Nominal resistor value and resistor value allowable error

As a user of smd resistor, when you need a 50kΩ smd resistor during the design and production of the circuit, please consider whether you really need to deliberately seek a resistor of exactly 50kΩ. Because it is difficult to buy 50kΩ resistor on the market. In fact, in most cases, replacing this 50kΩ resistor with a 51kΩ resistor may not affect the performance of the circuit. Otherwise, if you insist on buying a 50kΩ resistor and get it through a special order, the circuit cost will be greatly increased because of this resistor. It's like you are going to buy a 171cm piece of clothing. The operator recommends 170cm clothing to you. In fact, if you wear this 170cm clothing on your body, you can hardly understand the length between 170cm and 171cm. difference. Therefore, whether you are buying clothes, electronic components, or other commodities, you should follow standardized specifications.

The same phenomenon will also appear in production situations. When the producer makes an 800Ω resistor, maybe he will print the 820Ω logo without hesitation. Because the real resistor value of 800Ω is within the allowable error range of ±5% or ±10% of the 820Ω identification resistor value. The result of this is to reduce the rejection rate and reduce the production cost, without affecting or even facilitating the use of users. This kind of tacit understanding between producers and users is achieved through standardized work.

The standardized resistor value is printed on the surface of the resistor, and the marked resistor value is called the nominal resistor value. The deviation between the nominal resistor value and the true resistor value of the identified resistor is called the (actual) error of the resistor value. Obviously, the size of the error between the nominal resistor value and the real resistor value should have a limit. This limit is called the allowable error of the nominal resistor value. It can also be called the accuracy of the resistor value, or the allowable error and tolerance of the nominal resistor  value.