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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Control unit for the water supply system. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Home, household, hobby Based on his own experience, the author outlines the basic principles of building individual storage water supply systems and describes the control unit developed by him for such a system, which, in his opinion, meets the requirements for its reliability and safety of operation. It is simply impossible to do without water in a modern country house, farm or summer cottage. In remote places, centralized water supply is impractical, and a well, a well or even an open reservoir serves as a source of water. The latter option is highly undesirable due to the possibility of polluting the reservoir and spreading the pollutant throughout the water supply system. You can take water from a well, but when there is none, all that remains is to drill a well. The farther the territory from the city, the more often there are power outages, therefore, water supply systems with a storage tank are preferable, the supply of water in which is sufficient for a certain period of time. The simplest water supply systems, such as [1], are suitable for use only under supervision. There are pumping stations of various capacities for sale, but the prices for stations with a large supply of water in the storage tank are impressive. Therefore, self-production of a storage type water supply system can save a significant amount of money. Thinking over the design of a water supply system containing a water source, a pump, pipes for supplying and disassembling water, a storage tank for it, knowing the installation site of the system and the temperature conditions in which it will have to work, it is possible to imagine possible modes of operation, anticipate emergencies and, based on this , determine the requirements for the system as a whole and its control unit in particular. The operation of the water supply system must be safe, the manufacture, installation, maintenance and operation simple, and the control unit and sensors reliable. The system must be able to work flawlessly for years, and the control unit must be able to detect emergencies, signal them and prevent their development. The simplest of all possible water management systems are those that are equipped with electrode sensors for the presence of water and its level in the storage tank. Their manufacture does not require a large amount of locksmith work. The electrodes are easy to remove for tank flushing and other maintenance work, after which they are easy to install back. A similar construction is described in [2]. However, it is known that the stainless steel of the electrodes and the storage tank contains, in addition to iron, alloying additives - nickel, manganese, chromium and other metals. Getting into drinking water, and with it into the body, they adversely affect health. Therefore, when manufacturing a control unit that works with electrode level sensors, biological safety cannot be ignored. It is necessary to minimize the electrochemical processes occurring on the electrodes and the electrolysis of water. To do this, the voltage applied to the electrodes must be low and applied in short pulses. When starting to develop a water supply system, the features of water pumps should be taken into account. According to the principle of operation, they can be classified into two main types: vibratory and centrifugal. Vibratory pumps working intensively in the well cause damage to rubber or plastic water hoses due to their friction against the casing. If water stops flowing into the system through a damaged hose, the pump will work continuously until it fails, or it is turned off by automation or by a person. In such cases, it is necessary to urgently fix the malfunction, which is especially laborious and unpleasant in winter. It is also possible that the quality of the water will be worsened by particles of a rubbing hose, especially if it is rubber. If the aluminum casing of the pump touches the steel casing, a contact potential difference occurs, leading to electrochemical corrosion of the steel of the casing and the aluminum of the casing. Everything can end with the penetration of water to the pump winding and its damage. It has been noticed that the use of a pump in an aluminum casing noticeably worsens the taste of water even with polyethylene casing pipes. And this is especially noticeable with casing pipes made of black or stainless steel. If such water is used for drinking and cooking, there is a gradual poisoning of the body with aluminum, iron and alloying metals dissolved in it. The best solution to this problem is the use of a plastic casing and a centrifugal submersible pump in a plastic or stainless steel casing. After replacing the pump with an aluminum housing with a pump in a stainless steel housing, the improvement in the taste of water is felt in a day. Therefore, submersible pumps used in drinking water supply systems should not have housings and other parts in contact with water made of aluminum or its alloys with magnesium. The first requirement for the water supply system control unit is to maintain a predetermined water level in the storage tank. The second requirement is that it should not allow the pump to operate at a reduced or increased voltage of more than 10% in the mains supply. To control the pump, it is preferable to use an electromagnetic relay or a starter with normally open contacts. This ensures that the pump is turned off in case of typical malfunctions of the control unit or the absence of voltage in the mains. The control unit must necessarily turn off the pump if the pipes leading from the pump to the storage tank are damaged. This will prevent the pump from running indefinitely, accompanied by flooding of nearby buildings and territories. The unit should turn off the pump, stopping the filling of the storage tank and in case of leakage of water distribution pipelines. At the same time, the water supply to them from the storage tank must be shut off. To meet these requirements, it is necessary to have sensors for the flow of water entering the tank and humidity sensors in places of possible leaks. And finally, the control unit should not allow water to overflow from the storage tank, so a limit sensor for the water level in it is required. The practice of operating a home-made water supply system in automatic mode for decades shows that none of the described requirements can be considered superfluous. Speaking about the experience of operating the pump control units described in [3], it should be said that once a year they needed to clean the contacts. The pump control unit with reed switches required intervention every two to three years. The relatively simple control unit for the storage type water supply system, brought to the attention of readers, was designed based on the requirements listed above. The scheme of this block is shown in fig. 1. The simplicity and reliability of its operation is ensured by the use of microcircuits of parallel voltage stabilizers TL431ILP as threshold elements and electronic keys.
