Domestic appliances, especially instantaneous water heaters

Abstract

Domestic appliance, especially instantaneous water heater, with a heating section (100), a heating unit (200) for heating the water flowing through the heating section (100), a relay (8) for controlling a shutdown unit (20) which can disconnect the heating unit (200) from a supply network (L1 - L3), a flow sensor (1) for detecting a flow of a medium through the heating section (100) and for outputting a clock signal (2), wherein the clock of the clock signal (2) is dependent on the flow through the heating section (100), and a safety electronics unit (500) for controlling the relay (8), wherein the safety electronics unit (500) comprises: a flip-flop (3) which is designed to receive the clock signal (2) as an input signal and to output an enable signal (4), a microcontroller (5) which is designed to receive the clock signal (2) and to convert it into an output signal (10) with a higher frequency, an amplifier (6) which is designed to receive the output signal (10) of the microcontroller (5) and the enable signal (4) from the flip-flop (3) and to amplify the output signal (10) of the microcontroller (5) in the presence of the enable signal (4) from the flip-flop (3), and a DC voltage decoupling unit (7) which is designed to pass an output signal (9) of the amplifier (6) when the frequency of the output signal (9) is above a decoupling cut-off frequency, wherein the output signal of the DC decoupling unit (7) is designed to control the relay (8).

