Patent Description:
<CIT> discloses an apparatus for fluid flow detection. The apparatus makes use of a signal provided by a pipe temperature sensor and of a signal provided by an ambient temperature sensor. A low flow algorithm may attempt to detect flow leaks such as a dripping tap. If no leak is present during a quiet period, the ambient temperature and pipe temperature will generally tend to be close together. If, on the other hand, a low flow leak is present during a quiet period, there will be generally a noticeable difference between the ambient temperature and pipe temperature.

<CIT>, <CIT>, <CIT>, <CIT> as well as <CIT> and <CIT> A1disclose other prior art.

Against this background, a novel method for micro-leakage detection in a fluid system and a novel micro-leakage detection apparatus are provided as disclosed in the appended claims.

The novel method for micro-leakage detection in a fluid system comprises at least the following steps:
Measure the fluid flow through a fluid pipe by a flow meter.

Measure the pipe temperature of the fluid pipe by at least one pipe temperature sensor.

When there is no fluid flow measured by the flow meter, particularly because or when the fluid flow through the fluid pipe is stopped by the fluid valve being closed, analyze the pipe temperature for the micro-leakage detection.

The novel method for micro-leakage detection is based both on a flow measurement by a flow meter and a pipe temperature measurement by the at least one pipe temperature sensor. The novel method allows a very simple and reliable micro-leakage detection in a fluid system. The micro-leakage which can be detected by making use of the invention is below a measuring resolution or a measuring range of the flow meter.

The pipe temperature of the fluid pipe is measured by the at least one pipe temperature sensor when the fluid flow through the fluid pipe is allowed and when the fluid flow through the fluid pipe is stopped, wherein the measured pipe temperature is analyzed for the micro-leakage detection only if there is no fluid flow measured by the flow meter. In this case, the at least one pipe temperature sensor is active and measures the pipe temperature when fluid flow is measured by the flow meter and when no fluid flow is measured by the flow meter. However, the measured pipe temperature is analyzed for micro-leakage detection only under the condition that there is no fluid flow measured by the flow meter.

Alternatively, the pipe temperature of the fluid pipe is both measured and analyzed for the micro-leakage detection only when the fluid flow through the fluid pipe is stopped. In this case, the at least one pipe temperature sensor is inactive when fluid flow is measured by the flow meter. The at least one pipe temperature sensor then becomes activated when no fluid flow is measured by flow meter. In this case, the pipe temperature is measured and analyzed for micro-leakage detection only under the condition that there is no fluid flow measured by the flow meter.

According to a first embodiment of the method for micro-leakage detection the same has the additional following steps: When there is no fluid flow measured by the flow meter after the fluid flow through the fluid pipe has been stopped, calculate a temporal gradient of the pipe temperature. If the temporal gradient of the pipe temperature differs more than a first threshold from a first reference value, and if there is no flow measured by the flow meter, then detect micro-leakage.

According to a second embodiment of the method for micro-leakage detection the same has the additional following steps: Measure the pipe temperature of the fluid pipe by a first pipe temperature sensor and by a second pipe temperature sensor being positioned at different locations of the fluid pipe. When there is no fluid flow measured by the flow meter for the defined time interval, calculate a temperature difference between the pipe temperatures measured by the first and second pipe temperature sensors. If the temperature difference between the pipe temperatures differs more than a second threshold from a second reference value, and if there is no flow measured by the flow meter, then detect micro-leakage.

The above first and second embodiments are preferred. The same are ambient temperature independent and do not require the measurement of the ambient temperature. Such an ambient temperature independent micro-leakage detection is very simple and reliable. It is possible to use the first and second embodiment in combination, meaning that micro-leakage is detected if the temporal gradient of the pipe temperature differs more than the first threshold from the first reference value and/or if the temperature difference between the pipe temperatures differs more than the second threshold from the second reference value.

The novel micro-leakage detection apparatus suitable for micro-leakage detection in a fluid system is defined in claim <NUM>.

Preferred developments of the invention are provided by the dependent claims and the description which follows.

Exemplary embodiments are explained in more detail on the basis of the drawing, in which:.

