The Bently Nevada 991-01-XX-01-00 (MOD 284318-01) is a two-wire, loop-powered Thrust Transmitter designed for OEMs of centrifugal air compressors, small pumps, motors, and fans. It accepts input from a 3300 NSv proximity probe and converts axial shaft displacement into a standard 4–20 mA signal proportional to thrust position.
Item No :
991-01-XX-01-00 (MOD 284318-01)Order(MOQ) :
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EXWProduct Origin :
USAShipping Port :
WuhanLead Time :
3-5daysWeight :
3kg| Specification | