PREVENTING FROST DAMAGE OF FLOW METERS IN A DISTRIBUTION NETWORK

Abstract

The present invention provides a method for preventing frost damage to one or more flow meters installed in a fluid distribution network containing a fluid, wherein each flow meter is configured to measure a temperature, preferably an air temperature, and to wirelessly transmit the measured temperature, such as via a mobile or a fixed wireless reading system to a processing unit. The method comprises: 1) during a period continuously monitoring (M_TMP) the temperatures measured by the plurality of flow meters over a period of time, 2) performing a data analysis (P_DA) on the temperatures of the plurality of flow meters from the period, 3) based on the data analysis, identifying (I_FDC) one or more ones of the plurality of flow meters as frost damage candidates in a future frost period, and 4) transmitting (T_WS) a warning signal indicative of the frost damage candidates or initiating frost protection measures to protect the frost damage candidates. It has been found that it is possible to monitor temperatures in a no-frost period to identify a frost damage candidate, e.g. if a flow meter is positioned in a pit and the lid is removed thereby causing the risk of a frost damage of the flow meter.

Claims

1. A method for preventing frost damage to one or more flow meters installed in a fluid distribution network containing a fluid, wherein each flow meter is configured to measure a temperature, preferably an air temperature, and to wirelessly transmit via radio signals the measured temperature to a processing unit, the method comprising: continuously monitoring over a period of time the temperatures measured by the plurality of flow meters, performing a data analysis on the temperatures measured by the flow meters over the period of time, based on the data analysis, identifying one or more ones of the plurality of flow meters as frost damage candidates in a future frost period, and transmitting a warning signal indicative of the frost damage candidates or initiating frost protection measures to protect the frost damage candidates.

2. The method according to claim 1, comprising monitoring the temperatures measured by the plurality of flow meters over a period of time during a no-frost period.

3. The method according to claim 1 or 2, comprising continuously monitoring minimum and maximum temperatures measured for at least a group of the plurality of flow meters over a period of time, and identifying a frost damage candidate as having one of the following measured temperature characteristics: 1) exhibiting minimum and maximum temperatures deviating from its normal individual pattern when measured over a period of time, 2) exhibiting minimum and maximum temperatures deviating from a group of flow meters when measured over a period of time, or 3) exhibiting minimum and maximum temperatures deviating by more than a predetermined amount from a group of flow meters when measured over a period of time.

4. The method according to claim 3, comprising determining for each of the plurality of flow meters an averaged minimum temperature and an average maximum temperature in response to minimum temperatures and maximum temperatures observed over a period of time.

5. The method according to claim 1, wherein the plurality of flow meters monitored are placed in geographical proximity of each other and positioned in the fluid distribution network in the same type of installation configuration.

6. The method according to claim 1, wherein the temperature measured by each of the plurality of flow meters is an inside air temperature of the flow meter where at least a part of a flow measurement circuit of the flow meter is arranged.

7. The method according to claim 1, wherein a frost damage candidate is identified as a flow meter having a measured time series of temperatures which is dissimilar to corresponding time series of temperatures measured by a group of other ones of the plurality of flow meters as differing by more than a predetermined amount from corresponding time series of temperatures measured by a group of other ones of the plurality of flow meters.

8. The method according to claim 7, comprising calculating a statistical value for each flow meter based on the measured time series of temperatures during a no-frost period, and wherein a frost damage candidate is identified as a flow meter exhibiting a statistical value which differs by more than a preset threshold from the group of other ones of the flow meters.

9. The method according to claim 1, wherein the step of identifying a frost damage candidate involves taking into account a measured fluid flow for each of the plurality of flow meters in the period of time of monitoring.

10. The method according to claim 8, comprising identifying one or more of the plurality of flow meters as frost damage candidates only if the one or more flow meters exhibits a statistical value differing by more than a preset threshold from the group of other ones of the flow meters over a period of time.

11. The method according to claim 1, wherein the data analysis comprises calculating a correlation coefficient of temperatures measured by each of the plurality of flow meters in relation to temperatures measured in the same time period by other ones of the plurality of flow meters, and identifying a frost damage candidate as a flow meter having a measured one or more temperatures during a no-frost period or another period of time which result in a correlation coefficient which is numerically below a preset threshold value.

