Thermostats with air temperature sensor. Thermostat with remote sensor

The use of temperature controllers with an air temperature sensor is quite wide - they can be installed in the heating system, in the incubator, protection of the electric drive, etc. Moreover, you can either purchase this device, since there are many models on the market, or you can make them yourself from improvised materials. But before starting the process, you need to familiarize yourself with the design features and its most common schemes.

Device Diagrams

The scheme of a temperature regulator with an air temperature sensor is quite simple - there are no scarce elements in it, so most beginner radio amateurs during training give preference to just such designs. They simply hone their skills and abilities. There are a huge number of circuits in the public domain, but the most widely used comparators.

Before you make a thermostat yourself, carefully study the circuit and determine which specific function it will perform. According to the diagram shown in the figure, you can see that there are inputs and outputs:

1. A reference voltage is supplied to one input - it is with its help that the entire device works.
2. The second input receives voltage from a thermistor (temperature sensor).

Indications are given to the comparator, after which they are compared with each other. In the event that the generation of the output signal begins, the electromagnetic relay will trip. At the same time, current is supplied to the heater or compressor of the refrigerator.

What will be required for the manufacture

As an air temperature sensor in thermoregulators, a thermistor is usually used. When the temperature changes, the resistance fluctuates. Semiconductor elements are often used - both transistors and diodes. But only under the condition that if a change in temperature occurs an increase or decrease in any characteristic.

Suppose, when heating a heater, it is necessary that the current in the transistor circuit increases. And the element stops working, regardless of the signal received at the input. But semiconductors have a lot of shortcomings - the most important is that it is quite difficult to make calibration.

But there are elements such as, for example, the LM335 chip. It has a fairly low cost, often used in household appliances. Similar products are widespread in industry and military equipment (series 135 and 235, respectively). The assembly contains at least 16 transistors, so the microcircuit can also work as a stabilizer - the voltage is completely dependent on temperature.

Features of LM335

Immediately you need to highlight the key features of thermostats with an air temperature sensor, manufactured on the LM335 microassembly:

1. At 1 degree there is about 0.01 V. Moreover, if you focus on the scale in Celsius, then at zero degrees the output voltage will be 2.73 V.
2. The working temperature range is in the range of -40 .. + 100 degrees. This allows you to use the chip in any design.

But for the temperature sensor to work correctly, you need a comparator - the LM311 chip is ideal. To form the reference voltage, you will need to install a variable resistor - its resistance may need to be selected empirically. And of course, to work, you definitely need a good power supply and indicators.

Load and power

You need to turn on the LM335 chip in series, and the resistors are selected so that the value of the current passing through the temperature sensor is at the level of 0.45..5 mA. If you exceed the permissible current value, the sensor will begin to overheat, which will significantly distort the data. Be sure to consider the load and power of the thermostat with the sensor when manufacturing. Air temperature can fluctuate over a wide range.

Washing can be done in the following ways:

1. Using a 12 V power supply
2. Using any device with an output of no more than 12 V. The current must be less than 100 mA (in the secondary circuit of the transformer) - this indicator is not recommended to be exceeded.

Remember that the current in the sensor circuit must be less than 5 mA, so the transistor in the design must have more power. Good results are shown by KT814. In order to "get rid" of the transistor, you can install an electromagnetic relay with a lower tripping current.

Walkthrough

In order to make a thermostat with a remote sensor, you need to prepare all the elements necessary for assembly. Consider an example of manufacturing an example of a device operating from a 12 V network:

1. First you need to prepare the case - any, even plastic, even metal one will do.
2. Choose a scheme that can satisfy all your needs. Determine the installation location of all elements of the circuit.
3. For the thermostat to operate, it is necessary that a negative type connection be provided between the input and output of the comparator.
4. Prepare the printed circuit board, install all the elements on it and solder it.

After assembling the thermostat with an air temperature sensor, it is necessary to check its operation. To do this, use a proven thermometer and simulate the operation of the heater or the refrigerator in various modes.