DE102014219347B4 - Method for monitoring a heating device and heating device - Google Patents

Abstract

Method for monitoring a heating device (10), - wherein the heating device (10) has at least two different heating conductors (40) for heating a medium (30), the method comprising the steps of: determining an electrical instantaneous power of the heating conductors (40), Determining a temperature difference between the heating conductors (40) and the medium (30), calculating a thermal resistance by dividing the temperature difference by the instantaneous power, and determining a property from the thermal resistance, the method being successively determined by means of the at least two different heating conductors (40 ), and a number of properties of the heating conductors (40) are compared on the basis of the respectively determined thermal resistances

Description

AREA OF APPLICATION AND PRIOR ART

The invention relates to a method for monitoring a heating device and a heating device, wherein the heating device has at least two different heating conductors for heating a medium.

When operating heaters, various fault conditions can occur. For example, a heating device that comes into contact with water during heating, gradually calcify, which can significantly reduce their heating power. It may also be that the medium heated by the heater or the water is no longer present, for example because a feed valve is closed. In this case, it can lead to overheating and thus damage to the heating element.

It is known to measure temperatures of the heat conductor or the heating medium or the medium in the heating operation and to consider rates of change of these temperatures and to compare them with stored empirical values for normal or abnormal operation. However, customary tolerances with regard to the supply voltage and the nominal power range are typically covered in stored operating points or characteristic fields. Larger changes or deviations from temperatures are often only detected much later than incipient fault conditions such as deposits, calcification or dangerous overheating due to correspondingly wide permitted spreads during normal heating operation. Accordingly, a reaction can take place only at a relatively late time, which brings with it the risk of damage to the heating element.

The WO 2012/152 782 A1 describes the use of direct current sensors in the current path or of indirect current sensors, which detect, for example as Hall sensors, a magnetic field generated by a current-carrying conductor. Such current sensors and additional voltage sensors are used to determine actual current and voltage values in the operation of a heating device for the determination of a power consumption in real time. However, these are only raw data whose statement value is limited.

The DE 699 19 646 T2 describes the monitoring of a heating process by periodically interrupting the heating at fixed times, wherein at each interruption from the temperature-dependent resistance of a heating element, the temperature of the heating element is determined. Furthermore, a time constant of the cooling of the heating element is determined and compared with reference data. However, the procedure described in this document can not be used in particular for layer heating elements with low thermal mass and thermal inertia, since the time constants in these cases are extremely short. In addition, in the meantime, between the periodic checks, a layer heating element can already reach an abnormal or critical operating state, which is detected only at the next interruption. In other words, real-time monitoring is not possible.

The DE 10 2007 012 135 B3 describes an evaluation of temperature rise values of a radiator or heat conductor using an additional temperature sensor. Although this allows an evaluation in real time, but relies on an additional temperature sensor.

The DE 10 2012 213 385 A1 describes the use of two temperature sensors with negative temperature coefficients (NTC temperature sensors) in a heating device. In this case, a temperature sensor is arranged at a suitable distance from the heating element to detect the medium temperature.

The DE 197 21 976 A1 describes an optical method for determining thermal characteristics in a heating operation.

From the publication of Bedö, Gerlinde; Kraus, Werner; Müller, Rudolf: "Comparison of different micromechanical vacuum sensors" in Elsevier: Sensors and Actuators A: Physical, Vol. 85, 2000, no. 1, pp. 181-188, doi: 10.1016 / S0924-4247 (00) 00383-6, a method for monitoring a heating device with a heating conductor emerges. An instantaneous power and a temperature difference between the heating conductor and the medium to be heated are determined.

TASK AND SOLUTION

The invention has for its object to provide a method for monitoring a heater and a heating device designed for this, with which problems of the prior art can be avoided and it is in particular possible to recognize a calcification or other adverse effects on the function of the heater or to prevent.

This object is achieved by a method having the features of claim 1 and a heating device designed for carrying it out with the features of claim 11.