12. The method according to claim 1, wherein a signal strength of a radio signal is detected by the processing unit, and wherein the signal strength is used as a further parameter in the data analysis on the temperatures measured.

13. A system for monitoring a fluid distribution network which comprises pipes and a plurality of flow meters, said flow meters being placed at respective positions in the fluid distribution network wherein each of the flow meters are is configured for measuring a temperature, and for wirelessly transmitting the measured temperature to a processing unit wherein the processing unit can access a temperature database holding temperatures measured by the plurality of flow meters during a period, such as time series of temperatures for each of the flow meters over a period comprising a period, the processing unit has a data analysis unit which is configured to analyze the temperatures measured by the plurality of flow meters from the period, the processing unit has an identification unit which, based on a result from the data analysis unit, is configured to identify one or more of the flow meters as frost damage candidates in a future frost period, and the processing unit generates a warning signal indicative of the identified frost damage candidates or initiates frost protection activities to protect the frost damage candidates.

14. The system according to claim 13, wherein the warning signal is generated in a no-frost period.

15. The system according to claim 13, wherein the flow meters are arranged to transmit their respective positions to the processing unit, wherein the processing unit is arranged to group the flow meters into groups with geographically neighboring flow meters in response to their positions, and wherein the data analysis unit is arranged to perform the data analysis based on said groups of neighboring flow meters.

16. The system according to claim 13, wherein the flow meters are ultrasonic flow meters and the temperature measured is a temperature of the fluid calculated from transit-time measurements made by ultrasonic piezo transducers.

17. The system according to claim 13, wherein the flow meters are arranged to measure both an air temperature and a fluid temperature.

18. The system according to claim 13, wherein the flow meters are ultrasonic flow meters and wherein the temperature measured is an internal flow meter temperature measured by a temperature sensor placed inside a housing of the flow meter.

19. The system according to claim 13, wherein the temperature database of the server further includes meteorological temperature data provided by a third party meteorological weather data provider, and wherein the data analysis unit is arranged to analyze the temperatures of the plurality of flow meters from the no-frost period along with the meteorological temperature data.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0049] The present invention and in particular preferred embodiments thereof will now be disclosed in more detail with regard to the accompanying figures. The FIGS. show ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0050] FIG. 1a shows a flow meter placed in a pit;

[0051] FIG. 1B shows a flow meter placed in a pit with a cover removed;

[0052] FIG. 2 shows a flow meter inside an above-ground sensor box;

[0053] FIG. 3 shows a plurality of flow meters as part of a fluid distribution network;

[0054] FIG. 4 shows an embodiment of ultrasonic flow meter according to the present invention; and

[0055] FIG. 5 shows a flow chart illustrating a method according to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0056] FIGS. 1a and 1b show a flow meter 1 placed in a pit 7 in two different situations. In FIG. 1a, the flow meter 1 is placed in a pit 7 with a cover 8 serving to protect the pit 7 against dirt, rain, sun rays and frost, while in FIG. 1B the cover 8 is for some reason removed, and thus the pit 7 and thereby also the flow meter 1 is more directly exposed to dirt, rain, sun rays and frost. According to preferred embodiments of the invention, an air temperature is monitored in the pit, e.g. inside the flow meter 1, in a no-frost period, so as to determine if the cover 8 is fully or partly removed from the pit 7, and thereby exposing the flow meter 1 to frost in case of low temperature, i.e. thereby causing such flow meter 1 to be a frost damage candidate in a frost period. According to the invention, such frost damage candidate flow meter 1 can be identified already in a no-frost period, thus allowing early alarming and taking actions to e.g. replace the cover 8 in case it is misplaced or removed from the pit 7 before a period of frost, thereby preventing any damage of the frost damage candidate flow meter.

[0057] Preferably, the a frost damage candidate flow meter is identified by monitoring temperatures for a group of neighbouring flow meters 1 and performing data analysis on time series of such measured temperatures. The data analysis may involve various mathematical methods of identifying one or more flow meters 1 which exhibit temperatures considered as outliers from the group median or average, thereby indicating that such flow meters 1 could be a potential frost damage candidate, since the deviating temperature profile could be caused by the fact that the cover 8 is removed from the pit 7.

[0058] In order to obtain a robust condition monitoring without too many false positives the temperature data in a no-frost period from a group of a plurality of flow meters are monitored and a data analysis is preformed to determine any one or the flow meters which exhibit temperatures which can be considered as outliers or uncorrelated to the temperature profile for the group. The grouped of flow meters preferably comprises flow meters that can be considered as located under the same conditions, preferably located in the same geographical area, such as within an area of 1 km.sup.2. Thus in a large network of flow meters covering a large geographical area, the flow meters are preferably grouped into a number of neighbouring groups.

[0059] The flow meter 1 is preferably a digital smart meter with a radio transmitter 2 enabled for wireless communication with a server 3 by means of a dedicated reading network such as a LoRA based network, wireless M-Bus and/or via Nb-IoT or 4G or 5G mobile network communication or the like. The flow meter 1 may further or alternatively be configured for wireless communication with a mobile receiver by drive by using a mobile receiver. A radio transmitter 2 transmits RF signals with information about temperature T, flow Q and/or global positioning GPS in the shown example via the cloud to a remote server 3.

[0060] The temperature sensor is preferably arranged inside the ultrasonic flow meter 1, i.e. it is preferably an internal temperature T sensor 4 placed inside a housing of the flow meter 1, e.g. placed on a printed circuit board. The flow meter further comprises two ultrasonic sensors used for measuring the transit time of flight between the two sensors. From the transit time the fluid flow rate Q through the pipe can be determined. In some embodiments, the ultrasonic sensors are also used to determine the temperature of the fluid, since the transit time is a function of the fluid temperature. This may additionally or alternatively be used as a measure of temperature to be transmitted for identifying frost damage candidates.

[0061] The most preferred solution is to use the sensor 4, i.e. a separate temperature sensor 4, which is mounted inside a housing of the flow meter 1, e.g. on the printed circuit board on which electronic components of the flow meter are arranged, already when manufacturing the flow meter. Such temperature sensor 4 inside the flow meter housing will be protected from physical damage, and it can be connected directly to the electronic components inside the flow meter 1, such as the radio transmitter 2, and it can be built into the flow meter 1 easily in an existing process of manufacturing the flow meter 1. Especially, it may be preferred to transmit temperature data along with existing data packets for transmitting a measured liquid flow quantity Q and e.g. also GPS data.

[0062] The temperature T to be transmitted for frost damage candidate analysis can alternatively or additionally be the fluid temperature determined by a sensor 5 mounted on the fluid pipe and extending through the fluid pipe into the liquid or by a sensor 6 mounted on a wall of the pit 7.

[0063] According to the invention a number of temperatures representing the temperatures in the pit 7 are transmitted to the server 3 or another receiver. The temperatures are measured during a time period of no-frost, such as during 1, 2 or 3 months in Summer. The temperatures will have the same daily or weekly patterns and trends and no disruptive changes in the temperatures are to be expected.

[0064] In the situation shown in FIG. 1B, the cover 8 has been displaced from its original and intended position, thus leaving the pit 7 partly or fully unprotected. This can happen if a service technician forgets to put the cover 8 back in place after servicing the pit 7. In the situation of FIG. 1B the temperature measured during day time will increase markedly compared to the situation with the cover 8 in place, because the sun rays now warm up the flow meter 1 directly, since there is no protection from the cover 8. The rise in temperature will be readily detectable by the server 3 by suitable data analysis taking into account preferably time series of temperatures from other similar flow meters placed in pits in the neighbourhood, and thus basically under the same weather conditions. It has been found possible to detect a flow meter in a pit 7 with the cover 8 removed as an outlier when comparing statistical parameters, e.g. based on calculating a distance measure between time series for temperatures measured by each flow meter in a group of neighbouring flow meters.

