CN104897969B - Method and apparatus for detecting conductivity in instant electric water heater - Google Patents
Method and apparatus for detecting conductivity in instant electric water heater Download PDFInfo
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- CN104897969B CN104897969B CN201410077976.9A CN201410077976A CN104897969B CN 104897969 B CN104897969 B CN 104897969B CN 201410077976 A CN201410077976 A CN 201410077976A CN 104897969 B CN104897969 B CN 104897969B
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Abstract
The invention relates to a method and equipment for detecting conductivity in an instant electric water heater. The measuring device comprises: at least two measuring electrodes for spaced apart arrangement in the channel guiding the water; measurement electronics for providing and analyzing an electrical signal affected by the conductivity of the water; a transformer, wherein the measurement electronics are connected on the primary side and the two measurement electrodes are connected on the secondary side such that the measurement electronics are coupled with the measurement electrodes via the transformer; the measuring electronics provide the alternating voltage signal of the primary side on the primary side of the transformer in a defined manner, such that the alternating current via the measuring electrode and the secondary side via the water is set on the secondary side of the transformer as a function of the conductivity of the water, the current of the secondary side influencing the current of the primary side on the primary side of the transformer, and the measuring electronics measure the current of the primary side for determining the conductivity. The invention also relates to an electric quick-heating water heater for heating water.
Description
Technical Field
The invention relates to a measuring device for detecting the electrical conductivity of water in an electric quick-heating water heater, and to an electric quick-heating water heater provided with such a measuring device. Furthermore, the invention relates to a method of detecting the electrical conductivity of water in an electric instant heating water heater.
Background
Electric tankless water heaters are known, which heat water by means of one or more electric heating coils, in particular constituted by bare heating wires, or by means of similar heating devices, during the flow of water through said tankless water heater. Such an electric tankless water heater is particularly suitable for domestic use, and then the water heated by the electric tankless water heater is usually used directly after heating, which applies not only in time but also in location. Such use may be, for example, showering or hand washing. The danger caused by the current flow of the heating element is avoided in that the heated water establishing the electrical connection, in particular from the bare heating wire to the user, is only weakly conductive due to its purity (and defines the calculated discharge section). Such an electric tankless water heater is therefore not hazardous in this respect due to the defined discharge region.
However, another situation is exceptionally risky when contaminated, in particular salt-containing, water enters the pipeline. Furthermore, this can occur in areas of undersea pipe systems when contaminated or brackish water penetrates into the pipe system due to tidal fluctuations or flood disasters or other abnormal events.
To eliminate this problem, the use of tankless electric water heaters with bare wires is avoided in such potentially hazardous areas. There is therefore no risk. This also applies when using devices with tubular heating bodies, which are expensive and have poor regulating properties.
On the other hand, however, the tankless electric water heater is a relatively simple possibility to heat water. Such a water heater is less costly and space-saving and does not require much maintenance than some other systems with complex hot water reservoirs. Heating by means of electric current is therefore particularly cost-effective when the use of an electric quick-heating water heater avoids the need for pre-heating water and thus the expenditure of energy required for this.
Therefore, if an electric quick-heating water heater with bare wires is also to be used in such hazardous areas and the safety of the user is to be ensured as well, a safety system is required in order to eliminate the danger to the user. However, the expensive safety systems are contradictory to the low cost understanding of providing an electric tankless water heater.
Disclosure of Invention
The invention is therefore based on the following object: at least one of the above problems is solved. In particular, a solution is to be proposed which enables the provision of an electric tankless water heater even in such hazardous areas as mentioned above in a simple and cost-effective manner. At least in comparison with the solutions proposed so far, an alternative solution is to be proposed.
