The device controller
the Thermostat is designed to maintain in the refrigerator, the set temperature by automatically turned off and on of the compressor motor (compression refrigerators) or heater (absorption chillers). When the regulation of the cooling capacity by periodically stops and starts of the unit, the temperature in the refrigerator is going to fluctuate, which to a certain extent depends on the sensitivity of the thermostat.ustroystvo termoregulyatora.jpg On the principle of action thermostats household refrigerators are manometric type devices, which are based on the change in pressure of the filler in the change of its temperature (at the present time in some models of refrigerators foreign production use electronic thermostats). The thermostat household refrigerator is a lever mechanism with the power lever and the contact system, the electrical circuit of the refrigerator. On the power lever effect of the elastic element (bellows) thermosensitive system, and a main spring, an adjustable screw. Insulating gasket isolates the electrical circuit of the device from mechanical parts. Thermosensitive system gauge type consists of an elastic element – bellows (metallic container with corrugated walls or membranes with soldered thereto tube. The system is filled with a small amount of freon or chlormethyl and carefully sealed.
In the working conditions of freon is in a state of saturated vapor pressure which, as is well known, changes in specific dependencies (for this pair) on its temperature. The liquid phase refrigerant is in the end part of the tube. This part of the tube, especially in the section of liquid and vapor refrigerant reacts to changes of temperature, and it is placed controlled environment of the cooled object.
When lowering the temperature of the tube will decrease the vapor pressure in thermosysteme. Under the influence of the main spring of the corrugations of the bellows will be compressed and the power lever rotates on its axis, causing the contacts will open. With increasing temperature the vapour pressure will increase accordingly. Overcoming the resistance of the spring, the corrugations of the bellows will expand, and the lever will rotate in the opposite direction, and the contacts will close.
From this it follows that the set temperature, which will be opened contacts depends on the force of the spring. So, with a smaller force of the main spring contacts will be opened at a lesser vapor pressure in the temperature-sensitive system and therefore at a lower temperature.
on the Contrary, for higher temperatures, the spring force must be large. In this case, the spring must overcome the relatively greater resistance of the bellows, as higher temperatures will be greater the vapour pressure of the freon in the heat-sensitive system. Thus, to change the set temperature, it is necessary to change the force of the main spring. This practically carry handle thermostat, when the rotation of which varies the spring tension.
the Main elements of the controller.
In domestic refrigerators use controllers of different designs, but some of their items perform quite certain functions, the same for all structures.
Node sharp breaking of the contacts prevents the contacts of thermostat from burning when the debounce. In the above circuit diagram of a controller to facilitate the sliding contact is placed on the power lever, which directly operate the bellows and the main spring. With this arrangement, the rolling contact is inevitably a strong burning of the contacts and quick failure. The reason is that breaking of the circuit by opening contacts will occur slowly in accordance with the movement of the lever, which, in turn, is determined by the slow temperature changes and, accordingly, the vapor pressure of freon in the heat-sensitive system. In addition, with this arrangement movable contact, a slight rotation of the power lever will immediately rasmijoti or to short circuit the contacts, i.e., often to break the chain. Node sharp breaking of the contacts eliminates these disadvantages. In this case, the movable contact is located on the other lever (plate) connected to the power lever special rocker spring. When turning the power lever to certain provisions of the lever with the contact will remain stationary, and then flip the spring will dramatically change his position and contacts abruptly opens (or closes).
the Node temperature change is a device by which changes the tension of the main spring. In some controllers, the spring tension will change the rotation of the screw, which moves the nut abutting against the end of the spring in the other – the rotation of the roller pressed to his profile Cam acting on the spring. Screw (platen) rotate the knob having a pointer to install it in a certain position on the scale of the instrument.
the heat-sensitive system is a sensor that responds to temperature changes in the object under test and the current on the contact system of the device.
the Final part of the tube that is sensitive to temperature change, different controllers may be somewhat different, which depends mainly on the level of liquid phase refrigerant in it. With a small inner diameter tube or a relatively large amount of freon in the tube when the level of the liquid phase exceeds 80….100 mm, to provide such length tight fit of the tube to the wall of the evaporator difficult. In these cases, the end of the tube frizz into a spiral, bend in the knee or you solder spray greater than the tube inner diameter.
the configuration Node of the differential serves to regulate the magnitude of the differential. Differential thermostat call the difference between the temperature of the opening and closing of the contacts (at a particular tension of the main spring). The smaller the magnitude of the differential device, especially in narrow limits will be maintained the desired temperature. The temperature controllers of household refrigerators this site is used only for factory installation of the device. In many designs it is missing. The differential change by means of the screw, which, as a limiter to move the power lever, brings or removes the time of transfers of rocker spring loaded lever with a movable contact.
Node semi-automatic defrosting of the evaporator creates convenience when removing snow. The node is used in some designs of thermostats. The principle of its action and the device depends on the method of removal of snow taken in a particular refrigerator.
1 – heat-sensitive system ; 2, 7 – levers, 3-body, 4,5 – spring, 5-slide 6 - nut, 7,10,14 - adjustment screw, 8-pad, 9-additional contacts, 11 - main contacts 12 of the lever 13-spring, 16-axis, 17-lever