RU2105433C1 - Electric water heater - Google Patents

Abstract

FIELD: heating of water for domestic needs. SUBSTANCE: electric water heater incorporates body 1 made from heat insulation material with heat conductive upper cover 8 in which tubular U-shaped electric heating elements 2, 3, 4 with leads 7 located in cover 8 of body 1 are placed, U-shaped pipe-line 10 to feed cold water with pressure transducer 11 positioned together with knee of pipe-line not below upper part of heat transfer surface of electric heating elements 2, 3, 4. Pipe-line 10 to feed cold water is joined to lower part of body 1, pipe-line 23 to tap away heated water is connected to upper cover 8 of body 1 where local hydraulic resistance 22 and thermal regulator 17 of water are installed. Transducer of regulator 17 is confined in heat conductive enclosure that is joined to upper cover 8 with possibility of thermal contact. Height of enclosure does not exceed value 2,5λF_s,, where λ is thermal conductivity of material of enclosure; F_s is area of cross-section of side wall of body 1. There are also mounted safety thermal switch 24 installed in upper cover 8 and placed between A.C. network and power supply buses of electric water heater and control unit. Control unit has button element setting power of switched on electric heating elements with buttons 27 and 28. One stroke of button 27 causes increase of power in switched on electric heating elements, depression of button 28 results in decrease of this power. Control unit also includes limiter of maximum power. Buttons 27 and 28 are connected through resistors to power supply source and through pulse formers first one - to first input of first NOT-OR gate, second one through NOT gate - to second input of OR gate. First input of OR gate is connected to output of NOT-OR gate and output - to counting input of binary reversible counter which reverse input is connected to output of first NOT-OR gate and input of setting of initial state is coupled to output of initial setting unit of counter. EFFECT: increased reliability and improved user's qualities. 10 cl, 14 dwg

Description

 The invention relates to electrical household heating appliances and can be used to heat water for domestic purposes, for example, in the kitchen or in the bathroom.

 Known electric direct-flow water heater [1], containing at least one heating coil installed in the path of the heated water, the local hydraulic resistance installed in the pipeline for supplying cold water, a differential pressure sensor (flow sensor) with an electric switch connected to the control circuit.

 When water enters the chamber for heating, a pressure drop appears on the hydraulic resistance, a differential pressure sensor is activated and an electric switch is turned on, the signal from which is supplied to the control device, which, after a delay time sufficient to completely fill the housing cavity with water, turns on the thyristors in the heater power supply circuit .

The signs of this device, coinciding with the essential features of the claimed invention:
housing;
electric heating elements located in the housing;
cold water supply pipeline;
connection of a cold water supply pipe to the lower part of the housing;
water discharge pipeline;
local hydraulic resistance;
flow sensor installed on the cold water supply pipe and connected to the control device;
heater control device with a switch connected in series with electric heating elements.

The disadvantages of the known device are: a large delay in switching on the electric heating elements after opening the flow control valve, which causes water loss, especially when the valve is completely open, and creates inconvenience in use. Indeed, the delay in switching on the electric heating elements created by the control device is necessary for the electric heating elements to be completely filled with water after the tap is opened, and the value of this delay is set based on the minimum water flow for which the heater is designed. Therefore, when the crane is fully opened, this delay time will be excessively long;
risk of explosion of the heater in the event of a breaker switch or control device, in which after closing the tap the electric heating elements will not turn off (for example, welding of the switch contacts). In this case, after some time, the water will boil in a closed volume, the pressure will increase, which will cause the shell to break.

 Known electric heater [2], comprising a housing, a part of the wall of which is made in the form of a membrane, a cold water supply pipe with a tap for regulating the flow, connected to the lower part of the body, a water drain pipe connected to the body in the upper part, a spring-loaded valve mounted on the pipeline water outlet and having a through hole, the passage area of which is 0.002 - 0.004 of the membrane area, an electric heater located in the housing, and a power switch of the electric heater with w current abutting against the membrane.

 When you open the tap of the cold water supply pipe, but at a water flow below the minimum electric heater performance, all water passes through the valve through-hole, without creating enough pressure in the body to turn on the electric heater switch. With further opening of the tap on the cold water supply pipe, the water flow increases to the minimum electric heater productivity and the valve opening does not have time to let the entire water flow through itself, as a result of which the pressure in the body increases to a value sufficient to operate the switch and turn on the electric heater.

 After the water supply is shut off by shutting off the tap, the pressure in the housing decreases and the valve closes the water drain pipe. At the same time, thanks to the hole in the valve, the pressure in the housing drops rapidly, which leads to the shutdown of the electric heater.

The signs of this device, coinciding with the essential features of the claimed invention:
housing;
an electric heater located in the housing;
cold water supply pipeline;
connection of a cold water supply pipe to the lower part of the housing;
connection of a water drain pipe to the upper part of the housing;
local hydraulic resistance installed in the water drain pipe in the form of a plate with a hole.

A disadvantage of the known device is the low reliability due to the following factors:
the occurrence of self-oscillations of the valve plate at an average water flow rate, when, due to insufficient pressure of the water flow on the plate, the latter does not rest against the limiter. Self-oscillations of the plate in the water flow cause pulsations of fluid pressure, impacts of the plate on the limiter and valve seat, reduce the durability of the spring. Turning on a water heater with a broken valve spring will lead to premature switching on of electric heaters (at a flow rate of water less than the minimum allowable) and their burnout;
shrinkage of the valve spring, which also leads to premature inclusion of electric heaters and their burnout;
the selected ratio of the bore in the valve plate to the membrane area, which should be in the range 0.002 - 0.004. Indeed, with a small diameter of the hole in the valve plate, it is possible to become clogged with rust particles exfoliating from water pipes, which will cause premature activation of electric heaters due to the formation of an air "plug" in the body and their burnout. With a sufficiently large diameter of the hole in the valve plate, eliminating its clogging, the membrane area should be chosen large, which significantly increases the force acting on the membrane from the water side. This force can increase significantly if a sprinkler is installed at the end of the piping and becomes clogged. Then the pressure in the housing can reach the pressure in the water supply network and break the membrane.

For example, with a hole diameter in the valve plate of 2 mm, the membrane area should be selected in the range of 7.75 • 10 ^-4 - 1.55 • 10 ^-3 m ² . With an excess pressure in the water supply network of 0.3 MPa, the force acting on the membrane will be 233 - 465 H, which is tens to hundreds of times higher than the nominal force with which the membrane acts on the switch during normal operation of the heater.

 Known electric heater [3], comprising a housing, heating elements installed in it with current-carrying leads located in the lower part of the housing, a cold water supply pipe with a tap for regulating the flow and a water flow sensor containing a membrane enclosed in a casing connected through an opening to the pipeline supply of cold water, and a switch with a rod resting against the membrane. The water drain pipe is located so that its open end for the intake of heated water is located in the upper part of the housing.

 When you open the faucet in the cold water pipeline, the latter fills the housing and begins to flow out of the open lower end of the hot water pipeline. As soon as the force of water pressure in the housing acting on the membrane exceeds the resistance force of the switch, the latter operates and turns on the electric heating elements.

Signs of a known device that matches the essential features of the claimed invention:
housing;
electric heating elements located in the housing;
cold water supply pipeline;
connection of a cold water supply pipe to the lower part of the housing;
water discharge pipeline;
the location of the open end of the water drainage pipe in the upper part of the body cavity;
flow sensor installed on the cold water supply pipe.

 A disadvantage of the known device is its low reliability due to changes in the operation of the settings of the flow sensor and, as a result, premature inclusion in the network of electric heating elements that are not completely covered with water, followed by their overheating and combustion.

 The operation of the flow sensor occurs when the force of water pressure on the membrane exceeds the spring force of the switch spring. The force of the water pressure is the sum of the hydrostatic pressure of the water column in the housing and the pressure caused by the hydraulic resistance of the water discharge pipe (the hydraulic resistance in the housing can be neglected due to its large diameter, and in the section of the cold water supply pipe from the point where the flow sensor is connected to the cavity casing due to the small length of this section), and the pressure force caused by the hydraulic resistance of the pipeline depends on the flow of water, i.e. from the degree of opening of the tap on the cold water pipeline. And since the flow sensor should operate even at a low water flow set by the consumer, i.e. with a small pressure loss in the pipelines, the force of the hydrostatic pressure of the liquid is determining when the flow sensor is triggered. It should also be noted that the magnitude of the hydrostatic pressure force, at which full coverage of electric heating elements is guaranteed, is in the range from the value determined by the height of the water column in the housing, corresponding to the highest point of the heating element (full coverage), to the value determined by the height of the housing (full filling body cavity with water). Considering that due to the desire to reduce the dimensions of the water heater and increase its speed, the upper part of the electric heaters is located in close proximity to the upper part of the housing, we can conclude that this range is close and that the flow sensor needs to be fine-tuned. However, during long-term operation of the water heater, it is possible to weaken (shrink) the circuit breaker spring, which will lead to its operation when the electric heating elements are not completely covered with water, overheating of the electric heating elements and their failure.