According to the present invention, a measuring device for detecting the electrical conductivity of water in an electric quick-heating water heater is proposed, said measuring device comprising: at least two measuring electrodes for spaced apart placement in a channel of the tankless electric water heater that conducts water; the measurement electronics are arranged to measure the electrical characteristics of the device, for providing and analyzing an electrical signal influenced by the electrical conductivity of the water; a transformer having a primary side and a secondary side, wherein the measurement electronics are connected on the primary side and the two measurement electrodes are connected on the secondary side such that the measurement electronics are coupled with the measurement electrodes via the transformer, wherein the measurement electronics provide a primary-side alternating voltage signal on the primary side of the transformer as specified, such that an alternating current via the measuring electrode and a secondary side through the water is set on the secondary side of the transformer as a function of the conductivity of the water, the current of the secondary side influencing the current of the primary side on the primary side of the transformer, and the measuring electronics measures the current of the primary side for determining the conductivity. Thus, the measuring device comprises at least two measuring electrodes, measuring electronics, and may comprise a transformer. The measuring electrodes are arranged in a channel of the instant electric water heater in a spaced manner and are connected with measuring electronics via a transformer. The measuring electronics provide an alternating voltage signal on the primary side of the transformer, which alternating voltage signal is transmitted via the transformer to the secondary side of the transformer, to which the measuring electrodes are connected. On the secondary side, the alternating current then flows via the measuring electrode and through the water into the channel of the tankless electric water heater. The current is accordingly dependent on the conductivity of the water and is therefore reflected via the transformer on the primary side, where the conductivity-dependent current likewise forms. Measurement electronics then measure the current on the primary side and can determine the conductivity or resistivity of the water.
It is known in principle to determine the electrical conductivity via electrical measurements. In addition, however, the solution proposed here is characterized by a relatively simple and cost-effective design. In particular, the measuring device is purposefully designed for the task of determining the electrical conductivity of water in the value range where the use of an instantaneous electric water heater can be problematic. The measuring device of this simple design uses an alternating voltage signal which is fed to the measuring section via a transformer and via which its conductivity-related reaction is likewise counteracted and is then evaluated by the measuring electronics. In particular, only small currents are formed in relatively clean water with low conductivity, i.e. high resistivity, and the described coupling, which is based on alternating currents, via a transformer becomes correspondingly very inaccurate and even no longer usable.
But it has been recognized according to the invention that: the measuring device can in any case provide sufficient accuracy for the purposes of the described use. The measuring device can in principle be used in all domestic appliances which heat drinking water or domestic water by means of a flow-through method. In addition to the instantaneous electric water heater for heating tap water to be provided at a tap point like a tap or shower head, automatic coffee machines, washing machines and dishwashers belong to this class, to name a few examples.
Preferably, the measuring device is configured to measure a resistivity of 0k Ω cm to 10k Ω cm. Furthermore, it depends on the size and design of the probe. Within this range, according to one embodiment, measurements can be carried out with a measurement tolerance of less than 10%. The measuring device is therefore specifically adapted to this range. This relates in particular to the described structural configuration. But may also involve the design of some elements, such as the measuring electrodes used and the spacing at which the measuring electrodes are arranged. In particular, the voltage level used, which is provided as an alternating voltage on the primary side, can be used for this purpose. Preferably, a peak voltage of the alternating voltage signal of about 2.5V is proposed here, i.e. a voltage of about 5V from its minimum value to its maximum value.
One embodiment provides that the measurement electronics are electrically isolated from the measurement electrode by a transformer. Therefore, transformers are proposed which have no electrical contact between the primary side and the secondary side. In this way, the measurement electronics can be protected in a simple manner from the voltage in the measurement section, i.e. the water to be heated. The measuring device can therefore be used without problems in so-called direct heating electric water heaters of the bare heating wire type, in which a bare heating wire, in particular embodied as a heating coil, is arranged in a water channel, through which a correspondingly high current flows, and directly heats the water there. Such a bare heating wire can be directly excited with a mains voltage, which can be, for example, 230V with respect to the neutral line and thus, in a regular manner, with respect to the ground potential. Such high voltages can easily destroy the measurement electronics. By means of the electrical isolation via the transformer, this hazardous potential for the measurement electronics is avoided.
According to one embodiment, the measuring electronics have a voltage divider or other means for increasing the voltage in order to increase the alternating voltage signal on the primary side such that its median voltage is increased by a value above 0V, in particular above 2V. In particular, the alternating voltage signal on the primary side should be raised such that it is completely positive. Thus, an alternating voltage signal oscillating at ± 2.5V around the zero point of the transformer should be raised by, for example, 2.5V, so that it therefore no longer oscillates between +2.5V and-2.5V, but between 0V and 5V. By raising the zero point of the transformer by 2.5V, the switching voltage of the driver oscillating between 0 and 5V is considered as an alternating voltage with a +/-2.5V offset or becomes effective for the transformer. In particular, this simplifies the generation of the primary-side alternating voltage signal, and the proposed measuring device allows such a voltage offset due to its transformer design, which has virtually no effect on the resulting current.
According to another embodiment, in addition to measuring the current on the primary side, the temperature of the water whose electrical conductivity is to be determined is taken into account and used to determine the electrical conductivity. Therefore, the accuracy of the measurement can be further improved by: i.e. the temperature that would have an effect on the conductivity of the water, is considered as an additional variable.