[0065] A flow meter 1 detected as an outlier in such data analysis can be considered as a frost damage candidate, since the removed cover 8 will cause the flow meter 1 to be exposed to frost in the pit 7 compared to the situation in FIG. 1a with the cover 8 in place. Hence, the server 3 could act and signal a warning indicating the identified frost damage candidate flow meter, and since this is done already in the no frost period, there is sufficient time for service personnel to visit the frost damage candidate flow meter and to place the cover 8 in its original position before the frost period sets in and thus before there is an actual risk of frost damage of the flow meter 1.

[0066] FIG. 2 shows an alternative position of the flow meter, namely inside an above-ground sensor box. Inside the box a flow meter of the same kind as in FIG. 1a or 1b is placed, thus protected by the box. Inside the box, the flow meter is protected against mechanical attacks, against rain, sun and frost. However, in FIG. 2 it can be seen that a corner 21 of the box has been damaged, and thus an undesired opening into the flow meter 1 exists. Through this opening frost could potentially cause the flow meter to freeze, i.e. the flow meter inside such damaged box is a potential frost damage candidate which could be identified by means of the present invention in the manner similar to that described above for the pit position shown in FIGS. 1a and 1b.

[0067] FIG. 3 shows a plurality of flow meters M1 to M6 as part of a fluid distribution network. The fluid distribution network is supplied with water from a water utility company. From the main pipes service pipes are branched off, and in the service pipes, flow meters M1-M6 are installed to measure fluid flow quantities. E.g. these meters M1-M6 can be placed in pits as shown in FIG. 1a or 1b, or inside a box above ground level as shown in FIG. 2.

[0068] Each of the flow meters M1-M6 transmit temperature information to a receiver in the form of a computer or central server via a radio frequency communication network, such as LoRaWAN? or via a cellular network using e.g. Nb-IOT.

[0069] In order to get an even more reliable statement about being a frost damage candidate or not, the strength of the radio signal sent from the flow meter is included in the data analysis by the processing unit 3. The inclusion of the signal strength is relevant for those flow meters that have an RF antenna built into the flow meter or have the antenna placed in the pit or inside a box. Turning to FIG. 1a the radio signal will in the situation with the lid 8 correctly in place be dampened. The amount of dampening of the signal when passing through the lid is dependent on the material of the lid, say metal, plastic or wood, but in any case a removal of the lid as shown in FIG. 1B will result in a significant and detectable increase in signal strength. The processing unit 3 monitors over timetogether with the monitoring of the temperatures measured by the flow meterthe development in the signal strength and an abrupt increase in the signal strength is an indication of a removed lid. Also a broken lid with cracks caused e.g. by the passage of cars over the lid may be detected. The same considerations applies to the situation of FIG. 2 where the damaged corner 21 enables the increase in the strength of signal sent from flow meter 1.

[0070] A very robust frost damage candidate detection is achieved if the parameters internal temperature of the flow meter, fluid temperature and RF signal strength of the flow meter are included in the data analysis (P_DA) performed by the processing unit 3.

[0071] In preferred embodiments of the invention, flow meters M1-M6 are grouped based on their geographical location, e.g. based on their GPS coordinates transmitted to the computer or central server. Hereby it is ensured, that the expected temperature variation due to geographical and local weather conditions is similar or at least comparable. This facilitates the finding of a potential frost candidate as an outlier in the group by suitable data analysis on measured time series of temperatures for all meters in a group.

[0072] In FIG. 3 flow meters M1, M2 and M3 are grouped into one group N, and flow meters M4, M5 and M6 are grouped into another group P. These groupings P, N could be made e.g. because group P members are placed at a higher altitude above sea level than the meters in group N, i.e. groups N and P are geographically different and thus temperatures measured by a meter M1 in one group N can be expected to differ from temperatures measured by a meter M4 in the other group P.

[0073] Taking into account such groupings of meters based on geographical location of the meters has been found to allow a more robust and trustworthy frost damage candidate identification, and thus a more trustworthy alarm can be given because meters operating under the same environmental conditions are correlated with each other. Preferably, their GPS locations could be used for grouping, or in case the distribution network has a mix of flow meters in different installation configurations (e.g. pit and above-ground box installed meters), the grouping could be make according to the installation configuration rather than geographical location.

