Magnetic Bearing Controller (MBC 150/4-16, MBC 150/8-16) with THD 289 board and LEM sensors
The MBC 150/4-16 and MBC 150/8-16 are magnetic bearing controllers that support a magnetic compass, providing low‑friction, electronically controlled bearing operation with integrated THD 289 board and LEM sensors for precise heading information.
Inspector Detail
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Common issues
- Position sensor signal drift affecting rotor centering accuracy
- Power amplifier (THD board) card faults or overtemperature trips
- Backup/catcher bearing wear following touchdown events
- Control loop gain drift requiring re-tuning after long service periods
- Chafed or degraded sensor and power cabling in the machine space
- Cooling fan failure in the control cabinet leading to amplifier overtemperature
- Loss of communication between the controller and the plant DCS
Inspection checklist
- Backup/catcher bearing visual inspection, especially after any recorded touchdown
- Rotor position sensor gap readings compared against baseline commissioning values
- Power amplifier temperature trend and cabinet cooling fan operation
- Cable and connector condition, including LEM sensor wiring
- Controller alarm and event log review for repeated trips
- Backup power supply / UPS function test
- Correlation between AMB position signals and independent shaft vibration monitoring
Service intervals
| Backup/catcher bearing inspection | typically annually, and always after a recorded touchdown event |
| Position sensor calibration check | typically annual |
| Power amplifier cabinet filter/fan cleaning | typically every 6-12 months |
| Backup power supply/UPS battery check | typically annual |
Typical wear limits
| Backup/catcher bearing radial clearance | manufacturer-specified for this controller/bearing pairing - confirm the exact allowable clearance against SKF's documentation rather than assuming a generic figure |
| Position sensor air gap drift | monitor the trend against the commissioning baseline; a generic numeric tolerance is not meaningful without the specific sensor/rotor data |
Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.
Critical spares
- Position sensor set
- Power amplifier (THD) card
- Backup/catcher bearing set
- Control cabinet cooling fan
- Sensor and power cable harness
Safety
- Stored electrical energy in power amplifier capacitors, present even after the supply is isolated
- Rotor drop onto backup bearings if magnetic support is lost - the supported machine must not be run with a faulted or bypassed AMB control system
- High rotational speed hazard if backup bearings are worn beyond their allowable clearance
- Electrical hazards during work inside the controller cabinet
Class survey
This unit is an active magnetic bearing (AMB) controller/power amplifier supporting a rotating machine (the equipment record's 'Magnetic Compass' typing does not match the described function). Class surveys of the supported machine typically review AMB trip and alarm test records, backup power supply function, and the touchdown/catcher bearing event log rather than surveying the controller in isolation.
Components & Design
Component data being added…
Technical Data
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Common failures & inspection points
Service & Maintenance
Maintenance per manufacturer manual and classification society requirements. Annual inspection at class survey. Stock spare parts per manufacturer specification.
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