Advantageous and preferred embodiments of the invention are the subject of the other claims and are explained in more detail below. Some of the features are called or explained in connection only with the method or only with the heater. However, they should be able to apply independently for both the process and for the heater independently. The wording of the claims is incorporated herein by express reference.

The method serves to monitor a heating device, wherein the heating device has at least two heating conductors for heating a medium or water.

• – Ermitteln einer elektrischen Momentanleistung der Heizleiter,
• – Ermitteln einer Temperaturdifferenz zwischen den Heizleitern und dem Medium,
• – Berechnen eines Wärmewiderstands mittels Division der Temperaturdifferenz durch die Momentanleistung und
• – Ermitteln einer Eigenschaft aus dem Wärmewiderstand.

According to the invention, the method comprises the following steps:

• Determining an electrical instantaneous power of the heating conductors,
• Determining a temperature difference between the heating conductors and the medium,
• Calculate a thermal resistance by dividing the temperature difference by the instantaneous power and
• - Determining a property of the thermal resistance.

By calculating the thermal resistance according to the invention, it is possible to detect properties such as fault conditions or other problems of the heating device and in particular of the heating conductors contained therein in real time. In this case, it is possible to resort extensively to data which are present anyway in a conventional heating device. The thermal resistance in particular provides a measure of how efficiently a transfer of heat energy from the heating conductors to the medium or water takes place. If the thermal resistance increases over time, this may indicate, for example, that the heating device, possibly also the heating conductors, has calcified by heating water or other deposits on a surface of the heating device, possibly also the heating conductor, or a carrier or a carrier Substrate of the heating conductors have settled.

• – Heizleiter = Heiz-Widerstands(leiter)bahn auf einem Substrat/Träger = Schichtheizleiter = Dickschichtheizleiter,
• – Substrat + Kontaktschicht + Widerstandsbahn + Abdeckschicht(en) = Schichtheizelement,
• – Metall-Substrat + Kontakt + Widerstandsbahn + Abdeckung = Metallkernheizelement,
• – die Heizleiter sind Teil eines Heizelementes/Teil einer Heizvorrichtung.

Advantageously, the following definition applies:

• Heating conductor = heating resistor (conductor) track on a substrate / carrier = Schichtheizleiter = Dickschichtheizleiter,
• Substrate + contact layer + resistance path + cover layer (s) = layer heating element,
• Metal substrate + contact + resistor track + cover = metal core heater,
• - The heating conductors are part of a heating element / part of a heater.

Advantageously, the heating conductor does not come into direct contact with the medium because of the required coverage and electrical insulation of the heating conductor relative to the electrically conductive medium, for example water.

The temperature difference is preferably calculated by subtracting a temperature of the medium from a temperature of the heating conductor. The temperature of the medium is particularly preferably determined by a dedicated temperature sensor. This allows a reliable determination.

For the detection of the temperature of the heating conductors are several versions available, of which four possible and advantageous are described below.

According to one embodiment, the temperature of the heating element is determined by means of a mounted on a surface of the heating element temperature sensor, wherein heating element and temperature sensor should be electrically isolated from each other, for example by a cover and insulation layer. This allows a direct and very reliable determination of the temperature of the heating element.

According to an alternative embodiment, the temperature of the heating element is determined thermographically. This allows the use of a device for thermographic temperature determination, which can be mounted at a distance from the heat conductor. Thus, an electrical contacting of an applied on the heating element element can be avoided, for example, the aforementioned temperature sensor, including the aforementioned cover layer. Thus, for example, in one experiment, a reference measurement can be carried out, which can then later be used to determine the temperature based on certain other factors or measured values which are present at certain measured temperatures.

According to yet another alternative embodiment, the temperature of the heating conductors is determined by measuring a momentary resistance of the heating conductor using a known relationship between torque resistance and temperature. This avoids that additional components must be provided, since the torque resistance can be calculated from the normally determined and thus known quantities voltage and current. The dependence between torque resistance and temperature is known in the form of resistance characteristic curves in typical heat conductors.

