In term of control voltage it is possible to divide solenoids into two groups:
Electromagnets with direct current (DC) control – these types are the most frequently used electromagnets. Compared to electromagnets with alternating current control, the yoke does not have to touch down to end position, switching frequency is limited only by pick-up and release rates, there are no yoke vibrations. Their main disadvantage is slower pick-up and release times and lower pulling force. DC electromagnets can be supplied with rectifier for alternating current, but the electromagnet properties remain the same.
Electromagnets with alternating current (AC) control – their main advantage in comparison to DC types, is faster pic-up time. The magnetic circuit is adapted for alternating magnetic flux. The yoke must touch down the end position to avoid yoke vibrations, switchhing frequency is limited by pick-up and release rates and maximum allowed heating.
Electromagnetic devices are constructed to be functional and safe in the following conditions:
- voltage range from +6% to -10% of the nominal voltage; other values upon request
- installed altitude up to 1000 m (for higher altitude cooling is more complicated)
- ambient temperature from - 5 °C up to + 40 °C, daily average max. + 35 °C
- relative humidity up to 50% at 40°C, higher values are allowed for lower temperatures (90% at 20°C)
- surrounding air cannot be excessively contamined by dust, smoke, aggressive gasses and vapours with salts content.