The control unit is powered by 230 V AC mains, it is switched on with the SB1 push-button switch. With the help of transformer T1, diode bridge VD1 and smoothing capacitor C1, a constant voltage is obtained from a secondary alternating voltage of 8,5 V (12 V at nominal mains voltage). It goes to the voltage control unit, assembled on DA1, DA2, DA4 microcircuits. The idea of this knot was found in [4]. In addition, the rectified voltage through the contacts of the button SB3 and the normally closed contacts of the relay K1.3 is supplied to the node assembled on transistors VT2 and VT3 according to the recommendations available in [5]. It generates pulses with an amplitude of 12 V, the duration of which is set by the capacitance of the capacitor C4 and the resistance of the resistor R15, and the repetition period - by the capacitance of the same capacitor and the resistance of the resistor R14. The pulses feed the node assembled on the DA3 and DA5 microcircuits, the VT1 transistor and the K1 and K2 relays. Electrodes of level sensors E1-E3 and flow E4, as well as humidity sensors are connected to this node. The voltage between the electrodes of sensors E1-E4 and the body of the storage tank is about 12 V, and it is pulsed and applied to the electrodes only during the determination of the water level in the tank. The state of the DA5 chip during the pulse depends on the presence and resistance of water between the low level sensor (electrode E2) and the tank body. If there is no water in the storage tank or its level is below electrode E2, the DA5 chip opens (closes its anode-cathode circuit) and turns on relay K2. Contacts K2.1 and K2.2 supply mains voltage to the water pump M1. Contacts K2.3, having closed, stop the generation of pulses. The voltage at the collector of the transistor VT3 becomes constant (about 12 V). Contacts K2.4 turn off electrode E2. After the tank is filled and the electrode E1 (upper level sensor) and the tank body are closed with water, the DA5 chip and the K2 relay are turned off. Pump M1 stops, water supply to the tank stops. The nodes assembled on the DA1, DA2, DA4 microcircuits and on the DA3 microcircuit, the VT1 transistor and the K1 relay are designed to turn off the M1 pump in emergency situations, signal this and keep the control unit in the "emergency" mode. LEDs HL1 and HL2 serve as indicators of operating and emergency modes, respectively. The pump turns off, stopping the water supply to the storage tank, in the following emergency situations. Firstly, when the mains voltage goes beyond the tolerance (± 10% of the nominal value). To do this, the current value of the unstabilized rectified voltage on the capacitor C1, which is proportional to the voltage in the network, is continuously monitored. Chip DA1 closes, and DA2 opens when this voltage is below the lower threshold set by the tuning resistor R4. The DA4 chip opens when the rectified voltage exceeds the upper threshold set by the tuning resistor R13. In both cases, K1, an emergency shutdown and alarm relay, is activated and self-locking. The second emergency mode occurs when the pump fails or when the pump is running, but water does not enter the tank due to, for example, its absence from the source or pipeline damage. When the jet of water entering the tank, in which the electrode E4 is located, does not electrically connect it to the tank body, the capacitor C2 is charged. When the voltage on the capacitor reaches the threshold voltage of the DA3 microcircuit, it opens. Alarm relay K1 is activated. Capacitor C2 and resistors R7, R8 create a delay in switching on the emergency mode. It is necessary so that, with a working system, water has time to fill the pipe going to the tank after turning on the pump, enters the tank and gets to the E4 electrode. The next emergency mode occurs when the water flow pipes are damaged or there is a threat of water overflow from the tank. It is determined using humidity sensors and the E3 limit electrode, and is turned on by the VT1 transistor, the DA3 microcircuit and the K1 relay. In any emergency mode, relay contacts K1.3 disconnect the pulse generator from the 12 V supply voltage, thus preventing the pump from being energized. At the same time, contacts K1.4 block the relay K1 in the activated state, and contacts K1.1 and K1.2 supply voltage to the coil of the solenoid valve Y1. In this case, the normally open valve Y1 closes, stopping the flow of water