According to yet another alternative embodiment, the temperature of the heating conductor of applied voltage, current consumption and temperature coefficient of the resistance of the heating element and the Nominal resistance of the heating conductor determined. This embodiment can be used in particular when the heating conductor has a linear resistance-temperature characteristic. The use of completely stored characteristics can be dispensed with.

According to an advantageous embodiment, the medium is just water. According to another embodiment, the medium is a mixture of water and other liquids. According to yet another embodiment, air is also contained in the water or mixture of water and other liquids.

In principle, the method is also applicable to gaseous media, for example in the heating of air, where heating elements can dust / pollute or where the required removal of heat by a fan / fan can not work properly.

According to one embodiment, a type or a composition of the medium is determined as a property. This embodiment is based on the inventor's finding that the thermal resistance typically depends on the type or composition of the medium. This allows, for example, a rapid detection of a changing composition of the medium, which can be particularly problematic if the change takes place unintentionally, so for example due to a malfunction of upstream equipment. For example, can be detected in this way, when instead of the desired water, a mixture of water and additionally other liquids flows through the heater.

According to one embodiment, the presence or absence of the medium is determined as a property. As the inventor of the present application has recognized, even a lack of the medium immediately and immediately affects the thermal resistance, whereby it can be detected quickly and reliably. According to a preferred embodiment, the heating device or the heating conductor is switched off when a lack of the medium is determined. This can be avoided damage.

According to one embodiment, the method according to the invention is repeated several times in succession, wherein a calcification of the heating device or of the carrier of the heating conductors is determined as a property on the basis of a time characteristic of the thermal resistance. Such a calcification can be determined in particular by a continuous increase in the thermal resistance. In particular, it can be provided that a calcification can be detected if the increase has a temporal change within a certain range. For example, a determination of calcification may be displayed to a user to prompt him to replace or descal the heater.

According to the invention, the method according to the invention is carried out successively by means of at least two different heating conductors, wherein a number of properties of the heating conductors are compared on the basis of the respectively determined thermal resistances. For example, different heating rates of different heating conductors can be determined and compared. A heating rate can be calculated, for example, by means of measurements at a first time t ₁ and a second time t _{2 as} follows: Heating rate = (T _M2 - T _M1 ) / (t ₂ - t ₁ ) / P in K / time unit / watt

T_M2:

Temperatur des Mediums zum Zeitpunkt t₂,

T_M1:

Temperatur des Mediums zum Zeitpunkt t₁,

P:

Leistungsaufnahme (siehe die Formel weiter unten).

Where:

T _M2 :

Temperature of the medium at time t ₂ ,

T _M1 :

Temperature of the medium at time t ₁ ,

P:

Power consumption (see the formula below).

It should be understood, however, that other properties may be compared in this manner.

In particular, the embodiment just described, by means of which two different heating conductors are compared, be performed with heating conductors of different rated power. This allows an assessment of the influence of different power ratings.

According to respective embodiments, the heating conductors are Schichtheizleiter, in particular Dickschichtheizleiter, and part of a Schichtheizelements or a Metallkernheizelements. Such designs have proven to be advantageous for many heaters.

The heater is integrated according to respective versions in a Motorheizpumpe or integrated into a steam generator. In such engine heat pumps or steam generators heaters are often used with which the inventive method can be carried out advantageously. The heating element is particularly advantageously located on the outside of a tubular housing, which can form the essential part of a pump chamber, especially its jacket wall.

The method is preferably carried out in an electronic control device of the heating device. In particular it will typically automated. The electronic control device may comprise, for example, processor means and memory means, wherein program code is stored in the memory means, in the execution of which the processor means carry out the method according to the invention. Such an electronic control device may be, for example, a microcontroller, a microcomputer, a freely programmable computer, a programmable logic controller (SPSS) or an application-specific integrated circuit (ASIC).

The invention allows, for example, a quantitative assessment of the heat transfer from a heating element to the medium to be heated, wherein it may be, for example, a part of a thick-film heating system in a Motorheizpumpe in the heating element. It can be used in particular in safety concepts for the operation of Schichtheizelementen, for example in household appliances such as in Motorheizpumpen of dishwashers.

