When creating technical diagrams, details are needed. Resistors are among the most important. It is difficult to imagine a scheme even for five parts, wherever they find their application.
What is a resistor
This term was created thanks to the Latin "resisto", which can be translated as "resist". The main parameter of these elements, which is of interest, is the nominal resistance. It is measured in ohms (the number of ohms). Rated values are indicated on the case of the devices. But the real figure may be somewhat different. Usually this nuance is provided with the help of accuracy classes and tolerances. We will now consider them. If something is not clear to you about the types of resistors, the photos will help you fix it.
Classes and tolerances of accuracy
In general, classes are of the greatest interest. There are three of them:
- First. Provides for deviations of up to five percent of the specified face value.
- Second. Provides for deviations that can reach ten percent of the nominal value.
- Third. This includes devices in which the size of the deviations can reach twenty percentfrom face value.
And what if such large deviations are unacceptable? There are precision resistors, the types of which provide such a maximum difference:
- 0, 01%.
- 0, 02%.
- 0, 05%.
- 0, 1%.
- 0, 2%.
- 1%.
- 2%.
Other options
Of great importance when choosing an element for a circuit are indicators of the maximum operating voltage, rated power dissipation and temperature coefficient of resistance. The last indicator shows how changes in the degree scale will affect the operation of the device. Depending on the material used in the production, this figure may increase or decrease. The rated power dissipation shows the limits of the element's use. If the supplied characteristic is greater than it can be processed, then the resistor may simply burn out. The maximum operating voltage is understood as such an indicator at which reliable operation of the device will be ensured.
Main types of resistors
There are four of them:
1. Fixed:
a) permanent.
2. Fixed:
a) tuning;
b) variables.
3. Thermistors.
4. Photoresistors.
Unregulated fixed resistors are further divided into non/wire-wound ones. The latter type is additionally wound with wire so that they have a large resistivity. Fixed resistors are shown in the form of rectangles, from whichthere are special conclusions. The value of the allowable power dissipation is indicated inside the geometric figure. If the resistance value is in the range from 0 to 999 ohms, then the units of measurement are usually not indicated. But if this indicator is more than a thousand or a million, then the designations kΩ and MΩ are used, respectively. If this indicator is only approximate or it can change during setup, then add. Due to this, the types of resistors of different parameters are easily distinguished from each other.
Variable elements
We continue to consider the types of resistors. This type of device can also be called adjustable. In them, the resistance can vary in the range from zero to nominal. They can also be non/wire. The first type is a conductive coating that is applied to a dielectric plate like an arc, where a spring contact moves, which is attached to the axis. If you want to change the resistance value, it is moved. Depending on a number of features, this parameter may vary according to the following dependencies:
- Linear.
- Logarithmic.
- Demonstrative.
Trimming resistors
They don't have a protruding axle. Changing the parameters of this type of resistors is possible only with a screwdriver or an automatic / mechanical device that can perform its functions. This and the previous types of resistors are used in cases where a person must regulate their power, for example, in speakers.
Thermistors
Socalled semiconductor elements, when included in an electrical circuit, such an indicator as resistance changes with temperature. As it increases, it decreases. If the temperature decreases, then the resistance increases. If the process curve moves in one direction (it increases with increasing), then such an element is called a posistor.
Photoresistors
This is the name of the elements in which the parameter indicator changes under the influence of light (and in some cases electromagnetic) radiation. As a rule, photoresistors with a positive photoelectric effect are used. Their resistance decreases when light falls on them. Photoresistors have a simple design, small dimensions and high sensitivity, which allows them to be used in photorelays, meters, control systems, regulation and control devices, sensors and many other devices.
Conclusion
Here are the resistors, types, purpose, principle of operation of these devices.
