Inspection method and precautions for use of resistor

Date：2022-09-27 17:17:20 Views：2199

Resistance is the most numerous component in electrical equipment, but it is not the component with the highest damage rate. Open circuit is the most common resistance damage. It is rare for the resistance value to become larger, and it is rare for the resistance value to become smaller. The resistance of common carbon film, metal film resistor and wire wound resistor can be directly measured with the resistance gear of ordinary pointer multimeter. When the parameter mark of the resistor falls off for some reason or the precise resistance value is not known, it is necessary to measure it with an instrument. In order to help you understand, the following contents are organized by the Core Creation Testing Network for your reference.

Testing method of resistor

1. Visual inspection

For fixed resistance, firstly check that the mark is clear, the protective paint is intact, there is no scorch, scar, crack, corrosion, and the resistance body is in close contact with the pin. For the potentiometer, check that the shaft is flexible, tight and comfortable. If there is a switch, check whether the switch action is normal.

2. Multimeter detection

(1) Detection of fixed resistance

Use the resistance block of the multimeter to measure the resistance, and select different multiples of the multimeter to measure the resistance of different resistance values. For the pointer multimeter, the indication of the resistance gear is non-linear. The greater the resistance value, the denser the indication. Therefore, the appropriate range should be selected. The deflection angle of the pointer should be larger, indicating at 1/3~2/3 of the full range, and the reading is more accurate. If the measured resistance value exceeds the error range of the resistance, the resistance value is infinite, the resistance value is 0 or the resistance value is unstable, it indicates that the resistor is broken.

During the measurement, the hand holding the resistance shall not contact the two pins of the resistor, which will cause the resistance presented by the hand to be in parallel with the measured resistance, affecting the accuracy of the measurement. In addition, use the multimeter resistance block to detect the resistance value of the resistor in the circuit when it cannot be energized. For online detection, the power shall be cut off first, then the resistance shall be disconnected from the circuit, and then the measurement shall be carried out.

(2) Detection of fuse resistance and sensitive resistance

Generally, the resistance of the fuse is only a few to dozens of ohms. If the measured resistance is infinite, it is blown. It can also detect the resistance of the fuse online and measure the voltage to the ground at both ends. If one end is the power voltage and the other end is 0 V, the fuse resistance has blown.

There are many kinds of sensitive resistors. Taking thermistors as an example, there are positive temperature coefficient thermistors and negative temperature coefficient thermistors. For positive temperature system (PTC) thermistors, the resistance value is generally small at room temperature. In the measurement, use a hot soldering iron to approach the resistance. At this time, the resistance value should increase significantly, indicating that the resistance is normal. If there is no change, it indicates that the element is damaged. Negative temperature system thermistors are the opposite.

The resistance of the photosensitive resistor measured by the multimeter is large when there is no light (cover the light with hands or objects), and the resistance indicated by the light meter needle is significantly reduced. If there is no change, the element is damaged.

(3) Detection of variable resistor and potentiometer

First, measure whether the resistance value between two fixed terminals is normal. If it is infinite or zero ohm, or has a large difference from the nominal value and exceeds the allowable error range, it indicates that it is damaged; The resistance of the resistance body is normal. Then connect one probe of the multimeter to the sliding end of the potentiometer and the other probe to any fixed end of the potentiometer (adjustable resistance). Slowly rotate the shaft handle to observe whether the pointer changes steadily. When rotating from one end to the other, the resistance changes from zero ohm to the nominal value (or vice versa), and there is no jump or jitter, which indicates that the potentiometer is normal. If there is jump or jitter during the rotation, It indicates that the sliding point has poor contact with the resistance body.

3. Measure the resistance with a bridge

If it is required to accurately measure the resistance value of the resistor, it can be tested through a bridge (digital). Insert the resistance into the measuring terminal of the bridge element and select a suitable range to read the resistance value of the resistor from the display. For example, when a resistance wire is used to make a resistance or a fixed resistor is processed to obtain a more accurate resistance value, a bridge must be used to measure the resistance value of the self-made resistance.

Precautions for use of resistors

The resistance shall be checked before use. The check of its performance is to measure whether the actual resistance value is consistent with the nominal value and whether the error is within the allowable range. The method is to measure the resistance of the multimeter. Pay attention to two points when measuring

1. The measuring range shall be determined according to the measured resistance value, so that the pointer indicates at the middle section of the scale line, which is convenient for observation.

2. After the resistance range is determined, zero adjustment shall be carried out by short circuit (direct collision) between two probes. Adjust the "zero adjustment" appliance so that the pointer accurately points to the "0" of the Ω scale line, and then measure the resistance. In addition, do not touch the two ends of the resistance or the metal part of the probe. Otherwise, test error will be caused.

The resistance measured with the multimeter is close to the nominal value. It can be considered that the quality is basically good. If there is too much difference or no difference at all, it is bad.

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