The invention also allows an evaluation and linkage of the medium temperature and the Heizleitertemperatur and the power consumption of Schichtheizelementen and derived physical quantities. The Heizleiterertemperatur and the power consumption of Schichtheizelementen can be considered, for example, in relation to the medium temperature. It is also possible to consider heating rates or thermal parameters such as temperature differences between the heating conductor and the medium or a thermal resistance, in particular an overall thermal resistance between the heating conductor and the medium.

In particular, the invention enables real-time operation. The power consumption of the heating conductors, referred to above, for example, as instantaneous power, is typically present without a time delay. This allows a much faster response to critical conditions than in various embodiments according to the prior art.

It should be noted that the temperature difference between the heating conductor and the medium can also be referred to as the excess temperature of the heating conductor via the medium. For example, it may be a measure of the heat transfer from the heating conductor through a substrate material to the medium to be heated.

The temperature difference between the heating conductor and the medium can be influenced, for example, by deposits from the medium or water, in particular calcare, on the medium contact surface of a layer heating element, for example on a metal core heating element. An increasing temperature difference under otherwise identical operating conditions can thus be a measure of increasing deposits over the service life of a metal core heating element.

The temperature difference between the heating conductor and the medium can be a measure of the heat transfer from the heating conductor through a substrate material and a heat transfer structure, for example thermal adhesive and metallic support or heat sink, up to the medium to be heated for ceramic heating elements that indirectly heat the medium.

The physical magnitude of the thermal resistance, also referred to as thermal resistance, can be considered as an overall description of heat transport and transmission processes to also in real time the influence of variable power consumption of the Schichtheizelements, for example by fluctuating mains voltages, on the temperature difference between the heating conductor and medium consider. It can also be used to compare layer heaters of different ratings in one application. In addition, it can be used to compare layer heating elements and heating arrangements in different applications, for example in the heating of different media.

In analogy to the electrical resistance of the thermal resistance can be determined as the quotient of the resulting temperature difference between the heating element and the medium in the passage of a heat flow Φ _th by a heating arrangement and the heat flow Φ _th . Neglecting heat losses, the heat flow Φ _th , which can also be called thermal power, corresponds to the wattage of the electric power consumption of a layer heating element P in watts. In terms of formula, the thermal resistance R _th can be stated as follows: R _th = .DELTA.T / Φ _th = (T _HL - T _M) / Φ _th = (T _HL - T _M) / P in K / W.

R_th:

Wärmewiderstand,

ΔT:

Temperaturdifferenz,

T_HL:

Temperatur des Heizleiters,

T_M:

Temperatur des Mediums,

Φ_th:

Wärmestrom,

P:

Leistungsaufnahme.

Where:

R _th :

Thermal Resistance

.DELTA.T:

Temperature difference,

T _HL :

Temperature of the heating conductor,

T _M :

Temperature of the medium,

Φ _th:

Heat flow,

P:

Power consumption.

The temperature difference .DELTA.T between the temperature of the heating conductor and the temperature of the medium and the thermal resistance R _th can be used under otherwise identical operating conditions in real time conclusions on important medium characteristics such as type of medium, Mixing ratios or the like. For example, such a mixing ratio may indicate the ratio of water to other materials or media other than water. This is especially true when these medium characteristics affect the thermal properties of the medium heat conductivity, heat capacity or others. At the same time, the temperature difference ΔT between the heating conductor and the medium and the thermal resistance R _{th are influenced} by the heat transfer from a medium-side surface of the heating device or the heating element to the medium or fluid, wherein heat transfer coefficients, flow conditions and heat transport by free or forced convection can play a role.

The presence of the medium to be heated or missing medium in the event of a fault can be detected in real time, whereby critical operating conditions such as dry running or dry running of a Schichtheizelements can be detected.

