# VCI MAX Data Collector for Crusher Roll

QUESTION
Does anyone use the VCI MAX Data Collector. I need help with the balancing software. Specifically, in a two plane balance:

1. The software asks for trial weight in two planes. Can I put a weight in one plane and take data, then w/o putting weight in a second plane collect data and enter the weight as 0. Or do I need to put a trial weight in two seperate planes?
2. Does the software work with negative weights. Recently we attempted to balance a crusher that had a significant amount of weights already installed. Rather than adding weight can we subtract it.
3. How do I know whether to select the high spot or the low spot? What exactly doestthe term high spot or low spot mean?

REPLIES

spciesla
I’m not familiar with this data collector, but I’ll try to answer the fundamentals of your questions.

1. You need to put trial weights in two separate planes. A 0 weight does nothing for you. The colletor may be able to handle leaving the 1st trial weight in place (plane 1). This can be preferable for time considerations or if the 1st trial weight reduces the vibration amplitudes. The number of balance planes needed depends on the physical characteristics of your rotor (mass, stiffness, length, etc.) and operating speed. You should know where the rotor is operating (which mode) before you start balancing. What kind of equipment are you trying to balance? What are the operating speed(s)?

2. I’m not sure. If it won’t take a negative for the weight value, just change the weight location by 180 degrees (i.e. -5 ounces @ 45 degrees = 5 ounces @ 225 degrees).

3. I’m not sure what the software is exactly asking. The high spot corresponds to the positon on the rotating memeber represented by the 1X phase angle. If your rotor is operating at a speed well below the 1st balance resonance (critical speed), then the high spot (measured in displacement) should be equal/close to the heavy spot. If you use velocity or acceleration, the relationships between the high/heavy spots changes.

When dealing with phase lag (fairly normal convention for vibration measurements) the following relationships hold:

• Phase(displacement) = Phase(velocity) + 90 deg = Phase (acceleration) +180 deg
• Well below the 1st balance resonance (critical speed), the displacement phase (high spot) is “equal” to the phase of the heavy spot. Using the equation above, the velocity phase is 90 degrees out and the acceleration phase is 180 degrees out.
• An excellent reference is:
Machinery Malfunction Diagnosis and Correction by Robert C. Eisenmann (ISBN: 0132409461)
https://www.amazon.com/Machinery-Malfunction-Diagnosis-Correction-Eisenmann/dp/1941872336

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