Balancing

CoCo-80 field balancing function guides the user through the steps to balance a machine in normal operation with the rotor mounted in the bearings. Large machines, such as steam turbines, electric motors, and generator armatures, often require field balancing between major overhauls. Correction of unbalance situations involves characterizing the heavy spot in one or two planes of the rotor, depending on its length and stiffness. A heavy spot is the radial location at which excessive radial mass distribution exists. This heavy spot is always a location that is opposite the location where weight needs to be added. Unfortunately, unless previous balancing information is available, the location of the heavy spot cannot be identified directly. In this case, you use the Influence Coefficient method for calculation of correction weights as many field balancing solutions do.

Accelerometers are mounted on the bearings and used to acquire vibration signals. The tachometer signal is used to calculate the rotating speed and synchronize the vibration signals the angular rotation of the rotor.

Balancing Diagram

The influence coefficient is used to describe how the rotor system responds to the unbalanced weight changes. A trial weight is added to the rotor to produce a change in vibration amplitude and/or phase. The influence of unbalance caused by the known mass and location of the trial weight, or the influence coefficient, can then be calculated. A single-plane balance procedure will produce one balance response coefficient of mass and location. Multiple-plane balancing will produce a number of coefficients depending upon the number of balance planes. Since the initial vibration can be viewed as the response of the rotor to the initial mass unbalance, you can calculate the initial mass unbalance with the initial vibration and the influence coefficients. This allows the system to calculate a solution weight and location for each plane. Precision balancing often requires a second balancing run after the first has been completed.

Balancing Procedure


Measure Unbalanced Vectors for both Planes


Estimate the Trial Weight


Apply the Trial Weight


Summary of the Complete Process