The thermostat will save the set temperature on the boiler. Thermostats DIN rail relay
1) maintaining a comfortable microclimate in the premises;
2) saving money spent on energy and heat carriers.
The principle of operation and characteristics of temperature controllers
The thermostat (a device for monitoring and programming the temperature in the room) consists of the following main components:- the microcontroller that controls it has a non-volatile memory, which allows you to store user-defined parameters even when the power is off;
- a digital sensor that measures the ambient temperature;
- electromagnetic thermal relay, disconnecting or connecting the load.
On the body of the device there is a display showing indicators and buttons with which you can configure Temperature regulator:
- required t;
- deviation range;
- operating mode (heating or cooling);
The number and type of user settings depends on the model temperature switch.
The device constantly scans the t-background of the environment and, focusing on the values specified by the consumer, regulates it by controlling the operation of climate control units. Influencing the on/off of air conditioners, fans and heating systems, the device allows you to save up to 30% of consumed energy resources and achieve a comfortable indoor climate.
Temperature relay is selected to specific conditions, taking into account its functionality.
- Single channel. Since the control of t is carried out using a single channel, a device of this type is capable of operating in either cooling or heating mode.
- Dual channel. A pair of measuring channels of the air temperature relay allows the device to simultaneously serve two sectors using various combinations of modes (heating-cooling, heating-heating).
- Multichannel. The three-channel mechanism is used to optimize electric heating systems and allows you to implement the remote climate control principle by setting a weekly temperature schedule. Provides maximum savings.
Models of devices, in addition to the number of channels, may differ in a lot of parameters:
- types of user-configurable values;
- mounting - built into a socket or mounted on a DIN rail;
- temperature ranges;
- power;
- operating modes (heating, cooling).
Varieties of thermostats that can be bought in the DigiTOP online store
DigiTOP offers an impressive range of thermostats with any number of channels. On the site you can choose the model of the climate control device with the most suitable characteristics.- Single-channel.
TK-3. Maintains the set room temperature.
TK-4. It is intended for work with powerful climatic installations (to 11 kW).
TK-4TP. Used to control warm floors.
TK-4k. Able to work at t up to 1000° allows the device to be used in muffle furnaces and combustion chambers.
- Dual channel.
TK-6. temperature controller, containing two TK-3 devices at once and allowing you to save up to 70% of energy resources due to precise temperature control of various zones.
Multichannel. TK-7 is a device that provides automatic operation using a weekly programmer. It is enough for the user to set the temperature schedule, and the device will provide the optimal indoor climate using a modern controller and many sensors.
All devices presented by DigiTOP are powered by 220 V.
Benefits of buying from DigiTOP
Devices that can be bought in the DigiTOP online store are being developed the best specialists and have a number of advantages.- Made from quality components.
- Differ in compactness, simplicity of control and installation.
- They have an affordable price that does not depend on the margins of intermediaries.
- They make it possible to save resources due to low power consumption and optimal control of the operating mode of heating and cooling systems.
- A wide range of models allows you to buy a device that exactly meets the necessary requirements.
- The devices are universal: compatible with modern and outdated climate control systems.
The sale of DigiTOP equipment is carried out throughout the country (Moscow and regions) with the help of a Russian representative of the company (Rostok-Electro LLC). When purchasing in bulk, additional discounts may be provided, so the price of devices may be significantly less than stated on the site.
Production: "Ralsib"
Additional input for connecting a level sensor (in the version with p/n sensor)
. Ability to connect additional temperature protection devices: thermal relays, thermal switches, etc.
. Simplicity and convenience in work
. DIN rail mounting
Temperature controller Ratar-02, -02M universal
Production: "Ralsib"
Semi-universal entry
. Bright LED display
. Intuitive Programming
. High accuracy
. Ability to shift zero and tilt without violating alignment (for RT and TP)
. Five types of output device logic
Temperature controller Ratar-02A-1 for unattended premises
Production: "Ralsib"
Fully finished product, no cabinet installation required
. Built-in two-pole automatic load switch
. Convenient wall-mounted housing with terminal compartment
. Large LED two-digit display
. It is completed with a remote temperature sensor to maintain the temperature in industrial premises, storage facilities, garages, etc.
