WO1999064856A1

WO1999064856A1 - Method and device for measuring moisture in structural material

Info

Publication number: WO1999064856A1
Application number: PCT/FI1999/000491
Authority: WO
Inventors: Matti Lyyra; Heikki Joensuu; Antti PITKÄNEN
Original assignee: Vaisala Oyj
Priority date: 1998-06-05
Filing date: 1999-06-07
Publication date: 1999-12-16
Also published as: FI108891B; FI981296A; FI981296A0; AU4620799A

Abstract

The invention relates to a method and apparatus for measuring structural moisture. In the invention, only a measurement duct (2), in which sensors (7, 9) can be set for the duration of the measurement, is placed inside the structure. Measurement duct (2) is formed from a pipe that is impermeable by vapour, the first end of which is installed at the point inside the structure (1) that is to be measured and the second end of which extends to the surface of structure (1). The second end of measurement duct (2), which extends to the surface of structure (1), is shut off with a vapour-tight plug. A vapour-permeable plug (4) can be fitted to the first end of measurement duct (2) set inside structure (1). The measuring apparatus in turn comprises a measuring unit (5), to which a temperature and moisture sensor (7) and a second temperature sensor (9) are connected. When moisture is measured, the plug closing the second end of measurement duct (2) is removed and temperature and moisture sensor (7) is put in its place. The second temperature sensor (9) is pushed along measurement duct (2) to the first end of measurement duct (2). Once the moisture profile in measurement duct (2) has equalized, the moisture and temperatures are measured, and the moisture prevailing in the surroundings of the first end of measurement duct (2) is calculated from the results. Alternatively, a valve can be set in measurement duct (2), which valve is penetrated by a measuring head containing temperature and moisture sensors.

Description

Method and Device for Measuring Moisture in Structural Material

The present invention relates to methods according to the preambles of Claim 1 and 6. The invention also relates to a measurement connection according to the preamble of Claim 8 and a measuring apparatus according to the preamble of Claim 15.

Methods and apparatus of this kind are used to measure structural moisture inside structures. The moisture content inside a structure can be measured, for example, from the wall, flooring, ceiling, or intermediate floor. The structural material to be measured can be, for example, concrete, timber, or thermal insulation. The moisture content can be measured either at a single moment in time, or else its development can be monitored as a function of time. Measurements of moisture content made at a single moment can be used to determine the moisture content of a structure, for example, for a moisture damage analysis. Measurements of the moisture content as a function of time can be used, for example, to monitor the drying of a structure, such as a concrete slab, during construction, in connection with repairs after water damage has occurred, or in the long- term monitoring of the condition of structures.

According to the state of the art, the moisture content of the internal components of structures is measured by drilling a hole in the structure, and measuring the moisture content through this hole. Understandably, several problems arise when carrying out measurements requiring drilling, such as the need for drilling equipment, and the danger of damaging the structures and pipe runs embedded in them. This problem is solved in US patent publication 5,730,024, which discloses a measuring head that is embedded in the structure during construction. The measuring head includes a protective casing, which is watertight, but which is permeable by water vapour, and which has moisture and temperature sensors located inside it. The moisture sensor is a piece of hygroscopic material, with two electrodes embedded in it. In addition, the measuring head includes electrical leads from the measuring head to the outside of the structure being measured, and devices, by means of which the measuring head is secured inside the structure. The measurement of the moisture content is based on using the electrical leads to measure, from outside the structure, the resistance between the electrodes in the piece of hygroscopic material. Measuring heads of this kind are intended for installation in structures during their construction. The measurement heads are placed at apparently suitable locations, for example, within a concrete slab. The measurement sensors are thus installed permanently into the structures. The measuring apparatus as such need not be permanently connected to the structure to be measured; instead, it can be connected to the sensors for the duration of the measurement by means of the electrical leads.

A drawback in the state of the art is that the sensors, together with the measuring leads, must be placed inside the structure. This creates significant costs, as several different measuring heads, and thus numerous sensors, may have to be placed in each construction, to ensure adequate preparedness for comprehensive measurements. If moisture problems appear in a construction, it is generally necessary to ensure that the sensors are operating correctly and that the measurements are accurate, before beginning to dismantle and repair the structures. This is impossible when using permanently installed sensors.

