These versions are primarily used as speed controllers.This is beneficial for upstream control applications or when the devices are combined with control modules from the ZIEHL-ABEGG UNIcon product family. Alternatively, speeds can be pre-set. They can also be set to second stage operation with external switchover, or implemented via an external potentiometer.The Dcontrol voltage controllers also provide an option to control based on temperature or pressure (for example, refrigerant pressure in cooling equipment).