If you the radio fan or are engaged in repair of any equipment, to you, certainly, it was necessary to face problem of the correct selection of element of the electric circuit. Very often happens that only the main size of any given element is given in technical documentation, and additional parameters are not specified. One of typical questions in this area is the correctness of selection of power of dispersion at the resistor.
It is required to you
- tables of help data, shtangel-compasses, voltmeter, ampermeter
Instruction
1. In this case several solutions to this problem are possible. 1. On the resistor there is inscription, but you cannot decipher it. For resistors of domestic execution the value of power of dispersion is specified at once after type of the resistor, for example MLT-2 2K2 And – the resistor 2.2 kOhm with power of dispersion of 2 W.
2. 2. On the resistor there are no inscriptions, but there is certain quantity of strips or points. In this case color of any of strips will not interest you. Pay attention that on such resistance there are additional tags in the form of the strokes represented under various corners (see the drawing).
3. 3. On the resistor which you want to replace, owing to his old age or deposit neither inscriptions, nor strokes are visible. In this case you can be helped by the table in which the dependence of power of dispersion on diameter and length of resistance is shown.
4. 4. If you in stock have no resistor with the necessary size of power of dispersion it is possible to make it independently. For this purpose, first of all, it is necessary to decide on parameters of your scheme – on what current and tension it is calculated. It is easy to determine power by the law of Ohm: P=UI=I2R=U2/R. Having expressed current intensity, through its density we will receive: I=j/S, where j – density of current proceeding through the conductor from the set material, S – the section of this conductor. Thus, it is possible to make approximate assessment of section necessary for production of rezistoraprovod. Still it is worth making the additional correction on power, considering temperature change of the environment, the body of product in which there is this resistance and availability of forced cooling (its absence). The size of the correction has to be approximately additional 20-30% of the rated power of your scheme.
5. More exact calculation of power of dispersion can be made, proceeding from the provided table. For this purpose multiply all coefficients specified in it proceeding from limit operating conditions of the equipment.