The balancing application in Test.Lab runs in conjunction with Test.Lab Signature Acquisition.
Open the application in Signature Acquisition: go to “Tools --> User Applications --> Balancing”.
The balancing application in Signature consists of four tabs.
To do balancing in a single plane, you will need a tachometer, an accelerometer, a SCADAS data acquisition system (SCADAS XS shown below) and a PC with the LMS Test.Lab Balancing software loaded (Figure 3).
VERY IMPORTANT: The signal from the tachometer needs to be split. Insert one end of the split signal into a tachometer channel and insert the other end into a dynamic channel (see below). One split of the tachometer is used for measuring the rpm, the other split is used for phase referencing.
The accelerometer should be in or near the balancing plane. The balancing plane is where the correction mass is added; typically it is near where two components meet, like a coupler, the end of a shaft, or a bearing. In Figure 3 above, the balancing plane is labeled “Single plane” and the accelerometer is placed on the bearing.
For single plane balancing, the Channel Setup workbook should look something like the following:
NOTE: The tachometer is split and goes into two different channels: one in the Vibration group and one in the Tacho group.
A: What speed to perform the balancing operation at?
Do a system run-up. Measure the system in all three directions (which can be done at once with a triaxial accelerometer).
Cut the first order of the accelerometer in the +X, +Y, and +Z directions. Choose which direction to balance the system. Find the RPM at which the system has a peak in unbalance.
Here, it appears that at 2900 RPM, the system has a peak in unbalance in the +Z direction. Typically, balancing is performed near the RPM value corresponding to the peak in amplitude. Therefore the balancing operation will be performed at 2900 RPM in the +Z direction.
NOTE: Do not balance at a structural resonance! Look at a waterfall of the run-up to ensure you are not balancing at structural resonance.
B: Fill in the values in the “Measurement setup” tab of the balancing application
B.1: First column of balancing settings
1. Select the “Single plane” radio button.
2. Fill in the balancing speed (as determined in the previous section), RPM tolerance, and number of averages to be performed for the FFT.
3. For “Tacho channel” choose the tacho channel that you fed into the tachometer of the SCADAS.
For “Phase reference” choose the tacho channel that you fed into the dynamic channel of the SCADAS.
4. Set your bandwidth and block size (these will be extracted from the Acquisition Setup workbook if you prefer to set the values there).
5. Select an ISO defined balance target or define your own parameters. For this example, the vales are left at zero meaning we will target zero unbalance.
6. Define the “Sense of rotation”.
Choose which end to view your object from. Determine which direction it is spinning in that view. This will be the “Sense of rotation”.
The direction the shaft spins is relative to where the user is standing. It is KEY that the user remembers how he views the object.
NOTE: Angles are counted positive in the sense of rotation.
7. Select to leave the test mass on during the balancing procedure or to take it off. If you leave the test mass on during the balancing procedure, the final correction mass will take the test mass into account.
8. Choose which calculation method to use:
B.2: The second column of balancing settings
1. Select the dynamic channel with which you would like to do the balancing procedure. In this case, the unbalance is the worst in the Z direction, so the Accel:+Z channel is selected.
2. Plane radius: the radius of the shaft on which the plane is mounted. This is not critical and is used for graphical representation only (see Figure 10).
3. Test mass radius: the radius at which the test mass will be installed (see Figure 10).
4. Weight splitting allows the user to define the number of correction masses being used for balancing. If weight splitting is unchecked, the software will calculate the values for only one correction mass.
5. Select to place the weight(s) at any location on the plane or at fixed locations (which are defined by using count and offset).
EXAMPLE: Imagine you are balancing a fan and you can only place weights on the blades (Figure 11). If the fan is spinning clockwise, the count would be 5 and the offset would be 54°. If the can was spinning counter clockwise, the count would be 5 and the offset would be 18°.
NOTE: Zero degrees is where the reflective tape is located on the shaft.
6. Select to use any weight or enter predefined weights.
7. Finally, press the “Apply” button, this will transfer the settings of the balancing application to Signature Acquisition and switch the application to the “Balancing” tab.
Within the single plane balancing tab, there are six steps. The active step will be highlighted in green. To move forward / backward in the balancing procedure, use the “Previous step” and “Next step” buttons at the bottom of the screen (Figure 12).
1. Initial measurement: Arm the system (click Arm button in lower right corner). Then, bring the system to the balancing speed and hold it at that speed. Finally, click “Start” which will begin the acquisition. If taking more than one run, the runs will be averaged.
2. Add the test mass. Specify the weight of the mass to be added and the location where the mass will be added in the balancing plane. Remember, angles are counted positive in the sense of rotation.
3. Perform measurements with the first test mass. If taking more than one run, the runs will be averaged.
4. Calculated balanced masses: The calculated recommended mass and angle will be displayed. The “Used mass” column suggests a mass that you input in the “Available masses” section of the “Measurement setup” tab. The “Used angle” suggests an angle available as specified in the “Measurement setup” tab.
5. If you selected “Leave test mass on” in the “Measurement setup” tab, leave the test mass on and add the additional mass at the specified angle.
If you selected “Remove test mass”, remove the test mass and then add the additional mass at the specified angle.
6. Once the mass is added at the specified angle, acquire a few runs to verify the results. Ensure that the resulting unbalance amplitude is smaller than it originally was.
Looking at the first order of the Z direction (which is the direction we were balancing in), you can see there is a sharp decrease in the amplitude at all RPM values due to balancing the shaft.
LMS Test.Lab Acquisition Tips