from the tank to the flow pipe. You can restore the water supply from the storage tank by turning off and then (after eliminating the accident) turning on the control unit using the SB1 pushbutton switch, and block the water supply from the tank in operating mode using the SB2 pushbutton switch. Closing its contacts will close the Y1 solenoid valve and stop the water supply to the flow pipe. If the control unit was not turned off during the elimination of the accident, then after it is eliminated, you can remove the lock by pressing the SB3 button and put the control unit into operation. The SB4 button switch allows you to turn on the pump and supply water to the storage tank even when the control unit is turned off. It is better to start the selection of structural elements with a set of relays and a power transformer. Relays must have four groups of contacts. Fusible links FU2 and FU3 are selected according to the pump operating instructions. The author used relay K1 - REK78/4 5 A 12 V DC IEC, relay K2 - REK77/4 10 A 12 V DC IEC. Their parameters are given in [6]. Both relays are located in the control unit housing. They are installed in the PPM77/4 and PPM78/4 sockets intended for them. If the indicated relays could not be found, then others are selected with a coil operating voltage of 12 V and four groups of contacts for switching. Relay contacts K2 must be capable of switching a current greater than the starting current of pump motor M1 or three times its operating current. The step-down mains transformer T1 must have a secondary winding of 8,5 V (no load). So that it does not "sink" when the relay K1 or K2 is activated, the power of the transformer must be 15 ... 20 times greater than the total consumed by the relay coils. Usually 50...100 W is sufficient. It is impossible to use a stabilized voltage source of 12 V, since the control unit controls the voltage in the network by the value of this voltage. It is permissible to use a relay with 24 V coils and a transformer with a secondary voltage of 17 V. With such a replacement, 25 V oxide capacitors must be replaced with 35 or 50 V capacitors. The method for setting up the unit does not change. If the voltage on the secondary winding of the transformer is noticeably higher than 8,5 or 17 V, then between pin 1 of the SB3 button and pin 10 of relay K1, you should install an additional integrated voltage regulator 7812 or 7824 and feed it with an output voltage of 12 or 24 V pulse generator. The GT402G transistor can be replaced with a GT403B-GT403D or other medium power pnp transistor. Preferred germanium or silicon transistors with low saturation voltage ike. Transistors KT3102E and KT3107K are replaced by similar low-power transistors of the corresponding structure. Instead of the KVR206 diode bridge, for example, LT416, PBL405 are suitable. Diodes 1N4148 can be replaced by any others with a permissible forward current not less than the current through the relay windings and a reverse voltage greater than the operating voltage of their windings. Electrohydraulic valve Y1, which is installed on the water withdrawal pipe from the storage tank, must be normally open, operate from an alternating voltage of 230 V and match the connecting dimensions to the pipes used for water extraction. If the operating current of the relay coils exceeds 0,1 A, the integral stabilizers DA3 and DA5 should be replaced with field effect transistors, for example BUZ11. In this case, the method for establishing the control unit will remain, but the danger of static electricity for field-effect transistors should be taken into account. Sensor electrodes are made of stainless wire 2...5 mm in diameter or stainless steel strip 0,5...1 mm thick and 6...10 mm wide. It is possible, for example, to use steel carrier wires extracted from stranded aluminum wires. The electrodes are fixed on a common plate of waterproof insulating material. The connecting wires should be connected to them outside the tank due to the high humidity in it. The electrode of the flow sensor E4 is fixed so that a jet of water entering the tank falls on it. The electrode of the limit level sensor E3 is located below the water supply pipe, but always above the electrode of the upper level sensor E1. Humidity sensors are sections of a double copper wire, stripped of insulation over a length of 50 mm and located in increments of 100 ... 