According to one embodiment, the measuring electronics generate the alternating voltage signal on the primary side via pulse width modulation with a frequency in the range between 1kHz and 10 kHz. The generation of the primary-side alternating voltage signal can thereby be achieved in a simple manner and with a small apparatus construction. For example, only one microprocessor is required to supply the respective switching signal to a driver which generates a pulsed signal by means of a dc input voltage and generates an analog voltage change via a low-pass filter. In addition, the transformer can simultaneously assume the task of choking a low-pass filter for the pulsed signal.
Furthermore, the invention relates to an electric quick-heating water heater for heating water. Such an electric tankless water heater has at least one channel for guiding water, in which the water is heated by means of an electric heating element, in particular by means of bare wires. A plurality of such heating elements can also be arranged in a plurality of, in particular fluidically consecutive, channel sections. In the channels or in one of the channels if a plurality of channels are present, a measuring device is applied to measure the electrical conductivity. The measuring device has at least two electrodes which are arranged in at least one channel for conducting the water to be heated, for detecting the electrical conductivity of the water, and are connected to measuring electronics for evaluation. If the measuring device recognizes that the preset limit conductance value is exceeded, the power supply to the heating element is interrupted overall, if necessary in addition to the power supply to the measuring and control electronics. Thus, the tankless electric water heater with bare wires can also be used in hazardous areas, since it can be assumed that the electrical conductivity in these hazardous areas is only exceptionally, mostly only briefly, actually high.
Preferably, the interruption is active only for the duration of exceeding the limit conductance value, and the supply of power to the at least one heating element is activated again below a preset limit conductance value. Thus, the interruption of the supply of hot water may be limited to a minimum value in time.
An advantageous variant is; turn off via a relay. In this way, a shut-off can be carried out in a simple and rapid manner, which also achieves an electrical isolation in order to be able to avoid the risk of electric shocks occurring above the water section.
As an advantageous variant, provision is made here for: a measuring device according to one of the above embodiments is used. Accordingly, at least two electrodes are provided in the channel or one of the channels. This can be done in a close proximity or at a distance from the heating element. Preferably, the temperature sensor is likewise arranged in the channel, at least as close as possible to the measuring electrode, so that no active heating element is arranged between the measuring electrode and the temperature sensor.
Preferably, the tankless electric water heater is configured to switch off the at least one electric heating element as soon as the detected electrical conductivity exceeds a preset limit conductance value or the detected electrical resistivity is below a preset limit resistance value. The measuring device is therefore connected to the safety shut-off device. The measuring device can therefore provide a value for this to the control unit, which then prevents heating. Preferably, one or more electrical heating elements are switched off, so that the entire heating device, that is to say all the power electronics of the tankless electric water heater, is switched off. Once the conductivity is again acceptable, the switch-on can be made again.
Preferably, the inherently present elements of the tankless electric water heater can be used as electrodes. In particular, for this purpose, a water inlet pipe made of copper or a water outlet pipe likewise made of copper is proposed. In addition, a temperature sensor housing or a temperature sensor receptacle which accommodates the temperature sensor in the water channel and is itself made of metal, preferably copper, can be used as an electrode, in particular as an electrode cooperating therewith. In a preferred embodiment, the water channel can be made of an electrically non-conductive material, in particular plastic, but the temperature sensing element holder can be made of metal and used as an electrode, in particular in combination with the water inlet and outlet lines. Preferably, a cooling body, in particular a cooling body tube of a power semiconductor cooling device, is used for cooling the power semiconductor for activating the at least one heating element. Such power semiconductors, in particular power semiconductor switches, which generate heat when the bare heating wire is energized, can be cooled by the water to be heated, and for this purpose use is made of a metallic cooling body, which is in each case provided for cooling in domestic or industrial water, in accordance with one embodiment. Preferably, such a power semiconductor circuit, in particular its cooling body, which is provided for cooling on one or more power semiconductors, is not grounded and can thus be an independent electrode with respect to ground and thus with respect to the copper inlet or outlet pipe.
If these elements are used as electrodes, in particular if they have a spacing from one another which is significantly greater than the average diameter of the channel, the geometry of the channel in the region between the two electrodes can be used as the geometry of the measuring section in order to determine the conductivity from the measuring current.
