Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K3/00—Thermometers giving results other than momentary value of temperature
  • G01K3/005—Circuits arrangements for indicating a predetermined temperature
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
  • G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K3/00—Thermometers giving results other than momentary value of temperature
  • G01K3/08—Thermometers giving results other than momentary value of temperature giving differences of values; giving differentiated values
  • G01K3/14—Thermometers giving results other than momentary value of temperature giving differences of values; giving differentiated values in respect of space
  • G01K2003/145—Hotspot localization
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
  • G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
  • G01K2007/166—Electrical time domain reflectometry

Definitions

• the present invention relates to the technical field of danger detection technology.
• the present invention relates to an apparatus and method for spatially resolved temperature measurement within a spatially linear detection range.
• the present invention further relates to a danger detection system for detecting local temperature changes within a spatially linear detection range, which is particularly suitable for spatially resolved detection of fire sources.
• linear electronic heat detectors In order to be able to record the temperature within an elongated detection area with a justifiable technical outlay, so-called linear electronic heat detectors have therefore been developed.
• This is a typically relatively thick cable in which addressable, discrete sensors are placed at a freely selectable distance.
• Such heat meiders thus represent a technological mixture between a discrete fire alarm technology with a large number of individual sensors and a genuine linear fire alarm technology. Each sensor can be queried via the addressing. If a single sensor detects a dangerous temperature, this condition can be spontaneously transmitted to a central office with the corresponding address associated with the location of the sensor.
• linear electronic heat detectors have the disadvantage that, especially for large distances due to the limited number of sensors, the distance between the individual sensors is relatively large.
• the multiple contacting of the individual sensors in addition to a high installation and maintenance costs can also lead to quality problems, which is characterized for example by a poor compatibility with electromagnetic interference.
• an optical glass fiber in which the phenomenon of temperature-dependent Raman backscattering is evaluated.
• the Raman optical backscatter signal has a small frequency shift with respect to a fed primary light beam, which can be selectively evaluated.
• a spatial resolution with respect to the origin of the Raman backscatter can be done with the classical optical radar technology, the so-called Optical Time Domain Reflectometry (OTDR).
• OTDR Optical Time Domain Reflectometry
• the OTDR within optical glass fiber has the disadvantage that corresponding measuring systems require a high installation effort, since typically can not be used in buildings usual means of electrical installation.
• a highly stable laser for generating the primary light beam is required and the necessary for the analysis of the Raman optical backscatter sensor and evaluation is very expensive.
• the invention has for its object to provide an apparatus and a method which allow a spatially resolved measurement of the temperature within a spatially linear detection range in a simple manner.
• an apparatus for spatially resolved temperature measurement within a spatial detection range comprises (a) a measuring body having a first electrical conductor, a second electrical conductor and an insulating material which extends between the two electrical conductors, the insulating material having a temperature-dependent specific electrical resistance, and (b) a Measuring device which is connected to the first electrical conductor and the second electrical conductor and which has a transmitting unit and a Receiving unit has.
• the transmitting unit is set up to act on the two electrical conductors with a time-dependent electrical input signal.
• the receiving unit is set up to detect a time-dependent electrical response signal of the measuring body to the input signal.
• the described temperature measuring device is based on the finding that, given a temperature change of the measuring body due to the temperature-dependent electrical
• the insulating material may in principle be any material which has a correspondingly high temperature dependence of its specific electrical conductivity.
• the insulating material represents a basically infinite number of discrete individual resistors, which are connected between the two electrical conductors.
• a local temperature change at the corresponding point of the measuring body leads to an impedance change, which leads to an at least partial reflection of high-frequency input signals.
• the measuring body additionally has (a) at least one further first electrical conductor, (b) at least one further second electrical conductor, and (c) at least one further insulation material which is connected between the two other electrical conductors. extends electrical conductors, wherein the further insulating material has a temperature-dependent resistivity.
• the at least one further first electrical conductor and the at least one further second electrical conductor can likewise be connected to the measuring device described above, so that the transmitting unit of the measuring device can also apply a time-dependent electrical input signal to the at least two further electrical conductors. In a corresponding manner, the receiving unit of the measuring device can then receive a time-dependent electrical response signal of the two further electrical conductors to the input signal.