[0074] In the following, more detail about a possible specific data analysis and identification of a frost damage candidate is given based on appropriate groups of meters, where it can be expected that the measured temperature of most meters in the group to be similar. This is preferably obtained by grouping the meters based on their geographical position, e.g. determined by their GPS coordinates. Additionally or alternatively, the grouping can be based on the type of installation configuration for the flow meters, e.g. placed in a pit or placed inside a box above ground level.

[0075] Thus, suitably grouped so that the flow meter in a group can be considered as similar with respect to geographical position, i.e. equally exposed to same weather conditions etc., and all flow meters being installed in the same type of installation configuration, e.g. all placed in a pit or all placed in a box above ground level, then the measured temperatures of most flow meters can be expected to be similar, also seen over time.

[0076] If however one or more flow meters are exposed to different conditions, e.g. placed in a pit with the cover removed, or placed in a box above ground level which is damaged, then it has been found possible to detect a temperature difference between such flow meter and the remaining flow meters of the group by applying a suitable data analysis, and such deviating flow meter is then considered as a frost damage candidate, since it can be expected that its data deviates due to the deviating condition which also means that the flow meter will be vulnerable in a frosty period.

[0077] Therefore, the problem of finding a frost damage candidate among the flow meters of a group it to identify a flow meter exhibiting temperatures which can be considered as an outlier when compared to the flow meters of the group. In short, such outlier problem can be identified as to find a flow meter with a temperature time series that is the most dissimilar from the other flow meters in the group. Such problem can be solved by calculating a statistical measure (i.e. a parameter) for each flow meter compared to the group of flow meters, and then, based on the statistical measure, it can be determined if one or more flow meters stand out or deviates significantly from the group. Such statistical measure can be calculated in many ways.

[0078] In the table below, an example of sample data for 10 meters (0-9) grouped in two groups (N and P) with monitored temperatures (? C.) over seven days. The temperature per day can be a temperature calculated as an average of temperatures measured at a plurality of different times during the day.

TABLE-US-00001 TABLE 1 Day Day Day Day Day Day Day group meter_id 1 2 3 4 5 6 7 N 0 14.61 14.38 15.6 14.96 12.2 16.34 17.57 N 1 14.54 14.74 15.43 14.06 12.17 16.76 17.68 N 2 14.7 14.11 15.05 14.93 12.42 16.03 17.22 N 3 14.49 14.32 15.1 14.83 17.13 21.2 22.17 N 4 14.89 14.74 15.78 14.07 12.13 16.16 17.31 P 5 14.13 14.16 15.04 14.35 12.11 16.16 17.76 P 6 14.23 14.46 15.69 14.69 12.85 16.85 17.41 P 7 14.32 14.9 15.07 14.81 12.77 16.9 17.72 P 8 14.76 14.83 15.74 14.64 12.45 16.81 17.45 P 9 14.35 14.4 15.55 14.99 12.06 16.05 17.06

[0079] As seen from Table 1, the flow meter with id 3 has a significant higher temperature over the last three days (Day 5, Day 6 and Day 7) than the rest of its group. One example of a method for finding the most dissimilar temperature series would be to create a summary series per groupthis could be a mean or a median of the temperature per day. Using the median as an example:

t_i=Median(X.sub.i)(1)

where i is any day in the dataset, and X is the temperatures of the flow meters for that day. This produces a summary series for each group, and this series can then be used in similarity metrics to compare a flow meter series of the group to the summary series.

[0080] There are many possible metrics that can be used for the comparisonsuch as calculating the Euclidian distance of the flow meter's series to the summary series:

d=?{square root over ((x.Math.t_i))}(2)

where x is a flow meter series and t_i is the summary series per group.

[0081] Other possible metrics include: MSE (mean square error), MAPE (mean absolute percentage error), or dynamic time warping.

[0082] The data analysis may preferably also comprise determining a measure of variance in the series. However, for simplicity this is excluded in the present description.

[0083] The data analysis may preferably also comprise taking into account a liquid flow quantity measure by each flow meter. However, for simplicity this is also excluded in the present description.