где ρ - плотность воды (ρ=1000 кг/м³); g - ускорение свободного падения.Device failure can also be caused if a sprinkler with a small diameter of the holes and their clogging is installed at the end of the water drain pipe. Then the pressure in the housing can reach the pressure in the water supply network and under the influence of significant pressure the deformation of the membrane can exceed the permissible value. This can lead to irreversible plastic deformation and even rupture. For example, when the height of the water column in the housing causes the operation of the electric heater switch (H = 0.2 m), the operation force of the switch (P = 2H), the membrane area should be equal to

where ρ is the density of water (ρ = 1000 kg / m ³ ); g is the acceleration of gravity.

Then, with excess pressure in the water supply network P = 0.3 MPa, the force acting on the membrane will be
P _M = PF = 0.3 • 10 ⁶ • 1.02 • 10 ^-3 = 306 H,
which is 150 times the force acting on the membrane in normal operation.

 Low reliability is also due to the lack of protection against overheating of electric heating elements.

 A known electric heater [4], comprising a housing, inside which an electric heating element is installed, a current-carrying output of which is fixed on the upper part of the housing, an inlet pipe for supplying cold water, connected to the lower part of the housing, an output pipe for draining heated water, attached to the upper part of the housing, a temperature controller connected in series with a heating element, the temperature sensor of which is enclosed in a water-tight casing located inside the housing and connected to a differential erentsiruyuschey scheme. In addition, the electric water heater has a device that includes an electric heating element when water enters the housing.

The signs of this device, coinciding with the essential features of the claimed device:
housing;
an electric heating element located in the housing, the current-carrying terminal of which is fixed on the upper part of the housing;
a cold water inlet connected to the bottom of the housing;
a heated water outlet pipe connected to the upper part of the housing;
a temperature controller connected in series with the heating element;
installation of the temperature sensor in a waterproof casing inside the housing.

The disadvantages of this device are:
low reliability of the overheating protection system in the event of a failure or deregulation of the water flow sensor installed on the inlet pipe. This is explained by the following: if the heating element is switched on in the absence of water in the housing, the temperature sensor is heated due to thermal radiation and convection of heated air in the housing, since there is no direct thermal contact between the sensor housing and the electric heating element. Due to the relatively low intensity of these types of heat transfer, the rate of change of the temperature of the sensor will be sufficient to trigger the protection system with a significant overheating of the electric heating element, which can lead to its combustion. In the case of partial coating of the temperature sensor casing and the electric heating element with water, the overheating of the latter will be much larger, since only the part of the temperature sensor that is not covered by water will perceive;
the need for periodic reconfiguration of the differentiating circuit, since over time, the heat exchange rate of the electric heating element and the casing of the temperature sensor changes due to the formation of scale on them, surface oxidation, etc.

 Known electric heater [5], containing a housing, inside which are installed electric heating elements, the lead-in leads of which are fixed on the upper part of the housing, an inlet pipe for supplying cold water and an outlet pipe for removing heated water, a thermal switch mounted externally on the top cover of the case near the open end cold water supply pipe and connected in series with electric heating elements. When the body of the electric heater is overheated, the thermal switch cuts off the power to the electric heating elements.

The signs of this device, coinciding with the essential features of the claimed device:
housing;
electric heating elements located in the housing, the current-carrying leads of which are fixed on the upper part of the housing;
branch pipe for cold water supply;
pipe for supplying heated water;
thermal switch mounted externally on the top cover of the housing.

The disadvantages of the known device are:
danger of burns to the consumer in case of an unexpected drop in pressure in the water supply network, which is explained by the high inertia of the thermal switch. With a sharp drop in pressure in the water supply network, the water flow through the water heater decreases and the temperature of the outlet water increases. Since the sensitive element of the thermal switch does not perceive the temperature of the outlet water, but the temperature of the water near the open end of the cold water supply pipe, and even then indirectly through the top cover of the casing, there will be no timely shutdown of the heating elements, which will cause the outlet water to overheat;
low reliability, which is explained by the large current switched by the thermal switch (up to 25 A), the frequent closure of its contacts when the pressure in the water supply network changes and, as a result, the contacts burn out, increase of the transition resistance and even welding, which increases the fire hazard of the device. The absence of duplication of the thermal protection system of the water heater makes it dangerous for the consumer. In addition, if the protection system against switching on of electric heating elements fails in the absence of water in the case, there is also a risk of failure of the electric heater, since in this case the thermal switch will periodically turn on and off electric heating elements that are not covered with water, which will cause them to overheat and subsequent burnout.

 Known electric water heater [6], comprising a housing, inside which is installed an electric heating element with current-carrying contacts located in the lower part of the housing, pipes for supplying cold and heated water. The electric heating element is surrounded by a safety tube without contact, to which is attached the casing of the temperature control sensor connected in series with the electric heating element.

The signs of this device, coinciding with the essential features of the claimed device:
housing;
an electric heating element located in the housing;
branch pipe for cold water supply;
pipe for supplying heated water;
a thermal switch connected in series with the electric heating element;
installation of the temperature sensor in a waterproof casing inside the housing.

The disadvantage of this heater is low reliability. This is explained by the following:
the absence of duplication of the system of protection against overheating, which, if the thermostat fails, will lead to burnout of the electric heating element;
low heat transfer between the electric heating element and the temperature sensor when you turn on the device, not filled with water. The electric heating element and the casing of the temperature sensor are separated by an air gap and a safety tube, which increases the response delay of the thermostat, causes the electric heating element to overheat, which can lead to its combustion.

 Known electric heater with a safety thermostat [7]. The electric heater comprises a housing, inside of which electric heating elements are installed, the current-carrying leads of which are fixed to the upper housing cover; a cold water inlet pipe attached to the housing in the lower part; a heated water outlet pipe attached to the upper housing cover; a water temperature thermostat sensor installed in a sealed tube inside the housing; a safety thermoswitch sensor mounted on a side wall outside the housing, and the water temperature thermostat and the safety thermostat are connected in series, which ensures duplication of disconnection of electric heating elements when the heater overheats.

The signs of the device, coinciding with the essential features of the claimed invention:
housing;
electric heating elements located in the housing, the current-carrying leads of which are mounted on the top cover of the housing;
the implementation of the top cover of a heat-conducting material;
a pipe for supplying cold water, attached to the lower part of the housing;
a nozzle for the removal of heated water attached to the top cover of the housing;
safety thermal switch mounted outside the housing with the possibility of thermal contact with it;
a temperature controller with a sensor enclosed in a waterproof, heat-conducting casing installed inside the housing.

 The disadvantage of this device is the low reliability in the case of turning on the electric heater, not filled with water. Indeed, in this case, between the electric heating elements, on the one hand, and the safety thermal switch, as well as the thermostat sensor, on the other hand, there is an air gap that excludes thermal contact between them. Therefore, when heating the electric heating elements, heat will be transferred to the indicated sensitive elements through the air gap by radiation and convection, which will cause a significant delay in the operation of thermal protection and, as a result, overheating of the electric heating elements and their failure.

 Known electric flow heater [8], comprising a housing with installed inside the electric heating elements, the lead-in leads of which are located on the upper part of the housing; cold water supply pipe connected to the upper part of the housing; heated water discharge pipe connected to the lower part of the housing; flow control valve installed on the heated water discharge pipe; electronic switching components connected in series with electric heating elements and mounted on a radiator attached to the cold water supply pipe with the possibility of thermal contact; a control device with flow and water temperature sensors connected thereto, connected to electronic switching elements, the temperature sensors being installed in the water supply and discharge pipelines.

The signs of this heater, coinciding with the essential features of the claimed device:
housing;
electric heating elements located in the housing, the current-carrying leads of which are fixed on the upper part of the housing;
cold water supply pipe connected to the body;
heated water discharge pipe connected to the housing;
electronic switching components (triacs) connected in series with electric heating elements and connected to a control device;
installation of triacs on a radiator attached to a cold water supply pipe with the possibility of thermal contact;
control device connected to triacs;
heated water temperature sensor connected to the control device;
water flow sensor installed on the cold water supply pipe and connected to the control device.