Description

The present invention relates to a domestic appliance, in particular a continuous flow heater.An electric continuous flow heater serves to heat water as it passes through the continuous flow heater. According to the flow rate of the water, the electric energy for heating is increased or reduced. Typically, a safety system is provided which interrupts the electrical power supply to a heating element when water no longer flows through the continuous flow heater.DE 197 02 904 A1 shows a monitoring circuit for a continuous heater with a safety system.DE 28 41 283 C3 shows a circuit for controlling the pulse-to-pause ratio of the operating state of a heat source.DE 43 43 256 C2 shows a continuous flow heater with a temperature error detection circuit.DE 29 45 307 A1 shows a device for the follow-up control of a heating power supplied to a flowing medium as a function of a flow rate of the medium to be preset in a selectable manner for setting a desired temperature.The electric continuous flow heater is to be switched off when the water flow rate is below a limit value. For this purpose, a measurement of the flow rate is carried out by means of a flow sensor.It is an object of the present invention to provide an electronic monitoring device for a domestic appliance which is cost-effective and nevertheless enables a reliable shutdown of the appliance if a flow rate of the water through the appliance is below a limit value.This object is achieved by a domestic appliance according to claim 1.Thus, a domestic appliance, in particular a continuous flow heater, is provided with a heating section, e.g. a pipe, a heating unit for heating the water flowing through the heating section and a relay for switching the heating unit on or off. The monitoring circuit has a flow sensor for detecting a flow through a tube of the domestic appliance and for outputting a clock signal whose clock is dependent on the flow through the heating section. The monitoring circuit also has a monostable flip-flop which receives the clock signal as an input signal. The monitoring circuit further comprises a microcontroller which receives the clock signal and converts it into an output signal with a higher frequency. The monitoring circuit further comprises an amplifier which receives the output signal of the microcontroller and an enable signal from the flip-flop and amplifies the output signal of the microcontroller in the presence of the enable signal from the flip-flop. A DC voltage decoupling unit passes an output signal of the amplifier when the frequency of the output signal is above a cut-off frequency. The output signal of the DC voltage decoupling unit serves to control a relay of the domestic appliance.According to one aspect of the present invention, the flip-flop is configured as a frequency-dependent flip-flop and outputs an enable signal when the clock signal is presentAccording to a further aspect of the present invention, the tilting stage is configured to ensure follow-up even if no flow in the heating section is detected by the flow sensor.According to a further aspect of the present invention, the DC voltage decoupling unit has at least one capacitor for AC voltage coupling.The invention relates to the idea of supplying the (clock) signal of a flowmeter in parallel to both a microcontroller and a frequency-triggered flip-flop. An amplifier in the monitoring device is activated only when both the flip-flop stage and the microcontroller output an enable signal to the amplifier. The amplifier is coupled to a DC voltage decoupling unit which only allows control signals having a frequency above a cut-off frequency to pass through. The decoupling unit controls a relay which activates or deactivates a heating unit of the domestic appliance.The circuit according to the invention is advantageous because a transformer as in DE 197 02 904 A1 could be dispensed with. The transformer could be replaced by a capacitor for DC decoupling. The advantage of the capacitor is the substantially smaller size. Furthermore, such a capacitor is more cost-effective. The high-frequency drive required for the DC decoupling is provided by the microcontroller, which converts a low frequency of the clock signal 2 into a high frequency.Further embodiments of the invention are the subject matter of the dependent claims.Advantages and exemplary embodiments of the invention are explained in more detail below with reference to the drawings. FIG. 1 shows a schematic illustration of a domestic appliance according to a first exemplary embodiment, and FIG. 2 shows a schematic illustration of a domestic appliance with a safety electronics unit according to a first exemplary embodiment.FIG. 1 shows a schematic illustration of a domestic appliance according to a first exemplary embodiment. The domestic appliance can be designed, for example, as a continuous-flow heater and can have a heating system or a heating unit 200 (for example with three bare-wire heating elements HW 210). The home appliance further comprises a rectifying unit 70, a safety relay 80 and an electronic shutdown unit 20. The electronic shutdown unit 20 is coupled on the input side, for example, to three phases L 1-L 3 of a supply network. On the output side, the switch-off unit 20 can be coupled to the heating unit 200. When the shut-down unit 20 is activated, it disconnects the heating unit from the three-phase network L1-L3. Optionally, only one phase can also be used instead of the three phases.According to the first exemplary embodiment, the heating unit 200 can be designed as a bare wire heating unit, so that the current-carrying heating elements are directly located in the water which can flow through a heating section 100. The heating unit 200 may be controlled via a control unit not shown in FIG. 1. The disconnection unit 20 can be designed as a three-pole disconnection switch with an electromagnet 21, so that all-pole disconnection is ensured in the event of a fault. If the domestic appliance is connected to only one phase, the switch-off is configured as a single-pole switch-off. The switch-off unit 20 can be controlled via a safety relay 8. The safety relay 8 can in turn be actuated via a safety electronic unit 500. According to the invention, a capacitor can be used for DC-disconnection of the safety relay, as shown in detail in Fig. 2.The heating unit 200 comprises a plurality of bare wire heaters 210 and these are driven by triacs 220.The electronic shutdown unit 20 serves to supply the mains voltage at the respective phases L 1-L 3 to the heating unit 200.According to the invention, a flow of a medium through the heating section 100 is detected and the flow is converted into a frequency-proportional clock signal, which is analyzed by the safety electronics unit 500. If there is sufficient flow, then the electronic shut-off switch 20 can be deactivated, so that the heating unit 200 is supplied with mains voltage and the medium flowing through the heating section can be correspondingly heated. The control unit then controls the operation of the heating unit so that the medium flowing through the heating section 100 reaches the desired temperature. The safety electronic unit 500 is intended in particular to prevent the heating unit 200 from being activated when there is no throughflow in the heating section, i.e. when no water flows through the heating section. In addition, it can also be avoided that an unacceptably high discharge temperature is achieved in heating with an unduly high output. When this occurs, the heating unit is to be disconnected from the mains. The voltage rectified by the rectifier unit 70 can be conducted to the electronic shutdown unit 20 directly or via the diagnostic optocoupler 30.In the event of a fault, the electronic shutdown unit 20 is opened by the electromagnet 21 and can be closed again only manually by actuating, for example, a push pin.During normal operation of the domestic appliance, a redundant safety check should take place. In this case, it is to be checked in particular whether the safety measures are error-free and could possibly trigger in the event of a fault. For this purpose, a current can be driven through the protective drive 21 of the electronic shutdown unit 20 during normal operation. However, this current can be limited by a series resistor in such a way that the protective drive does not open the switch. This test current can flow through the optocoupler 30 and in particular through the transmitting diode 31. A receiving unit 32 can receive the light from the transmitting diode 31 and control electronics, not shown in detail, can identify how the optocoupler 30 behaves on the basis of the collector potential of the transistor 32. If an unacceptable condition is detected, the heating operation is terminated and the apparatus is deactivated. Thus, redundant safety checking can be ensured.FIG. 2 shows a schematic illustration of a domestic appliance, in particular a continuous-flow heater, having a safety electronics unit 500 according to a first exemplary embodiment. A flow sensor 1 detects a flow through one or a channel 100 and outputs a clock signal 2. The water to be heated flows through the heating path 100 and is heated by an electric heating unit 200. The operation of the heating unit 200 may be controlled by a control unit 600. This can be effected as a function of the flow rate detected by the flow sensor 1, a setpoint temperature 610 of the medium and / or the actual temperature 620 of the medium. The clock of the clock signal 2 of the flow sensor 1 is dependent on the flow of the medium through the heating section 100. The higher the flow rate, the higher the clock rate and thus the frequency of the output signal 2 of the sensor 1. the safety electronic unit 500 has a monostable multivibrator 3, a microcontroller 5, an amplifier 6 and a DC voltage decoupling unit 7. The clock signal 2 from the sensor 1 is fed to both the flip-flop 3 and the microcontroller 5. The microcontroller 5 converts the low-frequency clock signal 2 from the flow sensor 1 into an output signal 10 having a higher frequency. The first frequency can be assigned to a minimum flow rate. In other words, at a minimum flow rate, the flow sensor generates a signal having a frequency. This frequency can then be considered a first frequency. If the frequency or the clock of the output signal 2 of the flow sensor 1 is below this first frequency, then the flow through the heating section is too small and the heating unit is deactivated. The flip-flop 3 generates an enable signal 4 when the frequency of the clock signal 2 at the input of the flip-flop 3 exceeds a first frequency. The flip-flop 3 ensures a certain follow-up.The amplifier 6 can amplify the constant clock signal 10 only when the enable signal 4 is present. The output signal 9 of the amplifier 6 serves as an input signal of the DC voltage decoupling unit 7. The capacitance C can be selected to be small.The flip-flop 3 switches on when a clock signal 2 having a frequency is present at its input. Because the flip-flop 3 is arranged in parallel with the microcontroller 5, it can check the function of the microcontroller 5. Thus, as a redundant safety measure, the flip-flop 3 can ensure that the amplifier 6 does not output a signal even if a faulty signal is output by the microcontroller 5. This reaches the flip-flop 3 by the enable signal 4. Rather, the tracking implements a delay in the shutdown.According to the invention, the microcontroller 5 converts the low frequency clock signal at a high and constant frequency. Microcontroller 5 is designed in such a way that input clock signal 2 is only converted into output signal 10 from a cut-off frequency.The DC voltage decoupling unit 7 has a capacitor for galvanic decoupling. It is thus possible to prevent a DC voltage fault in the safety electronic unit from being transmitted to the relay 8. The capacitor in the DC voltage decoupling unit 7 is designed such that a minimum frequency must be present in the input signal 9 in order to drive the relay 8. The DC voltage decoupling unit 7 thus allows signals to pass only if these signals have a frequency above the limit frequency for the decoupling unit. The DC voltage decoupling unit 7 is designed in such a way that it operates in principle like a frequency-controlled Schmidt trigger.By means of the relay 8, a heating unit 200 for heating the fluid located in the pipe 100 can be switched on or off.According to a further exemplary embodiment, the continuous-flow heater can also be designed as a 1-phase continuous-flow heater.

