Commercial balancing machines are designed to handle the situation through appropriately selected measurement transducers.  The alternative, to spin the rotor at 1500 RPM, might require a vacuum spin pit (to reduce windage losses) and a significantly larger motor and related accessories.  Rotor dynamics might also be a factor, for example the rotor at 1500 RPM may have passed through one of more flexural modes, whereas at 250 RPM it likely would be have exhibited a rigid body behavior.

You should check the specific specifications of your balancing machine and make sure it can properly handle the rotor parameters.  These will include rotor weight, operating RPM, and desired level of balance.  You might also consider purchasing ISO - ISO 21940-1:2019 - Mechanical vibration — Rotor balancing — Part 1: Introduction or one of the other parts (there might be as many as 16) of the specification.

Afaik, you calculate the residual unbalance at operating speed g-mm or oz-inch etc, the balancing machine must be able to read this balance requirement (sensitive enough) at their operating range (low speed or actual speed).... Does that makes sense?

ISO 21940-11 (and 12) deal with low speed balance of rotors with 'rigid behaviour.'

The calculation of imbalance for declared running speed is covered in ISO 21940-11. The basics are that permissible imbalance multiplied by running speed frequency in rad/sec divided by rotor mass is the balance grade G, when done in consistent units to obtain mm/s for G. Divide the balance grade by the running speed (rad/sec) and muiltiply by the mass of the rotor to obtain the permissible imbalance. (Imbalance is in units of mass-length)

Divide the residual imbalances (think 2-planes) by the rad/sec, and you see if you meet your required balance grade.

@Registered Member posted:

The calculation of imbalance for declared running speed is covered in ISO 21940-11. The basics are that permissible imbalance multiplied by running speed frequency in rad/sec divided by rotor mass is the balance grade G, when done in consistent units to obtain mm/s for G. Divide the balance grade by the running speed (rad/sec) and muiltiply by the mass of the rotor to obtain the permissible imbalance. (Imbalance is in units of mass-length)

Divide the residual imbalances (think 2-planes) by the rad/sec, and you see if you meet your required balance grade.

Bill, I've often wondered why ISO specifications use radians/second (rad/s) as opposed to RPM?  Why introduce a needed calculation (subject to error) when the RPM is known?  I know you have served on many of the committees.  Can you clarify why rad/s is used as opposed to RPM?

John,

9.55 (60/(2pi) )--you find this conversion needed on many vibration certification tests, also. This has been useful for many years.

@Registered Member posted:

John,

9.55 (60/(2pi) )--you find this conversion needed on many vibration certification tests, also. This has been useful for many years.

Bill, you really didn't address my question and I hope you know me well enough to know that I'm capable of making the conversion, in spite of being almost 80 years old.  So why does the specification use radians/sec as opposed to just using RPM?

rad/sec is consistent units. What else would one use? The standard could add conversion formulae; that might be helpful, particularly for some.

I do not know when the next update is, but it should be possible to comment on the standard. Let me know, I can possibly help with a contact if you want to comment.

Radius-1200mm
Actual operating speed -960mm
weight of the job -1500kg
Grade -6.3
Residual unbalance-94018.62gram mm
Tolerance per place -39.174gram

actual we done shop floor dynamic balancing 250 RPM final reading 6.3 gram left plane / 8.6 Gram right plane

client asking tolerance collected by operating speed  on site how it match the low speed balancing,for my understand kindly pls help technically.

As I read, your customer asked you to verify the balance measurement at speed. This would not be technically proper.

One of the old ISO 1940 (as I recall) had some comments regarding this. Measuring at speed (often) will not produce a valid measure of a low speed balance, particularly insitu if this were to be the case.

@Registered Member posted:

As I read, your customer asked you to verify the balance measurement at speed. This would not be technically proper.

One of the old ISO 1940 (as I recall) had some comments regarding this. Measuring at speed (often) will not produce a valid measure of a low speed balance, particularly insitu if this were to be the case.

Then low speed balancing and high speed variation ?

For a low speed balance, i.e., a rotor with rigid behavior, I do not understand high speed variation. The rotor is balanced as a rigid body. High speed (if meaning similar to that in ISO 1925 for high speed balancing) does not apply.