Preferably, the electrodes are arranged at a minimum distance from one another which is greater than a distance of a few millimeters of two measuring electrodes which can be arranged in particular in a laboratory device for measuring conductivity. Preferably, the spacing is greater than 1cm, greater than 5cm, in particular greater than 10 mm. Preferably, metals can be used as materials. In the case of very narrow spacing of the two electrodes, the use of copper is difficult, since the smallest deposits already strongly reduce the spacing of the electrodes in a relative sense. With the proposed large spacing, the above-mentioned problems occur less frequently and the advantage of the particularly high electrical conductivity of copper can then be utilized.
Preferably, the measuring device, in particular the measuring electronics or the measuring circuit electronics, is a separate, attachable component which is connected to the electrode and via a data interface, preferably via I2The C-bus is connected to and supplied with voltage by the conditioning electronics of the tankless electric water heater. The measuring device can be embodied in an attachable manner. For this purpose, the measuring device is arranged, for example, in a carrier for fastening. The electrodes can be connected only by flexible lines and can be arranged only in the predetermined positions in which the respective channels are arranged, in particular at a predetermined distance from one another. In order to cause an interruption in the event of too high a conductivity, a relay can be used, or an existing relay interrupting the supply of power can be used, which relay is also energized via the measuring device. According to one embodiment, the interruption is performed by means of a power semiconductor switch, in particular a TRIAC.
Advantageously, the measurement circuit electronics have a microcontroller, and the microcontroller of the measurement circuit electronics determines the resistance between the electrodes via the measurement circuit. A microcontroller may also be referred to as a microprocessor or a microcontroller.
For the calculation of the electrical conductivity value, the temperature of the medium can be transmitted via a data interface of a superordinate control device of the tankless electric water heater, so that a current electrical conductivity value of the medium is calculated from the temperature and the resistance and compared with a reference value. The release signal can also be transmitted via the data interface to a higher-level control device of the instantaneous electric water heater, in order to cancel the interruption again if the current conductance value is again smaller than the limit conductance value.
Preferably, a limit conductance value, which may also be referred to as reference conductance value, is settable. In particular, the settable property can be realized via a potentiometer, or via a parameter which can be set at the operating unit and which can be executed or adjusted via a measuring device, in particular via a microprocessor.
According to one embodiment, the electrodes are not arranged in the immediate vicinity of a few millimeters, as is known from conventional measuring techniques, but rather at a large distance from one another. A better ratio of the resistance of the medium forming the actual measured variable, which resistance is formed by the electrode spacing, to the surface resistance of the electrodes, which resistance changes due to aging and/or calcification, should thereby be achieved, in order to achieve a better long-term stability of the measurement signal, and in order to be able to use more favorable electrode materials that are subject to greater aging. Thus, for example, copper may be used. This is also advantageous for the application of the water inlet or outlet tube, the cooling body or the receptacle of the temperature sensor as an electrode.
The measurement circuit electronics board can advantageously be arranged on the control electronics board and form a unit and/or the microcontroller of the measurement circuit electronics and the microcontroller of the control electronics can form a unit. Advantageously, therefore, after the heating power has been activated when the conductance value is exceeded, an interruption of the supply of power to the heating element, in particular to the bare heating wire, is displayed on the operating part, for example by a flashing indicator or a symbol on the display.
According to the invention, a method for detecting the electrical conductivity is also proposed, which method operates as explained above in connection with the explanation of the measuring device and/or which method operates as explained above in connection with the explanation of the embodiment of the instant electric water heater proposed.
Drawings
The invention will now be elucidated in detail hereinafter, exemplarily according to embodiments, with reference to the appended drawings.
Fig. 1 schematically shows the structure of a measuring device according to one embodiment.
Fig. 2 shows a schematic circuit diagram of an electric tankless water heater according to an embodiment.
Fig. 3 shows a simplified flow diagram of a method for monitoring the conductivity of domestic or fresh water in an apparatus for heating water and electricity.
Detailed Description
The schematic illustration of fig. 1 shows two channel walls 1 of a channel for guiding water 2, which is thus here the measuring medium whose electrical conductivity or resistivity is to be detected. Two electrodes 3, which may also be referred to as probes 3, are guided in a liquid-tight manner through one of the channel walls 1 in order to conduct a measuring current between the electrodes for detecting the conductivity of the water 2 or the measuring medium 2. The electrode 3 is connected to its secondary side 52 at the transformer 5. The transformer 5 has a primary side 51 to which an alternating voltage is applied, which is generated by the alternator 6. For this purpose, the alternator 6 is driven by a microcontroller 7, which is also referred to as a μ Controller for short, by means of a corresponding switching signal. The alternator 6 thus generates an alternating voltage via pulse width modulation, which alternating voltage is thus input at this primary side 51 of the transformer 5.