Temperature controller Ratar-02U with built-in level control relay
Production: "Ralsib"
Two devices in one: thermostat and level switch
. Simultaneous maintenance of temperature and liquid level
. Load current up to 16 A
. Ability to set input type: 50M, 100P, Pt100
. Possibility to control the heater and refrigerator
. High accuracy of temperature measurement and maintenance
. DC and AC supply voltage in a wide range
. Blocking heating in the absence of liquid
. Adjustable for any conductive liquid
. Wave protection function
Temperature controller Ratar-03.2UV.Shch1 two-channel with universal inputs
Production: "Ralsib"
Measurement and regulation of temperature or other physical quantity through two independent channels according to the on-off law
. One channel control according to the three-position law (two setpoints, two control devices)
. Display of measured values in desired units (zoom)
. Ability to connect to two sensor inputs different types
. Measurement and regulation: on one channel - physical quantity, on the other channel - differences in physical quantities
. Display on the alphanumeric LCD display of both the measured values and the set settings
. Operation in millivoltmeter mode
Thermostat with timer and humidity control function for drying chamber PUSK-1
Production: "Ralsib"
A turnkey solution for automating drying chambers for clothes, wood, herbs, grain, etc.
. Automatic end of the drying process by time or relative air humidity
. Clear user interface
. Easy Installation and connection
. One specialized device replaces three standard
Thermostat OGD-011
- Temperature control ranges: 0...60°С, −10...50°С
- 2 relays: ~10 (2) A, 250 V
- Mounting: DIN rail
- 2 bimetal thermostats in one housing
- Simultaneous control of heaters and cooling devices, each device has its own rotary dial
Thermostat KTO-011
A device for maintaining the temperature in a residential or industrial premises, office, etc. by controlling actuators (heaters, cooling devices, fans, heat exchangers), as well as for turning on signaling devices
- Temperature control ranges: -20...40°C, -10...50°C, 0...60°C
- Relay: ~10 (2) A, 250 V
- Protection: IP20
- Mounting: DIN rail
- Heater control
Thermostat KTS-011
A device for maintaining the temperature in a residential or industrial premises, office, etc. by controlling actuators (heaters, cooling devices, fans, heat exchangers), as well as for turning on signaling devices
- Temperature control ranges: -10...50°C, 0...60°C
- Relay: ~10 (2) A, 250 V
- Protection: IP20
- Mounting: DIN rail
- Control of cooling devices
Thermostat FTO 011
A device for maintaining the temperature in a residential or industrial premises, office, etc. by controlling actuators (heaters, cooling devices, fans, heat exchangers), as well as for turning on signaling devices
- On/off temperature: 5°C/15°C, 15°C/25°C
- Relay: ~5 (1.6) A, 240 V
- Protection: IP20
- Mounting: DIN rail
- Control of heaters, heaters
Thermoregulators: types, purpose and principle of operation
An electric thermostat is a device that allows you to maintain a certain temperature level in any heating system. It will turn off the heating element when the medium temperature reaches the set value and will automatically turn on again when it drops below the limit level. Such work does not require the involvement of personnel, therefore, it allows you to autonomously maintain the optimal temperature at any facility.
The classification of regulators is practiced simultaneously according to several criteria:
- according to its intended purpose (thermostat for an incubator, for controlling the temperature in a room, a heating boiler);
- over the operating temperature range;
- by type of working substance (thermoregulator with a temperature sensor for air, liquids, solids);
- by functionality (the availability of programming, remote control, etc. matters),
- according to the principle of operation and design (it can be an electronic, mechanical or electromechanical thermostat).
The price for a thermostat is made up of the factors described above, as well as depending on the purpose for which you want to use it.