 A disadvantage of the known device is its low reliability when used in water supply networks, where the water supply is cut off. After turning off the water in the network and then turning it on again, a mechanical mixture of water and air can leave the water tap for several minutes, and since this mixture will pass through the flow sensor, the control device may work and turn on the electric heating elements before they leave the water supply network all air bubbles. Consequently, part of the heat transfer surface of the electric heating elements will for some time come in contact not with water, but with air, which will cause it to overheat and lose tightness with subsequent burnout of the electric heating elements.

 In addition, the known heater is unprotected from overheating in case of failure of the delay forming circuit of the control device. In the event of a failure or during the adjustment of the delay generation circuit, the control device may prematurely turn on the electric heating elements when they are not yet completely covered with water, and since the heated water does not yet have time to approach the temperature sensor installed in the water drain pipe, the protection against overheating of the water heater will not work. Consequently, overheating of electric heating elements and their failure is inevitable.

 In addition, this electric heater is not protected against overheating in the event of a control device failure.

 The closest technical solution (prototype) is a water heater [9], comprising a housing made of heat-conducting material with tubular electric heating elements installed inside, the current-carrying leads of which are located on the upper part of the housing; cold water supply pipe connected to the lower part of the housing; heated water discharge pipe connected to the lower part of the housing; water flow control valve installed on the cold water supply pipe; triacs connected in series with electric heating elements and mounted on a radiator attached to the body; a control device comprising a power adjuster having two control buttons connected to a pulse generator and connected to a binary counter, the outputs of the decoder are connected to the And elements; a detector of a zero level of supply voltage, also connected to AND elements, the outputs of which are connected to switches based on triacs; a logical unit that performs the initial installation of the binary counter and the implementation of the algorithm of the electric heater; a water flow sensor mounted on a cold water supply pipe and connected to a control device; a temperature controller with a heated water temperature sensor connected to the control device; safety thermal switch mounted on the side wall of the housing with the possibility of thermal contact and connected to the control device.

When the electric heater is turned on, the control device turns on all the electric heating elements and when the outlet temperature, measured by the temperature sensor on the heated water discharge pipe, reaches a value of 40.5 ^o C, the temperature regulator includes such a combination of electric heating elements to ensure a steady-state value of this temperature at a given flow rate and water temperature at the entrance. After that, the temperature controller is not involved in the control process.

 If it is necessary to change the water temperature, the consumer holds for some time one of the buttons of the power setter in the pressed state, achieving the required degree of heating. In case of overheating, the safety thermal switch is activated and the control device turns off the electric heater.

The signs of this heater, coinciding with the essential features of the claimed device:
case with a heat-conducting top cover;
electric heating elements located in the housing, the current-carrying leads of which are mounted on the top cover of the housing;
cold water supply pipe connected to the lower part of the housing;
heated water discharge pipe connected to the housing;
three switches, triacs of which are connected in series with electric heating elements;
a control device containing a power controller having two control buttons, a binary reversible counter and a decoder and an initial installation unit connected thereto, three AND elements connected to a decoder, a zero-voltage detector connected to the input to the power supply bus, and the output to the first inputs of the three AND elements, the outputs of which are connected to the switches;
a temperature controller with a heated water temperature sensor connected to the control device;
safety thermal switch installed with the possibility of thermal contact with the housing;
installation of triacs on a radiator with the possibility of thermal contact;
a water flow sensor installed on the cold water supply pipe and connected through a signal conditioner to a control device;
DC power supply.

 The disadvantages of the prototype device are low reliability and consumer qualities.

 Low reliability is due to the following factors.

 The inclusion of electric heating elements occurs with a time delay, the value of which is determined by the data on the flow rate of water passing through the flow sensor on the cold water supply pipe. However, in the water supply network, for example, after turning off the water, the formation of compressed air bubbles is possible, which, passing through the flow sensor, will also cause the rotation of the turbine and, consequently, the appearance of false data on the magnitude of the water flow. Therefore, the control device will incorrectly determine the time of filling the housing with water and turn on the electric heating elements that have not yet been completely covered with water. This will lead to overheating and even burnout.

 Long response time of the overheat protection system in the event of a failure of the water flow sensor, which also leads to overheating of the electric heating elements. In the case of switching on electric heating elements in the absence of water in the housing, the temperature sensor installed on the water drain pipe and the safety thermal switch connected to the side wall of the housing are heated mainly due to thermal radiation and convection of heated air in the housing, since between the sensor and the safety switch , on the one hand, and electric heating elements, on the other hand, thermal contact is made through the top cover of the housing and its side walls y having a large heat resistance due to the large heat propagation paths.

 Due to the relatively low intensity of these types of heat transfer, as well as the high heat capacity of the housing, made entirely of heat-conducting material, the temperature of the housing will be sufficient for the protection system to operate only with a significant overheating of the electric heating elements, which can lead to their combustion.

 In case of failure of the control device and in case of overheating of the electric heater, the safety thermal switch will not disconnect the electric heating elements from the AC mains, as it controls them through the control device, which will cause the combustion of electric heating elements.

 When the contaminants present in water are deposited on the elements of the optical flow sensor, it may fail due to loss of transparency of the light distribution channel.

 Lack of duplication in system of protection against an overheat since the heated water temperature control device operates only in the process of the electric heater reaching the steady-state operating mode, and after the “Ready” indicator lights up, this device is disconnected from operation. Therefore, the control of overheating is carried out by only one safety thermal switch, and when it comes out of standing, combustion of electric heating elements can occur.

 When using an electric heater for heating water with a high content of minerals, scale formation on the metal surfaces of parts in contact with water is possible. In this case, scale on the heat transfer surface of the electric heating elements will cause them to overheat and subsequently burn out.

 Low consumer qualities are explained by the following reasons.

 After the heater is turned on and the operating mode reaches the steady state, when the feedback on the temperature of the heated water stops, the total power of the included electric heating elements, ensuring this temperature, is "remembered" by the control device and is subsequently adjusted depending on the temperature and water flow rate at the inlet. However, in the event of electromagnetic interference caused, for example, by turning on household electrical equipment, a “malfunction” of the power setting to the higher side and, therefore, turning on of the heater to a large power may occur, which will cause a significant and rapid increase in the output temperature and the appearance of unpleasant sensations for the consumer . The absence of any indication warning of an involuntary change in the number of included electric heating elements can develop a consumer’s complex of insecurity when using an electric heater.

 Low consumer qualities are also explained by the selected method of controlling the power of the electric heater by keeping one of the two buttons pressed for a while. Moreover, the button holding duration determines the value of the installed power of the electric heating elements. The consumer’s lack of information about the total power of the electric heating elements turned on makes him measure the button holding time and the outlet temperature, which, due to the inertia inherent in the electric heater, makes this process tedious. In addition, with repeated use of the electric heater in the same conditions, the consumer must repeat this procedure each time again, since the lack of information about the installed power does not immediately allow you to set the required power of the electric heating elements, determined experimentally by the consumer for such operating conditions.

 The inability to limit the maximum power of the electric heater will cause inconvenience for the consumer in the case of using electrical wiring in an apartment with a low load capacity, since the erroneous inclusion of the electric heater for high power will cause the protection of the apartment network to trip.

The essential features of the claimed device, distinctive from the prototype, are:
the implementation of the cold water supply pipeline U-shaped;
the use of a pressure sensor as a flow sensor and its location together with the bend of the cold water supply pipe not lower than the upper part of the heat transfer surface of the electric heating elements;
connecting the heated water discharge pipe to the upper case cover and installing local hydraulic resistance in it;
the implementation of the lower part and the side wall of the housing of insulating material;
installation of a safety thermal switch on the top cover of the case and its inclusion between the AC network and the busbars for supplying power to the electric heater;
installation of a temperature sensor of heated water in a heat-conducting casing attached to the top cover of the casing with the possibility of thermal contact, the height of which does not exceed 2.5λF _b , where λ is the thermal conductivity of the casing material, F _B is the cross-sectional area of the side wall of the casing;
the introduction of two resistors, a power limit switch, two pulse shapers, two OR-NOT elements, an OR element, an NOT element into the electric heater control device; indicator of the set power;
attaching the first contact of each button through a resistor to a DC power source;
attaching the first and second pulse shapers to the first contact of the first and second buttons of the power setter, respectively;
the connection of the first input of the first element OR NOT with the output of the first pulse shaper;
connection of the first input of the OR element with the output of the first element OR-NOT;
connection through the element NOT of the output of the second pulse shaper to the second inputs of the OR element;
the connection of the output "3" of the decoder through the power limit switch with the second input of the first element OR-NOT;
the connection of the first input of the second element OR-NOT with the output of the detector zero level supply voltage;
the connection of the second and third inputs of the second element OR-NOT with the outputs of the driver of the signal of the flow sensor and thermostat, respectively;
the connection of the second inputs of the three elements AND with the output of the second element OR NOT;
connection of the input of the reverse of the binary counter with the output of the first OR-NOT element, the counting input - with the output of the OR element;
the connection of the output "0" of the decoder with the second contact of the second button, and the output "5" with the second contact of the first button.