A measurement signal is accordingly formed, which in fig. 1 is associated with a line, which (intuitively) leads from the transformer 5 to the microcontroller 7, in the manner described as measurement signal 8. The microcontroller 7 therefore also evaluates the measurement signal 8. In practice, the measurement signal 8 is also the signal formed on the primary side 51 of the transformer 5.
The microcontroller 7 therefore energizes the alternator 6 in order to generate an alternating voltage signal as sinusoidal as possible and to input it at the primary side 51 of the transformer 5. Then, a secondary-side measurement current is formed, which flows from the secondary side 52 via one of the electrodes 3 through the water 2 or the measurement medium 2 to the other electrode 3 and back to the secondary side 52 of the transformer 5. Accordingly, a measurement signal 8 is formed which is terminated by the microcontroller 7.
Furthermore, a temperature sensor 4, which may also be referred to as a temperature sensor, is guided in a liquid-tight manner through the channel wall 1 and can detect the temperature of the water 2 or of the measurement medium 2. The temperature sensor 4 correspondingly transmits the temperature value 9 back to the microcontroller 7. The microcontroller 7 therefore analyzes the measured current 8 and the temperature value 9 to determine the conductivity of the water 2.
Fig. 2 shows a simplified circuit diagram of an tankless electric water heater 200 having a bare heater wire 202 and control and power electronics 204. The bare heater wire 202 is shown schematically here and is also representative of other bare heater wires. The electric tankless water heater 200 operates in principle in that water to be heated flows in through the water inlet 206 and is guided in a channel or channel system 208 of the electric tankless water heater 200. Wherein water is heated in a bare wire or a section of the bare heating wire 202 and finally flows out through the water outlet 210 in a heated state.
Here, the bare heater wire 202 is energized by the control and power unit 204. The control and power unit has a drive triac 212, which is only schematically depicted here, or a drive triac 212, which is only schematically depicted here, for each bare heating wire. For cooling the triac 212, a cooling body 214 is provided, which is connected to the not yet heated water in the channel or in the channel system 208. This not yet heated water can thus be used first as cooling water for energizing the triac 212. The heat sink 214 can be designed here as a cooling tube through which all the water to be subsequently heated flows.
Here, a three-phase power supply 216 is provided for supplying energy. To energize the energized triac 212 and, as a result, each bare heater wire 202, a microprocessor 218 is provided. Once the water is discharged, the flow meter 220 detects the volumetric flowSo that the control and power unit 204 controls the heating, in particular may initiate the heating. An inlet water temperature sensor 222 is also provided near the flow meter 220, which detects the inlet water temperatureAnd is provided with a water outlet temperature sensor 224 which provides the water outlet temperature. The microprocessor 218 may analyze the values to thereby control heating and thus activation of the bare heater wire 202 as optimally as possible. The heater can be switched on, in particular, in the event of a volume flow. If the volume flow is weak and/or the inlet water temperature is already high or the outlet water temperature is high, it is possible to energize only the bare heating wires in a decreasing manner, or to energize only one or two of the bare heating wires when, for example, there are three bare heating wires.
In addition, a conductivity measuring device 226 is shown as a functional module, which detects the conductivity of the water in the channel or channel system 208 by means of a conductivity sensor 228. As a result, the conductance value or its inverse, i.e. the resistance value, can be supplied to the control and power electronics 204, in particular to the microprocessor 218, which is symbolized there as the resistance Ω.
Conductivity sensor 228 may, for example, directly measure conductivity in channel or channel system 208. For this purpose, electrodes can also be provided in the channel 208 at the positions shown in fig. 2, in order to measure the resistance there. The signal, in particular the current signal, can be analyzed in the conductivity module 226 or in the conductivity measurement module 226 and supplied as a resistance value Ω to the control and power electronics unit 204, in particular to the microprocessor 218. If necessary, taking into account the temperature, in particular the temperature of the feed waterIn the case of (2) a microprocessor218 may also improve the value of the electrical conductivity or resistance value omega.
