Does the instrument give magnitude and phase or only magnitude.
Does the instrument have magnitude at rotor speed filter.
Will you be able to take data during rotor coast down.
Also a basic model of the unit being balanced.
Try google search "rotor balancing four-run method". It only gives 30 hits, none of them details the procedure, but they give books and software for sale that will do the four-run method of balancing when only vibration severity can be measured.
If you don't want to splash the dosh, then intelligent trial and error might take a bit more than 4 runs, but to be honest unless you are pretty sure of the answer anyway then the 4 run method takes more than 4 runs. That is, with a truly unknown system you have to mess about to get an appropriate trial mass size.
If you have phase information then life is a lot simpler.
If you are able to measure phase, and have a mux type connector, this can be accomplished by relocating cables on the mux and simply moving the sensor from one plane to the other and manualy entering data at those reference points, be sure and relocate the sensor as close as possible to the original position, a half inch off the mark can result in angle chasing for trim balancing.