<FIG> shows a schematic diagram of a fluid flow system <NUM>, namely of a potable water system, of a building <NUM>. The fluid flow system <NUM> comprises a fluid pipe <NUM> running at least partially inside of the building <NUM>. This fluid pipe <NUM> is connected to a main water pipe <NUM> running outside of the building <NUM>. This fluid pipe <NUM> comprises a fluid valve <NUM>. The fluid valve <NUM> may be a water tap. A fluid flow through the fluid pipe <NUM> is stopped when the fluid valve <NUM> is closed. A fluid flow through the fluid pipe <NUM> is allowed when the fluid valve <NUM> is opened. The fluid pipe <NUM> may be made from a metal like copper or from a plastic like polypropylene.

The present invention relates to a method for micro-leakage detection in the fluid system <NUM> and to a micro-leakage detection apparatus. <FIG> shows such a micro-leakage detection apparatus <NUM>.

The micro-leakage detection apparatus <NUM> receives at least signals from a flow meter <NUM> and from at least one pipe temperature sensor 17a, 17b.

The flow meter <NUM> is assigned to the fluid pipe <NUM> and measures the fluid flow through the fluid pipe <NUM>.

The flow meter <NUM> has a measuring range or measuring resolution. The flow meter <NUM> is configured to measure a fluid flow through the fluid pipe <NUM> when the fluid valve <NUM> is opened, meaning that there is a regular fluid consumption across the fluid valve <NUM>. However, when the fluid valve <NUM> is closed, there may be an irregular fluid consumption caused by micro-leakage. The micro-leakage causes a certain fluid flow being below the measuring range or measuring resolution of the flow meter <NUM>. So, micro-leakage cannot be detected by the flow meter <NUM> as such, namely by the flow meter <NUM> alone.

The at least one pipe temperature sensor 17a, 17b is also assigned to the fluid pipe <NUM> and measures the pipe temperature of the fluid pipe <NUM>.

<FIG> shows a first pipe temperature sensor 17a and a second pipe temperature sensor 17b. Further, <FIG> shows an ambient temperature sensor <NUM> measuring an ambient temperature within the building. The ambient temperature sensor <NUM> may be positioned in the proximity of the fluid pipe <NUM>. Only one of the first and second temperature sensors 17a, 17b and the flow meter <NUM> are mandatory units for the present invention. The ambient temperature sensor <NUM> is an optional unit. If an ambient temperature sensor <NUM> is present, the same is preferably positioned in the proximity of the fluid pipe <NUM>.

A first embodiment of the invention makes use of at least one pipe temperature sensor 17a, 17b and of the flow meter <NUM> only.

A second embodiment of the invention makes use of the first and second pipe temperature sensors 17a and 17b and of the flow meter <NUM>.

The micro-leakage detection apparatus <NUM> has an interface 15a being configured to receive signals or data from the flow meter <NUM> and an interface 15b being configured to receive signals or data from the at least one pipe temperature sensor 17a, 17b.

A third embodiment makes use of at least one pipe temperature sensor 17a, 17b, of the flow meter <NUM> and of the ambient temperature sensor <NUM>. In this case the micro-leakage detection apparatus <NUM> has an interface 15c being configured to receive signals or data from the ambient temperature sensor <NUM>.

The method for micro-leakage detection in the fluid system <NUM> comprises at least the following steps:
Measure the fluid flow through the fluid pipe <NUM> by the flow meter <NUM>.

Measure the pipe temperature of the fluid pipe <NUM> by at least one pipe temperature sensor 17a, 17b.

When there is no fluid flow measured by the flow meter <NUM> because or when the fluid flow through the fluid pipe <NUM> is stopped by the closed fluid valve <NUM>, analyze the pipe temperature for the micro-leakage detection.

The pipe temperature of the fluid pipe <NUM> is measured by at least one pipe temperature sensor 17a, 17b when the fluid flow through the fluid pipe <NUM> is allowed and when the fluid flow through the fluid pipe <NUM> is stopped, wherein the measured pipe temperature is analyzed for the micro-leakage detection only when there is no fluid flow measured by the flow meter <NUM>.