The invention is intended to eliminate the defects of the state of the art disclosed above and for this purpose create an entirely new type of method and apparatus for measuring structural moisture.

The basis of the invention is the installation inside the structure of only a measurement duct, in which the necessary sensors can be placed for the duration of the measurement. The measurement duct is formed by a pipe that is impermeable to vapour, with one end placed inside the structure at the point to be measured and the other end extending to the surface of the structure. The measurement duct is closed by means of at least one essentially vapour-tight plug, valve, or similar, which is located in the measurement duct, and which prevents the point being measured from drying out before and between measurements. It is also preferable to close the measurement duct during measurement.

More specifically, the method according to the invention is characterized by what is stated in the characterizing sections of Claims 1 and 6. In turn, the measurement connection is characterized by what is stated in the characterizing section of Claim 8, the measuring apparatus being characterized by what is stated in the characterizing section of Claim 15. Considerable advantages are gained with the aid of the invention.

The use of the invention inside structures eliminates the need for the permanent installation of sensors. This makes it highly economical to arrange the possibility in structures to make measurements according to the invention. As the same sensor can be used at several different measurement points, it is economically possible to use better quality sensors in connection with the invention.

The invention also has the additional advantage that routine screening measurements for moisture damage, for example, can be made with a cheaper measuring device, and, if moisture damage is found, it can be analysed by a more accurate method through the same duct.

In the following, the invention is examined with the aid of examples and with reference to the accompanying drawings.

Figure 1 shows a diagram of one measurement duct according to the invention installed in a structure, with one measuring device according to the invention connected to it.

Figure 2 shows a diagram of a second and third measurement duct according to the invention and a second measuring device according to the invention connected to the second measurement duct.

Figure 3 shows a cross-section of a valve that can be installed in a measurement duct according to the invention.

Figure 4 shows a cross-section of the end of one measurement duct according to the invention, with the valve shown in Figure 3 installed on it, and the measuring head of a measuring device being pushed towards the valve in the measurement duct.

Figure 5 shows a cross-section of the measurement duct in Figure 4, with the measuring head pushed into the measurement position.

Figure 1 shows a structure 1, in which measurements are to be made, a measurement duct 2, 3, 4 embedded in the structure, and a measuring device 5, 6, 7, 8, 9 connected to the measurement duct 2, 3, 4. The structure to be measured can be, for example, a wall, flooring, an intermediate floor, or a ceiling structure. Measurement duct 2, 3, 4 embedded in structure 1 comprises a vapour duct 2, a measurement box 3 forming an extension to the second end of the vapour duct 2, and a protective plug 4 fitted into the first end of vapour duct 2. Measuring device 5, 6, 7, 8, 9 in turn comprises a measuring unit 5, a vapour barrier 6 connected to measuring unit 5, lead 8 taken through vapour barrier 6 to measuring unit 5, and a moisture and temperature sensor 7. Measuring device 5, 6, 7, 8, 9 also includes a second temperature sensor 9 attached to the second end of lead 8.

In addition, Figure 2 shows a vapour barrier plug 10 that closes the second end of vapour duct 2, a measuring head 11, and a cable 12 connecting measuring head 11 to measuring unit 5 ' .

Vapour duct 2 is installed in structure 1 so that the first end of duct 2 is inside structure 1 close to the desired measurement area, while the second end extends to either the surface of structure 1 or to the base or side wall of a measurement box 3, if measurement box 3 is being used. Vapour duct 2 is intended to act as a diffusion route, along which any possible moisture in structure 1 at the first end of vapour duct 2 will diffuse to the second end of vapour duct 2. In this case, the moisture content of structure 1 can be measured at the second end of vapour duct 2, which has been led to the surface of structure 1, without any need for expensive cabling extending to measuring device 5, 6, 7, 8, 9 and to the first end of vapour duct 2. Vapour duct 2 is manufactured from a pipe or pipe-like piece made from a suitable essentially vapour-tight material. The material of the pipe should also preferably be cheap, mechanically durable, and such as can be easily bent into a suitable shape. One preferable manufacturing material for vapour duct 2 is the plastic indoor installation conduit widely used for installing electrical cables indoors.

Measurement box 3 can form an extension of the second end of vapour duct 2, being then installed on the surface of structure 1. Though measurement box 3 is not essential, it can facilitate measurements. Measurement box 3 is intended to act as a holder, in which measuring device 5, 6, 7, 8, 9 is mounted, when structure 1 is being measured. Thus the opposing surfaces of measurement box 3 and measuring device 5, 6, 7, 8, 9 are shaped to fit each other. Measurement box 3 also protects the second end of vapour duct

2. In addition to measurement box 3, a detachable vapour-barrier plug 10 (Figure 2) is fitted to the second end of vapour duct 2, with the purpose of preventing moisture from moving from the second end of vapour duct 2 to the surrounding air, or vice versa. The second end of vapour duct 2 is always kept closed when vapour duct 2 is not being used for measurement. If vapour-barrier plug 10 is not used, any possible moisture in structure 1 can evaporate locally around the first end of vapour duct 2, so that the moisture values measured from vapour duct 2 will no longer represent the moisture content generally prevailing in structure 1. Vapour-barrier plug 10 is used both in conjunction with measurement box 3 and in conjunction with vapour ducts 2 installed without measurement box 3.

A protector plug 4 is, in turn, fitted to the first end of vapour duct 2, being intended, among other things, to prevent building material in structure 1 entering vapour duct 2. It is especially important to use protector plug 4 when casting vapour duct 2 in concrete. In certain cases, however, for instance when placing vapour duct 2 in a hole drilled in timber, protector plug 4 is not essential. Protector plug 4 should permit the passage of water vapour. Protector plug 4 can be manufactured from, e.g., a collar and a small- mesh metal net, or from timber or vapour-permeable plastic.

Measuring unit 5 contains the electronics needed to control the moisture and temperature sensor 7 and the second temperature sensor 9, and to process the measurement results. Measuring unit 5 is preferably located in a case shaped externally to conform to the internal shape of measurement box 3, allowing measuring unit 5 to be easily set in an advantageous measuring position in measurement box 3. This means that, among other things, vapour barrier 6 and moisture and temperature sensor 7 will then automatically be positioned correctly over the mouth of vapour duct 2. Alternatively, the measuring device can also be implemented so that measuring unit 5' is not designed to be placed directly in measurement box 3 (Figure 2), in which case, measuring unit 5' is connected to a separate measuring head 11 placed on the mouth of vapour duct 2. Measuring head 11 is connected to measuring unit 5', for example, by means of cable 12. Vapour barrier 6 is connected to measuring unit 5 or separate measuring head 11. Vapour barrier 6 is intended to isolate the second end of vapour duct 2 for the duration of the measurement. Vapour barrier 6 can be manufactured from a material such as rubber. Moisture and temperature sensor 7 and second temperature sensor 9 are selected from the range of suitable sensors. It is advantageous to select such a sensor 9 that will, if desired, conduct heat output to its environment. In this way temperature sensor 9 preferably operates as both a heating and measuring resistance.

In the method of forming the measurement duct, an elongated measurement duct 2 is formed in structural material 1 , having a first and a second end, and being enclosed by an essentially vapour-tight material over the section between the first and second ends. Measurement duct 2 is preferably formed in connection with the formation of structure 1 , for example, by placing an indoor installation conduit in the structure. In the case of concrete, for instance, this can be carried out by setting one or more suitably positioned indoor installation conduits in the area to be cast, before casting the concrete. Measurement duct 2 is formed with its first end remaining inside structure 1 and its second end extending to the surface of structure 1. The first end of measurement duct 2 is preferably protected by vapour-permeable protector plug 4. After this, structure 1 can be closed, or, in the case of a concrete structure, the concrete slab can be cast. The second end of measurement duct 2 is suitably shaped then closed with a vapour-tight vapour-barrier plug 10. This procedures forms a measurement duct 2 in structure 1, along which the moisture content around the first end of measurement duct 2 inside structure 1 can be conducted by diffusion to the second end of measurement duct 2.

In the method for measuring moisture, vapour-barrier plug 10 is removed from the second end of measurement duct 2, into which temperature sensor 9 is pushed.

Temperature sensor 9 is pushed along measurement duct 2 at least until it has more or less reached the first end of measurement duct 2. Temperature sensor 9 is pushed, by, for example, the leads connected to it. Next, moisture and temperature sensor 7 is pushed into measurement duct 2, which is closed by means of vapour barrier 6 to become essentially vapour-tight. Alternatively, moisture and temperature sensor 7 can be placed in the mouth of measurement duct 2 and a vapour barrier formed around the mouth of measurement duct 2 and moisture and temperature sensor 7. Temperature sensor 9 and moisture and temperature sensor 7 are connected to measuring unit 5, 5'.

After the measuring device has been set in place in measurement duct 2, a wait is made, to ensure that diffusion can even out possible disturbances in measurement duct 2's moisture profile arising during these operations. The typical time for evening out is about one minute for each centimetre of length of measurement duct 2. After the evening-out period, the temperature 7/ at the first end of measurement duct 2 is measured using temperature sensor 9, and the temperature T₂ and relative humidity ?/2₂ of the air at the second end of measurement duct 2 are measured using moisture and temperature sensor 7. If temperatures Tj and T₂ differ, the value ?Λ₂ of the relative humidity measured at the second end of measurement duct 2 will not directly depict the relative humidity Rhi prevailing at the first end of measurement duct 2. The relative humidity Rhi prevailing at the first end of measurement duct 2 and in structure 1 around it is obtained by calculation from the formula:

The use of a temperature sensor 9 heated in pulses also permits a check to be made for water in liquid form at the first end of measurement duct 2. One way of doing this is to switch on power to temperature sensor 9 and measure the temperature of the sensor as a function of time. Whether temperature sensor 9 is in air or in water can be decided from the change in the temperature of sensor 9 per unit of energy fed to it. A change in temperature essentially smaller than that in a sensor 9 located freely in air is interpreted to signify the presence of liquid water at the first end of measurement duct 2.

Alternatively, the invention can be implemented so that the entire length of vapour duct

2 is not utilized to conduct moisture from the point of measurement to the sensors of the measuring device. Instead, a measurement chamber is isolated at the first end of vapour duct 2. While the measurement chamber preferably encloses the immediate vicinity of the first end of vapour duct 2, it can also extend, for example, to halfway along the vapour duct. The measurement chamber is separated vapour-tightly from the beginning of vapour duct 2 by means of a plug or valve. The measurement chamber or related structure is also arranged to fill vapour duct 2 in such a way that it normally prevents an exchange of vapour between the first and second ends of the vapour duct. Thus, in this embodiment, the measurement chamber is connected to exchange vapour with the area being measured, and is normally isolated from the surrounding atmosphere, thus preventing the object being measured drying. Besides this, however, it is preferable to close the second end of vapour duct 2 with an essentially vapour-tight plug, to prevent moisture from the air surrounding the structure condensing inside vapour duct 2. Such condensed moisture can interfere with measurements, and appears especially when the temperature of vapour duct 2 drops towards its first end located inside the structure.

The embodiment utilizing a separate measurement chamber has the advantage over the embodiment with a unified vapour duct 2, that moisture does not condense in vapour duct 2, even if the temperature further down vapour duct 2 is lower than at the first end of vapour duct 2 in the building material. The measurement chamber should also not be unnecessarily long, to prevent condensation.

The measuring device used in conjunction with vapour ducts of the type disclosed above also differs from that disclosed in the previous example. This is because moisture or temperature measurements made at the second end of vapour duct 2 are not required in the case of vapour ducts incorporating a measurement chamber. Instead, temperature and moisture are measured from the measurement chamber, by means of sensors that are pushed into it. To allow such sensors to be pushed easily into the measurement chamber, they are placed on a measuring head; the measurement chamber being closed by a valve that can be opened with the aid of the measuring head.

Figure 3 shows one preferred valve, which can be used, in connection with the invention, to isolate the measurement chamber from the rest of the vapour duct. The valve in Figure 3 incorporates a cylindrical body component 20, which is closed at one end by means of a perforated base 21. The valve also includes a pipe 22, which is located inside body component 20 in such a way that a gap 23 for a pipe-like vapour duct 2 remains between body component 20 and pipe 22. The valve also includes a plug 24 arranged to slide inside pipe 22, and a spring 25 fitted between plug 24 and base 21, which allows the measurement chamber remaining inside pipe 22 to be isolated, in a manner that is essentially vapour- tight, from the remainder of vapour duct 2. The internal surface of pipe 22 has a conical shape, so that, if plug 24 is pressed against spring 25, a vapour exchange connection opens past plug 24 to the rear end of pipe 22, and, if plug 24 is released, the vapour exchange connection closes by spring 25 pressing plug 24 against the inner surface of front end of pipe 22. In the embodiment in the figure, guide surfaces 28 are also formed in the front end of pipe 22, to guide the measuring head. In addition, the figure also shows a vapour-permeable protector membrane 26, which, in the preferred embodiment, can be placed on base 21, in a depression made for it in base 21, on top of holes 27.

