When creating technical schemes, details are needed. Resistors are one of 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). The ratings are indicated on the device enclosure. But the real indicator may be slightly different. Usually this nuance is provided with the help of accuracy classes and tolerances. We will now consider them. If you don't understand something about the types of resistors, photos will help fix this.
Accuracy classes and tolerances
In the general case, classes are of most interest. There are three of them:
- The first. It provides for deviations of up to five percent of the indicated face value.
- Second. It 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 percent of the nominal.
But 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%.
- one%.
- 2%
Other options
Of great importance when choosing an element for the circuit are indicators of the limiting operating voltage, rated power dissipation and
temperature coefficient of resistance. The last indicator shows how much a change in the degree scale will affect the operation of the device. Depending on the material used in the production, this indicator may increase or decrease.
The rated power dissipation indicates the limits of use of the element. If the supplied characteristic is greater than can be processed, then the resistor may simply burn out. Under the maximum operating voltage is understood such an indicator at which reliable operation of the device will be ensured.
The main types of resistors
They are distinguished by four:
1. Unregulated:
a) constants.
2. Unregulated:
a) tuning;
b) variables.
3. Thermistors.
4. Photoresistors.
Non-adjustable constant resistors are further divided into non / wire. The wire is additionally wound on the latter type so that they have a large resistivity. Constant resistors are shown in the form of rectangles, from which special conclusions come. The value of the permissible power dissipation is indicated inside the geometric figure. If the resistance value is in the range from 0 to 999 Ohms, then the units are usually not indicated. But if this indicator is more than a thousand or a million, then the designations kOhm and MOhm, respectively, apply. If this indicator is indicated only approximately or it may change during setup, add *. Due to this, the types of resistors of different parameters easily differ among themselves.
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 may also be non-wire. The first type is a conductive coating that is applied to the dielectric plate as an arc, where the spring contact moves, which is attached to the axis. If you want to change the resistance value, its movement is carried out. Depending on a number of features, this parameter can vary according to the following dependencies:
- Linear.
- Logarithmic.
- Indicative.
Trimmer Resistors
They do not have a protruding axis. Changing the parameters of this type of resistor is possible exclusively 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 adjust their power, for example, in speakers.
Thermistors
This is the name of semiconductor elements, when included in an electric circuit, an indicator such as resistance varies with temperature. With its increase, it decreases. If the temperature decreases, the resistance increases. If the process curve moves in one direction (increases with increasing), then such an element is called a posistor.
Photoresistors
So called elements in which the parameter parameter changes under the influence of light (and in some cases, electromagnetic) radiation. Typically, 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 photocells, counters, monitoring systems, control and regulation devices, sensors and many other devices.
Conclusion
These are the resistors, types, purpose, principle of operation of these devices.