of the rotor will be subject to maximum temperature variation while the 34 cold 34 end will be subjected to a lesser amount causing the rotor to become distorted like an inverted dish called rotor 34 turndown 34 movable sector plates that automatically adjust the sector plates at the 34 hot 34 end of the rotor have been disclosed in my u s pat no 4 124 063 and in the u s pat no 4 122 891 of roderick j baker in both of these patents the sector plate is forced to closely conform to known rotor 34 turndown 34 to minimize fluid leakage in practice a sensor rod carried by the rotor housing is adapted to extend axially into contact with the end edge of the rotor the sensor rod is adapted to follow any variation in the rotor turndown but a rapid temperature change frequently results in rapid turndown more rapid and extensive than the sensor rod can follow when conditions change rapidly the end edges of the rotor including the sealing means frequently interfere with the remote end of the sensor rod causing breakage of interfering parts and a loss of sealing effectiveness this invention is therefore directed to an arrangement by which a sensor rod that extends axially into contact with an end edge of a rotor may be quickly.