Though protector membrane 26 is permeable by vapour, it must not allow liquid water to pass. Thus, protector membrane 26 corresponds to protective plug 4 disclosed in the embodiments in Figures 1 and 2. Further, when the vapour duct is set in concrete, it is preferable for protector membrane 26 to be impermeable to the salts appearing in concrete, so that they cannot accumulate in the valve construction. A salt-impermeable protector membrane 26 can be manufactured from, e.g., polytetrafluoroethylene.

Figure 4 shows the plug of figure 3 installed at the end of vapour duct 2. The figure also shows measuring head 31 , containing temperature and moisture sensors and connected by cable 30 to the measuring device. Measuring head 31 is pushed by means of cable 30 along vapour duct 2 to the vicinity of the valve. At this stage, the valve is closed, i.e.; plug 24 is being pressed by spring 25 against the front end of pipe 22. The moisture state prevailing in the measurement chamber inside pipe 22 has been equalized, through holes 27, with that in the structure surrounding the valve.

Figure 5 shows in turn the apparatus in Figure 4, with measuring head 31 pressed against plug 24 and pushed inside pipe 22. In this case, measuring head 31 is in the measurement chamber and the apparatus is in the moisture-measurement position. It can also be seen from Figure 5 that the outer surface of measuring head 31 is arranged to fit tightly against the inner surface of the rear end of pipe 22, which reduces the exchange of vapour between the measurement chamber and the rest of vapour duct 2 to a level with an insignificant effect on measurement.

Claims

Claims:

1. A method for forming a measurement connection to a structure (1) for measuring the internal moisture content of the structure (1), in which method the measurement connection is created during the construction of the structure (1), characterized by

- forming a pipe-like vapour duct (2), having a first and a second end, and an essentially vapour-tight surface enclosing the vapour duct (2) over the section between the ends of the vapour duct (2),

- setting the vapour duct (2) inside the structure (1), with the first end of the vapour duct (2) inside the structure (1) and the second end extending to the surface of the structure (1), or to a cavity made in the surface, such as a measurement box (3),

- closing the second end of the vapour duct (2) to be essentially vapour-tight.

2. A method according to Claim 1, characterized by

forming the vapour duct (2) of plastic piping bent into a suitable shape and

closing the second end of the vapour duct (2) by placing an essentially vapour-tight shut-off plug (10) in it.

3. A method according to Claim l or2, characterized by closing the first end of the vapour duct (2) with a protector plug (4) that is permeable by water vapour.

4. A method according to one of Claims 1-3, characterized by installing a valve, which can be penetrated by a suitable measuring head (31), in the vapour duct (2), to isolate a measurement chamber in the vapour duct (2), between the valve and the first end of the vapour duct (2).

5. A method according to Claim 4, characterized by locating the valve at the first end of the vapour duct.

6. A method for measuring the internal moisture content in a structure (1), through a measurement connection located in the structure (1) and extending from the structure's (1) surface to its interior, in which method the relative humidity of the air in the measurement connection is measured, characterized by

- using a vapour duct (2) as the measurement connection, the first end of which extends to the interior of the structure (1) and the second end to the surface of the structure (1), and which is essentially vapour-tight between its first and second ends,

- measuring the temperature of the air in the first end of the vapour duct (2),

- measuring the temperature of the air in the second end of the vapour duct (2),

- measuring the relative humidity of the air in the second end of the vapour duct (2), and

- determining the relative humidity of the air in the first end of the vapour duct from the measured relative humidity and temperatures.

