100 safe from surge as shown in block 845 the other essentially simultaneous operation involves continuing to increase the compressor 39 s rotational speed according to block 855 until the minimum operating speed n min or some predetermined value of speed is reached continuing to increase the compressor 39 s rotational speed is effected as explained with regard to block 810 the rotational speed set point used by the vfd controller 650 or the speed controller 720 is increased with time those of ordinary skill in this art are intimate with this aspect of startup control when the comparator block 840 determines the compressor 100 has reached its minimum operating speed the control system is shifted from its startup mode to its run mode as shown in block 860 at that point the capacity or performance control system takes over varying the compressor speed according to the needs of the process note that the minimum operating speed n min in comparator block 840 may be the compressor 39 s operating speed if the compressor 120 is to be operated at a constant speed an additional embodiment is shown in fig9 this embodiment is particularly useful for compressors 120 that may.