From previously mentioned, often already existing measured values of sensors such as temperature sensors, current sensors or voltage meters can be obtained with existing processing units such as microcontrollers for program control and monitoring and storage units in devices in real-time, quasi-standardized information on the operating state of the heating element, if Heizleiterertemperaturen be related to the respective medium temperature or if temperature differences between Heizleiterertemperatur and medium temperature based on the respective power consumption. The normalized characteristic values of the operating state determined in real time can be used for device control, especially for the safety functions. Changing conditions of heat transfer from the layer heater to the medium, for example as a result of deposits, can be detected and quantified in real time.

Layer heating elements are typically characterized by low thermal mass, low thermal inertia and high dynamics in the operating behavior. Permanent monitoring in real time is often required for proper safe operation in order to prevent overheating, failure or even consequential damage. This can be done with the present invention in an advantageous manner.

Furthermore, the invention allows to better evaluate heating conditions for media having temperature dependent properties, for example mixtures of water with other materials.

The invention can be carried out, for example, in such a way that setpoint parameters are recorded in normal operating states during an initial startup in an application. For example, a Heizleiterwiderstand can be recorded in the unheated state together with the measured media temperature. Subsequently, for example, an increasing hindrance of the heat transfer can be detected by an increase in the thermal resistance due to deposits or calcification. This is especially true with unchanged flow rate of the fluid.

These and other features will become apparent from the claims but also from the description and drawings, wherein the individual features each alone or more in the form of sub-combinations in an embodiment of the invention and in other fields be realized and advantageous and protectable Represent embodiments for which protection is claimed here. The subdivision of the application into individual sections as well as intermediate headings does not restrict the general validity of the statements made thereunder.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and features will be apparent to those skilled in the embodiment described below with reference to the accompanying drawings. It shows the 1 a heating device, which is designed for carrying out a method according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

1 shows an embodiment which serves to illustrate the invention. A heater 10 has a pipe 20 on, through which a medium 30 in one by an arrow 35 predetermined direction flows, either only and exactly along this direction or with a component in this direction. In the medium 30 it may be, for example, water or a mixture of water and other liquids. The medium 30 in particular by means of the heater 10 heated.

For heating the medium 30 indicates the heater 10 one inside the tube 20 arranged heating conductor 40 on, which in the present case is designed as a thick-film heating conductor of a layer heating element, not shown. Alternatively, he can also outside the medium 30 be arranged, preferably on the outside of the tube 20 , For supply and control of the heating conductor 40 indicates the heater 10 Furthermore, an electronic control device 50 which is adapted to an electrical voltage and an associated electric current to the heating conductor 40 as well as current and voltage at the heating conductor 40 to monitor.

The heater 10 also has one inside the tube 20 arranged temperature sensor in the form of a temperature sensor 60 on to the temperature of the medium 30 to eat. The temperature sensor 60 is electrically connected to the electronic control device 50 connected, so that the electronic control device 50 over one of the temperature sensor 60 delivered output signal the temperature of the medium 30 can determine. Also the temperature sensor 60 can on the outside of the pipe 20 be arranged.

The electronic control device 50 is further adapted to carry out a method according to the invention. This will be further described below. The electronic control device 50 has processor means and memory means (not shown) for this purpose, program code being stored in the memory means and, when executed by the processor means, the electronic control means 50 is in the sense of the inventive method described below behaves.

The electronic control device 50 continuously determines an electrical instantaneous power of the heating conductor 40 by multiplying the heat conductor 40 applied voltage with the through the heating conductor 40 flowing electricity. Furthermore, it constantly determines the temperature of the heating element 40 by dividing the voltage by the current strength of the electrical resistance of the heating conductor 40 calculated and from a stored temperature-resistance characteristic which leads to this resistance of the heating conductor 40 read out the associated temperature. This is possible because of the electrical resistance of the heating conductor 40 depends in a defined way on its temperature. From the determined temperature of the heating conductor 40 pulls the controller 50 then the over the temperature sensor 60 determined temperature of the medium 30 and thus reaches a temperature difference between the heating conductor 40 and the medium 30 ,

Subsequently, the electronic control device determines 50 a respective current thermal resistance by dividing the temperature difference by the instantaneous power. This thermal resistance is used to detect fault conditions of the heater 10 used as will be described in more detail below. For this purpose, the values determined at each point in time are stored in particular and compared with each other in the sense of a time series.

