Analyzing vibration of rotating blades

Apparatus for characterising the vibration of rotating blades, the apparatus including:

• a plurality of blades mounted for rotation on a rotor and extending radially outwardly therefrom;
• a casing at least partially surrounding the blades;
• a strain gauge mounted on one of the blades;
• at least one timing probe mounted on the casing for indicating the passage of each of the individual blades;
• means for analysing data from the strain gauge to provide information about the frequencies of vibration of the blade and the vibrationally induced stresses in that blade;
• means for analysing data from the at least one timing probe to obtain information about the amplitudes and/or velocities of vibration of each of the plurality of blades;
• and
• means for determining in the relationship between vibrationally induced stress as measured by the strain gauge and vibrational amplitude or velocity as measured by the at least one timing probe for the blade on which the strain gauge is mounted for a particular frequency of vibration;
• and assuming that the above relationship is applicable to each of the plurality of blades, calculating the vibrationally induced stress for each blade from its amplitude or velocity of vibration as measured by the at least one timing probe and said relationship.