The modified logging tool with 3arm caliper responds to changes of hole inner diameter by serial potentiometers.On the basis of a mathematics model of this system,simulated are changes of downhole and the varying decentrations by computer programs.Analyses show that caliper measured is less than or equal to the actual value of the well.This measuring method causes negative system(error),which is interrelated with the decentration of 4209XA.Based on analysed result,proposed is a method for reducing the error.The proposed method is able to acquire three caliper signals simulta-(neously.)
