EP2387015A1

EP2387015A1 - System for remotely monitoring the moisture content in wood elements

Info

Publication number: EP2387015A1
Application number: EP10382108A
Authority: EP
Inventors: Ivan Araquistain Marquina; Oriol Munne Caballero; José Miguel Abascal Muro
Original assignee: Fundacion Cidemco
Current assignee: Fundacion Tecnalia Research and Innovation
Priority date: 2010-05-05
Filing date: 2010-05-05
Publication date: 2011-11-16

Abstract

The invention relates to a system and method for monitoring and predicting moisture in wood elements by means of sensors and measurements at multiple independent points as a result of a conductive tape and connector system The data are transmitted by radio frequency to a remote control central unit for the analysis and access thereto through a web interface and through one or more user access interfaces in order to connect with user equipment by means of USB, PCMCIA, Ethernet, Wi-fi GSM, GPRS, UMTS,...

Description

Field of the Invention

The field of application of the present invention is in the industrial sector dedicated to the assembly of electronic instrumentation and to the programming of electronic devices for detecting failures in the construction sector, as well as in the maintenance and rehabilitation of constructions.

Background of the Invention

Moisture is a serious problem for the buildings which affect all types of construction materials and especially wood, since it can negatively affect the constructive processes (such as the installation of wood floors, for example).
The early detection of failures in the building translated into moisture ingresses seeks to prevent future defects or degradations which result in high repair costs. In addition to the deterioration of materials, moisture affects the comfort and wellbeing of the building and of the people who live in it. Therefore, tools have arisen for controlling the moisture content of any wood product, both in relation to the quality of the constructive processes (such as the installation of wood floors) and to the durability and maintenance of already existing buildings. The following patent documents are found by analyzing the state of the art:
International patent application WO2005/010837 describes a conductive tape system for measuring the moisture in the surface of a wood element. To that end, two parallel metal cables coated by a cellulose paper which, when it is wetted, makes the current circulate through the two cables, decreasing the resistance to the passage of the electric current measured between both, are used. Thus, water leakages can be detected, but only in the surface and it is furthermore impossible to know at which point of the entire length of the cable the moisture has been detected.
Systems based only on hardware can be found, such as Ukrainian patent UA27458 , which describes a system for measuring moisture frequently used in xylohygrometers, in which the temperature compensation is achieved as a result of a temperature-sensitive resistor in series with an adjustment potentiometer. There is also an electric resistance converter connected between a moisture detector and the actual temperature compensation unit. The entire process is therefore performed by means of hardware.
Another system which responds to a very specific use is the case of international patent application WO2008/082681 , which relates to a system for measuring moisture for wood in a kiln which uses a capacitive sensor A coaxial cable is used to transmit the signal between distances from 15 to 300 meters. What is most interesting is that the electronics can thus be outside the kiln and safe from the adverse conditions which it would suffer from inside it.
Compared to the aforementioned wired options, there are wireless alternatives which support mesh networks. Wireless mesh networks, coupled networks, or infrastructure wireless mesh networks are basically networks with an infrastructure topology but they allow devices, which, despite being outside the coverage range of the access points, are inside the coverage range of a network card which is directly or indirectly inside the coverage range of an access point, to be joined to the network
They allow the network cards to communicate with one another, independently of the access point. This means that the devices acting as a network card may not directly send their packets to the access point but rather they can pass them to other network cards so that they reach their destination.
This is the case of international patent application WO2009/018650 and United States patent US2006/092031 .
Patent application WO2009/018650 describes a method for monitoring moisture in a building, which indicates the need to control moisture to prevent fungi in the wood. It has an alarm based on a moisture threshold and allows a risk assessment of potential damage using the values of the moisture detectors. It uses a calculation of the risk assessment to identify the critical exposure to the moisture, warning the maintenance personnel. It supports mesh networking.
Patent application US2006/092031 discloses equipment for monitoring the surveillance of the presence of areas of moisture in buildings, among other wood structures. The system uses multiple moisture detectors, each installed in a location of the structure. A remote sensor unit is associated with each area to be supervised and is joined to the detectors in the associated area. The system is programmed so that the sensors and detectors (which comprise a pair of electric conductors in a dielectric substrate) send the reading of what they are supervising every certain time to a supervision unit.
Therefore, there are various solutions today for detecting and monitoring moisture; but in order to fully attain the objective of assuring the correct preservation of wood structures or flooring, not only is the momentary moisture content of the wood, as provided by current equipment, important, but also the future tendency. The dimensional changes of wood and the serious associated damage thereof result in high repair costs insofar as the behavior thereof cannot be foreseen.