The technical result achieved by the proposed electric heater is:
in increasing reliability due to:
a) the exclusion of the inclusion of electric heating elements that are not completely covered with water;
b) increase the response time of the overheat protection system;
c) duplication of the system of protection against overheating;
d) eliminating the formation of scale on metal parts in contact with water:
in improving consumer qualities due to:
a) simplifying the adjustment of the electric heater to the required degree of heating water;
b) the possibility for the consumer to limit the maximum power of the electric heater.

The technical result of the invention is achieved in that in an electric heater containing a housing with a heat-conducting top cover, in the cavity of which electric heating elements are installed with current-carrying leads located in the upper housing cover, a cold water supply pipe connected to the lower part of the housing, three switches, which triacs connected in series with electric heating elements and mounted on a radiator with the possibility of thermal contact, control device, having a power controller with two buttons, a binary reversible counter and a decoder connected to it, three AND elements connected to the decoder with their first inputs; a detector of a zero level of supply voltage connected by an input to the AC power supply bus, and by an output to the first inputs of AND elements, the outputs of which are connected to the control inputs of the switches, respectively, and an initial installation unit connected to a binary reversible counter; a temperature controller with a heated water temperature sensor connected to the control device; a water flow sensor installed on the cold water supply pipe and connected through a signal conditioner to a control device; safety thermal switch installed with the possibility of thermal contact with the housing; DC power supply the cold water supply pipeline is made U-shaped, a pressure sensor is used as a flow sensor, located with the elbow not lower than the upper part of the heat transfer surface of the electric heating elements, the heated water discharge pipe is connected to the upper housing cover and local hydraulic resistance is installed in it; the lower part and the side wall of the housing are made of heat-insulating material; a safety thermal switch is installed on the upper case cover and is connected between the AC mains and the busbars for supplying power to the electric heater; the temperature sensor of heated water is enclosed in a heat-conducting casing attached to the top cover of the casing with the possibility of thermal contact, and the casing height does not exceed 2.5λF _b , where λ is the thermal conductivity of the casing material, W / (mK); F _B is the cross-sectional area of the side wall of the housing, m ² , and two resistors are introduced into the control device, through which the first and second buttons of the power adjuster are connected to the DC power source by their first contact; the first and second pulse shapers connected to the first contact of the first and second buttons of the power setter, respectively; the first OR-NOT element, the first input of which is connected to the output of the first pulse shaper; an OR element, the first input of which is connected to the output of the first OR-NOT element; an element NOT connected between the output of the second pulse shaper and the second input of the OR element; the second element OR NOT, the first input of which is connected to the output of the detector of the zero level of the supply voltage; set power indicator connected to decoder outputs; a power limiting switch connected to the output “3” of the decoder and to the second input of the first OR-NOT element, and the outputs of the signal generator of the pressure sensor and thermostat are connected to the second and third inputs of the second OR-NOT element, respectively, the output of which is connected to the second inputs of the three elements AND; the reverse input "± 1" of the binary reverse counter is connected to the output of the first element of the first element OR-NOT, the counting input to the output of the OR element, the output "0" of the decoder is connected to the second contact of the second button of the power setter, and the output "5" to the second contact of the first button of the power adjuster.

 Using a pressure sensor as a flow sensor, attaching a heated water discharge pipe to the upper case cover, installing local hydraulic resistance in it, connecting the first input of the second OR-NOT element to the output of the zero-voltage detector, and the second input to the output of the pressure sensor signal shaper , outputs - with the first inputs of three AND elements, and their outputs - with control inputs of the first, second and third switches, respectively, excludes the inclusion of an electric heater elements not completely covered by water. After the start of the flow of water into the electric heater, the pressure in the housing will increase after the water begins to flow through the local hydraulic resistance, and this will happen only after the housing is completely filled with water and, therefore, the heat transfer surface of the electric heating elements is completely covered.

 The implementation of the U-shaped cold water supply pipeline and the location of the pressure sensor together with the elbow not lower than the upper part of the heat transfer surface of the electric heating elements is necessary to prevent premature operation of the pressure sensor under the influence of the hydrostatic pressure of the liquid column when the body is incompletely filled with water.

 Indeed, since the case and part of the U-shaped cold water supply pipe with the upper knee (from the point of attachment to the lower part of the body to the knee) are communicating vessels, then the influence of a liquid column in the body on the membrane of the flow sensor is not possible until the electric heating elements are coated with water (pressure sensor is installed above )

 Installing a safety thermal switch on the top cover of the case with the possibility of thermal contact allows you to increase the response time of the safety thermal switch in the case of switching on an electric heater not filled with water, caused by a malfunction of the protection system. This is achieved by reducing the thermal resistance between the electric heating elements and the safety thermal switch, because, unlike the prototype, the latter is in close proximity to the place of thermal contact of the electric heating elements and the heat-conducting upper housing cover.

 The implementation of the lower part and the side wall of the casing of heat-insulating material also increases the response time of the overheat protection system due to a decrease in the heat capacity of the casing and, in addition, increases the efficiency of the heater.

 The inclusion of a safety thermal switch between the AC mains and the busbars for supplying power to the heater ensures protection of the heater from overheating and short circuiting of electrical circuits even in the event of a control device failure.

 The connection of the casing of the temperature sensor of heated water to the upper cover of the casing with the possibility of thermal contact, as well as the choice of casing height not exceeding the above value, is necessary to ensure timely disconnection of electric heating elements when the casing is incompletely filled with water or in its absence. This is illustrated in FIG. 1, which shows a section through a heat-conducting casing 26 connected to the top cover of the casing 8. A temperature sensor 25 is installed inside the casing. When the casing of the electric heater is completely filled with water, the temperature sensor determines the temperature of the water in the upper part of the casing, which enters the consumer. Moreover, the heat flow from the heated water is mainly transmitted to the sensor through the bottom of the casing, having the smallest thickness allowed by the manufacturing technology and providing sufficient strength of the casing bottom.

 In the event of a malfunction of the electric heater and the inclusion of electric heating elements not covered by water, heating of the casing and the temperature sensor enclosed in it begins. In this case, the heating of the sensor occurs due to heat transfer from the upper cover of the housing through the side wall of the casing, the thermal radiation of the heated electric heating elements, as well as heat transfer from the air heated in the housing. An increase in the heating rate of the temperature sensor can be achieved by increasing the heat flux transmitted from the heating top cover due to the thermal conductivity of the casing walls.

где H - высота кожуха относительно внутренней плоскости верхней крышки корпуса, м;
λ - коэффициент теплопроводности материала кожуха, Вт/(мК);
F_Б - площадь поперечного сечения боковой стенки кожуха, м².Since the magnitude of this heat flux is determined by the thermal resistance of the casing, it can be argued that providing a given speed of shutdown of electric heating elements can be achieved by reducing the thermal resistance of the casing, determined by the formula:

where H is the height of the casing relative to the inner plane of the upper housing cover, m;
λ is the coefficient of thermal conductivity of the casing material, W / (mK);
F _B - the cross-sectional area of the side wall of the casing, m ² .

 For domestic electric heaters with a maximum power not exceeding 3 mW, the authors experimentally set an upper limit for the thermal resistance of the casing, which was 2.5 K / W, which ensures that the electric heating elements are switched off by the water temperature thermostat (in the absence of water in the case) when the top cover is heated housing to a temperature of T = 353K.

Отсюда получим неравенство, которому должна удовлетворять высота кожуха
H ≤ 2,5λF_б (1)
Нижний предел для высоты кожуха определяется величиной, достаточной для расположения датчика температуры внутри кожуха за пределами верхней крышки корпуса. Это необходимо для уменьшения погрешности определения температуры воды, вызванной тепловым потоком от верхней части крышки корпуса, температура которой отличается от температуры воды.Thus, the thermal resistance of the casing must satisfy the inequality

From here we obtain the inequality that the casing height must satisfy
H ≤ 2.5λF _b (1)
The lower limit for the height of the casing is determined by a value sufficient to position the temperature sensor inside the casing outside the top cover of the housing. This is necessary to reduce the error in determining the temperature of the water caused by the heat flux from the upper part of the housing cover, the temperature of which differs from the temperature of the water.

 The connection of the output of the thermostat with the third input of the second element OR-NOT allows you to disable the electric heating elements when the set water temperature is reached, which ensures duplication of protection of the electric heater from overheating.

 This ensures increased reliability of the electric heater.