7. A method according to Claim 6, characterized by

- taking a first temperature sensor (9) to the first end of the vapour duct (2),

- bringing a moisture sensor (7) into contact with the air at the second end of the vapour duct (2), - bringing a second temperature sensor (7) into contact with the air at the second end of the vapour duct (2),

- closing the second end of the vapour duct (2) to be essentially vapour-tight,

waiting until the moisture profile of the air has equalized sufficiently, and

- measuring the relative humidity of the air at the second end of the vapour duct (2) and the temperatures at its first and second ends with the aid of the first (9) and the second (7) temperature sensors and of the moisture sensor (7).

8. A measurement connection for measuring moisture in the interior of a structure (1), comprising

- a first end, extending to the interior of the structure (1),

a second end, extending to the surface of the structure (1), and

- a unified space connecting the first end to the second end,

characterized in that it includes a pipe-like vapour duct (2), which is arranged to isolate the unified space connecting the first end to the second end essentially vapour- tightly over the section between the first and second ends.

9. A measurement connection according to Claim 8, characterized in that it includes a protector plug (4), permeable by water vapour, fitted to the first end of the vapour duct (2).

10. A measurement connection according to Claim 9, characterized in that the water-vapour-permeable protector plug (4) is essentially impermeable by salts.

11. A measurement connection according to one of Claims 8-10, characteriz e d in that it includes a vapour shut-off plug (10), which is essentially impermeable by water vapour, fitted to the second end of the vapour duct (2), to prevent the exchange of moisture between the vapour duct (2) and the space surrounding its second end.

12. A measurement connection according to one of Claims 8-11, characteriz e d in that it includes a measurement box (3) fitted to the second end of the vapour duct (2).

13. A measurement connection according to one of Claims 8-12 characteriz e d in that it includes a valve located inside the vapour duct (2) or at the first end of the vapour duct (2), which is arranged to isolate a measurement chamber from the vapour duct (2), which measurement chamber is connected to allow the exchange of vapour with the structure surrounding the first end of the vapour duct (2), but which is essentially vapour-tightly isolated from the section of the vapour duct (2) extending towards the second end, and which valve is arranged to allow a measuring device to be brought to the measurement chamber.

14. A measurement connection according to Claim 13, characterized in that the valve includes

- a cylindrical body component (20), closed at one end by a perforated base (21).

a pipe (22), with an internal surface narrowing in one direction, set inside the body component (20),

- a gap (23) left between the body component (20) and the pipe (22) for the pipe-like vapour duct (2), - a plug (24), arranged to slide the inside pipe (22) and shaped to correspond to the inner surface of the pipe (22), and

- a spring (25), fitted between the plug (24) and the base (21), to press the plug (24) towards the narrower end of the pipe (22) and to close the valve when not loaded and to open the valve when the plug (24) is suitably loaded.

15. A measuring device for measuring the moisture in the interior of a structure (1) through a vapour duct (2) fitted to the structure (1), c h a r a c t e r i z e d in that it includes

- a measuring unit (5, 5') for controlling measurements and for managing the measurement results,

a flexible lead (8) connected at its first end to the measuring unit (5, 5'),

- a second temperature sensor (9), connected to the second end of the flexible lead (8), for measuring the temperature prevailing at the first end of the vapour duct (2),

a moisture sensor (7), connected to the measuring unit, for measuring the humidity of the air prevailing at the second end of the vapour duct (2),

a first temperature sensor (7), connected to the measuring unit, for measuring the temperature prevailing at the second end of the vapour duct (2), and

- a vapour barrier (6) for closing the second end of the vapour duct (2) in an essentially vapour-tight manner.

16. A measuring device according to Claim 15, c h a r a c t e r i z e d in that

- the second temperature sensor (9) includes a resistance and

- measuring unit (5, 5') includes components for supplying power to the resistance of the temperature sensor (9), whereby the temperature of the temperature sensor (9) can, if desired, be both raised and measured, to detect liquid water that may surround temperature sensor (9).

17. A measuring device according to Claim 15 or 16, characterized in that the first temperature sensor (7) is mechanically connected to the moisture sensor (7).

18. A measuring device according to one of Claims 15 - 17, for use together with a vapour duct (2), one end of which is connected to a measurement box (3), characte r i z e d in that the measuring device includes a case that fits inside the measurement box (3) and which conforms to the shape of the inner surface of the measurement box

(3).