In our Captive power plant Frame-5 Machine Velocity sensor of Matrix 5485C installed in Turbine Compartment, Load Gear and generator compartment. In Turbine Compartment One vibration sometimes showing erratic value and cross the alarm point 12.7mm. At the same time rest reading are constant value at below 2 mm/sec. We have tighten the probe and not solved. Please suggest where we have to checked.