 Introduction to the control device of two resistors, two OR-NOT elements, an OR element, NOT element, a decoder, attaching the first contact of each button of the power adjuster through a resistor to a power source, connecting the first input of the first OR-NOT element to the output of the first pulse shaper, the first input OR element - with the output of the first OR-NOT element, the output of the second pulse shaper through the element NOT-with the second input of the OR element, the input of the binary counter reverse - with the output of the first OR-NOT element, the counting input - with you with the OR element, decoder inputs with binary counter outputs and with the second inputs of AND elements, respectively, and outputs with the installed power indicator, with output "0" also with the second contact of the second button, output "5" also with the second contact of the first buttons, solves the problem of setting and indicating the power of the electric heater by pressing one of the buttons the required number of times. A single press of the first button causes an increase in the total power of the included electric heating elements by one step. A single press of the second button causes a decrease in the total power of the included electric heating elements by the same amount.

 The connection of the output “3” of the decoder with the second input of the first OR-NOT element through the power limit switch allows you to limit the maximum power of the heater, which is necessary to avoid overloading the apartment wiring, designed for low power and, therefore, to prevent the protection of the apartment network from tripping when the heater is turned on .

 This simplifies the adjustment of the electric heater to the required degree of water heating, eliminates the overload of the apartment wiring and, therefore, improves the consumer qualities of the electric heater.

 In the particular case of the implementation of the electric heater according to claim 2, the second and third, fourth and fifth electric heating elements are connected in parallel, which ensures that the power of the switched on electric heating elements changes each time one of the buttons of the power adjuster is pressed by an amount equal to the power of one electric heating element.

 In the particular case of the implementation of the electric heater according to claim 3 of the claims, light indicators are included in parallel with the electric heating elements, allowing the consumer to compare the value of the set power and the real power of the included electric heating elements and to timely detect a malfunction of the electric heater.

 In the particular case of the implementation of the electric heater according to claim 4, the local hydraulic resistance installed in the heated water discharge pipe is made in the form of a washer of non-metallic material, for example, heat-resistant plastic with a through hole, which simplifies its manufacture and eliminates scale formation.

 In the particular case of the implementation of the electric heater according to claim 5, the pressure sensor comprises a membrane enclosed in a casing; a switch mounted on the casing with a rod resting against the membrane; the deflection limiter of the membrane, made in the form of a conical washer, the inner surface of which is located on the side of the membrane having a through hole for the rod, mounted in this hole with the possibility of movement. This embodiment of the pressure sensor ensures that the switch trips when the pressure in the body of the electric heater rises after it is filled with water and eliminates the rupture of the membrane with a significant increase in pressure in the case.

 In the particular case of the implementation of the electric heater according to claim 6, a radiator with triacs is installed on the cold water supply pipe with the possibility of thermal contact, which ensures the most intensive cooling of triacs.

 In the particular case of the implementation of the electric heater according to claim 7 of the claims, the surfaces of the electric heating elements, the upper housing cover and the casing of the temperature sensor in contact with water are coated with a non-metallic electrically insulating material, for example, fluoroplastic. This eliminates the formation of scale and increases the electrical safety of the electric heater.

In the particular case of the implementation of the electric heater according to claim 8, the outer side surface of the casing of the heated water temperature sensor is hexagonal, the casing is connected to the upper cover of the casing using a conical threaded connection, the temperature sensor is filled with a heat-conducting electrically insulating paste inside the casing, the bottom of the casing is conical with angle at the apex of the cone 60 ^o C. The specified design of the casing provides the convenience of its mounting, tightness of the connection with the top cover case and the minimum thickness of the bottom of the casing, the inner cavity of which is drilled with a standard drill.

где β - угол отклонения оси пружины от вертикали;
a - величина перекрытия третьего и первого неподвижного контактов;
b - высота крепления второго конца пружины относительно верхней плоскости второго неподвижного контакта.In the particular case of the implementation of the electric heater according to claim 9, the safety thermal switch is made in the form of two thermal switches installed in one housing and containing the first and second fixed contacts, equipped with vertical leads, installed with a constant gap between them on a heat-conducting and electrically insulating plate and overlapped with a third spring-loaded contact by means of an electrically conductive fusible substance with a melting temperature equal to the required temperature switching off the electric heater, and two fixed and third contacts inserted between the contacting planes, the last of which is separated from the vertical output of the second fixed contact by a distance exceeding the overlap of the third and first fixed contacts, and connected to the first end of the coil spring, the second end of which is attached to the vertical the output of the second fixed contact at a distance from this output in excess of half the outer diameter of the spring and with the possibility of rotation around an axis passing through the attachment point of the second end of the spring parallel to the opposite sides of the fixed contacts, and the axis of the spring is deviated from the vertical by an angle satisfying the inequality:

where β is the angle of deviation of the axis of the spring from the vertical;
a is the amount of overlap of the third and first fixed contacts;
b - mounting height of the second end of the spring relative to the upper plane of the second fixed contact.

 The housing is provided with a bottom made of heat-conducting material and a vertical partition, moreover, the heat-conducting and electrically insulating plate is sandwiched between the housing and the bottom, and the vertical partition presses the first fixed contact to it.

 The supply of the first and second fixed contacts with vertical terminals allows to reduce the dimensions of the device in terms of.

 The introduction of an electrically conductive fusible substance between the contacting planes of two fixed and third contacts is necessary to prevent oxidation of the contacting contacts due to the solder layer connecting them.

 The use of a coil spring and its installation at an angle to the vertical is necessary to increase the reliability of the device by eliminating its false operation.

 To eliminate false triggering caused by a decrease in the strength of the fusible material during heating, it is necessary to reduce the spring elasticity, and in order to not change the speed of the device, reduce the adhesion forces of the melt and the surface tension acting on the third contact until it comes off. The magnitude of these forces is proportional to the area wetted by the melt of the contact interaction surface. Therefore, by reducing this area after the fusion of the fusible material, it is possible to tear the third contact from the stationary contact by the spring with less elastic force. The location of the spring at an angle to the vertical allows you to create a horizontal component of the elastic force, under the action of which the horizontal shift of the third contact is relative to the first stationary contact and, consequently, the decrease in the intermolecular interaction force and surface tension acting on the third contact. The choice of the angle β satisfying inequality (2) ensures the action of the horizontal component of the elastic force until the overlap of the third and first fixed contacts disappears completely.

 The installation of the third contact at a distance from the vertical output of the second fixed contact, exceeding the overlap of the third and first fixed contacts, provides freedom of horizontal movement of the third contact until its overlap with the first fixed contact disappears.

 The fastening of the second end of the spring to the vertical terminal of the second fixed contact at a distance exceeding half the outer diameter of the spring with the possibility of rotation around an axis passing through the fastening point parallel to the opposite sides of the fixed contacts is necessary to ensure free rotation of the spring during horizontal movement of the third contact.

 In the particular case of the implementation of the electric heater according to claim 10 of the claims, the shutdown temperature of the safety thermal switch exceeds the temperature setting of the thermostat by at least 25 K. This is necessary to prevent premature operation of the safety thermal switch with a working temperature regulator and control device if the water is heated to the maximum permissible temperature.

 In the particular case of the implementation of the electric heater according to claim 11, the casing is made with an inner, centrally located, cylindrical tube hermetically connected to the top cover, and the electric heating elements are made U-shaped with the arrangement of straight sections at an equal distance from the central tube of the casing, the lower parts two non-adjacent electric heating elements are bent to the Central tube of the housing and cover without touching the tube of the adjacent electric heating element. This achieves a decrease in the volume of heated water in the housing and, therefore, a decrease in the thermal inertia of the electric heater.

 Figure 2 shows a General view of the electric heater in section; figure 3 is a bottom view of a block of electric heating elements with a cut of the lower part of the housing; in FIG. 4, 5 is a top view of an electric heater with a cut of the casing and a cut of the top cover of the casing on which the casing with the temperature sensor is mounted; figure 6 is an example of a pressure sensor; in FIG. 7 is an example of a safety thermal switch; on Fig - an example of a circuit of the electronic unit of the temperature controller; figure 9 is a structural diagram of a control device; figure 10 is an example of a block diagram of the initial installation; figure 11 is an example of the implementation of the indicator circuit; on Fig - an example implementation of the detector circuit of the zero level of the supply voltage; on Fig - timing diagrams of voltages illustrating the operation of the detector zero level supply voltage; on Fig - an example implementation of the circuit of the switches.