The principle of operation of thermostats
The device is installed in an area that does not have a direct heating effect of the devices (in this case, it can be a thermostat with a remote sensor or an element of an embedded structure). Thus, the device can obtain information about the temperature level in the sensor location area and, based on them, control the operation of heating elements or heating devices.
The main types of thermostats and thermostats
- Mechanical devices - e These are the simplest and most affordable devices in their design, which are especially often used when working in a small area. They are not susceptible to power surges or electronic failures, so they are reliable and easy to use. For their price, mechanical thermostats are the most democratic of all.
- Electric thermostat - such devices are often used in the configuration of household electric stoves, electric kettles. Depending on the principle of operation, you can buy devices whose operation is based on the use of a working membrane (bimetallic plate) or a capillary tube.
- Electronic thermostat with temperature sensor - such devices are most often used today: they are accurate, reliable, convenient. Their work is based on the fact that the temperature sensor, which is installed in the area where there is no intense heating or draft, constantly transmits information about the temperature of the environment to the controller. The latter processes the data and sends a control signal to the heaters.
You call, order, experts of the Terainsvest company are always ready to help with the choice, to consult on all questions.
You can buy temperature controllers, thermostats from the Terainvest company at affordable price in Russian cities.
In consumer electronics, temperature control is very often required. For this, a special sensor is used. It is a bimetallic contact that opens when heated above a certain temperature.
In everyday life, this sensor is called a thermostat, thermal fuse, thermal switch, thermal relay, thermal sensor, thermal interrupter. In general, they just don’t call it, although the part itself is a rather simple device.
This miracle looks like this.
Thermoswitch KSD 301 for a response temperature of 115°C without fixing the flange.
Thermal switches of the KSD 201, KSD 301, KSD 302 series are included in almost all household electrical appliances that are used for heating. They can be found in the electrical circuits of thermos kettles (thermo pots), storage water heaters (boilers), electric stoves, ovens, microwave ovens.
These temperature switches have a movable or fixed flange required for surface mounting for temperature control. Some models may not have a flange. To reduce the temperature resistance between the thermal switch and the object of control (tank, reservoir, chamber, etc.), heat-conducting paste can be used. The terminals of the KSD series thermoswitches are stamped and are designed for connection of conductors without soldering.
The use of temperature switches.
Thermal switches are very simple and easy to use. Used in electrical engineering for the following purposes:
Emergency shutdown of an electrical appliance during thermal overload. So, for example, if the main circuit of the water heater thermostat fails, then the temperature of the water tank will soon reach the critical temperature (more than 100 - 105 ° C). In this case, the thermal switch opens its contacts and removes voltage from the electrical appliance. This is how the fire safety of the electrical appliance is ensured.
It is worth noting that the reason for the inoperability of an electrical appliance can be just a thermal switch. The fact is that there are self-resetting thermal switches, such as, for example, the KSD 201 type, and thermal relays with forced switching on. Thermal relay (thermostat) type KSD 302S just refers to devices with forced inclusion.
When this sensor is triggered, its thermal contacts open. To re-close the thermal contacts of the sensor, you need to press the small button on the side of the thermal relay contacts. The photo shows that there is a button on the side of the thermal relay contacts. It then serves to restore the working state of contacts.
Thermal relay KSD 302S
The appearance and pinout of the thermostat type KSD 302S are shown in the figure.
Dimensions and appearance thermostat KSD 302S
Appearance and typical dimensions of thermal switches with one pair of thermal contacts and a fixed flange
Temperature control . Thermal switches are very actively used in thermos teapots (thermo pots). There they are used both as a protective thermal fuse and to turn off the heating element when the boiling point of water is reached.
You can find out more about the construction of thermos kettles and their repair.
Basic parameters of KSD series thermal switches.
Response temperature. The temperature at which thermal contacts open. Indicated on the body of the device. It rarely exceeds 150°C, as these sensors are mainly used in water heating appliances.
Rated voltage and current. Operating voltage and permissible current for the thermal switch. Typically, the rated voltage is 250V and the allowable current is at least 10 amps.
Type-nominal. For example, KSD 201.