In this case, the at least one pipe temperature sensor 17a, 17b is active and measures the pipe temperature when fluid flow is measured by the flow meter <NUM> and when no fluid flow is measured by the flow meter <NUM>. However, the measured pipe temperature is analyzed for micro-leakage detection only under the condition that there is no fluid flow measured by the flow meter <NUM>.

Alternatively, the pipe temperature of the fluid pipe <NUM> is both measured and analyzed for the micro-leakage detection only when the fluid flow through the fluid pipe <NUM> is stopped by the fluid valve <NUM>.

In this alternative case, the at least one pipe temperature sensor 17a, 17b is inactive or becomes inactivated when fluid flow is measured by the flow meter <NUM>. The at least one pipe temperature sensor 17a, 17b is active or becomes activated when no fluid flow is measured by flow meter <NUM>. In this case, the pipe temperature is both measured and analyzed for micro-leakage detection only under the condition that there is no fluid flow measured by the flow meter <NUM>.

The method for micro-leakage detection is based both on a flow measurement by the flow meter <NUM> and pipe temperature measurement by the at least one pipe temperature sensor 17a, 17b. The method allows a very simple and reliable micro-leakage detection in the fluid system <NUM>. The invention allows to detect micro-leakage that causes a fluid flow being below the measuring range or measuring resolution of the flow meter <NUM>.

The micro-leakage detection apparatus <NUM> is configured to execute the above method steps. The interface 15a of the micro-leakage detection apparatus <NUM> is configured to receive signals or data from the flow meter <NUM> measuring the fluid flow through the fluid pipe <NUM>. The interface 15b of the micro-leakage detection apparatus <NUM> is configured to receive signals or data from the at least one pipe temperature sensor 17a, 17b measuring the pipe temperature of the fluid pipe <NUM>.

A processor 15d of the micro-leakage detection apparatus <NUM> is configured to detect micro-leakage by analyzing the pipe temperature provided by the at least one pipe temperature sensor 17a, 17b when there is no fluid flow measured by the flow meter <NUM>. The micro-leakage detection apparatus <NUM> further comprises a memory 15e.

If the pipe temperature of the fluid pipe <NUM> is both measured and analyzed only when there is no fluid flow measured by the flow meter <NUM>, then the processor 15d of the micro-leakage detection apparatus <NUM> is configured to active the least one pipe temperature sensor 17a, 17b under the condition that there is no fluid flow measured by the flow meter <NUM>.

As mentioned above, a first embodiment of the invention makes use of at least one pipe temperature sensor 17a and/or 17b and of the flow meter <NUM> only. In the following description of the first embodiment it is presumed that the pipe temperature sensor 17a is used for the measurement of the pipe temperature. In this first embodiment a temporal gradient of the pipe temperature measured by the pipe temperature sensor 17a is calculated when there is no fluid flow measured by the flow meter <NUM> after the fluid flow through the fluid pipe <NUM> has been stopped. The condition that the fluid flow has been stopped can be detected on basis of the signal provided by the flow meter <NUM>, namely when there is fluid flow measured by the flow meter <NUM> and subsequently no fluid flow measured by the flow meter <NUM>. The temporal gradient is also often called gradient over time. If the temporal gradient of the pipe temperature differs more than a first threshold from a first reference value, and if there is no flow measured by the flow meter <NUM>, then micro-leakage is detected.

<FIG> shows a signal flow diagram for the first embodiment of the invention.

In step <NUM> the flow meter <NUM> measures the fluid flow though the fluid pipe <NUM>. In step <NUM> the pipe temperature sensor 17a measures the pipe temperature of the fluid pipe <NUM>.

In step <NUM> it is determined if the flow meter <NUM> measures a fluid flow through the fluid pipe <NUM>. If it is determined in step <NUM> that the flow meter <NUM> measures a fluid flow through the fluid pipe <NUM>, then the method goes back to step <NUM>. If it is determined in step <NUM> that the flow meter <NUM> measures no fluid flow through the fluid pipe <NUM>, then the method goes to step <NUM>.