 The electric heater contains (Fig. 2-4) a housing 1, electric heating elements 2-6 with current-carrying contacts 7, a top cover 8 that seals the housing 1, a fitting 9 for connecting to a water supply, a cold water supply pipe 10, a pressure sensor 11, a radiator 12 on which triacs 13-15 and a board 16 are installed with a water temperature controller 17 and a control unit 18 mounted on it, indicators 19, 20, 32 of electric heating elements that are turned on, a fitting 21 for connecting to a heated water discharge device, for example, to a spray y (not shown in Fig. 2), local hydraulic resistance 22, heated water discharge pipe 23, safety thermal switch 24, temperature sensor 25 of thermostat 17 (Fig. 4), temperature sensor cover 26, electric heater power control buttons 27, 28 (27 - increase in power, 28 - decrease in power), power indicator of the electric heater 29, indicator of supply of the supply voltage 30, the casing of the electric heater 31.

 The housing 1 is made of a non-metallic material with low thermal conductivity, for example, heat-resistant plastic, which ensures greater efficiency of the electric heater and eliminates the formation of scale. The housing 1 has a tube inside, designed to reduce the volume of water washing the electric heating elements 2-6 and, therefore, to reduce the thermal inertia of the electric heater.

 The tubular electric heating elements 2-6 (see FIG. 3) in the amount of five pieces are made U-shaped, with straight sections located at an equal distance from the central tube inside the housing and the lower parts of two non-adjacent electric heating elements are bent to the central tube of the housing and cover without touching the tube of an adjacent electric heating element. This achieves a decrease in the volume of water in the housing and, consequently, a decrease in the thermal inertia of the electric heater.

 The current-carrying contacts 7 of the electric heating elements 2-6 are located above the housing 1 to prevent contact closure in case of depressurization of the housing 1 and water leakage from it.

 The top cover 8 is made of heat-conducting material. Tubular electric heating elements 2-6 are attached to the upper cover 8 with the possibility of thermal contact.

 The cold water supply pipe 10 is made U-shaped, connected to the lower part of the housing 1 and consists of two tubes, between which a radiator 12 is installed. The pipe bend 10 is located not lower than the upper part of the heat transfer surface of the electric heating elements 2-6.

 The pressure sensor 11 is designed to control the pressure in the cold water supply pipe 10 and contains (see FIG. 6) a membrane 11.1, a casing 11.2, a deflection limiter 11.3 of the membrane made in the form of a conical washer, the inner surface of which is located on the side of the membrane, and having a through hole, switch 11.4 with a rod 11.5 entering the hole of the limiter 11.3 with the possibility of movement and abutting against the membrane 11.1. A pressure sensor 11 is installed on the cold water supply pipe 10 not lower than the upper part of the heat transfer surface of the electric heating elements 2-6. The switch 11.4 is connected to a power source 18.18 (shown in Fig. 9) so that when the water pressure in the electric heater reaches the set value and the switch 11.4 is activated, the signal "logical 0" appears at its output. The response pressure of the pressure sensor is determined by the area of the membrane 11.1 and the spring force of the spring switch 11.4.

 The radiator 12, on which the triacs 13-15 are installed with the possibility of thermal contact, is cooled by water entering the cold water supply line 10 and passing through the internal passage of the radiator 12.

 The temperature controller 17 is designed to generate a signal "logical 0" when the temperature of the heated object does not exceed the set value, and the signal "logical 1" - when this value is exceeded.

The temperature sensor 25 of the temperature controller 17, for example, a thermistor, is installed inside the heat-conducting casing 26 and filled with heat-conducting paste necessary to improve the thermal contact of the temperature sensor 25 with the casing 26. The latter is located inside the housing 1 and is connected to the top cover 8 with the possibility of thermal contact. The connection of the casing 26 with the top cover 8 is a conical threaded connection, which ensures the tightness of the joint without the use of gaskets. The side surface of the casing 26 is made hexagonal for the convenience of attaching the casing 26 to the upper cover 8. The bottom of the casing 26 is conical with an angle at the apex of the cone of 60 ^° , which is necessary to obtain the same minimum thickness of the bottom of the casing, the inner cavity of which is drilled with a standard drill.

 Figure 7 shows an example implementation of the circuit of the temperature controller 17.

 The temperature controller 17 contains a bridge circuit on the resistors R17.1-R17.5 and a thermistor 25 (Fig. 4), which is a water temperature sensor. Resistor R17.4 is a potentiometric setpoint for the temperature of the heated water. The bridge circuit is connected to the comparator on the operational amplifier DA17.1, which generates the output signal "logical 1" if the heating temperature of the water temperature sensor exceeds a predetermined value.

 The control unit 18 contains (Fig. 9) power control buttons 27 and 28 connected to resistors R1 and R1, respectively, a maximum power limit switch 18.1, pulse shapers 18.2 and 18.3, the first element OR NOT 18.4, element NOT 18.5, element OR 18.6 , the initial installation block 18.7, the reverse counter 18.8, the decoder 18.10, the second element OR-NOT 18.11, the three elements AND 18.12, 18.13, 18.14, the three switches 18.15, 18.16, 18.17 and the power source 18.18. The switches 18.15, 18.16 and 18.17 are connected in series with the corresponding electric heating elements 2-6, and the elements 3 and 4, as well as 5 and 6 are connected in parallel. A safety thermal switch 24 is connected between the AC mains and the power supply busbars of the electric heater 24. The pressure sensor 11 is connected to the second input of the second OR-NOT 18.11 element, and the temperature regulator 17 is connected to the third input of the OR-NOT 18.11 element. The power control buttons 27 and 28 are designed to increase and decrease the setting of the total power of the electric heating elements, respectively. In the particular case of the implementation of the device according to claim 2, when the power of the second and third electric heating elements is twice the power of the first, a single press of each button causes a corresponding change in the setting of the total power of the electric heating elements by an amount equal to the power of the first element.

 The switch 18.1 is designed to limit the maximum power of the electric heater, for example, equal to the triple power of the first electric heating element, which is necessary to exclude the operation of the protection device of the apartment AC mains configured to a low value of the maximum power.

 The pulse shapers 18.2 and 18.3 are designed to generate a single pulse with a single press of buttons 27 or 28, i.e. to prevent the appearance of several pulses caused by the "bounce" of contacts. In the simplest case, the shapers can be made in the form of an RC-integrating chain.

 The first element, OR NOT 18.4, is necessary to invert the signal "0" coming from the output of the pulse shaper 1 when button 27 is pressed, as well as to prevent the passage of these pulses when the electric heater reaches its maximum power, limited by turning on the switch 18.1.

 The element NOT 18.5 is necessary to invert the signal "0" coming from the pulse shaper 18.3, when the button 28 is pressed.

 The OR 18.6 element is necessary for passing one of the pulses generated by pressing the buttons 27.28 to the counter 18.8.

 Counter 18.8 is designed to count the number of pulses arriving at its counter input C and present it in binary form. If button 27 is pressed, the pulse arrives not only at the counting input C, but also somewhat earlier - at the reverse input ± 1, which causes an increase of 1 on the counter reading 18.8. When the button 28 is pressed at the reverse input ± 1, the signal "1" is not received and the reading of the counter 18.8 decreases by 1.

 The initial installation block 18.7 is designed to generate a pulse "1", which sets the counter 18.8 to zero when the electric heater is connected to the network, as well as at the request of the user, and can be performed according to the scheme shown in Fig.9.

 Decoder 18.9 is designed to convert the binary number of electric heaters turned on into a decimal code.

 The indicator 29 is necessary to indicate the value of the total power of the included electric heating elements and can be performed according to the circuit shown in Fig.11. Electric heater power values of 0-5 kW are set when using 2-6 electric heating elements with a power of 1 kW, respectively.

 The detector of the zero level of the supply voltage 18.10 is designed to generate pulses "logical 0" start the switches 18.15-18.17 at the beginning of each half-cycle of the supply voltage and can be performed according to the circuit shown in Fig.11. It contains a voltage divider on resistors R10.1 and R10.2 connected to the AC power supply bus, a voltage limiter on diodes VD10.1 and VD10.2, two inverters DD10.1 and DD10.2, a delay circuit on the integrating circuit R10 .3-C10.1, two differentiating chains C10.2-R10.4 and C10.3-R10.5 and the element OR NOT DD10.3.

The operation of the detector 18.10 is illustrated by timing diagrams of the voltages measured relative to the phase "0" of the supply network and shown in Fig.13. The alternating voltage removed from the voltage divider R10.1 and R10.2 (Fig.13, a) is limited to the values of U _ogp1 and U _ogp2 using diodes VD10.1 and VD10.2. When this voltage reaches the threshold U of _the operation _{pores of} the inverter DD10.1, the voltage at its output (see Fig. 13, b) changes abruptly. However, the fronts of the pulses generated by the inverter DD10.1 and marked in FIG. 13, b with two strokes are at the end of the previous half-cycle of the supply voltage, and not at the beginning of the next. Therefore, such fronts after a delay on the integrating chain R10.3-C10.1 (Fig. 13, c), inversion on the element DD10.2 (Fig. 13, d) and differentiation on the differentiating chain C10.3-R10.5 generate impulses at the beginning of the next half-cycle (Fig.13, e). The fronts of pulses generated by the inverter DD10.1, occurring at the beginning of the half-cycle (marked with one stroke in Fig. 13, b), are differentiated by the chain C10.2-R10.4 (Fig. 13, e). The pulses from the differentiating chains C10.3-R10.5 and C10.2-R10.4 are added to the OR-NOT DD10.3 element (Fig.13, g).