Reset temperature. The temperature at which cooled thermal contacts close again. This parameter is not indicated on the body of the thermal switch, but usually it is on 13 - 30° С below the operating temperature. More precisely, this parameter can be found in the description of a specific type of thermal switch.
Thermostat check.
Since the thermal switches of the KSD series are a conventional thermally controlled contact, they are checked by a simple "dialing" method using a tester. In the normal "cold" state, the thermal switch contacts are closed.
To check the operation of the thermal switch, you can heat it above the switch-off temperature with a conventional lighter and measure the resistance of the contacts. Since the operating temperature range of the KSD series thermal switches is mainly in the range from 50 to 160 ° C, they can also be heated with a conventional soldering iron.
In some cases, to restore a non-working KSD series thermostat, you can shake it vigorously several times. Oddly enough, but strong shock vibration helps to restore the normal operation of thermal contacts. Of course, it is advisable to replace a faulty thermal switch with a new one. This recommendation applies only to those cases where a suitable replacement for the defective part is not at hand.
As already mentioned, thermal switches (thermostats, thermal relays) of the KSD series are actively used in household electrical appliances. When repairing them, sometimes it is necessary to replace just a thermostat such as KSD 301, KSD 302, KSD 201 and similar. Where can I buy them if I could not find them in the nearest radio stores? You can buy online at AliExpress. Prices are very affordable, however, if you choose free shipping, then its terms can reach 1 - 1.5 months. If you do not know how to purchase parts on AliExpress, then
Efficient heating control is a vital part of the efficient operation of the boiler and home heating system. Competent use control elements will reduce the energy consumption of the unit, while creating a comfortable temperature in every room of the house, avoiding overheating of the premises. And the thermostat (or programmer) controls the operation of the boiler, depending on the temperature in the room.
Up to 20% of the volume of consumed energy carriers can be saved using this kind of automation. And energy prices are quite high and the desire of everyone normal person reduce your costs.
We consider the situation when the boiler is designed correctly, the necessary insulation of the premises has been completed, and the heating system is functioning normally.
Main types of boilers and temperature control
There are several types of boilers: solid fuel, gas, electric and liquid fuel.
Boilers are widely used all over the world. There are domestic samples, there are boilers and imported ones. The material of manufacture is steel or cast iron. Easy to operate, economical, with the function of adjusting the temperature of the coolant. In cheaper models, this function is implemented using a special device - a thermocouple.
Structurally, a thermoelement is a metal product, the geometric dimensions of which, under the influence of temperatures, decrease or increase (depending on the degree of heating). And this, in turn, changes the position of a special lever that closes and opens the draft damper. The photo shows an example of such a regulator:
Photo: sample thermostatThe more the damper is open, the stronger the combustion process, and vice versa. Thus, the volume of air that enters the closed-type combustion chamber is fully controlled by the thermostat, and if necessary, its supply is stopped and the combustion process dies out. In more modern models controllers are installed, which, depending on the specified thermal conditions, control the air flow, turning on (or turning off) a special fan (see photo below):
gas boilers- the most common and cheapest to operate units. Boilers are single-circuit and double-circuit. Single-circuit boilers have one heat exchanger and are intended only for heating. The switching circuit is shown in the figure below:
Scheme of switching on a single-circuit boiler Double-circuit boilers have two heat exchangers and are designed for heating and receiving hot water. The boiler connection diagram is shown below:
Some boilers have separate controls for heating and hot water temperature.
Electric boilers
A fairly common alternative to gas and solid fuel boilers. A lot of advantages, high efficiency, but a long payback period. The connection is simple, like for gas boilers, but without a supply cold water. Temperature control and overheating protection are provided.
Boiler mechanical timer Using a simple mechanical electric boiler timer There are three options for starting the central heating system:
- The boiler is off;
- The boiler supplies hot water;
- The boiler turns on and off at the set time.