In step <NUM> is determined if the flow meter <NUM> measures no fluid flow through the pipe. If this is not the case, the method goes back to step <NUM>. If this is the case, the method goes to step <NUM>. In step <NUM> the temporal gradient - also often called gradient over time - of the pipe temperature measured by the pipe temperature sensor 17a is calculated.

Then, in step <NUM> it is determined if the temporal gradient of the pipe temperature differs more than a first threshold from a first reference value or not.

If the temporal gradient of the pipe temperature does not differ more than the first threshold from the first reference value, no micro-leakage is detected in step <NUM>. If the temporal gradient of the pipe temperature differs more than the first threshold from the first reference value, and if there is still no fluid flow measured by the flow meter <NUM>, then in step <NUM> micro-leakage is detected.

In connection with the first embodiment, alternatively the pipe temperature sensor 17b may be used for the measurement of the pipe temperature. Further on, both pipe temperature sensors 17a, 17b may be used and an average value may be calculated for the pipe temperature.

The first reference value for the temporal gradient of the pipe temperature may be determined as follows: If there is no fluid flow measured after the fluid flow through the fluid pipe has been stopped, then calculate and store the temporal gradient of the pipe temperature. Calculate an average value from the stored temporal gradients. Determine the first threshold from this average value.

The average value may be multiplied by a security-factor to determine the first reference value.

The above method is executed by the micro-leakage detection apparatus <NUM> in or at a defined sampling rate. The calculation of the temporal gradient may take place at each sampling time of the sampling rate. However, the calculated temporal gradient may not be stored at each sampling time of the sampling rate. It is possible that the calculated temporal gradient is only stored example given every <NUM> times or every <NUM> times or every <NUM> times or every <NUM> times after calculation of the same. These calculated temporal gradients may be stored in a ring buffer of the memory 15e of the micro-leakage detection apparatus <NUM>. The ring buffer may have a defined buffer size. If the ring buffer is completely filled, then the average value from the stored temporal gradients may be calculated. If the the ring buffer is not completely filled, then the average value may not be calculated. If the ring buffer is completely filled and if a newly calculated temporal gradient is to be stored, then the oldest one of the stored temporal gradients becomes replaced by the newly calculated temporal gradient and the average value is newly calculated.

The calculated temporal gradient may only be stored and used to calculate the average value if the absolute value of a difference between the calculated temporal gradient and a previously calculated temporal gradient or the absolute value of a difference between the calculated temporal gradient and an average value of previously stored temporal gradients is below a respective threshold.

<FIG> shows a time diagram further illustrating the first embodiment of the invention. <FIG> shows as a function of the time t a fluid flow rate <NUM> and a pipe temperature <NUM> measured by the pipe temperature sensor 17a.

At point of times t1, t3 and t5 a respective fluid flow <NUM> through the fluid pipe <NUM> starts. At point of times t2, t4 and t6 the respective fluid flow <NUM> through the fluid pipe <NUM> stops because of a closed the fluid valve <NUM>.

After the fluid flow through the fluid pipe <NUM> has been stopped at the point of times t2, t4 and t6, the temporal gradient <NUM> of the pipe temperature <NUM> is calculated. If the calculated temporal gradient <NUM> of the pipe temperature <NUM> differs more than the first threshold from the first reference value, and if there is no flow measured by the flow meter <NUM>, then micro-leakage is detected.

In <FIG>, the temporal gradients <NUM> calculated at point of times t2, t4 do not differ more than the first threshold from the first reference value. So, no micro-leakage is detected at point of times t2, t4. The temporal gradient <NUM> calculated at point of times t6 differs more than the first threshold from the first reference value. So, micro-leakage <NUM> is detected at point of times t6. The first reference value may correspond to the average of the temporal gradients <NUM> calculated at point of times t2, t4.

As mentioned above, a second embodiment of the invention makes use of the first and second pipe temperature sensors 17a, 17b and of the flow meter <NUM>.