 The second element, OR NOT 18.11, is designed to transmit the “logical 0” pulses generated by the zero-level detector of the supply voltage 18.10 and invert them provided that the “logical 0” signals are received at the other inputs from the pressure sensor 11 and from the temperature control electronic unit 17.

 The AND 18.12-18.14 elements are necessary for transmitting start pulses to the switches 18.15-18.17, corresponding to the number of connected electric heating elements, determined by the binary code at the output of the counter 18.8.

 The switches 18.15-18.17 are designed to connect electric heating elements 2-6 to the AC busbars and can be performed according to the circuit shown in Fig. 14. The switch is a triac VS, the anode of which is connected to the first AC power bus, and the cathode is connected to the first output of the heating element, the second output of which is connected to the second AC bus. The control electrode of the triac VS is connected to a power amplifier on a composite transistor VT1, VT2, namely: to the connection point of the series-connected resistors R4, R5. The amplitude of the output pulses of the composite transistor VT1, VT2 is divided on this divider to the value necessary to turn on the triac by the control electrode.

 The power source 18.18 is designed to power electronic circuits of the control device of the electric heater.

 The heated water discharge pipe 23 is attached to the top cover 8 of the housing 1.

 The local hydraulic resistance 22 is made in the form of a washer in the bore of the nozzle 21. The diameter of the washer hole is selected theoretically or experimentally from the condition that the pressure sensor 11 is activated at the minimum water flow rate for which the electric heater is designed.

где a - величина перекрытия третьего 24.5 и первого 24.2 контактов;
B - высота крепления второго конца пружины 24.7 относительно верхней плоскости второго неподвижного контакта 24.3.The safety thermal switch 24 is attached externally to the top cover 8 with the possibility of thermal contact and is formed (see Fig. 7) by two thermal switches located in a common housing 24.1. Each thermal switch is connected to the corresponding power wire and contains the first 24.2 and second 24.3 fixed contacts with vertical terminals, supported by a heat-conducting and electrically insulating plate 24.4, made, for example, of mica, the third contact 24.5, soldered by means of a fuse 24.6 lapped to contacts 24.2 and 24.3, moreover, the melting point of the fusible substance 24.6 is equal to the required temperature of the emergency shutdown of the electric heater, a cylindrical spring 24.7, one end connected to the 24.5 emu contact and the other end - the vertical terminal contact 24.3, 24.8 hull bottom formed of heat conductive material, the plate 24.4 is clamped between the bottom housings 24.8 and 24.1, and 24.1 vertical partition body presses the first stationary contact 24.2 of the plate 24.4. The axis of the spring 24.7 is deviated from the vertical by an angle β, satisfying the inequality:

where a is the overlap value of the third 24.5 and the first 24.2 contacts;
B - mounting height of the second end of the spring 24.7 relative to the upper plane of the second fixed contact 24.3.

 The shutdown temperature of the safety thermal switch 24 exceeds the temperature of the thermostat by at least 25 K, which is necessary to exclude the operation of the safety thermal switch with a working thermostat. The indicated value is determined experimentally for electric heaters with a capacity of not more than 5 kW.

 Electric heater operates as follows.

 Installation by the consumer of the required power of electric heating elements can be carried out in the following order.

 After turning on the electric heater in the AC network and supplying to the initial installation block 18.7 of the control unit 18 (see Fig. 9) the supply voltage from the power source 18.18, the differentiating circuit R7.2-C7.1 (see Fig. 10) generates a pulse to the input PE of the installation of the zero state of the counter 18.8 (see Fig.9). This counter is set to the zero state and “logical 0” signals appear on its outputs 1–4, which are fed to the I elements 18.12, 18.13, 18.14 and exclude the operation of the switches 18.15, 18.16, 18.17 and, therefore, the inclusion of electric heating elements 2-6. Zero state of the counter 18.8. causes the appearance of the decoder 18.9 at the “0” output as logical “1” (the rest of the outputs of the decoder 18.9 are in the “logical 0” state) and the LED “0 kW” of the indicator 29 (see FIG. 2), the remaining LEDs are off.

 The upper terminals of the resistors R1 and R2 (see Fig. 9) are supplied with a logic 1 voltage from a power source 18.18. The signal “logical 0” from the output 5 of the decoder 18.9 is supplied to the lower output of the button 27, and the signal “logical 1” from the output “0” of the decoder 18.9 is supplied to the lower output of the button 28. Therefore, with the zero state of the counter 18.8, only the pressing of the button 27 will change its state (increase in the setting of the total power of the switched on electric heating elements).

 To turn on the electric heating element 2, it is necessary (but not sufficient) to press the button 27 once, which will cause the appearance of a single pulse "logical 0" at the output of the pulse former 18.2 and, therefore, the pulse "logical 1" at the output of the first element OR NOT 18.4. This pulse arrives at the reverse input ± 1 of the counter 18.8 and through the OR element 18.6 to the counting input C (the signal “logical 0” from the output of the element NOT 18.5 is received at the second input of the element OR 18.6). As a result, 1 is added to the binary number located in counter 18.8 (in our case 0) 1. At the output 1 of counter 18.8, the signal "logical 1" appears (at the other outputs - signals "logical 0", which goes to the decoder 18.9, at the output of 1 of which a logical 1 signal also appears, which causes the “1 kW" LED of indicator 29 to glow (see figure 2) (the rest of the LEDs are off). From output 1 of the counter 18.8, the logical 1 signal is fed to the second input of the And 18.12 element, preparing switching on the electric heating element 2. Pressing the button 27 is another leads to the preparation of the inclusion of parallel-connected electric heating elements 3,4 (a "logical 1" signal appears at the output "2" of the counter 18.8 and, therefore, at the second input of the And 18.13 element) and excludes the inclusion of the electric heating element 2. Thus, the total power of the electric heating elements increases to be included.

 The table shows the correspondence between the number of button presses 27, the numbers of electric heating elements prepared for switching on and their total power (provided that the power of one electric heating element is 1 kW). It is assumed that the switch 18.1 is not turned on.

 After pressing the button 27 five times at the output 5 of the decoder 18.9, the state “logical 1” is set, which is fed to the lower output of the button 27, which excludes the counter 18.8 when the button is pressed again. When the switch 18.1 is turned on, the logic 1 signal appears at the input of the first OR-NOT 18.4 element after pressing the button 27 three times, which eliminates the change in the state of the counter 18.8 upon subsequent pressing of the button 27 and, therefore, the inclusion of electric heating elements for a total power exceeding 3 kW.

 Using the button 28, you can reduce the total power of the included electric heating elements. Pressing the button 28 has an effect on the counter 18.8 when the signal “logical 1” disappears from the output “0” of the decoder 18.9, that is, when the power setting is other than 0. When the button 28 is pressed once, the pulse “logical 0 appears at the output of the pulse former 18.3 ", which is inverted by the element NOT 18.5 and through the element OR 18.6 enters the counting input C of the counter 18.8. Since the “logical 1” signal is not input to the reverse input “± 1” of this counter (button 27 is not pressed), 1 will be subtracted from the number stored in counter 18.8, which will lead to a decrease in the total power of the included heating elements by 1 kW

 While the consumer has not opened the water tap (not shown in FIG. 2) and cold water does not enter the body of the electric heater, pressure signal 11 enters the second input of the OR-NOT 18.11 element of the control unit 18 (see Fig. 9) a logical 1 signal " At the first input of the OR-NOT 18.11 element, “logical 0” pulses are received, continuously generated by the zero-level detector of the supply voltage 18.10 and following with a frequency equal to twice the frequency of the AC network. The third input of the OR-NOT 18.11 element receives a signal, “logical 0” from the temperature controller 17. The “logical 1” signal from the signal shaper of the pressure sensor 11 excludes the appearance of the “logical 1” pulses required to start the switches 18.15 at the output of the OR-NOT 18.11 element , 18.16, 18.17. Thus, despite the setting of the total power of the electric heating elements, the switches 18.15, 18.16, 18.17 do not start and the electric heating elements 2-6 are disconnected from the AC mains.

