What is the relations of the nominal and actual value of resistance for a resistor?
during manufacture, the target value of the race is attributed to a resistance. however, the actual value may be different due to variations in production. Normally a resistance will have its stated nominal value as well as the tolerance that can be expected, such as 5%, 10% or 1%. the closer the tolerance is, the higher the price.
the resistance of a resistor is the value indicated by the colored bands it contains.
Let’s take a 1k ohm resistance example. each component has a tolerance in% to which it is manufactured, for example 1%. Thus, a resistance of 1 k ohm has a nominal resistance of 1000 ohms and 1% of 1000 is 100 ohms; the actual resistance can therefore be between 950 ohms and 1050 ohms.
nominal is the target value (center) that the resistance should be.
the actual value depends on several factors and current states. Resistors
are designed to be normally within the tolerance range for which they are designed. (as +/- 10.5.2.1% of par value)
some other factors are: temperature, heat and heat dissipation history, age, current actual resistance, etc.
nominal is the value specified by the factory, as part of the list of business values. The actual value is the value you can read using an ohmmeter. it can differ a little for several reasons, manufacturing defect (the most common) and temperature dependent. ordinary resistances increase its value as the temperature increases. there are of course resistances manufactured in order to increase significantly its resistance value when the temperature increases (ptc – positive temperature coefficient), and others made for the contrary (ntc – negative temperature coefficient)
the nominal value is in the middle of the resistance tolerance. the actual value can be anywhere in the tolerance band. common, variety of garden, the resistances have a tolerance of 5%. the nominal value of the resistor is in the middle of this band, but the actual value could be +/- 2.5%.
for critical applications, precision resistors are used. but even in this case, it may be necessary to accurately measure the resistance and select those that are specified for the application.
There are (at least) two common methods of manufacturing resistors: molding a conductive mastic around anchored end wires and plating or spraying metal films onto a ceramic substrate or other inert substrate, with end caps and lead wires.
after having prepared a batch of resistors in this way, you may be faced with a production requirement of several values within a tolerance of + – 10%, or several additional values within a tolerance of 1%.
you will configure a sorting / testing machine to select the composition resistors in the required series of values. or you will configure the laser potentiometer to cut the metal oxide resistors in the appropriate spiral – a method that allows you to easily cut in 1% increments, for laser-adjusted types, rather than selecting them in increments of 1%. if we then examine the actual values against their nominal marks, we can notice a fairly uniform distribution of values around the nominal value – for the selected types, or a fairly high distribution around the mean that will be close enough to the value rated for laser cut types.
Nowadays, you may notice that a surface-mount resistor or resistance matrix is applied or scattered on a substrate that is more likely to be laser-adjusted than the one selected.