General Description of the Invention

The described invention relates to a system for remotely monitoring moisture in a wood element which solves the aforementioned problems of predicting the future behavior of wood elements, such that the preservation thereof with suitable treatments can be assured before the dimensional changes of wood and its serious associated damage thereof result in high repair costs due to not having been able to foresee its behavior.
The invention relates to a system for remotely monitoring moisture in a wood element which comprises a plurality of electric current-conducting terminals (for example a nail or a screw) connectable to a wood element, at measurement points, by means of at least one connector (3) installable in a wood element, which in turn comprises a card (1) comprising a microcontroller, the moisture measurement electronics and a wireless communications module in communication with a computer.
Said system is characterized in that the card furthermore comprises a temperature sensor and another relative air humidity sensor which provide the necessary measurements for obtaining, as a result of previously calculated values, the equilibrium moisture of the wood. This equilibrium moisture is compared with the reading of the moisture of the wood and the moisture tendency value is thus obtained.

The calculation of the equilibrium moisture of wood is based on the following table, obtained from the book Principles of Wood Science and Technology: Sold Wood. Kollmann F. (1959 ):

100	28	28	28	28
95	26	25	24.7	24
90	22	21 7	21.5	21
85	19	19	19	18.5
80	17.5	17	16.7	16.5
75	16	15.5	15	14.7
70	13.7	13.6	132	12.5
65	12.5	12.5	12.2	11.7
60	11.2	11.5	11	10.5
55	10.4	10.1	9.8	9.7
50	9.6	9.5	9.2	9
45	9	8.7	8.5	8
40	8	7.7	7.5	7.5
35	7.5	7.5	7	7
30	6.5	6.5	6	6
25	5.5	5.5	5.5	5.5
20	4.8	4.8	4.8	4.8
15	4	3.9	3.8	3.7
10	2.8	2.6	2.4	2.2
5	2	1.8	1.6	1.4
0	10	20	30	40

This table represents in its x-axis the ambient temperature in degrees centigrade and in its y-axis the moisture in percentage.
Therefore, in order to be able to calculate the equilibrium moisture tendency value with the process described below, it is necessary to have momentary wood moisture data, the relative air humidity and the ambient temperature.
Following the previous table, the moisture percentage at which wood reaches equilibrium is found in the intersection between the relative air humidity and the ambient temperature If the moisture measured in wood is less than the equilibrium moisture, the moisture tendency value is increasing. However, if the moisture measured in wood is greater than the equilibrium moisture the tendency is decreasing.
The cards are clustered together forming nodes. These cards are therefore in a hibernation state, i.e., there is no activity as long as they do not receive a request for reading the moisture content by a computer (4) acting as a coordinator of these nodes. The communication with said computer is carried out by means of the wireless communications module of the cards.
The moisture measurement in wood is based on measuring the electrical conductivity of wood. This means that the electrical conductivity of wood varies very considerably depending on its moisture content. The calculation is performed according to the following formula. See the following equation, where R is the electric resistance in ohms and M is the moisture content in %. $Log [logR - 4] = 1.009 - 0.0322 M$
The system follows the formula described above to calculate the moisture content of wood in a generic manner. However, the calculation formula is adjusted by software to calibrate the measurement for different wood species and different ambient temperatures. The system can be configured by software to measure in two moisture ranges. In the low moisture range, moisture is measured between 7% and 15%, whereas in the high range it is measured between 16% and 30%.
The cards have a potentiometer for adjusting the signal amplification level for each point to be measured. This potentiometer allows the system to adjust the moisture measurement range at hardware level for different wood species.
The connectors and the cards are joined by means of an FPC type flexible plastic conductive tape (2) (Figure 1). The tape is formed by n wires, i.e., one wire for each connector. The tape also has boreholes with a conductive rim in which the conductive elements are introduced.
The wireless communications module of the cards and the radio frequency interface work in the 868 or 869 Megahertz band
A final aspect of the invention is a webpage which has among its functionalities the representation of a history of measurements which is saved in a server enabled to that effect and the representation of the moisture tendency value.

Description of the Drawings

To complement the description which is being made and for the purpose of aiding to better understand the features of the invention according to a preferred practical embodiment thereof, a set of drawings is attached as an integral part of this description, in which the following has been depicted with an illustrative and nonlimiting character:

Figure 1 shows how the conductive tape is a flexible plastic tape with n wires which is used to join the card with the different connectors inserted in different pieces of wood, according to a preferred embodiment of the invention.
Figure 2 shows in detail a set of interconnected cards in communication with a computer, according to a preferred embodiment, forming a network.

