A large number of electrical and electronic appliances or assemblies must be adjusted and set after the production process. Even when servicing, when fitting new components or when electrical values have altered owing to age, adjustment is usually necessary in order to restore the optimum functioning of the appliance. Although this should be reduced to a minimum by design measures and technological processes, in order to save costs and to attain a high degree of reliability, adjustment cannot be eliminated completely.
The number of examples which can be quoted is vast: pulse generators in digital systems have a quartz crystal whose nominal frequency is set by a trimming capacitor (this is the case in each digital clock). The offset adjustment in operational amplifiers is carried out using helis. The band-pass filter curve of selective amplifiers must be set in accordance with specific regulations by adjusting the inductances. The list of these problems is endless.
Trimming potentiometers, ten-turn trimmers, adjusting capacitors, inductor cores, adjusting hands of shell-type cores etc. can be set.
Not just any screwdriver should be used. There are special tools which ensure that the setting mechanism is not damaged and that sensitive setting can be carried out. The use of special materials prevents the electrical functioning of the appliance from being affected.