Identification and measurement of resistors and trimmer potentiometer

Resistors are called resistors for short. They are the most basic and commonly used electronic components. There are many kinds of resistors due to different materials and structures. Common ones are carbon film resistors, metal film resistors, organic solid core resistors, wire wound resistors, fixed tap resistors, variable resistors, sliding line resistors, sheet resistors and so on. Carbon or metal film resistors are commonly used in amateur electronic fabrication. The character symbol of the resistor is "R"

The main parameters of resistor are resistance value and rated power. Resistance value is short for resistance value, the basic unit is ohm, abbreviated as (Ohm). Commonly used units are kiloohms (kOhm) and megaohms (MOhm). The conversion relationship between them is: 1M = 1000k, 1K = 1000_. There are two ways to mark the resistance value of resistors: one is direct marking method, such as "5.1" or "5R1" on 5.1 resistors, and the other is "6.8k" or "6k8" on 6.8K resistors.

The other is the color ring method. There are four or five color rings on the resistor to indicate the resistance value. For 4-ring resistors, rings 1 and 2 represent two significant digits, rings 3 represent multipliers, and rings 4 represent allowable deviations, as shown in the left figure. For 5-ring resistors, the first, second and third rings represent three significant digits, the fourth ring represents multiplier, and the fifth ring represents allowable deviation.

Rated power is another main parameter of resistors. The power of common resistors is 1/8W, 1/4W, 1/2W, 1W, 2W, 5W, etc. Its symbols are shown in the left figure and are directly indicated by numbers larger than 5W. Resistors with rated power equal to or greater than circuit requirements should be selected in use. Not marked in the circuit diagram indicates that the power consumption of the resistor is very small, so it is not necessary to consider. For example, in most amateur electronic production, there is no requirement for the power of the resistor. At this time, 1/8W or 1/4W resistors can be selected.

The trimmer potentiometer is one of the most commonly used adjustable electronic components. The trimmer potentiometer is derived from the development of variable resistor. It consists of a resistor body and a rotating or sliding system. The contact brush of its arm slides on the resistor body, which can continuously change the resistance between the arm and the two ends. There are many kinds of trimmer potentiometer, such as ordinary rotary potentiometer, switched potentiometer, miniature switched potentiometer, direct-slip potentiometer, multi-loop potentiometer, fine-tuning potentiometer, double-connected potentiometer and so on.

The character symbol of the trimmer potentiometer  is "RP"

In addition to nominal resistance and rated power, the main parameters of potentiometer also have resistance variation characteristics, which refers to the relationship between resistance and the rotation angle or sliding stroke of the arm. Commonly used are linear (X), exponential (Z) and logarithmic (D). Linear type is suitable for most occasions, exponential type is suitable for volume control circuit, logarithmic type is suitable for voice control circuit.

The trimmer potentiometer can also be tested by the resistor of the multimeter. When detecting the nominal resistance value, according to the nominal resistance value of potentiometer, the multimeter is placed in the appropriate_gear, and the two pens (positive and negative) are connected with the two fixed arms of potentiometer respectively. The needle should be pointed at the corresponding resistance value scale. The potentiometer has been damaged if the needle is not moving, the indication is unstable or the indication value differs greatly from the nominal value of the potentiometer. Test whether the contact between the arm and the resistor is good. The multimeter pen is connected with the movable arm of the trimmer potentiometer, and the other pen is connected with the fixed arm A. It rotates the rotator handle of the potentiometer back and forth. The multimeter pin should move smoothly thereafter. If the needle is not moving or moving steadily, the potentiometer's arm is not in good contact. Then the pen connected with fixed arm A is changed to fixed arm B, and the above detection steps are repeated.