In addition or as an alternative, existing elements can be used as electrodes in order to perform the conductivity measurement. This variant is shown in fig. 2, so that the conductivity module 226 uses as an alternative or alternative, on the one hand, a water inlet tube 230 made of copper as an electrode and, on the other hand, a cooling body 214 made of the same metal, in particular aluminum, as a second electrode. The inlet pipe 230 and the cooling body 214, which are made of copper, are at a relatively large distance from one another, and in any case the measuring section between the inlet pipe 230 and the cooling body or cooling pipe 214, which passes through the water in the channel or channel system 208, is relatively large, in any case very large, compared to other customary conductivity measuring devices. The measurement section is also large compared to the average channel diameter. Furthermore, by means of a large spacing it is possible to achieve: the spacing fluctuations between the water inlet pipe 230 and the cooling pipe 214 are in any case very small in relation to their absolute spacing and thus have a small influence on the conductivity measurement. The water inlet pipe 230 may be grounded via a ground terminal 232. The cooling pipe 214 is accordingly not allowed to be grounded, since otherwise the measuring current would not flow from the inlet pipe 230 through the water to the cooling pipe 214, and it is also self-evident that the channel or channel system 208 is in any case formed in an electrically non-conductive manner, i.e. for example from plastic, in this region between the inlet pipe 230 and the cooling pipe 214.
Alternatively, the outlet pipe 234, which is also made of copper, serves as an electrode for the conductivity measurement. The temperature sensor accommodating portion 236 accommodating the outlet water temperature sensor 224 may be used as a counter electrode so that a measurement current may flow between the two electrodes. The conductivity measurement here also approximately analyzes the water with the same temperature for the total measurement range. In this case, the outlet pipe 234 may also be grounded via the ground terminal 232, in which case the temperature recorder 236 is not grounded at all times.
The relatively long measuring section for measuring the electrical conductivity of the water via the measuring current between the respectively selected electrodes can be extremely inaccurate. However, for this purpose, the measuring section can also reduce the problem of air bubbles in the water. In particular, a very long measuring section, such as between the water inlet line 230 and the heat sink 214, when the water inlet line 230 and the heat sink 214 are used as electrodes, may lead to extremely small, possibly even undetectable measuring currents in the case of very pure water and thus extremely low electrical conductivity. However, if the water is heavily contaminated, in particular with high salt content, a measuring current can flow through and the measuring accuracy can thereby also be increased significantly. In principle, only a high degree of precision is required, even for this case.
Fig. 2 thus also shows: in the event that the conductivity of the water is very high, the energization of the bare heater wire 202, and in particular even the three-phase power supply 216, is interrupted so that substantially the entire tankless electric water heater 200 is voltage-free. Preferably, the functionality of the microprocessor 218 and the conductivity measurement module is maintained. The switching off of the power electronics can take place in any case when the conductivity rises above a predefined limit conductivity value, which can be predefined by means of the limit value setting device 238.
Fig. 3 shows a method and a method for switching off according to at least one embodiment. The process is initiated in an initialization block 350 and after initialization, a query is made in a query block 352. Interrogation, i.e. comparison: whether the detected conductivity is greater than a predetermined conductivity reference value or whether the resistivity is less than a corresponding predetermined resistivity reference value. According to one embodiment, the reference value for comparison can be set in the limit value setting device 238 shown in fig. 2. The reference value may also be related to, for example, what regulations are enforced in the country or how far a water section up to the user follows after the bare heating wire.
In any event, a positive comparison causes a branch to shutdown module 354 in query module 352, but the shutdown module causes shutdown of the tankless electric water heater 200, at least the bare heater wire 202 or all of the bare heater wires 202.
Then, accordingly, at that moment, the tankless electric water heater cannot be used and, in order to display this to the user, the signal module 356 performs a signal output, for example, generates a flashing signal.
The query may then be immediately re-queried in the query module 352. The successive queries can be performed substantially quickly by correspondingly frequently clocking the queries executed by the computer. If this results in the result that the conductance value does not exceed the reference conductance value or the resistivity does not fall below the limit resistance value, the energy supply, at least the excitation of the bare heating wire 202, is switched on, or when it has been switched on beforehand, the energy supply is kept switched on. The above describes the turn-on module 358. In particular, the same switch, in particular a current source or voltage source main switch, can be accessed by the turn-off module 354 on the one hand and the turn-on module 358 on the other hand, wherein the turn-off module 354 causes the turn-off and the turn-on module 358 causes the turn-on. This also causes the signal module 356 to no longer signal the display device to turn off when turned on by the turn on module 358.
Therefore, a bare heating wire type electric instant heating water heater has been known, which is also characterized by directly heating a medium (drinking water) through an extremely short heating time. The usually based discharge sections in the inlet and outlet are used in a safe operating mode together with the necessary grounding of the metal entry and exit points of the medium to be heated (drinking water).
