Saturday, 7 March 2015



Relays are electromechanical components. They are mainly used for the following applications:

simultaneously and Floating connecting several load circuits with only one control circuit
for switching high electrical performance with low power (amplifier)
to achieve electrical isolation between steuerndem and a switching circuit
to low switching resistances in the closed state of the contact to achieve with very large contact resistance in the open state

Advantages and disadvantages

Electromechanical relays have been replaced in many applications of electronic switches which operate with transistors. Relays have some disadvantages compared to transistors, but also advantages, among others:


Depending on the insulation capacity of the air pressure or on the height above sea level (except for hermetically sealed relay box)
Vibration and shock sensitivity
Noise when switching

high and fall time (milliseconds compared to micro- and nano seconds in semiconductors, ie three to six orders of magnitude)
depending on the contact material, the contact resistance with the service life can change depending on the connected load

principal wear (electrical and mechanical), that is, it must always have the maximum possible number of switching life of the unit are compared


low contact resistance in the milliohm combined with low capacity of the switching path
high starting power and high overload
high insulation resistance and high blocking voltage of the switching path

Relays require no cooling (exceptions are semiconductor relays at high loads)
Relays can switch slightest signals to high RF performance and show this little tendency to crosstalk
Relays depending on the contact material and short-circuit current turn short circuits, without losing their function

Switching state is often seen with the naked eye
Immunity by pronounced hysteresis and robustness of the coil, it takes surge several times without prejudice towards (EMC and ESD)