Mechanical timers usually have a large round dial with a 24-hour scale in the center. By turning the dial, you can set the desired time and then leave it at that position. The boiler will turn on at the right time. The outer part consists of a set of tabs with a 15-minute period, which are inserted for the convenience of adjusting the operation and setting modes. An emergency reconfiguration is possible, which is performed when the boiler is connected to the network.
Mechanical timers are easy to set, but the boiler always turns on and off at the same time every day, and this may not satisfy the owners if the family is large and bath procedures are performed several times a day at different times.
Types of thermostats
According to the type of functions, they can be divided into several groups:
- with one function (temperature maintenance);
- with a large number of functions (programmable).
By design, thermostats are divided into types: wireless and with wires for communication with the boiler. Install thermostats in comfortable spot, connect the temperature sensor, connect it to the boiler control system and use it.
Room thermostats need a constant supply of air to function properly, so they should not be covered by curtains or blocked by furniture. Appliances adjacent to the electric thermostat may interfere with the correct operation of the device: lamps, televisions, heaters located nearby.
The programmable electronic room thermostat allows you to select the desired and comfortable temperature at any time, it is easy to reconfigure and change the operating mode. The timer allows you to set a different heating pattern for weekdays and weekends. Some timers allow you to set different settings for each day of the week, which can be useful for people who work part-time or in shifts. Many Terneo and KChM models are equipped with such thermostats.
A programmable room thermostat allows you to set individual heating standards for each day in accordance with your lifestyle and maintain the temperature at home all the time, regardless of the presence or departure of the owners.
Video: Connecting a room thermostat to a gas boiler
If a boiler with a radiator is responsible for the heating system, as a rule, only one programmable room thermostat is needed to control the entire house. Some patterns need to be adjusted in the spring and fall when the clocks have gone back and forth or there has been a certain change. climatic conditions. We also recommend changing the temperature settings when changing day and night.
Such a climate controller has several options that expand its capabilities:
- "Party", which stops heating for several hours, then resumes;
- "Override" allows you to temporarily change the programmed temperatures during one of the configured periods;
- "Holiday", increases the intensity of heating or reduces it for a certain number of days.
Central thermostat
Such a thermostat is located far from your boiler and usually allows you to turn the heating on or off throughout the house. Older versions are wired to the boiler, newer systems tend to send signals to the device's command post. It is with devices of a new type that quite expensive, but effective devices are equipped: double-circuit boilers Ferroli, Beretta and domestic AOGV.
The most famous are room thermostats for a double-circuit boiler of the Gsm and Protherm trademark. They have a built-in dilatometric thermostat for the boiler, which, depending on the model, can work remotely, often this technology is used for an electric boiler or solid fuel units.
The room thermostat turns off the heating of the system as needed. It works by measuring the air temperature and turning the heating on when the air temperature drops below the thermostat setting and turning it off when the set temperature is reached.
Adviсe:
- It is recommended to set the thermostat at 20°C;
- At night, the set temperature should be between 19-21 ° C.
- It is desirable that in the children's room it was about 22 ° C.
- The temperature should not fall below 22°C in a room for the elderly and people with disabilities.
As a rule, the temperature of the whole house or individual rooms is based on only one climate microcontroller in the heating system. The best option its location in the living room or bedroom, which should probably be the most visited place in the house.
Room thermostats need a free flow of air to sense the temperature, so they should not be covered by curtains or blocked by furniture. Appliances adjacent to the electric thermostat may interfere with the correct operation of the device. These include lamps, televisions, neighbor's boilers through the wall, touch switches.
Thermostatic control valves
A thermostatic valve is a simple solution to the problem of obtaining a coolant of a given temperature by mixing colder water with warmer water. The view of the three-way valve is shown below:
The thermostatic radiator valve allows you to control the temperature in the room by changing the flow of hot water through the radiator. They regulate the flow of hot water through the radiator, but do not control the boiler. Such devices must be installed in order to adjust the temperature that is needed in each individual room.
This idea should be considered as an addition to a thermal control plant. Also, such devices need periodic readjustment and regular performance checks (every six months during the change of operating modes).