In this second embodiment the pipe temperature of the fluid pipe <NUM> is measured by the first pipe temperature sensor 17a and by the second pipe temperature sensor 17b being positioned at different locations of the fluid pipe <NUM>.

The pipe temperature sensors 17a and 17b have a different distance to the fluid valve <NUM>. The pipe temperature sensor 17b is positioned closer to the fluid valve <NUM> than the pipe temperature sensor 17a. The distance between the pipe temperature sensors 17a and 17b may be at least <NUM>.

When there is no fluid flow measured by the flow meter <NUM> for a defined time interval, a temperature difference between the pipe temperatures measured by the first and second pipe temperature sensors 17a and 17b is calculated. If the temperature difference between these pipe temperatures differs more than a second threshold from a second first reference value, and if there is no flow measured by the flow meter <NUM>, then micro-leakage is detected.

<FIG> shows a signal flow diagram for the second embodiment of the invention.

In step <NUM> the flow meter <NUM> measures the fluid flow though the fluid pipe <NUM>. In step <NUM> the first pipe temperature sensor 17a measures the pipe temperature of the fluid pipe <NUM>. In step <NUM> the second pipe temperature sensor 17b measures the pipe temperature of the fluid pipe <NUM>.

In step <NUM> it is determined if the flow meter <NUM> measures no fluid flow through the pipe. If this is not the case, the method goes back to step <NUM>. If this is the case, the method goes to step <NUM>.

In step <NUM> it is determined if the flow meter <NUM> measured no fluid flow through the fluid pipe <NUM> for a defined time interval after the fluid flow has been stopped. If this is not the case, the method goes back to step <NUM>. If this is the case, the method goes to step <NUM>.

In step <NUM> the temperature difference between the pipe temperatures measured by the first and second pipe temperature sensors 17a and 17b is calculated.

Then, in step <NUM> it is determined if this temperature difference differs more than a second threshold from the second reference value or not.

If this temperature difference does not differ more than the second threshold from the second reference value, no micro-leakage is detected in step <NUM>.

If this temperature difference differs more than the second threshold from the second reference value, and if there is still no fluid flow measured by the flow meter <NUM>, then in step <NUM> micro-leakage is detected.

The second reference value is determined as follows: If there is no fluid flow measured for the defined time interval, then calculate and store the temperature difference between the pipe temperatures measured by the first and second pipe temperature sensors 17a, 17b. Calculate an average value from the stored temperature differences. Determine the second threshold from this average value.

The average value may be multiplied by a security-factor to determine the second reference value.

The calculation of the temperature difference between the pipe temperatures measured by the first and second pipe temperature sensors 17a, 17b may take place at each sampling time of the sampling rate. However, said temperature difference may not be stored at each sampling time of the sampling rate. It is possible that said calculated temperature difference is stored example given every <NUM> times or every <NUM> times or every <NUM> times or every <NUM> times after calculation of the same. Said calculated temperature difference may be stored in a ring buffer of the memory 15e of the micro-leakage detection apparatus <NUM>. The ring buffer may have a defined buffer size. If the ring buffer is completely filled, then the average value may be calculated. If the ring buffer is not completely filled, then the average value may not be calculated. If the ring buffer is completely filled and if a newly calculated temperature difference between the pipe temperatures measured by the first and second pipe temperature sensors 17a, 17b is to be stored, then the oldest one of the stored temperature differences becomes replaced by the newly calculated temperature difference and the average value is newly calculated.

The calculated temperature difference may only be stored and used to calculate the average value if the absolute value of a difference between the calculated temperature difference and a previously calculated temperature difference or if the absolute value of a difference between the calculated temperature difference and an average value of previously stored temperature differences is below a threshold.

<FIG> shows a time diagram further illustrating the second embodiment of the invention. <FIG> shows as a function of the time t a fluid flow rate <NUM> and pipe temperatures <NUM>, <NUM> measured by the pipe temperature sensors 17a, 17b.

At point of times t1, t3 and t5 a respective fluid flow <NUM> through the fluid pipe <NUM> starts. At point of times t2, t4 and t6 the respective fluid flow <NUM> through the fluid pipe <NUM> stops.