• the measuring device can also have a switching device, so that individually a pair of electrical conductors is coupled to the transmitting unit or the receiving unit. In this way, a temperature measurement can be carried out sequentially by means of a plurality of conductor pairs, without causing unwanted interference between different signal components of an input signal fed simultaneously into different conductor pairs.
• the insulating material and the further insulating material may be the same material.
• the described temperature measuring device can therefore be a uniform one
• the various electrical conductors be taken in pairs in any spatial arrangement. This means that the different conductor pairs can be arranged within the measuring body in spatially arbitrary manner.
• the pairs of conductors may for example be cast in a suitable manner in the insulating material.
• the different pairs of conductors can be arranged, for example, within a flat or curved surface.
• a close-meshed area occupancy can be realized, for example, by a meander-shaped arrangement of the conductor pairs within the plane or curved area.
• a temperature measurement can be achieved not only within a linear detection range along a single conductor pair but within a two-dimensional detection range.
• the wing of an aircraft can be monitored flat for local temperature changes.
• the different conductor pairs can also be laid within the measuring body in a three-dimensional arrangement. As a result, local temperature changes within a three-dimensional detection range can be detected spatially resolved.
• the exact spatial position of the various conductor pairs within the measuring body should be known as accurately as possible.
• the spatial arrangement of the conductor pairs should not change over time. This also applies in view of adverse environmental conditions such as the presence of chemically aggressive substances, the exposure of extreme temperatures and / or temperature fluctuations or other material-contaminating environmental conditions.
• the device additionally has a terminating resistor, which is connected at one of the measuring device opposite end of the electrical conductor to the electrical conductors.
• the termination resistor preferably has a resistance which corresponds to the characteristic impedance of the cable under normal temperature conditions.
• normal conditions in this context means the temperatures that are usually present in the detection area. Thus, under normal temperature conditions, the entire
• Measuring body is a measuring system with a uniform impedance, so that no or only very weak reflections of a high-frequency signal can be expected.
• the impedance at the relevant point of the measuring body will change.
• the previously optimal impedance matching is disturbed and reflections occur for the first time, which can then be detected reliably by the receiving unit.
• the termination resistor may also be a combination of a plurality of passive components such as an ohmic resistor, a capacitor and / or a diode.
• a terminating resistor which has an ohmic resistance in series and has a capacitor, by applying the corresponding voltage
• Conductor pair with a DC voltage ohm 'see resistance of the insulating material are measured, without taking into account the ohmic resistance of the terminating resistor. As a result, the ohmic resistance of the insulation material can be measured particularly accurately.
• the termination resistor may also comprise a series circuit of (a) an ohmic resistor and (b) a parallel circuit of a capacitor and a diode.
• a polarity-dependent resistance measurement of the insulating material can be carried out. Selecting a polarity of the input voltage at which the diode in the forward direction is switched, then the capacitor is bridged apart from the voltage drop occurring at the diode. If one selects a polarity of the input voltage at which the diode is reverse-connected, then the influence of the terminating resistor on the resistance measurement of the insulating material can be eliminated in a simple and effective manner in the case of a DC voltage measurement.
• the insulating material is a material whose specific electrical resistance decreases with increasing temperature.
• the insulating material may be a plastic material, which shows a so-called. NTC (Negative Temperature Coefficient) behavior.
• NTC Near Temperature Coefficient
• a thin-film composite material with carbon nanoparticle polyimides carbon nanoparticle-polyimide composite thin films (BTDA-ODA)
• BTDA-ODA carbon nanoparticle-polyimide composite thin films
• This material is described, for example, in the publication "MURUGARAJ P., MAINWARING D., MORA-HUERTAS N:” Thermistor Behavior in a Semiconductor Polymer-Nanoparticle Composite Film "; Journal of Physics 2006, vol. 39, no. 10, pp. 2072-2078 ".
• the measurement of the DC resistance can be used for a kind of pre-alarming, before the exact location of the local temperature change within the measuring body is determined with more complex methods.
• a measuring body with the above-described insulating material BTDA-ODA under normal conditions, i. at typical room temperatures, on the one hand a low attenuation and on the other hand has a relatively high impedance. If the cable is then heated at a certain point, then the specific resistance of the insulation material drops there. At the end of the relevant pair of conductors can then be determined by the described resistance measuring unit a decrease in the total resistance and possibly triggered a collective for the entire temperature measuring device pre-alarm.
• the electrical input signal is an electrical pulse.
• the electrical pulse can be, for example, a temporal rectangular pulse, which at a junction of the impedance, ie at the point of a local impedance change from a high-impedance insulation section to a low-resistance insulation section or vice versa at least partially is reflected.
• a temporal rectangular pulse which at a junction of the impedance, ie at the point of a local impedance change from a high-impedance insulation section to a low-resistance insulation section or vice versa at least partially is reflected.
• the position of the section of the respective conductor pair with a changed specific electrical resistance of the insulating material can thus be determined by the reflection behavior of electrical running waves. In this case, it is possible to fall back on the principles of the known line-bound radar technology, which is also referred to as time domain reflectometry (TDR).
• TDR time domain reflectometry
• the reflection factor r of a pulse fed into the cable can be calculated according to the line theory from the following equation (1):
• R is the electrical resistance of the insulating material at the defect and Zw is the characteristic impedance of the undisturbed measuring body measured at the respective pair of conductors.
• the electrical input signal has a plurality of periodic and, in particular, sinusoidal individual signals which have a different frequency relative to one another.
• the various periodic individual signals can be fed sequentially into the measuring body and in each case the phase shift of the individual response signals can be measured, which are reflected back at a junction of the impedance.
• the distance from the measuring device to the location of the measuring body can also be determined from the phase shifts of the respective individual response signal for different frequencies in relation to the individual signal fed into the measuring body in accordance with the basic principles of known frequency domain reflectometry (FDR). which has a local temperature increase.
• FDR frequency domain reflectometry
• the measuring body is a cable.
• a cable which may have one or more conductor pairs, has the advantage that a spatially resolved temperature measurement can be carried out by simply laying the cable along a linear monitoring area within this monitoring area.
• the cable is a coaxial cable.
• the insulating material is located between an inner conductor and the outer conductor arranged cylindrically symmetrically with respect to the inner conductor. It can be optimized by the geometric shape and in particular by the ratio of the radii of the inner conductor and the outer conductor in an advantageous manner, the properties of the waveguide of the cable.
• the formation of the cable in the form of a coaxial cable may cause a heat exposure to the temperature-sensitive insulation material delayed by the outer conductor something becomes. As a result, the entire linear temperature measuring device has a slightly higher thermal inertia.
• the cable has two strip conductors running next to one another.
• the two strip conductors can be arranged substantially parallel to one another along the entire cable length. A twisted arrangement between the two strip conductors is possible. All that matters is that between the two strip conductors is the temperature-dependent insulation material with respect to its specific conductivity.
• the stripline can be mounted or arranged in an area to be monitored such that the heat radiation generated by a heat source acts directly on the temperature-sensitive insulation material. As a result, a particularly fast response of the linear temperature measuring device can be achieved.
• the cable additionally has an outer layer.
• the outer layer may be a mechanical protective layer that protects the possibly sensitive cable from mechanical damage.
• the outer layer may also be an additional insulating layer which ensures reliable electrical insulation of the cable from other electrical conductors.
• the outer layer comprises a material which has at least one predetermined heat absorption against heat radiation.
• the outer layer may, for example, have a black color which, in the case of thermal radiation caused by a heat source, has a rapid and significant increase in temperature of the insulation material that is temperature-dependent with respect to its electrical conductivity.
• a hazard detection system for detecting local temperature changes within a spatial detection range.
• the danger reporting system is particularly suitable for spatially resolved detection of fire sources.
• the hazard reporting system includes (a) a central office and (b) at least one apparatus of the type described above for spatially resolved temperature measurement within a spatial detection area.
• the device is coupled to the center via a communication link.
• the described danger reporting system is based on the finding that one or more temperature measuring devices of the type described above, which each have the ability to detect temperature changes spatially resolved, can be connected to a control center.