500 mm along the length of the wire. This wire is laid so that the bare areas are located in places where water can drain when the tank is overfilled or from leaky joints in plumbing fittings. You can assemble the control unit in any case made of insulating material. For example, in a housing from a faulty uninterruptible power supply, from which a transformer can also be used if it remains serviceable. A terminal block XT 1 is installed in the housing to connect the wires going to the sensors. The printed circuit board, on which almost all the elements of the block are located, is shown in Fig. 2. It is better to mount them on the board in stages with the verification and adjustment of each assembled node. They begin work with a rectifier and a voltage control unit, then mount the pulse generator and check their presence. Then they assemble the pump control unit on the DA5 chip and the K2 relay and check its operation. The last to assemble the emergency control unit on the transistor VT1 and the DA3 chip and check its operation. After that, you can install switches, a terminal block, a transformer, a relay, a board in the case and connect them together. In order for the installation to be error-free, care is required.
The establishment of the assembled control unit begins with checking the constant voltage on the capacitor C1 and the presence of pulses on the collector of the transistor VT3. Empirically determine the duration of the drain of water from the tank from the electrode E1 to the electrode E2. Then set the same duration of the pause between pulses, reducing or increasing the capacitance of the capacitor C4 and the resistance of the resistor R14. For the ratings indicated on the diagram, the pulse duration is about 5 s, and the pauses between pulses are 1 min. The adjustment is completed by setting the upper and lower thresholds in the mains voltage control node. To do this, it is convenient to use a laboratory adjustable autotransformer (LATR). The work is carried out in the following order. The electrode of the flow sensor E4 is connected by a jumper to the common wire of the block (pins 1 and 6 of the block XT1). The outputs of the relay contacts K2.4 are also connected with a jumper. The engine of the tuning resistor R4 is set to the top, and the engine of the tuning resistor R13 is set to the bottom position according to the diagram. With the help of LATR, the voltage supplied to the primary winding of the transformer T1 is set to 230 V. Slowly, the voltage on this winding is reduced, setting it to 207 V. The trimming resistor R4 is slowly moved down (according to the diagram) until the relay K1 operates. The voltage taken from the LATR is increased to 230 V, and by pressing the SB3 button, the "Emergency" mode is canceled. Now, with the help of LATR, the voltage is increased to 253 V. Having done this, the engine of the tuning resistor R13 is slowly moved up (according to the circuit), again achieving relay K1 operation. After turning off the power to the unit, remove the jumper connecting the E4 electrode to the common wire. Next, check the operation of the flow sensor E4. To do this, turn off the pump and disconnect the electrodes E1 and E2 from the control input of the DA5 chip. After 20...40 s after the unit is connected to the network, relay K1 should work. Then the unit is turned off, the jumper is removed from contacts K2.4 and sensors E1 and E2 are connected. After that, the operation of the humidity sensor is checked by applying a damp cloth to the bare sections of its wires. When arranging the water supply system, the temperature factor should be taken into account. Pipes supplying water from the source must be straight and have a constant slope of 20 ... 30 mm per meter of length towards the source of water. This will prevent the water from freezing in the pipes, because after the centrifugal pump stops, it will drain through the pump back to the source. The storage tank must be installed above all consumers in a heated room or in the attic (where it is thermally insulated along with the chimney). The control unit of the water supply system is installed in any convenient place. It may be useful to replace the HL2 LED with a piezo sound emitter with a built-in generator, such as KRE-842. In this case, the resistor R2 is recommended to be replaced by any switch in order to be able to turn off the emergency sound signal. Literature
Author: M. Muratov
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