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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Basement thermostat. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers In winter, many are concerned about how to preserve vegetables harvested in the summer. This is especially true for regions of Siberia, and other places where the temperature at night remains low for a long time of the year. It is known that in the cellars of Khrushchevs, where there are pantries, it is also rather difficult to store vegetables without taking special measures due to the proximity to heat supply communications. My idea is this: a thermostat is installed in the basement, using cold air forced in by a fan. You can use a window fan with a capacity of approximately 50 cubic meters. air per hour per 20 sq. meters of basement area. Figure 1 shows a diagram of a thermostat.
Two STZ-19 thermistors were used as temperature sensors. One is installed 10 ... 20 cm from the basement floor, the second - on the street. In addition, an economical electronic unit is installed in the room in compliance with fire safety rules for such rooms. .The scheme is quite simple and does not contain particularly scarce details. With some deterioration in the parameters, it can be assembled from almost any available parts. Power for the thermostat comes from a 220 V network through a transformer with a secondary winding designed for 12 V and a power of 10 W. The rectifier used is a bridge type, better than KTs405, but any other will do. The stabilizer is made on the KR142EN8V chip, but it is possible to replace it with the KR142EN5 with an additional zener diode in the "ground" wire. Main Uout.=12...14V. On VT1 and VT2, identical emitter follower-stabilizers are assembled for Uout = 4,7 ... 6,2 V. Voltage and polarity are not of fundamental importance. If there are no transistors indicated in the diagram, you can put others, it is only important that they do not differ in type. The stabilizer is thermally compensated by the VD2 diode. The thermistor R1 is installed outside, and R2 - in the basement. Resistor R3 serves to compensate for the spread of thermistor parameters in the selected temperature range. R5 is selected according to the current through the zener diode VD1 by 1 - 2 mA more than Ict.min for the one set in the circuit. R6 is needed to install Uon., i.e. to set the required temperature. Comparators are assembled on DA1 and DA2, which provide switching according to the set temperature (DA1) and switching according to the outdoor temperature (DA2). If the temperature outside is higher than in the basement, DA2 will switch and block the inclusion of DA1 by element DD1. In other words, if it is warmer outside than in the basement, then warm air from the street will not be supplied to the basement, even if the temperature in the basement is higher than the set one. Air supply from the street will occur only when the temperature is at least a degree lower than in the basement, although this depends on how the thermostat is debugged. Elements DD2 and DD3 are matching, but you can do without them by changing the inputs DA1 and DA2. Signals from DD2 and DD3 are fed through resistors to the switch DD4. Instead of a rather rare K1109KT2 assembly, transistors can be used with circuit changes shown in Fig. 2.
Chains R11, VD3, C1 and R12, VD4, C2 - "anti-voicing", i.e. excluding triggering of logic elements at points of uncertainty, when the comparator switches almost when the voltages at its inputs are equal, which eliminates relay bounce and increased wear of their contacts from electroerosion. The relay can be any one that reliably operates at U<9V, but with contacts designed for switching 220 V. The author used a reed switch with a glass bulb length of 50 mm, winding 1500 turns of PEV 0,1 wire on it. Thus, we got a relay with Ucp>6B at Icp<10mA. The switching current is at least 1A at 220 V. To prevent the winding from heating up, and at the output of the rectifier to be U-18 V, it is necessary to shunt the winding with resistor R16. To protect against breakdown of DD4, the winding of the KV relay is shunted by VD6. The purpose of the LEDs is as follows: VD5 - indication of turning on the fan, VD7 - turning on the lock when Tu>Tp, VD9 - turning on the unit in the network. Diode VD8 serves to protect ROLL from reverse voltage breakdown, its installation is mandatory. After assembling the thermostat, check if there are any errors in the installation, if there are, eliminate them. Then, turning off the power from the microcircuits, turn on the network. With a voltmeter, better than a lamp one, and even better digital, it is necessary to set the voltage at points A and B with the help of resistor R2 to be the same at different temperatures, for example, at 0 and 10 degrees Celsius, using vessels with water for this. Then the setting must be carried out at the temperature that you want to have in the basement (+3, for example). After that, the resistor R6 at point C. must be set to the same voltage. Then you can check the logic of the entire installation. Touch the street resistor with your finger - the VD7 LED should work. When touching the basement resistor, in the absence of blocking, the VD5 LED and the KV relay should work. If the temperature outside is higher than in the basement, then the relay should not work. The most accurate operation of the device is ensured by the use of thermistors with a short time constant and preferably with the selection of resistors R7 ... R10, which have the highest accuracy in the range from 10 to 33 kOhm in pairs. Installation - arbitrary. It is desirable to arrange the controls and controls (LEDs) in one place. It is desirable to place the entire device and a metal box from industrial ballasts. It is better to place the wires from the thermistors into the shield, without using the shield as a wire. The instrument and fan housing must be properly grounded. The wires of the network and the fan must be connected to the device through a terminal connection of industrial production, designed for the corresponding voltage. It is required to pay special attention to security measures, because the device will have to be operated almost unattended, in the basement, and there is dust and, to be honest, garbage. If you do everything reliably, you will enjoy the harvest saved until the summer.
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