Detailed Description of the Invention

A possible practical implementation of the invention is described in detail below:
The scenarios which can be contemplated when applying the system are diverse and very different (buildings with a wood structure, wood flooring in buildings, transport means, etc.), although all of them can be comprised within the same philosophy. In a building provided with the system for monitoring moisture, there are distributed the cards (1) formed by a microcontroller, the moisture measurement electronics, a relative humidity sensor, an ambient temperature sensor and optionally a wireless communications module (Card [1... n]), which can be arranged following a scalable architecture by joining [1..n] cards, at least one of which has a radio frequency transmission module. Each of them can measure the moisture at 10 independent points through the system of FPC type plastic conductive tape (2) (Figure 1) with n wires. Said tape, in addition to allowing the measurement at several points (not necessarily in a straight line, since it is manufactured from flexible plastic and enables drawing curves between the measurement points)).
The connectors (3), depicted in Figure 2, comprise boreholes (5), depicted in Figure 1, with a conductive rim through which the conductive elements are introduced, which conductive elements are arranged in a semicircular manner and in a manner equidistant to a conductive element (6) common for all the measurement points, which can be a nail or a screw of a material having low resistance to the passage of electricity and which, inserted in the wood, allow measuring the moisture content at that point at the depth at which they have been introduced. Or, according to another possible embodiment of the invention, the boreholes are arranged in two vertical parallel lines separated by the distance which must exist between the conductive elements. Thus, if a measurement is to be taken at measurement point one, conductive elements will be introduced in the boreholes of the horizontal line 1. If a measurement is to be taken at point two they will be introduced in those of the horizontal line 2, and so on and so forth.
In each node, formed by [1..n] cards a temperature and relative air humidity sensor is installed in at least one card. A system for predicting the equilibrium moisture of wood which is dependent on the three parameters read (moisture of the wood, relative air humidity and ambient temperature) is thus completed. Wood is a hygroscopic material, therefore it balances its moisture content depending on the ambient temperature and moisture. The calculation process for estimating the tendency value of wood in terms of its equilibrium moisture is described below

100	28	28	28	28
95	26	25	24.7	24
90	22	21.7	21.5	21
85	19	19	19	18.5
80	17.5	17	16.7	16.5
75	16	15.5	15	14.7
70	13.7	13.6	13.2	12.5
65	12.5	12.5	12.2	11.7
60	11.2	11.5	11	10.5
55	10.4	10.1	9.8	9.7
50	9.6	9.5	9.2	9
45	9	8.7	8.5	8
40	8	7.7	7.5	7.5
35	7.5	7.5	7	7
30	6.5	65	6	6
25	5.5	55	5.5	5.5
20	4.8	4.8	4.8	4.8
15	4	3.9	3.8	3.7
10	2.8	2.6	2.4	2.2
5	2	1.8	1.6	1.4
0	10	20	30	40

This table represents in its x-axis the ambient temperature in degrees centigrade and in its y-axis the moisture in percentage.
Therefore, in order to be able to calculate the equilibrium moisture tendency value with the process described below, it is necessary to have momentary wood moisture data, the relative air humidity and the ambient temperature.
Following the previous table, the moisture percentage at which wood reaches equilibrium is found in the intersection between the relative air humidity and the ambient temperature. If the moisture measured in wood is less than the equilibrium moisture, the moisture tendency value is increasing. However, if the moisture measured in wood is greater than the equilibrium moisture the tendency is decreasing.
In the frequent case in which the relative humidity and the ambient temperature do not exactly correspond with a value which is in the table, the software performs an approximation to the closest value.
The cards have a potentiometer for adjusting the signal amplification level for each point to be measured. In other words, each card has 10 potentiometers for an independent adjustment of each point. They are connected to a common information processing module (microcontroller) and a wireless communications module.
Acting as a concentrator of all these nodes there is the computer (4) as a central unit, which acts as a controller of all the nodes formed by the cards (Cards[1...n]), to which it is connected by means of a wireless link to monitor the state of each of them, offering at the same time various modes of interaction with the user. The interaction can be performed remotely, by means of an integrated web interface and different user access interfaces, for example, based on GSM, GPRS, Ethernet..., as a result of which it can access the monitoring by means of different user terminals: mobile telephones, PDAs, PCs or laptops connected to Internet, such that the applications are completely programmable and configurable by the user.
The computer includes a wireless communications module operating in the 868 MHz ISM band, which is tunable and programmable, through which it receives the radio messages with the moisture, temperature and relative humidity data obtained by the conductive and sensor elements, and notifies them to the web server by means of series communication. The wireless communications modules have an indoor range of 200 meters and an outdoor range of 1 Km and are configured according to a mesh topology.
Thus, the previous platform has the necessary access interfaces for being connected, on one hand, with the wireless terminals located in the building under supervision and, on the other hand, with the terminal of the supervisor, which may or may not be wireless also. Thus, the computer acts in a dual role as concentrator of the controlled sensor devices and allowing the complete interaction of the end user with all the controlled devices, adapting to the topology of the specific operations scenario.
Once all the connectors and the card are joined by means of the conductive tape as can be seen in the diagram of Figure 1, the sensors are turned on and the communication is tested with a computer and the developed software. Said software allows, among other things:

