On the display
The OptiView panel shows MBC - ROTOR ELONGATION. This exact wording is the only variant of the message on this model, and it belongs to the Safety Shutdown messages of the control center.
What it means
This Safety Shutdown is set when the MBC has calculated that the algebraic difference between the displacement at the shaft impeller end axial position sensor and the displacement at the shaft opposite-impeller end axial position sensor is greater than the allowed limit. The manuals print the limit itself in two versions, listed under the limits below. While the shutdown is active, the MBC ESD Fault contacts open — one manual prints them as the MBC Fault contacts — and the MBC remains in Levitation mode with the motor shaft levitated. The MBC stays levitated until it is commanded to de-levitate over serial comms or, as one manual adds, until the VSD DC buss power depletes.
Why it appears
- The algebraic difference between the displacements at the shaft impeller end axial position sensor and the shaft opposite-impeller end axial position sensor is greater than the trip limit — the interpolated limit in one manual, 700 µm in the other. This is the only cause the manuals name for this shutdown.
Setpoints and thresholds
- Trip limit (interpolated version): the shutdown sets when the difference is greater than the value calculated by linear interpolation between 300 µm at 436 Hz and 350 µm at zero Hz.
- Trip limit (fixed version printed in the other manual): a difference greater than 700 µm.
- Release threshold: the shutdown is released when the difference in displacements no longer exceeds these same values.
Reset and restart
The release comes from the measured condition, not from a button: the shutdown is released when the difference in displacements no longer exceeds the limit. Once the condition has released, the restart sequence is:
- Allow the condition to release — the difference in displacements no longer exceeds the limit.
- Press the CLEAR FAULTS button on the OptiView panel.
- Start the chiller.
As the manual words it: The chiller can be started when the condition is released and the OptiView panel CLEAR FAULTS button is pressed.
Questions engineers ask
What does MBC - ROTOR ELONGATION mean on a YORK YMC2?
It is a Safety Shutdown: the MBC has calculated that the algebraic difference between the displacements at the shaft impeller end and the shaft opposite-impeller end axial position sensors is greater than the limit. The MBC ESD Fault contacts open and the shaft stays levitated.
What is the trip limit for rotor elongation on the YMC2?
The manuals print two limits: one gives a linear interpolation between 300 µm at 436 Hz and 350 µm at zero Hz, the other a fixed 700 µm.
How do I reset MBC - ROTOR ELONGATION?
The shutdown releases itself when the difference in displacements no longer exceeds the limit. Then press the CLEAR FAULTS button on the OptiView panel and the chiller can be started.
Why is the motor shaft still levitated after the shutdown?
The MBC remains in Levitation mode until it is commanded to de-levitate over serial comms or, as one manual states, until the VSD DC buss power depletes.
Messages next to this one
Source
Written from the manufacturer's manuals for the YORK YMC2; every number and designation on this page is checked against them before publication. The row of the manual this message comes from:
All YORK YMC2 messages: fault codes · YORK YMC2 documentation · YORK manuals