Homemade external thermostat for the boiler: instructions
Below is a diagram of a home-made thermostat for a boiler, which is assembled on Atmega-8 and 566 series microcircuits, a liquid crystal display, a photocell and several temperature sensors. The programmable Atmega-8 chip is responsible for compliance with the set parameters of the thermostat settings.
In fact, this circuit turns the boiler on or off when the outdoor temperature drops (rises) (sensor U2), and also performs these actions when the temperature in the room changes (sensor U1). Adjustment of the work of two timers is provided, which allow you to adjust the time of these processes. A piece of circuit with a photoresistor affects the process of turning on the boiler according to the time of day.
Sensor U1 is located directly in the room, and sensor U2 is outside. It is connected to the boiler and installed next to it. You can add if necessary electrical part schemes that allow you to turn on and off high-power units:
Another thermostat circuit with one control parameter based on the K561LA7 chip:
The assembled thermostat based on the K651LA7 chip is simple and easy to adjust. Our thermostat is a special thermistor that significantly reduces resistance when heated. This resistor is connected to the electricity voltage divider network. This circuit also has a resistor R2, with which we can set the required temperature. Based on such a scheme, you can make a thermostat for any boiler: Baksi, Ariston, Evp, Don.
Another circuit for a thermostat based on a microcontroller:
The device is assembled on the basis of the PIC16F84A microcontroller. The role of the sensor is performed by a digital thermometer DS18B20. A small relay controls the load. Microswitches set the temperature that is displayed on the indicators. Before assembly, you will need to program the microcontroller. First, erase everything from the chip and then reprogram, and then assemble and use it to your health. The device is not capricious and works fine.
The cost of parts is 300-400 rubles. A similar regulator model costs five times more.
A few last tips:
- even though most models fit different variants thermostats, it is still desirable that the thermostat for the boiler and the boiler itself be produced by the same manufacturer, this will greatly simplify the installation and the operation process itself;
- before buying such equipment, you need to calculate the area of \u200b\u200bthe room and the required temperature in order to avoid “downtime” of equipment, and changing wiring due to the connection of devices of higher power;
- before installing the equipment, you need to take care of the thermal insulation of the room, otherwise high heat losses will be inevitable, and this is an additional expense item;
- if you are unsure that you need to purchase expensive equipment, then you can conduct a consumer experiment. Get a cheaper mechanical thermostat, adjust it and see the result.
In everyday life and subsidiary farming, it is often necessary to maintain temperature regime any room. Previously, this required a rather huge circuit made on analog elements, we will consider one such circuit for general development. Today, everything is much simpler, if it becomes necessary to maintain the temperature in the range from -55 to + 125 ° C, then the programmable thermometer and thermostat DS1821 can perfectly cope with the goal.
Scheme of a thermostat on a specialized temperature sensor. This DS1821 temperature sensor can be bought cheaply from ALI Express (click on the picture just above to order)
The temperature threshold for switching on and off the thermostat is set by the values TH and TL in the sensor's memory, which must be programmed into the DS1821. If the temperature exceeds the value recorded in the TH cell, the level of a logical unit will appear at the sensor output. To protect against possible interference, the load control circuit is implemented in such a way that the first transistor is locked into that half-wave of the mains voltage when it is zero, thereby applying a bias voltage to the gate of the second field-effect transistor, which turns on the opto-triac, and it already opens the load-controlling VS1 . The load can be any device, such as an electric motor or a heater. The reliability of locking the first transistor must be adjusted by selecting the desired value of the resistor R5.
The DS1820 temperature sensor is capable of detecting temperatures from -55 to 125 degrees and operating in thermostat mode.
The scheme of the thermostat on the sensor DS1820
If the temperature exceeds the upper threshold TH, then the output of the DS1820 will be a logical unit, the load will turn off the network. If the temperature drops below the lower programmed level TL, then a logical zero will appear at the output of the temperature sensor and the load will be turned on. If there are any unclear points, homemade construction was borrowed from #2 in 2006.