Claims

Domestic appliance, in particular continuous flow heaters, having a heating section (100), a heating unit (200) for heating the water flowing through the heating section (100), a relay (8) for controlling a switch-off unit (20) which can disconnect the heating unit (200) from a supply network (L1 - L3), a flow sensor (1) for detecting a flow of a medium through the heating section (100) and for outputting a clock signal (2), wherein the clock of the clock signal (2) is dependent on the flow through the heating section (100), and a safety electronics unit (500) for controlling the relay (8), wherein the safety electronics unit (500) has: a flip stage (3) which is configured to receive the clock signal (2) as an input signal and to output an enable signal (4), a microcontroller (5) which is configured to, the clock signal (2) being received and converted into an output signal (10) having a higher frequency, an amplifier (6) which is configured to receive the output signal (10) of the microcontroller (5) and the enable signal (4) from the flip-flop (3) and to amplify the output signal (10) of the microcontroller (5) in the presence of the enable signal (4) from the flip-flop (3), and a DC voltage decoupling unit (7) which is configured to pass an output signal (9) of the amplifier (6) if the frequency of the output signal (9) is above a decoupling cut-off frequency, wherein the output signal of the DC voltage decoupling unit (7) is configured to control the relay (8).Domestic appliance according to claim 1, wherein the flip-flop stage (3) is configured as a frequency-dependent flip-flop stage and is configured to output the enable signal (4) when the clock signal (2) is present.Domestic appliance according to claim 1 or 2, wherein the tilting stage (3) is configured to ensure follow-up even if no flow in the pipe (100) is detected by the flow sensor (1).Domestic appliance according to one of claims 1 to 3, wherein the DC voltage decoupling unit (7) has at least one capacitor for AC voltage decoupling.

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