Comparative horizontal and vertical phase readings usually differ either by O Largest vibration occurs at 1 X RPM of eccentric component in a direction thru cenler1ines of the two rotors. Thus, correction weights will most always have to be placed in 2 planes to counteract both forc e and couple unbalance.Įccentricity occurs when center of rotation is offset from geometric centerline of a pulley, gear, bearing, motor armature, etc. Overhung rotors have both force and c ouple unbalance, each of which will likely require correction. However, the horizontal phase differences will usually match the vertic a! phase differences on the unbalanced rotor (± 30"). Axial readings tend to be in-phase whereas radial phase reading s might be unsteady. Overhung Rotor Unbalance causes high 1 X RPM in both Axial and Radial direclions. Secondarily, rt unbalance predominates, roughly a 90° phase difference usually results between the horizontal and vertical readings on each bearing (± 40"). However, the horizontal phase difference should closely match the vertical phase difference, when comparing outboard and inboard bearing measurements (z 30"). Here, the radial phase diHerence between outboard and inboard bearings can range anywhere from 0° to 180°. 1X RPM dominates the spectrum, and truly requires 2 plane correction. a 900 difference between the horizontal & vertical phase readings on each bearing usually OccurS (± 30j Dynamic Unbalance is the dominant type of unbalance found and is a comb ination of both force and coup le unbalance. 180° phase difference should exist between 08 & 18 hOrizontals, as well as between 08 & IB verticals. Correction requires placement of balance weights in at least 2 planes. May cause high axial vibration as well as radial. vertical readings usually occurs on each bearing of unbalanced rotor (~_3_0_")~'_ _ _ _ _ _ _ _ _ _ _ _Ĭouple Unbalance results in 18()Q out-ot-phase motion on same shatto lX RPM always present and normally dominates spectrum_ Amplitude varies with square of increasing speed below first rotor critical speed. 90a phase d ifference between horizontal &. phase difference should exist between 08 & 18 horizontals, as well as between 08 & 18 verticals. Can be corrected by placement of only one balance correction weight in one plane at Rotor conter of gravity (CG). 1 X RPM always present and normally dominates spectrum. Amplitude due to unbalance will increase by the square of speed below first rotor critical (8 3X speed increase = 9X higher vibration). REMARKS Force Unbalance will be in-phase and steady. TABLE I ILLUSTRATED VIBRATION DIAGNOSTIC CHART TYPICAL SPECTRUM