Temperature and humidity stabilizer. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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The device described here allows you to simultaneously stabilize the temperature and humidity of the air in the room. Unlike most similar stabilizers, which use the principle of measuring the resistance of a hygroscopic material, in the proposed version, a psychrometric method of its control is used, when the temperature decrease of the sensor is the greater, the more intense the evaporation from its surface. This made it possible to simplify the design of the sensor and increase the reliability of its operation.

However, it should be noted that the setting of the stabilized humidity must be carried out according to the psychrometric table, which is not very convenient.

A schematic diagram of the temperature and humidity stabilizer is shown in the figure. In fact, it consists of two thermostats. One of them is assembled on the DA1 comparator and the functions of the temperature-sensitive element are performed in it by the "dry" thermistor R3. A heating device with a power of about 1 kW is connected to the output of this controller (connector XS1), maintaining a constant temperature in the room. The comparator DA2 works in the second thermostat, to which the "wet" thermistor R8 is connected. The temperature, and hence the resistance of a constantly moistened resistor, depend on the humidity of the air in the room. A humidifying device can be connected to the output of this regulator (connector XS2) - an evaporator or a pump motor that sprays water through nozzles.

The first thermostat works as follows. When the temperature of the air, and hence the thermistor R3, is lower than the value set by the variable resistor R1, the voltage at the inverting input (pin 4) of the DA1 comparator is less than that at the non-inverting one (pin 5). In this case, the voltage at the output of the DA1 microcircuit (pin 10) is close to its supply voltage (about 11 V), the VS1 trinistor is open and the heater is connected to the power source. When the air temperature rises to the required level, the resistance of the thermistor R3 will decrease, the voltage at the inverting input of the DA1 microcircuit will increase, and the output will drop to almost zero. As a result, the VS1 trinistor will close and the heater power supply circuit will break. When the temperature drops, the process will repeat.

The operation of the humidity controller on the DA2 chip is practically no different from the operation of the thermostat, but instead of the trinistor, a transistor VT1 is connected to the output of its comparator, which controls the triac VS2 using relay K1.

The temperature of the thermistor R8 of the humidity controller depends not only on the temperature, but also on the humidity of the air. At low humidity, the rate of evaporation of water from its constantly wetted surface is increased, as a result, it cools and the resistance of the thermistor R8 increases. In this case, the voltage at the inverting input of the comparator DA2 will be low, and at its output - high. As a result, the transistor VT1 will open, the relay K1 will work and its contacts K1.1 will close. The triac VS2 will also open and the humidifier connected to the XS2 connector will receive power. But as soon as the air humidity rises to the required level, the evaporation of water from the surface of the resistor R8 will decrease and its resistance will decrease. Triac VS2 will close and the power supply to connector XS2 will stop.

All elements used in the stabilizer are widely known and available. NTC thermistors MMT-4 can be replaced with others with a resistance of 2 ... 20 kOhm, but the ratio of the resistances of the resistors R1: R3: R5 and R6: R8: R10 must be preserved. Trinistor KU202N can be replaced with KU201L, diodes VD3-VD6 are any powerful ones for voltages over 300 V. Fuse FU1 is selected based on the power of the devices connected to the XS1 and XS2 connectors. Relay K1 - RES-15 passport RS4.591.003 can be replaced by any other with a trip current of not more than 10 mA and winding resistance up to 1000 Ohm. When using a relay with a low winding resistance, it is necessary to include a current-limiting resistor R14 with a resistance of several hundred ohms in its power circuit. All elements, with the exception of VS1, VS2, R1, R6, R16, FU1 and VD3-VD6, are installed on a single-sided foil getinax board. Trinistor, triac and diodes VD3-VD6 are placed on small heat sinks.

The described device uses a transformerless power supply, so all conductive circuits must be well isolated. When setting up the device, you must use low-voltage stabilized power supplies.

A strip of material with good capillary properties is tied to the body of the resistor R8, the other end of which is immersed in water. It is important that the body of the thermistor is constantly wetted. The adjustment of the device consists in setting the operating threshold of the trinistor VS1 and relay K1. To do this, the sliders of resistors R1, R6 should be set to the position corresponding to the highest resistance. Resistors R11 and R12 are gradually transferred from the lower (according to the scheme) position to the position at which the trinistor VS1 opens accordingly and relay K1 operates. The device must be calibrated using a thermostat and variable resistor knobs R1, R6 provided with temperature scales. During the calibration process, the resistor R8 should not be moistened.

The desired temperature in the room is set by resistor R1, and humidity - R6. For this, a psychrometric table is used, on which the temperature of the dry thermometer corresponds to the temperature set by the resistor R1, and the wet thermometer corresponds to the temperature set by the resistor R6.

It is important to note that due to the galvanic connection of the device with the network, adding water to the container for wetting the resistor R8 is possible only when the mains voltage is turned off.

In this device, the control of the trinistor VS1 and the triac VS2 is not very well solved. The fact is that the output current of the power supply circuit R15VD1C7 - 16 mA - may not be enough to operate two op amps, turn on relay K1 and trinistor VS1 (rectification current - up to 100 mA at 20 ° C). In addition, the resistance of the resistor R16 ensures the guaranteed inclusion of the VS2 triac only when the instantaneous value of the mains voltage is 80 V, which causes noticeable interference with radio reception. Therefore, it is advisable to change the thyristor control circuits. Variants of schemes of nodes for their pulsed inclusion have been repeatedly cited on the pages of the magazine.

Author: M. Kutsev, village of Volchno-Burla, Altai Territory

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