The discharge sections in the inlet and outlet are dimensioned such that, in the case of the worst quality of domestic water with high conductivity, the fault leakage current is kept low so that, in this case, no life-threatening currents are formed without the device being grounded.
Overall, the tankless electric water heater thus obtains a very high level of protection compared to conventional tubular heating bodies, since the maximum fault leakage current or contact voltage is limited, as determined by the design, even in the case of a poor or non-existing ground connection, so that there is no danger to the user.
In some areas, the conductance may rise temporarily strongly due to the particular conditions of the water supply, so that the leakage current reaches several hundredths of amperes. In the case of a protective conductor connection that is implemented professionally, the hazardous potential is low for the user and can be compared with conventional tubular heating systems.
With the solution according to the invention, it is now possible in a simple manner to implement: even in the case of extremely high water conductivity and the absence or poor connection of the protective conductor, inadmissibly high contact voltages do not occur.
In general, the leakage current is used as a standard instead of the conductance value. In this case too, an excessively high leakage current, i.e. an impermissibly high leakage current, can be reliably prevented. For this purpose, according to one embodiment, it is provided that the electrical resistance between the first or last heating body pin present in the water and the respective inlet and outlet pipes is measured. Thus, a lateral measurement of the electrical resistance between the first heating body plug present in the water and the inlet pipe, or a measurement of the electrical resistance between the last heating body plug present in the water and the outlet pipe, is performed. Other elements may also be used as measuring electrodes.
In the case of a known geometry of the flow channel, which thus simultaneously forms a discharge channel for the leakage current, the resistance value of the discharge section can be inferred from the resistance between the measuring electrodes. When, for example, the outlet section is considered as a 100cm long hose and the measuring section between the electrodes is 1cm = e.g. 1kOhm, the resistance of the outlet discharge section, i.e. the discharge section at the outlet, can be calculated to be 100 kOhm. In the case of a known grid voltage of, for example, 230V, the leakage current is then 2.3 mA. This calculation may be performed before the heating power is switched on. Switching on can then be prevented if a value exceeding the determined limit value is calculated, for example exceeding 10 mA.
Claims (11)
1. A measuring device for detecting the electrical conductivity of water in an electric tankless water heater (200), said measuring device comprising:
-at least two measuring electrodes (3) for being arranged spaced apart in a channel (208) of the tankless electric water heater (200) guiding water,
measurement electronics for providing and analyzing an electrical signal influenced by the electrical conductivity of the water,
a transformer (5) having a primary side (51) and a secondary side (52),
wherein
-the measurement electronics are connected on the primary side (51), and
-two of the measuring electrodes are connected on the secondary side (52) such that the measuring electronics are coupled with the measuring electrodes (3) via the transformer (5),
wherein the content of the first and second substances,
-the measurement electronics provide a primary-side alternating voltage signal on the primary side (51) of the transformer (5) as specified,
so that
-setting an alternating current on the secondary side (52) of the transformer (5) via the measuring electrode (3) and through the secondary side of the water as a function of the electrical conductivity of the water,
-the current of the secondary side influences the current of the primary side on the primary side (51) of the transformer (5),
the measurement electronics measure the current of the primary side for determining the conductivity,
the measurement electronics are electrically isolated from the measurement electrode (3) by the transformer (5), and
the measuring electronics have a means for raising the voltage in order to raise the alternating voltage signal on the primary side such that the median voltage value of the alternating voltage signal on the primary side is raised by a value exceeding 0V and the alternating voltage signal on the primary side is completely positive.
2. The measuring device as set forth in claim 1,
it is characterized in that the preparation method is characterized in that,
the measuring device is configured for measuring a resistivity of 0k Ω cm to 10k Ω cm.
3. The measuring device as set forth in claim 1,
it is characterized in that the preparation method is characterized in that,
in addition to the measurement of the electrical conductivity value, the temperature of the water in the region of the measuring electrode (3) is measured and taken into account for determining the electrical conductivity.
4. The measuring device as set forth in claim 1,
it is characterized in that the preparation method is characterized in that,
the measurement electronics generate the alternating voltage signal of the primary side via pulse width modulation with a frequency in the range of 1kHz to 10 kHz.