When there is no fluid flow measured by the flow meter <NUM> for a defined time interval after the fluid flow through the fluid pipe <NUM> has been stopped by closing the fluid valve <NUM> at the point of times t2, t4 and t6, a temperature difference <NUM> between the pipe temperatures <NUM>, <NUM> measured by the first and second pipe temperature sensors 17a, 17b is calculated. The condition that the fluid flow has been stopped can be detected on basis of the signal provided by the flow meter <NUM>, namely when there is fluid flow measured by the flow meter <NUM> and subsequently no fluid flow measured by the flow meter <NUM>.

If the temperature difference <NUM> between the pipe temperatures <NUM>, <NUM> differs more than the second threshold from the second reference value, and if there is no flow measured by the flow meter <NUM>, then micro-leakage <NUM> is detected.

In <FIG>, the temperature differences <NUM> calculated a defined time interval after the point of times t2, t4 do not differ more than the second threshold from the second reference value. So, no micro-leakage is detected. The temperature difference <NUM> calculated a defined time interval after the point of time t6 differs more than the second threshold from the second reference value. So, micro-leakage <NUM> is detected. The second reference value may correspond to the average of the temperature differences <NUM> calculated the defined time interval after the point of times t2, t4.

The above first and second embodiments are preferred. The same do not require the measurement of the ambient temperature. Such an ambient temperature independent micro-leakage detection is very simple and reliable.

It is possible to use the first and second embodiment in combination. So, micro-leakage may be detected if the temporal gradient of the pipe temperature differs more than the first threshold from the first reference value or if the temperature difference between the pipe temperatures differs more than the second threshold from the second reference value.

A third embodiment makes use of the ambient temperature sensor <NUM>.

In this third embodiment, the ambient temperature is measured by the ambient temperature sensor <NUM>. When there is no fluid flow measured by the flow meter <NUM> for a defined time interval, then a temperature difference between the pipe temperature and the ambient temperature is calculated.

If the temperature difference between the pipe temperature and the ambient temperature differs more than a third threshold from a third reference value, and if there is still no flow measured by the flow meter <NUM>, then micro-leakage is detected.

<FIG> shows a signal flow diagram for the third embodiment of the invention.

In step <NUM> the flow meter <NUM> measures the fluid flow though the fluid pipe <NUM>. In step <NUM> at least one of pipe temperature sensors 17a, 17b measures the pipe temperature. In step <NUM> the ambient temperature sensor <NUM> measures the ambient temperature.

In step <NUM> it is determined if the flow meter <NUM> measures no fluid flow through the fluid pipe <NUM>. If this is not the case, the method goes back to step <NUM>. If this is the case, the method goes to step <NUM>.

In step <NUM> it is determined if the flow meter <NUM> measured no fluid flow through the fluid pipe <NUM> for a defined time interval. If this is not the case, the method goes back to step <NUM>. If this is the case, the method goes to step <NUM>.

In step <NUM> the temperature difference between the pipe temperature measured by the respective pipe temperature sensor 17a, 17b and the ambient temperature measured by the ambient temperature sensor <NUM> is calculated.

Then, in step <NUM> it is determined if this temperature difference differs more than a third threshold from the third reference value or not. If this temperature difference does not differ more than the third threshold from the third reference value, no micro-leakage is detected in step <NUM>. If this temperature difference differs more than the third threshold from a third reference value, and if there is still no fluid flow measured by the flow meter <NUM>, then in step <NUM> micro-leakage is detected.

The third threshold for the temperature difference between the pipe temperature and the ambient temperature may be determined as follows: If there is no fluid flow measured for the defined time interval, then calculate and store the temperature difference between the pipe temperature and the ambient temperature. Calculate an average value from the stored temperature differences. Determine the first threshold from this average value. The average value may be multiplied by a factor to determine the third reference value.

