Application Scenarios
In a centrifugal air compressor, axial thrust position must be continuously monitored to prevent rotor-to-stator contact that could cause catastrophic damage. The 991-01-XX-01-01 proximity probe installs through the bearing housing with minimal clearance, targeting the thrust collar to measure axial displacement. When paired with the 991 Thrust Transmitter, this probe system provides a 4-20 mA signal representing rotor position, enabling the control system to alarm or trip if thrust movement exceeds safe limits. The probe’s compact design addresses a critical constraint in OEM compressor packages where traditional larger probes cannot fit, while its stainless steel construction withstands the vibration and temperature extremes present in rotating machinery.
Parameter
| Parameter | Value/Description |
|---|---|
| Product Model | 991-01-XX-01-01 |
| Manufacturer | Bently Nevada |
| Product Category | Proximitor Sensor / Proximity Probe |
| Compatible Transmitters | 991 Thrust Transmitter, 990 Vibration Transmitter |
| System Type | 3300 NSv proximity probe system |
| System Length (XX) | 5.0 m, 7.0 m, or other specified lengths |
| Mounting Option (01) | 35 mm DIN rail clips |
| Approval Option (01) | Multiple approvals |
| Cable Option (A) | Without stainless steel armor, with connector protector |
| Probe Tip Diameter | 5.26 mm (0.207 in) maximum |
| Linear Range | 0.25 to 1.65 mm (10 to 65 mils) for Prox Out |
| Incremental Scale Factor | 7.87 mV/µm (200 mV/mil) ± 6.5% |
| Target Material | AISI 4140 steel (standard) |
| Operating Temperature | Depends on probe and cable configuration |
| Environmental Protection | Potted construction for high humidity (up to 100% condensing) |
Technical Principles and Innovative Values
Innovation Point 1: Integrated Proximitor Design Eliminates External Hardware. The 991-01-XX-01-01 incorporates the Proximitor signal conditioning function within the transmitter housing rather than requiring a separate external module. This integration reduces installation complexity, saves panel space, and eliminates a common failure point in traditional probe systems where interconnect cabling and connectors are vulnerable to damage.
Innovation Point 2: Compatibility with 3300 NSv Probe Technology. The 991-01-XX-01-01 is part of the 3300 NSv probe family, which features a narrower probe tip (5.26 mm maximum) than standard 3300 XL probes. This reduced form factor enables installation in small areas with minimal clearance, making it ideal for OEM centrifugal compressors where space around the bearing housing is severely constrained.
Innovation Point 3: Connector Protector for Environmental Protection. The cable option “A” in the 991-01-XX-01-01 model number indicates the probe includes a connector protector with FEP-covered stainless steel armor. This feature provides additional protection for the connector in humid or moist environments, preventing moisture ingress that could degrade signal quality or cause intermittent faults.
Innovation Point 4: Not OK/Signal Defeat Circuit Prevents False Alarms. When the 991-01-XX-01-01 probe detects a fault condition such as an open circuit or loose connection, the associated transmitter’s output is driven below 3.6 mA within 100 microseconds. This “signal defeat” behavior allows the control system to distinguish between a genuine machinery fault and sensor failure, preventing unnecessary trips while maintaining protection integrity.