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The working principle of the temperature controller

Article Source:Thermal protectorAuthor:Kangding MetalPopularity:Published time:2019-07-02 15:59

Keywords: temperature controller, Sudden jump thermostat, liquid expansion thermostat, pressure thermostat
 In the process of using temperature controller, many manufacturers often encounter the problem of inertia temperature error, so they can not solve this technical problem. They rely on manual voltage regulation to control temperature. Yaxun's electronic technology innovation uses PID fuzzy control technology to better solve the problem of inertia temperature error. The conventional temperature controller is a switch controller that uses a thermocouple wire to generate a varying current as a control signal in the case of temperature change, and to make a fixed point for the electrical component. Computer controlled temperature controller: Using PID fuzzy control technology, using advanced digital technology through Pvar, Ivar, Dvar (proportional, integral, differential) three aspects of the combination of a fuzzy control to solve the inertia temperature error problem.

The electric heating elements of the conventional temperature controller are generally made up of electric heating rods and heating coils, both of which are made of heating wires. When the heating wire is heated by electric current, it usually reaches 1000 ° C or more, so the internal temperature of the heating rod and the heating ring is high. Generally, the temperature control of electrical machinery, the control temperature is mostly between 0-400 ° C, so the traditional temperature controller during the temperature control period. When the temperature of the heated device rises to the set temperature, the temperature controller will send a signal to stop heating. However, the internal temperature of the heating rod or the heating ring will be higher than 400 ° C, and the heating rod and the heating ring will also heat the heated device. Even if the temperature controller sends a signal to stop heating, the temperature of the heated device tends to continue to rise a few degrees before it begins to fall. When falling to the lower limit of the set temperature, the temperature controller starts to send a heating signal to start heating, but the heating wire needs to transfer the temperature to the heated device, which depends on the heating wire and the heated device. Depending on the media situation. When the reheating begins, the temperature continues to drop by a few degrees. Therefore, the traditional fixed-point switch control temperature has a positive and negative error a few degrees, but this is not a problem of the temperature controller itself, but the structural problems of the entire thermal system, so that the temperature controller temperature control produces an inertia temperature error .

To solve this problem of temperature controller, it is a wise choice to adopt PID fuzzy control technology. PID fuzzy control is a new temperature control scheme developed for the above situation. Using advanced digital technology to adjust the combination of Pvar, Ivar and Dvar to form a fuzzy control to solve the inertia temperature error problem. However, in many cases, due to the large inertia temperature error of the traditional temperature controller temperature control method, many people will give up automatic control and use a voltage regulator instead of the temperature controller when precise temperature control is required. Of course, this is perfectly achievable when the speed of the voltage stabilization operation is constant, the outside air temperature is constant, and the air flow rate is constant. However, it is clear that the above environmental factors are constantly changing. At the same time, when a voltage regulator is used instead of a temperature controller, it must be adjusted to a large extent by manpower. As the working environment changes, the degree of the required temperature is manually adjusted, and then the power is heated by a relatively stable voltage, which is barely operated, but this is by no means automatic temperature control. When there is a lot of key to temperature control, you will be in a hurry. In this way, the voltage regulator can not be used, because the manpower can not adjust the key to the need for temperature control at the same time, only the use of PID fuzzy control technology can solve this problem, making the operation handy and smooth. For example, the hot stamping machine has a relatively stable temperature requirement, and usually operates within plus or minus 2 ° C. When the high-speed hot stamping machine heats the same product pattern, as the speed increases, the heating speed also increases accordingly. At this time, the traditional temperature controller method and the operation of the regulator are not competent, and the quality of the product cannot be guaranteed. Because it is necessary to adjust the operating speed of the hot stamping machine before bronzing, use the speed to absorb the weakness of the temperature controller and the voltage regulator. However, if the PID controller with PID fuzzy control is used, the above problem can be solved. Because the P in the PID, that is, the Pvar power variable control, can increase the percentage of power output as the working speed of the hot stamping machine increases.