[0084] If calculating for each flow meter a distance measure N_d calculated as:

N_d=?{square root over (?(T_m?T_s).sup.2)}(3)

where T_m is the temperature values for the time series of the seven temperatures for the flow meter, while T_s it the average temperature values for the time series of the seven temperatures for the remaining flow meters in the group.

[0085] With the distance calculated as N_d described above, Table 2 shows the resulting distances for the temperature measurement values in Table 1.

TABLE-US-00002 TABLE 2 Group meter_id N_d N 0 0.21 N 1 0.96 N 2 0.71 N 3 8.32 N 4 1.01 P 5 1.07 P 6 0.44 P 7 0.79 P 8 0.61 P 9 0.99

[0086] From Table 2, it can be seen that the flow meter with id of 3 has a significant larger distance N_d to the summary series than the other meters in its group (N). Consequently, the flow meter with id 3 can be identified as a frost damage candidate.

[0087] The other group (P) does not show any significant distances for any of the meters (5-9), and thus none of these flow meters (5-9) is identified as a frost damage candidate.

[0088] In the above example, frost damage candidate flow meters are identified by determining temperature deviations in each single flow meter with respect to a time series of temperatures measured in a group of flow meters. However, in a simpler data analysis version, the daily minimum and maximum temperatures for each individual flow meter is monitored over a period of time, e.g. 10 days, and if one flow meter exhibits a pattern over time deviating from its normal behaviour, the flow meter may be identified as a frost damage candidate, since this could indicate an abnormal condition of the flow meter. Especially, an abnormal behaviour may be observed, and if the same abnormal behaviour continues over several days, the flow meter may be identified as a frost damage candidate. Hereby, with such delay in identifying a frost damage candidate, the risk of false identified frost damage candidates can be reduced.

[0089] FIG. 4 illustrates a specific ultrasonic flow meter 1 configured for the present invention. Namely, a flow meter 1 with a housing H and flow tube FT for mounting on a pipe of a fluid distribution network for measuring a fluid flow quantity by ultrasonic piezo transducers T1, T2 arranged inside a cavity CV formed by the hosing H and being configured for transmitting ultrasonic waves through the wall of the flow tube FT and for transmitting ultrasonic waves (dashed lines) along the fluid flow direction (arrow) via reflectors inside the flow tube FT. In this way a fluid flow quantity can be calculated by transit-time measurements made by ultrasonic piezo transducers T1, T2, and this quantity can be transmitted in a wireless radio frequency signal by transmitter 2 placed inside the cavity CV of the housing H.

[0090] Further, a temperature sensor 4 for measuring the air temperature inside the cavity CV of the housing H is seen, here illustrated as mounted on a printed circuit box which allows easy manufacturing and facilitates electric connection to a measurement circuit which may be also mounted on the same printed circuit board. The temperatures measured by the temperature sensor 4 are also transmitted via the radio transmitter 2, and these transmitted temperatures can then be used for data analysis for frost damage candidate identification according tot the invention.

[0091] FIG. 5 illustrates steps of a method embodiment, where each of a plurality of flow meters are configured to measure air temperature, and to wirelessly transmit the measured temperature to a processing unit. The method comprises during a no-frost period monitoring M_TMP the temperatures measured by the plurality of flow meters over a period of time, such as monitoring for each flow meters, a time series of temperatures measured at respective times during the no-frost period. Then, performing a data analysis P_DA on the temperatures, preferably temperature series, of the plurality of flow meters from the no-frost period. Further, based on the data analysis, identifying I_FDC one or more ones of the plurality of flow meters as frost damage candidates in a future frost period, and finally transmitting T_WS a warning signal indicative of the frost damage candidates, which in turn allows service personnel to initiate frost protection measures to protect the frost damage candidates.

[0092] Instead of or additionally to the warning signal a signal can be send to auxiliary equipment such as a valve built into the flow meter or placed in the pipe up stream or down stream of the flow meter, and then actuate such valve to close or open the fluid flow in order to prevent or mitigate frost damage.

[0093] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms comprising or comprises do not exclude other possible elements or steps. Also, the mentioning of references such as a or an etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.