The calculation of the temperature difference between pipe temperature and the ambient temperature may take place at each sampling time of the sampling rate. However, said temperature difference may not be stored at each sampling time of the sampling rate. It is possible that said calculated temperature difference is stored example given every <NUM> times or every <NUM> times or every <NUM> times or every <NUM> times after calculation of the same. Said calculated temperature difference may be stored in a ring buffer of the memory 15e of the micro-leakage detection apparatus <NUM>. The ring buffer may have a defined buffer size. If the ring buffer is completely filled, then the average value may be calculated. If the ring buffer is not completely filled, then the average value may not be calculated. If the ring buffer is completely filled and if a newly calculated temperature difference between the pipe temperature and the ambient temperature is to be stored, then the oldest one of the stored temperature differences becomes replaced by the newly calculated temperature difference and the average value is newly calculated.

<FIG> shows a time diagram further illustrating the third embodiment of the invention. <FIG> shows as a function of the time t a fluid flow rate <NUM> and a temperature difference <NUM> between the pipe temperature measured by one of the pipe temperature sensors 17a, 17b and the ambient temperature.

At point of times t1, t3 and t5 a respective fluid flow <NUM> through the fluid pipe <NUM> starts. At point of times t2, t4 and t6 the respective fluid flow <NUM> through the fluid pipe <NUM> stops by closing the fluid valve <NUM>. When there is no fluid flow measured by the flow meter <NUM> for a defined time interval after the fluid flow through the fluid pipe <NUM> has been stopped at the point of times t2, t4 and t6, the temperature difference <NUM> is determined. If the temperature difference <NUM> between the pipe temperature and the ambient temperature differs more than the third threshold from the third reference value, and if there is no flow measured by the flow meter <NUM>, then micro-leakage <NUM> is detected.

In <FIG>, the values V1, V2 of temperature difference <NUM> determined a defined time interval after the point of times t2, t4 do not differ more than the third threshold from the third reference value. So, no micro-leakage is detected. The value V3 of the temperature difference <NUM> determined a defined time interval after the point of time t6 differs more than the third threshold from the third reference value. So, micro-leakage <NUM> is detected. The third reference value may correspond to the average of the temperature difference values V1, V2 calculated the defined time interval after the point of times t2, t4.

It is possible to use the third embodiment in combination with the first and/or second embodiment. So, micro-leakage may be detected if the temporal gradient of the pipe temperature differs more than the first threshold from the first reference value or if the temperature difference between the pipe temperature and the ambient temperature differs more than the third threshold from the third reference value.

Further on, micro-leakage may be detected if the temperature difference between the two pipe temperatures differs more than the second threshold from the second reference value or if the temperature difference between the pipe temperature and the ambient temperature differs more than the third threshold from the third reference value.

Claim 1:
Method for micro-leakage detection in a fluid system (<NUM>),
wherein the fluid system (<NUM>) has a fluid pipe (<NUM>) with a fluid valve (<NUM>),
wherein a fluid flow through the fluid pipe (<NUM>) is stopped when the fluid valve (<NUM>) is closed, and
wherein a fluid flow through the fluid pipe (<NUM>) is allowed when the fluid valve (<NUM>) is opened,
the method comprising the following steps:
measuring the fluid flow through the fluid pipe (<NUM>) by a flow meter (<NUM>),
measuring the pipe temperature of the fluid pipe (<NUM>) by at least one pipe temperature sensor (17a, 17b),
when there is no fluid flow measured by the flow meter (<NUM>), namely because or when the fluid flow through the fluid pipe (<NUM>) is stopped by the fluid valve (<NUM>) being closed, analyzing the pipe temperature for the micro-leakage detection, characterized by that
the pipe temperature of the fluid pipe (<NUM>) is measured by the at least one pipe temperature sensor (17a, 17b) when fluid flow is measured by the flow meter (<NUM>) and when no fluid flow is measured by the flow meter (<NUM>), and the measured pipe temperature is analyzed for the micro-leakage detection only under the condition that there is no fluid flow measured by the flow meter (<NUM>), or
the pipe temperature of the fluid pipe (<NUM>) is both measured by the at least one pipe temperature sensor (17a, 17b) and analyzed for the micro-leakage detection only under the condition that there is no fluid flow measured by the flow meter (<NUM>).