 After opening the water tap, water flows through the cold water supply pipe into the housing 1 and fills it. When the housing 1 and the heated water discharge pipe 23 are completely filled with water, the water pressure in the housing 1 rises due to the outflow of water through the local hydraulic resistance 22. Under the influence of this pressure, the membrane 11.1 (Fig. 6) of the pressure sensor 11 bends, acts on the rod 11.5, which turns on the switch 11.4 and at the input of the driver of the signal of the pressure sensor 11, the signal "logical 0" appears. At the output of the OR-NOT 18.11 element, triggering pulses of "logical 1" appear, arriving at the second inputs of the AND elements 18.12, 18.13, 18.14. These pulses appear at the outputs of those elements And 18.12, 18.13, 18.14, the first inputs of which receive the signal "logical 1" from the corresponding output of the counter 18.8. Thus, those switches 18.15, 18.16, 18.17 are turned on, which provide the inclusion of part of the electric heating elements 2-6 with a given total power. The inclusion of electric heating elements is indicated by the corresponding indicators 19-21.

 The consumer can change the degree of water heating by changing the setting of the total power of the included electric heating elements using buttons 27 and 28. The operation of the control unit 18 of the electric heater is described above.

 If the water temperature in the upper part of the housing 1, perceived by the temperature sensor 25 (Fig. 4), exceeds the limit value set when setting the thermostat, and there is a danger of burns to the consumer, thermostat 17 generates a signal "logical 1", which is fed to the third input of the OR element NOT 18.11, excluding the passage of the start pulses of the switches 18.15, 18.16, 18.17 from the detector of the zero level of the supply voltage 18.10. Therefore, previously included electric heating elements are disconnected from the AC mains. Since the trip temperature of the safety thermal switch 24 is at least 25 K higher than the temperature of the temperature controller 17, the operation of the safety thermal switch 24 does not occur.

 In case of failure of the temperature controller 17, the water temperature in the housing 1 and, therefore, the temperature of the top cover 8 increase and when the temperature of the safety switch 24 is reached, the fusible substance 24.6 melts (see Fig. 7). Under the action of the spring 24.7, the contact 24.5 is disconnected from the fixed contacts 24.2, 24.3 and opens the electric circuit. This occurs in each thermal switch included in the safety thermal switch 24, thereby the electric heater is completely disconnected from the network.

 In the event of a failure of the pressure sensor 11 (Fig. 2) and the inclusion of electric heating elements when the housing 1 is not filled completely with water or without water, the heating elements 2-6 and, therefore, the heat-conducting top cover 8 are heated. At the same time, the casing 26 is heated (see Fig. 4) with a temperature sensor 25 and a safety thermal switch 24 (Fig. 2), which are in thermal contact with the top cover 8. When the temperature limit value of the sensor 25 (Fig. 4), set when the temperature regulator 17 was set, off Operation of electric heating elements 2-6 (as described above). In case of failure of the thermostat, the electrical heating elements are switched off by a safety thermal switch 24.

Claims (11)

1. An electric heater comprising a housing with a heat-conducting top cover, in the cavity of which tubular electric heating elements with current-carrying leads located in the upper housing cover are installed, a cold water supply pipe connected to the lower part of the housing, three switches, whose triacs are connected in series with the electric heating elements and mounted on a radiator with the possibility of thermal contact, a control device having a power controller with two buttons, binary reverse an external counter and a decoder connected to it, three AND elements connected to the decoder with their first inputs, a zero-voltage detector connected to the input to the AC power supply bus, and an output to the first inputs of the I elements, the outputs of which are connected to the control inputs of the switches, respectively , and the initial installation unit, connected to the binary reversible counter, a thermostat with a heated water temperature sensor connected to the control device, a water flow sensor, installed A dc thermal power supply connected to the cold water supply pipe and connected through a signal conditioning device to the control device, a thermal safety switch installed with the possibility of thermal contact with the housing, characterized in that the cold water supply pipe is made U-shaped, a sensor is used as a flow sensor pressure, located with the elbow not lower than the upper part of the heat transfer surface of the electric heating elements, the heated water discharge pipe is connected local hydraulic resistance is installed to the upper housing cover and the housing is installed in it, the lower part and the side wall of the housing are made of heat-insulating material, a safety thermal switch is installed on the upper housing cover and is connected between the AC mains and the busbars for supplying power to the electric heater, the temperature sensor of the heated water is connected to the heat-conducting a casing attached to the upper cover of the housing, with thermal contact, and the height of the casing does not exceed 2,5λF _b, where λ - coefficient teplop ovodnosti material casing, W / (mK), F _b cross sectional area of the side wall of the housing, m ^2, and two resistors incorporated control device through which the first and second setpoint power button to its first terminal connected to a DC power source, the first and the second pulse shapers connected to the first contact of the first and second buttons of the power adjuster, respectively, the first OR-NOT element, the first input of which is connected to the output of the first pulse shaper, the OR element, the first input of which is connected the output of the first OR-NOT element, the NOT element connected between the output of the second pulse shaper and the second input the OR elements, the second OR-NOT element, the first input of which is connected to the output of the zero-voltage detector, the indicator of the given power connected to the outputs of the decoder, switch power limitations, connected to the output "3" of the decoder and the second input of the first element OR-NOT, and the outputs of the signal shaper of the pressure sensor and thermostat are connected to the second and third inputs of the second e OR-NOT element, respectively, the output of which is connected to the second inputs of the three AND elements, the reverse input "± 1" of the binary reverse counter is connected to the output of the first OR-NOT element, the counting input with the output of the OR element, the decoder output "0" is connected to the second contact of the second button of the power setter, and the output "5" with the second contact of the first button of the power setter.  2. An electric heater according to claim 1, characterized in that the second and third, fourth and fifth electric heating elements are connected in parallel.  3. The electric heater according to claim 1, characterized in that in parallel with the electric heating elements included light indicators.  4. The electric heater according to claim 1, characterized in that the local hydraulic resistance is made in the form of a washer with a through hole made of a non-metallic material, for example, heat-resistant plastic.  5. The electric heater according to claim 1, characterized in that the pressure sensor comprises a membrane enclosed in a casing, a switch mounted on the casing with a rod resting on the membrane, a deflection limiter of the membrane made in the form of a conical washer, the inner surface of which is located on the side of the membrane, and having a through hole for a rod mounted in the hole with the possibility of movement.  6. The electric heater according to claim 1, characterized in that the radiator is installed on the cold water supply pipe with the possibility of thermal contact.  7. An electric water heater according to claim 1, characterized in that the surfaces of the electric heating elements, the upper housing cover and the temperature sensor housing contacting with water are coated with a non-metallic electrical insulating material, for example fluoroplastic. 8. The electric heater according to claim 1, characterized in that the outer side surface of the casing of the heated water temperature sensor is made hexagonal, the casing is connected to the top cover of the casing using a conical threaded connection, the temperature sensor is filled inside the casing with a heat-conducting, electrically insulating paste, the bottom of the casing is made conical with an angle at the apex of the cone equal to 60 ^o . 9. The electric heater according to claim 1, characterized in that the safety thermal switch is made in the form of two thermal switches installed in one housing and containing the first and second fixed contacts, equipped with vertical leads, installed with a constant gap between them on a heat-conducting and electrically insulating plate and connected lapped with a third spring-loaded contact by means of an electrically conductive fusible substance with a melting point equal to the required temperature a heater, and inserted between the contacting planes of two fixed and third contacts, the last of which is separated from the vertical output of the second fixed contact by a distance exceeding the overlap of the third and first fixed contacts, and connected to the first end of the coil spring, the second end of which is attached to the vertical output the second fixed contact at a distance from this terminal in excess of half the outer diameter of the spring, and with the possibility of rotation around an axis passing h through the attachment point of the second end of the spring parallel to the opposite sides of the fixed contacts, and the axis of the spring is deviated from the vertical by an angle satisfying the inequality

where β is the angle of deviation of the axis of the spring from the vertical;
a the amount of overlap of the third and first fixed contacts;
B mounting height of the second end of the spring relative to the upper plane of the second fixed contact,
the housing is provided with a bottom made of heat-conducting material and a vertical partition, moreover, the heat-conducting and electrically insulating plate is sandwiched between the housing and the bottom, and the vertical partition presses the first fixed contact to it.  10. A water heater according to claim 1, characterized in that the shut-off temperature of the safety thermal switch exceeds the temperature of the thermostat by at least 25K.  11. The electric heater according to claim 1, characterized in that the housing is made with an inner, centrally located, cylindrical tube, hermetically connected to the top cover, and the electric heating elements are made U-shaped with the arrangement of straight sections at an equal distance from the central tube of the housing, the lower parts of two non-adjacent electric heating elements are bent to the central tube of the housing and surround without touching the tube of the adjacent electric heating element.

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