• the center may also be connected to other peripheral units, which may be set up to detect other types of dangers such as the formation of smoke, the presence of toxic gases or burglary attempts.
• the central office can then jointly evaluate various message results of the various peripheral units in a suitable manner and initiate suitable security measures.
• a method for spatially resolved temperature measurement within a spatial detection range comprises (a) applying a measuring body with a time-dependent electrical input signal using a transmitting unit of a measuring device, and (b) detecting a time-dependent electrical response signal of the measuring body to the input signal using a receiving unit of the measuring device.
• the measuring body has a first electrical conductor, a second electrical conductor and an insulating material which extends between the two electrical conductors and which has a temperature-dependent specific electrical resistance.
• the measuring device is connected to the first electrical conductor and to the second electrical conductor.
• the described method is also based on the knowledge that the impedance of the measuring body changes when the temperature of the insulation material changes due to its deliberately temperature-dependent electrical resistance.
• the impedance of the cable changes, in particular for a high-frequency input signal, at least within a certain range of the measuring body.
• This impedance change in turn leads to a specific reflection behavior of the measuring body, in particular for a high-frequency and / or for a temporally very rapidly changing input signal.
• the corresponding reflections are detected by the receiving unit of the measuring device and can be analyzed by an evaluation device connected downstream of the receiving unit.
• FIG. 1 shows an equivalent circuit diagram of a linear temperature measuring device.
• Figure 2 shows in a cross-sectional view a strip cable with an insulating material, which is a plastic material with an NTC behavior.
• FIG. 3 shows a cross-sectional view of a coaxial cable with an insulating material which is a plastic material with an NTC behavior.
• FIG. 4b shows an output pulse which results from an at least partial reflection of the input pulse and which propagates in the negative direction within the cable along the path s.
• FIG. 6 shows a terminating resistor which has a series connection of an ohmic resistor and a capacitor.
• FIG. 7a shows a terminating resistor which has a series connection of an ohmic resistor and a parallel circuit of a capacitor and a diode.
• FIG. 7b shows a resistance measurement of the temperature-dependent insulation carried out under DC voltage conditions. onsmaterials using the terminating resistor shown in Figure 7a at a first polarity.
• FIG. 7c shows a resistance measurement of the temperature-dependent insulating material carried out under DC voltage conditions using the terminating resistor shown in FIG. 7a for a second polarity.
• FIG. 1 shows a linear temperature measuring device 100 according to an embodiment of the invention.
• the temperature measuring device 100 has an electrical cable 110, which serves as a temperature sensor and can be arranged within a linear detection range. It should be noted that the linear detection range does not necessarily have to be straightforward.
• the linear detection area can also be curved and, for example, run around corners and / or edges.
• the cable 110 has a first electrical conductor 112 and a second electrical conductor 114. Between the two conductors 112 and 114 is an insulating material 116, which has a temperature-dependent electrical resistivity.
• the insulating material 116 is a plastic which has a Negative Temperature Coefficient (NTC) behavior. This means that the electrical resistivity of the insulating material 116 decreases as the temperature increases.
• FIG. 1 shows the specific electrical resistance of the insulating material 116 in the form of an equivalent circuit diagram by a multiplicity of discrete electrical resistors 116a. In reality, the effective resistance between the two conductors 112 and 114 is distributed continuously over the entire length of the cable 110.
• NTC Negative Temperature Coefficient
• the described linear temperature measuring device 100 is based on the physical effect that the characteristic impedance of the cable 110 depends not only on the spatial arrangement of the two conductors 112 and 114 but also on the specific resistance of the insulating material 116. If a partial section of the cable 110 has a changed temperature compared to the remaining cable 110, the characteristic impedance within this partial section is different from the characteristic impedance of the remaining cable 110. This means that within the cable 110 the impedance has a change. This change in impedance then causes a high-frequency signal, which otherwise propagates largely without interference in the cable 110, to be reflected at least in part at the point of impedance change.
