per day, and data is transmitted to the pipeline data collection centre periodically, such as once per day.

37. The system according to any one of the claims 26-36, wherein the at least two pipes are arranged adjacent to one another.