5. Tankless electric water heater (200) for heating water, having a measuring device according to claim 1, wherein
-at least one electric bare wire heating element (202) is provided in at least one channel (208) guiding the water to be heated for heating the water,
-a measuring device provided for measuring the electrical conductivity of the water to be heated or of the heated water, having two electrodes (3) which are provided in the at least one channel (208) for conducting the water to be heated for detecting the electrical conductivity of the water, both electrodes being connected for analysis to measuring electronics, and wherein,
-causing the measuring device to interrupt the power supply of the at least one bare wire heating element when a preset limit conductance value is exceeded.
6. The tankless electric water heater (200) of claim 5,
it is characterized in that the preparation method is characterized in that,
after the interruption of the power supply when the preset limit conductance value is exceeded, the interruption is only active for the duration of the exceeding and, when the preset limit conductance value is undershot, the power supply to the at least one bare wire heating element (202) is activated again.
7. The tankless electric water heater (200) of claim 5,
it is characterized in that the preparation method is characterized in that,
a relay is provided for interrupting the power supply.
8. Instant heating electric water heater (200) with a measuring device according to claim 1,
it is characterized in that the preparation method is characterized in that,
using as the electrode (3) an electrically conductive element in contact with the water, wherein at least one of the following elements is used as the electrode:
-an inlet pipe (230) through which water flows into the tankless electric water heater (200),
a cooling body (214) of a power semiconductor cooling device for cooling a power semiconductor for energizing the at least one bare wire heating element (202),
-a temperature sensor housing (236) for accommodating a temperature sensor (224) for measuring the temperature of the water, and
-an outlet pipe (234) through which water exits the tankless electric water heater.
9. The tankless electric water heater (200) of claim 8,
it is characterized in that the preparation method is characterized in that,
electrode (3)
-is arranged at a minimum distance from each other, said minimum distance being greater than 1cm, and
-made of copper.
10. A method for detecting conductivity, comprising the steps of
-generating an alternating voltage signal on the primary side,
-transmitting the alternating voltage signal of the primary side from a primary side (51) of the transformer to a secondary side (52) of the transformer by means of a transformer (5),
-leading the alternating voltage signal transmitted onto the secondary side (52) of the transformer (5) via one of the two electrodes (3) through the water to be heated to the other of the two electrodes (3) and from there back to the transformer (5),
-detecting an alternating current signal formed on the secondary side on the transformer (5), and
-determining the conductivity from the alternating voltage signal formed and detected on the primary side,
-wherein the alternating voltage signal of the primary side is boosted by a voltage median value exceeding a value of 0V with a mechanism for boosting the voltage.
11. The method of claim 10, wherein the first and second light sources are selected from the group consisting of,
it is characterized in that the preparation method is characterized in that,
the measuring device according to any of claims 1 to 4 is used for carrying out the method, wherein the tankless electric water heater (200) according to any of claims 5 to 9 is used.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201410077976.9A CN104897969B (en) | 2014-03-05 | 2014-03-05 | Method and apparatus for detecting conductivity in instant electric water heater |
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| CN201410077976.9A CN104897969B (en) | 2014-03-05 | 2014-03-05 | Method and apparatus for detecting conductivity in instant electric water heater |
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| DE102016013052A1 (en) | 2016-10-27 | 2018-05-03 | Stiebel Eltron Gmbh & Co. Kg | Instantaneous water heater and method for controlling a continuous flow heater |
| CN108008200A (en) * | 2016-11-28 | 2018-05-08 | 芜湖美的厨卫电器制造有限公司 | Water resistance detection device and watering equipment |
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| US4093847A (en) * | 1974-09-10 | 1978-06-06 | Datametrics Corporation | Temperature control system for electric fluid heater |
| CN1541320A (en) * | 2001-08-13 | 2004-10-27 | ϣ | System and method for rapid heating of fluid |
| CN200990702Y (en) * | 2006-12-26 | 2007-12-12 | 杨九思 | Immediate heating microwave water heater |
| CN102116756A (en) * | 2009-12-30 | 2011-07-06 | 上海城投原水有限公司 | Single chip microcomputer-based liquid electrical conductivity measurement method |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4093847A (en) * | 1974-09-10 | 1978-06-06 | Datametrics Corporation | Temperature control system for electric fluid heater |
| CN1541320A (en) * | 2001-08-13 | 2004-10-27 | ϣ | System and method for rapid heating of fluid |
| CN200990702Y (en) * | 2006-12-26 | 2007-12-12 | 杨九思 | Immediate heating microwave water heater |
| CN102116756A (en) * | 2009-12-30 | 2011-07-06 | 上海城投原水有限公司 | Single chip microcomputer-based liquid electrical conductivity measurement method |
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