• Termination resistor 120 is sized so that no reflections are caused under normal temperature conditions at the end of cable 110. Under normal temperature conditions, the entire cable 110 thus represents a linear measuring line with a uniform impedance at which no or only very weak reflections of a high-frequency signal are to be expected. In the case of a local temperature change, the impedance at the relevant location of the cable 110 will then change. As a result, the previously optimal impedance matching is disturbed and it occurs for the first time
• the measuring device 130 For feeding an input signal into the cable 110, the measuring device 130 has a transmitting unit 132. For detecting reflected output signals, the measuring device 130 has a receiving unit 134.
• the transmitting unit 132 and the receiving unit 134 may be separate electronic circuits. Alternatively, these units 132 and 134 can also be realized by means of a single circuit arrangement.
• the measuring device 130 additionally has a resistance measuring unit 136.
• the resistance level measuring unit 136 is arranged to measure the DC resistance of the cable 110.
• the localization of the cable defect can also be carried out using the time domain reflectometry (TDR) or Frequency Domain Reflectometry (FDR) radio-frequency methods described above.
• TDR time domain reflectometry
• FDR Frequency Domain Reflectometry
• the smallest of the partial resistors 116a always dominates at the cable ends at the terminals 130a and 130b.
• the maximum measurable resistance to the Terminals 130a and 130b is equal to the termination resistor 120. In this consideration, the resistance of the conductors 112 and 114 is neglected. This limits the dynamics of the resistance measurement.
• the termination resistor 120 can also be replaced by a series connection of an ohmic resistor and a capacitor with a relatively large capacitance. With an alternating voltage with a sufficiently high frequency, only the ohmic resistance is seen and no change in the impulse response is to be expected. Under DC conditions, the termination resistance at terminals 130a and 130b is not seen at all, and the range of measurable resistance is accordingly increased.
• the measurement of the DC resistance can be used for a kind of pre-alarming, before the exact location of the above-described and above with reference to FIGS. 4 a and 4 b local temperature change is determined.
• FIG. 2 shows in a cross-sectional view a strip cable 210 which can be used as measuring line 110 for the linear temperature measuring device 100 shown in FIG.
• the strip cable 210 has a first electrical conductor 212 and a second electrical conductor 214, which are embedded in an insulating material 216.
• the insulation material 216 is a plastic material with an NTC
• PTC Positive Temperature Coefficient
• the insulating material 216 is surrounded by a thin outer layer 218.
• the outer layer 218 may protect the insulating material 216 from mechanical influences.
• the outer layer 218 has a black color or at least a dark color, so that heat radiation 240 incident on the cable is well absorbed and thus leads to a significant temperature increase of the insulating material 216 in the relevant cable section.
• the absorption of the heat radiation 240 can additionally be improved by the outer layer having a certain roughness, so that reflections of the heat radiation 240 on smooth surfaces are largely prevented.
• FIG. 3 shows in a cross-sectional view a coaxial cable 310, which can likewise be used as measuring line 110 for the linear temperature measuring device 100 shown in FIG.
• the coaxial cable 310 has a first electrical conductor 312, which represents the inner conductor of the coaxial cable 310.
• a second electrical conductor 314 represents the outer conductor of the coaxial cable 310.
• Between the inner conductor 312 and the outer conductor 314 is an insulating material 316, which is also a plastic material with an NTC behavior.
• An outer layer 318 surrounds the outer conductor 314. Also, the outer layer 318 has a black color or at least a dark color, so that the coaxial cable 310 incident heat radiation is well absorbed and leads to a significant increase in temperature of the insulating material as 316.
• the measurement of the location of a local temperature increase by means of an electrical input pulse fed into the cable and of the corresponding output pulse partially reflected back at a temperature-induced impedance change is explained below with reference to FIGS. 4a and 4b. In this case, when calculating the location of the local temperature increase, the time difference between the input of the input pulse and the reception of the output pulse reflected at a local impedance change is measured. Since the propagation speed of electrical signals in the
• the spatial distance between the local temperature change and the measuring device can be determined from the measured time difference. In this case, it is possible to fall back on the principles of the known line-bound radar technology, which is also referred to as time domain reflectometry (TDR).
• TDR time domain reflectometry
• an electrical input pulse 450 a propagates within a cable along a running distance s in the positive running direction 451 a.