Entering photographs or plans of the area to be monitored and graphically placing the sensors thereon, providing a graphical representation of the area to be monitored, directly from the computer following the sequence:
- Open file image > Select the directory and file name > Open > Drag the sensor icons onto the image >Save image > Indicate directory and file name > save
Or by means of Web access following the sequence:
- Upload file image > Select directory and file name > Upload
Configuring the telephone number, mail address, or user account in Internet for the management of alarms.
Selecting the moisture range in which measurements are to be taken.

The developed webpage in turn allows:

Selecting the type of product which is to be monitored
(depending on the product in question, the program will be in charge of establishing the limits for the transmission of alarms. There is also the possibility of the user configuring by himself the limit values at which he wishes to receive a warning) following the sequence:
- Select the type of product which the user wishes to monitor > structural wood, raised parquet, mosaic parquet ... > limit predefined in the software
  Or:
- Select the type of product which the user wishes to monitor > others > limit configurable by the user
Accessing the application through a webpage, with a user name and password to be able to track the locations monitored by each user.
Viewing the moisture measurements of the monitored wood elements and viewing their tendency in terms of their future equilibrium moisture.
Describing the monitored location by means of a tree structure representing different levels.
Uploading and viewing the representative photographs for each monitored area.

To provide the devices with complete autonomy, the power supply is provided with a 9V battery which, together with the necessary software allowing the device to remain on standby for the time in which it is not performing any task and increases the lifetime of the device, reducing at the same time the costs and the size of the described modules.
The moisture measurement in wood is based on measuring the electrical conductivity of wood. This means that the electrical conductivity of wood varies quite considerably depending on its moisture content. The calculation is performed according to the following formula. See the following equation, where R is the electric resistance in ohms and M is the moisture content in %. $Log [logR - 4] = 1.009 - 0.0322 M$
The system follows the formula described above to calculate the moisture content of wood in a generic manner. However, the calculation formula is adjusted by software to calibrate the measurement for different wood species and different ambient temperatures.
The system can furthermore be configured by software to measure in two moisture ranges. In the low moisture range, moisture is measured between 7% and 15%, whereas in the high range it is measured between 16% and 30%. The main application of the low moisture range is the monitoring of wood flooring, whereas the main application of the high moisture range is the monitoring of wood structures.
In this text, the word "comprises" and its variants must not be interpreted in an exclusive manner, i.e., they do not exclude the possibility that what is described includes other elements, steps, etc.
On the other hand, the invention is not limited to the specific embodiments described herein but rather it also covers the variants which can be performed by the person having ordinary skill in the art without departing from the scope of the invention which is inferred from the claims included below.

Claims

1. System for remotely monitoring moisture in a wood element which comprises:

- a plurality of electric current-conducting terminals connectable to a wood element at measurement points by means of connectors installable in the wood element

- a card, connected to the conductive terminals by a cable, configured to read a moisture value of the wood comprising a microcontroller, an electronic moisture measurement circuit and a wireless communications module

- a computer in communication with the wireless communications modules of the cards
characterized in that it furthermore comprises at least one temperature sensor and a relative air humidity sensor configured to obtain data corresponding with a certain equilibrium moisture value and upon comparing the equilibrium moisture value with the reading of moisture of the wood, in a measurement range, it estimates a moisture tendency value.

2. System according to claim 1, characterized in that it has a potentiometer adjusting the moisture measurement range for different wood species.

3. System according to any of the previous claims, characterized in that the cards remain in a hibernation state until the computer requests from the cards a reading of the moisture content in the wood element.

5. System according to any of the previous claims, characterized in that the at least one connector with the card are joined by means of an FPC type flexible plastic conductive tape.

6. System according to the previous claim, characterized in that the conductive tape is a flexible plastic tape with a plurality of wires which has boreholes with a conductive rim through which the plurality of conductive terminals is introduced and which are arranged in a semicircular manner and equidistant to a conductive terminal common for all the measurement points

7. System according to any of the previous claims, characterized in that the wireless communications module of the cards uses a 868 or 869 Megahertz band.