The thermal resistance is fundamentally dependent on the composition of the medium 30 , The electronic control device 50 has stored data in which typical thermal resistances are stored for different compositions. By an appropriate assignment of a measured thermal resistance can thus the electronic control device 50 a composition of the medium 30 determine.

Should the thermal resistance change significantly within a very short period of time, for example within 10 seconds or 20 seconds, this indicates a lack of medium 30 out. In this case, the electronic control device 50 the power supply of the heating conductor 40 immediately switch off to avoid damage.

Should the thermal resistance increase continuously slowly over time, for example in the range of 10 or 20 to 30 operating hours, this indicates a calcification or addition of other substances to the heating device 10 out. In this case, the electronic control device 50 provide a signal to a user to perform a descaling or cleaning of the heater 10 prompt.

It should be noted that the described heater 10 can be used in particular for use in a Motorheizpumpe or in a steam generator. It should also be mentioned that the heating conductor 40 against another heating conductor, in particular a heat conductor with a different rated power, can be replaced. This allows a comparison of properties with different heating conductors, especially at different power ratings.

Claims (11)

Method for monitoring a heating device ( 10 ), - wherein the heating device ( 10 ) at least two different heating conductors ( 40 ) for heating a medium ( 30 ), the method comprising the following steps: - determining an instantaneous electrical power of the heating conductors ( 40 ), - determining a temperature difference between the heating conductors ( 40 ) and the medium ( 30 ), - calculating a thermal resistance by dividing the temperature difference by the instantaneous power, and - determining a property from the thermal resistance, the method successively by means of the at least two different heating conductors ( 40 ) and a number of characteristics of the heating conductors ( 40 ) are compared on the basis of the respectively determined thermal resistance A method according to claim 1, characterized in that the temperature difference is calculated by the fact that from a temperature of the heating conductor ( 40 ) a temperature of the medium ( 30 ) is subtracted, wherein preferably the temperature of the medium ( 30 ) is determined by a dedicated temperature sensor ( 60 ). Method according to claim 2, characterized in that - the temperature of the heating conductors ( 40 ) by means of a on a surface of the heating conductor ( 40 ) is detected, wherein preferably the heating conductors and the temperature sensor are electrically isolated from each other, in particular by a covering and insulating layer; and / or the temperature of the heating conductors ( 40 ) is determined thermographically; and / or the temperature of the heating conductors ( 40 ) by measuring a momentary resistance of the heating conductors ( 40 ) is determined using a known relationship between instantaneous resistance and temperature; and / or the temperature of the heating conductors ( 40 ) of applied voltage, current consumption and temperature coefficient of the heating conductor ( 40 ) and the nominal resistance of the heating conductors ( 40 ) is determined. Method according to one of the preceding claims, characterized in that the medium ( 30 ) Water or a mixture of water and other liquids. Method according to one of the preceding claims, characterized in that a type or a composition of the medium ( 30 ) is determined as a property. Method according to one of the preceding claims, presence or absence of the medium ( 30 ) is determined as a property, wherein preferably the heating conductors ( 40 ) are switched off if a lack of the medium ( 30 ) is determined. Method according to one of the preceding claims, characterized in that the method is repeated several times in succession, wherein a calcification of the heating conductors ( 40 ) is determined as a property based on a time curve of the thermal resistance. Method according to one of the preceding claims, characterized in that the different heating conductors ( 40 ) have different power ratings. Method according to one of the preceding claims, characterized in that the heating conductors ( 40 ) Schichtheizleiter, in particular Dickschichtheizleiter, and part of a Schichtheizelementes or a Metallkernheizelementes are. Method according to one of the preceding claims, characterized in that the heating device ( 10 ) is integrated in a motor heating pump and / or in a steam generator. Heating device ( 10 ), which is designed to carry out the method according to one of the preceding claims and which has an electronic control device ( 50 ) for carrying out the method.

Images