• the current i and the voltage u are in phase with the input pulse 450a designed as a rectangular pulse in time.
• the input pulse 450a is at least partially reflected.
• the reflection factor results from the o. G. Equation (1).
• the current level i and the voltage level u are in antiphase. This means that the current i and the voltage u have a mutually different sign.
• FDR Frequency Domain Reflectometry
• FIG. 5 shows a danger detection system 560, which has a central unit 565 and a total of four linear temperature measuring devices 500, which are connected to the central unit via a respective signal line 565a.
• linear temperature measuring devices 500 are connected to the control center, with which temperature changes can be detected spatially resolved in each case.
• the central station 565 can of course also be connected to other, different peripheral units or alarm units. These different types of danger reporting units may be, for example, smoke detectors, gas detectors and / or intrusion detectors.
• the central unit 565 can then jointly evaluate various message results of the various peripheral units in a suitable manner and initiate suitable security measures.
• FIG. 6 shows a terminating resistor 620 which has a series connection of an ohmic resistor 625 and a capacitor 626.
• Termination resistor 620 is connected at terminals 620a and 620b to a cable, not shown in FIG. According to the example shown here For example, this cable is identical to the cable 110 of FIG.
• the described series connection of the ohmic resistor 625 to the capacitor 626 has the advantage that the dynamics of a resistance measurement can be significantly increased. Under alternating voltage conditions, with a sufficiently large capacitance of the capacitor 626, only the ohmic resistance 625 is detected. A change in the impulse response is not expected. Under DC voltage conditions, the terminating resistor is not seen by the resistance measuring unit 136 shown in FIG. 1, and the range of the measurable resistance is correspondingly increased.
• FIG. 7 a shows a terminating resistor 720, which has a
• Termination resistor 720 is connected at terminals 720a and 720b to a cable, not shown in FIG. According to the embodiment shown here, this cable is identical to the cable 110 of FIG.
• the use of the series circuit shown in FIG. 7a has the advantage that the static resistance measurement can be carried out at the terminals 720a and 720b with two different polarities. By a suitable choice of the polarity can thus be determined whether one wants to see the terminator 720 or not.
• FIG. 7b shows a resistance measurement of the temperature-dependent insulation material of the cable 710, carried out under DC voltage conditions, using a terminating resistor 720, which is a series connection of a Ohm 'see resistance 725 and a parallel circuit of a capacitor 726 with a diode 727 west.
• FIG. 7b shows the DC resistance measurement at a first polarity of a voltage source 735, in which the terminating resistor is statically seen or detected by a current measuring device 736a and a voltage measuring device 736b. This is achieved by the diode 727, which is turned on in the first polarity of the voltage source 735 in the forward direction. Under alternating voltage conditions, the diode 727 is short-circuited by the capacitor 726, and only the ohmic resistance 725 is seen or detected as the terminating resistor.
• FIG. 7c shows the resistance measurement of the temperature-dependent insulation material of the cable 710 shown in FIG. 7b for a second polarity of the voltage source 735, in which the ohmic resistance 725 is not seen or detected under DC voltage conditions.
• Resistance measurement under DC voltage conditions shows, when the resistance of the two electrical conductors of the cable 710 is neglected, the pure resistance of the insulation material of the cable 710.
• the described linear temperature measuring device can be installed with the normal tools of electrical installation. No special tools are needed.
• a signal evaluation based on the TDR or FDR technology is insensitive to the drift of an internal clock of the measuring device.
• the transmitter is thus long-term stable and insensitive to temperature fluctuations.

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• General Physics & Mathematics (AREA)
• Fire-Detection Mechanisms (AREA)
• Measurement Of Resistance Or Impedance (AREA)

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• 2008
  • 2008-03-20 CN CN200880129292.1A patent/CN102037338B/zh not_active Expired - Fee Related
  • 2008-03-20 WO PCT/EP2008/053408 patent/WO2009115127A1/de active Application Filing
  • 2008-03-20 EP EP08718117A patent/EP2255168A1/de not_active Withdrawn
  • 2008-03-20 US US12/933,572 patent/US20110102183A1/en not_active Abandoned

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