Most of the heating and measuring items that we use in everyday life require the use of special control elements. Such controllers (thermocouples) protect devices from overheating and damage. The thermocouple can be used for both small home measurements and laboratory experiments. To do this, you do not need to specifically look for it in stores. You can understand its device and make a thermocouple for a multimeter with your own hands.
Content
- Description and characteristics
- Principle of operation
- Manufacturing of a thermal sensor
Description and characteristics
A thermocouple is a deviceconsisting of two different conductors that are connected at one or more points by compensating wires. When the temperature is measured at one end of the wire, a voltage of a certain value and strength is created at the other. This device is used to control temperature as well as to convert temperature into electrical current.
The thermal sensor is quite inexpensive. This device is quite standard and measures a wide range of temperatures. The only drawback in the operation of the element is the inaccuracy, which can be up to 1 ° C, which is a lot for such values.
Making a thermocouple at home is easy. It is only necessary to remember that these devices are created from special alloys, therefore, a predictable and stable relationship between voltage and temperature can be traced.
There are different types of sensors. They are classified according to the type of metals used for the alloy:
- chromel - alumel;
- platinum rhodium - platinum.
The environment of application also depends on the composition, because such controllers are used both in science and industry, and at home - for boilers, speakers, ovens.
Principle of operation
Thermocouple is the most popular thermocouplek, which was discovered in 1822 by the German physicist Thomas Seebeck. That is why the principle of operation of such an element is often called the Seebeck effect.
In books and textbooks, this effect is described as follows: if the junctions of conductors have non-identical temperatures, then an electric force (thermopower) is formed between them, the value of which is proportional to the temperature difference adhesions.
It should be emphasized here that it is the temperature difference that should be taken into account, and not any indicator at all. In addition, if both junctions have the same temperature, the thermoelectric power will not appear in the circuit.
Before proceeding with the manufacture of the temperature sensor, you need to prepare all materials and tools. Thermocouple electrodes consist of dissimilar materials, for the selection of which you need to determine the type of product and the scope of use.
The types of temperature sensors are designated by letters of the Latin alphabet and have their own characteristics. For example, the popular TYPE K model consists of a chromel-alumel alloy and has a measuring range of 200-1200 ° C. Having made simple calculations, we can talk about nonlinearity (thermoelectric power -35 - 32 μV / ° C), while the nonlinearity of the characteristic should be the smallest. In this case, the measurement error will be very small.
The thermocouple can be located at a remote distance from the equipment itself. To do this, it is connected using a special cable. The cable itself is made from the same materials as the thermocouple. The only difference is in diameter.
Manufacturing of a thermal sensor
To make a thermocouple with your own hands, you need to purchase a wire from suitable materials. The diameter is important here, since the temperature measurement error depends on it. It is recommended to take a wire of a smaller diameter, especially if objects of small dimensions are to be examined.
The material depends on the temperature range with which it is supposed to work. The most common options are chromel-alumel, copper-constantan. The production itself consists in creating a connection, an alloy of two wires. Often, some kind of voltage source is used for this (for example, a car battery or a transformer).
Further stages of work are as follows:
- the free ends of the twisted wire are connected to one of the poles of the voltage source;
- the output is connected to the other of the poles, which is additionally connected to a graphite pencil.
When an electric arc occurs, the thermocouple wires are connected. In this case, the voltage for connecting the wires is selected by experiment. As a rule, the optimal value is 40-50 V, but it may be less, since it depends on the materials and the length of the product.
Another main point is compliance with safety regulations. It is very important not to use too high a voltage or touch exposed wires. It is better to insulate them with special tape or close them with a ceramic tube.
This is the easiest and most affordable way to make a thermocouple for a multimeter with your own hands. Sometimes thermocouple wires are soldered with a soldering iron. But then you will have to additionally purchase a special solder and adhere to certain temperatures in the work.
