Application Scenarios
In a centrifugal air compressor package used in a petrochemical plant, the OEM needed a simple, reliable way to feed axial thrust position data into the unit’s PLC-based control system without adding a full rack-based monitoring system. The 991-01-XX-01-00 was specified for each compressor stage because its integrated Proximitor sensor eliminates the need for a separate external transducer driver, reducing panel space and wiring complexity.
The key pain point it addressed was the OEM’s requirement for a standard 4–20 mA interface that could be wired directly into their existing control cabinet. Unlike traditional 3300-series monitoring systems that output raw voltage signals requiring additional conditioning cards, the 991-01-XX-01-00 delivers an industry-standard current loop signal that the PLC’s analog input card reads directly. This simplification cut commissioning time per compressor unit and reduced the spare parts inventory the plant needed to maintain.
3. Parameter
| Parameter | Value / Description |
|---|---|
| Product Model | 991-01-XX-01-00 |
| Manufacturer | Bently Nevada |
| Product Category | Thrust Transmitter (Axial Position) |
| Input | One 3300 NSv Proximity Probe with extension cable |
| Power Supply | +12 to +35 Vdc at transmitter terminal |
| Output Signal | 4–20 mA, 2-wire current loop |
| Loop Accuracy | ±1.5% over full-scale range |
| Maximum Loop Resistance | 1,000 Ω including cable at 35 Vdc |
| Linear Range | 0.6–0–0.6 mm (25–0–25 mils) for current loop |
| Operating Temperature | -35°C to +85°C |
| Mounting | 35 mm DIN-rail clips or bulkhead screws |
| Weight | 0.43 kg (transmitter only) |
4. Technical Principles and Innovative Values
- Integrated Proximitor Architecture: The 991-01-XX-01-00 embeds the Proximitor sensor function directly into the transmitter housing, eliminating the external transducer driver that traditional 3300-series systems require. This consolidation reduces the number of interconnections between probe and control system, which is a common source of signal degradation and wiring faults.
- Not OK / Signal Defeat Circuit: When the proximity probe fails, the cable disconnects, or a loose connection develops, the 991-01-XX-01-00 drives its output below 3.6 mA within 100 microseconds. This failsafe behavior prevents the control system from interpreting an open circuit as a valid high-thrust reading and triggering a false alarm or unnecessary trip.
- Non-Interacting Zero and Span Adjustments: Field calibration of the 991-01-XX-01-00 uses external potentiometers accessed under the transmitter label. Adjusting zero does not shift span, and adjusting span does not shift zero, which shortens the calibration procedure during commissioning.
- Test Input Pin for Loop Verification: A dedicated test input pin on the 991-01-XX-01-00 allows technicians to inject a variable DC voltage and confirm the entire 4–20 mA loop responds correctly, without physically moving the machine shaft or disconnecting the probe.
- Potted Construction for Harsh Environments: The 991-01-XX-01-00 is potted to withstand 100% condensing humidity and operates across -35°C to +85°C, making it suitable for compressor rooms and outdoor installations where temperature swings and moisture are routine.
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