The signal from the sensor goes to the direct output of the comparator on the operational amplifier CA3130. The inverting input of the same op-amp receives a reference voltage from the divider. Variable resistance R4 set the required temperature.
Thermostat circuit on the LM35 sensor
If the potential at the direct input is lower than that set at pin 2, then at the output of the comparator we will have a level of about 0.65 volts, and if vice versa, then at the output of the comparator we will get a high level of about 2.2 volts. The signal from the output of the op-amp through transistors controls the operation of the electromagnetic relay. At a high level, it turns on, and at a low level it turns off, switching the load with its contacts.
TL431 is a programmable zener diode. Used as a voltage reference and power supply for low power circuits. The required voltage level, at the control output of the TL431 microassembly, is set using a divider on resistors Rl, R2 and a negative TCR thermistor R3.
If the voltage on the TL431 control pin is higher than 2.5V, the microcircuit passes current and turns on the electromagnetic relay. The relay switches the control output of the triac and connects the load. As the temperature rises, the resistance of the thermistor and the potential at the control contact TL431 drops below 2.5V, the relay releases its front contacts and turns off the heater.
Using resistance R1, we adjust the level of the desired temperature to turn on the heater. This circuit is capable of driving a heating element up to 1500 watts. The relay is suitable for RES55A with an operating voltage of 10 ... 12 V or its equivalent.
The design of the analog thermostat is used to maintain the set temperature inside the incubator, or in a box on the balcony for storing vegetables in the winter. Meals are organized from car battery at 12 volts.
The design consists of a relay in the event of a temperature drop and turns off when the set threshold rises.
The temperature of the thermostat relay operation is set by the voltage level on pins 5 and 6 of the K561LE5 chip, and the relay off temperature is set by the potential at pins 1 and 21. The temperature difference is controlled by the voltage drop across the resistor R3. In the role of the temperature sensor R4, a thermistor with a negative TCR is used, i.e.
The design is small and consists of only two blocks - a measuring unit based on a comparator based on an op-amp 554CA3 and a load switch up to 1000 W built on a power regulator KR1182PM1.
The third direct input of the op-amp receives a constant voltage from a voltage divider consisting of resistances R3 and R4. The fourth inverted input is supplied with voltage from another divider at the resistance R1 and the thermistor MMT-4 R2.
The temperature sensor is a thermistor located in a glass flask with sand, which is placed in the aquarium. The main node of the design is the m / s K554SAZ - voltage comparator.
From the voltage divider, which also includes a thermistor, the control voltage goes to the direct input of the comparator. The other comparator input is used to adjust the desired temperature. A voltage divider is made of resistances R3, R4, R5, which form a bridge sensitive to temperature changes. When the temperature of the water in the aquarium changes, the resistance of the thermistor also changes. This creates a voltage imbalance at the comparator inputs.
Depending on the voltage difference at the inputs, the output state of the comparator will change. The heater is made in such a way that when the water temperature drops, the aquarium thermostat automatically starts, and when it rises, on the contrary, it turns off. The comparator has two outputs, collector and emitter. To control a field effect transistor, a positive voltage is required, therefore, it is the collector output of the comparator that is connected to the positive line of the circuit. The control signal is obtained from the emitter terminal. Resistors R6 and R7 are the load output of the comparator.
The IRF840 field effect transistor is used to turn the heating element on and off in the thermostat. To discharge the gate of the transistor, there is a diode VD1.
The thermostat circuit uses a transformerless power supply. Excess alternating voltage is reduced due to the reactance of capacitance C4.
The basis of the first design of the thermostat is the PIC16F84A microcontroller with a DS1621 temperature sensor with an l2C interface. At the time of power-up, the microcontroller first initializes the internal registers of the temperature sensor, and then configures it. The thermostat on the microcontroller in the second case is already made on the PIC16F628 with the DS1820 sensor and controls the connected load using the relay contacts.
DIY temperature sensor |
The dependence of the voltage drop on p-n junction semiconductors on temperature, is the best suited for creating our homemade sensor.