Mechanical type and electronic type:
The mechanical type adopts bimetallic strip. When the temperature changes, the curvature will change. When the curvature reaches a certain level, the circuit is connected (or disconnected) to make the refrigeration (or heating) equipment work.
Electronically type passed temperature sensing devices such as thermocouples and platinum resistors. The temperature signal is converted into an electrical signal, and the heating (or cooling) device is operated (or stopped) by a circuit such as a single chip microcomputer or a PLC.
There is also a mercury thermometer type, when the temperature is reached, there will be contacts and mercury connected.

The thermostat generally consists of two parts: temperature detection and temperature control. Most thermostats also have alarm and protection functions.
The working principle of the thermostat is to automatically sample and monitor the measured temperature through the temperature sensor. When the acquisition temperature is higher than the control set value, the control circuit is started, and the control hysteresis can be set. If the temperature is still rising, when the temperature rises to the set over-limit alarm temperature point, the over-limit alarm function is activated. When the controlled temperature cannot be effectively controlled, in order to prevent the destruction of the device, the function of the trip can be used to stop the device from continuing to operate. Mainly used in various high and low voltage switchgear, dry type transformers, box substations and household refrigerators, air conditioners and other related temperature fields used in the power sector.

According to the principle of thermostat manufacturing, the thermostat is divided into:
1. Sudden jump thermostat: Various types of sudden-jump thermostats are collectively called KSD, such as KSD301, KSD302 and so on. The thermostat is a new type of bimetal thermostat. It is mainly used as a thermal protection for various electric heating products. It is usually used in series with a thermal fuse. The snap-type thermostat is used as a primary protection. The thermal fuse is used as a secondary protection when the sudden-type thermostat fails or fails to cause the electric heating element to overheat, thereby effectively preventing the burning of the electric heating element and the fire accident caused thereby.

KSD301 Sudden jump thermostat

2, liquid expansion thermostat:
It is a physical phenomenon (volume change) in which the substance (generally liquid) in the temperature sensing portion of the temperature controller generates a corresponding thermal expansion and contraction when the temperature of the controlled object changes. The bellows connected with the temperature sensing portion generates expansion or contraction, and the lever principle is adopted to drive the switch to open and close, thereby achieving the purpose of constant temperature. The liquid expansion type thermostat has the characteristics of accurate temperature control, stable and reliable, small temperature difference between start and stop, large temperature control adjustment range and large overload current. The liquid rise type thermostat is mainly used in temperature control occasions such as home appliance industry, electric heating equipment and refrigeration industry.
liquid expansion thermostat

3, pressure thermostat:
The temperature controller changes the temperature of the controlled temperature into a change of space pressure or volume through the temperature envelope and capillary of the sealed internal temperature sensing medium. When the temperature set value is reached, the contact is automatically closed by the elastic element and the quick-acting mechanism to achieve the purpose of automatically controlling the temperature. The utility model is composed of a temperature sensing part, a temperature setting main body part, a micro switch which performs opening and closing, or an automatic damper. Pressure thermostats are suitable for applications such as refrigeration appliances (such as refrigerator freezers) and heaters.
pressure thermostat

4, electronic thermostat:
The electronic temperature controller (resistive type) is measured by the method of temperature sensing of the resistor. Generally, white gold wire, copper wire, tungsten wire, and thermistor are used as temperature measuring resistors, and these resistors have their own advantages. Most household air conditioners use thermistor type.

Vapor pressure type: The action of the bellows acts on the spring. The spring force of the spring is controlled by the knob on the control panel. The capillary is placed in the air inlet of the air conditioner to absorb the temperature of the indoor return air. When the room temperature rises to the set temperature, the temperature sensing agent gas in the capillary tube and the bellows expands, causing the bellows to elongate and close the switch contact against the spring force of the spring. At this point, the compressor is running and the system is cooled until the room temperature drops to the set temperature. The bellows contraction acts with the spring, placing the switch in the open position, causing the motor circuit of the compressor to be shut off. This is repeated to achieve the purpose of controlling the temperature of the room.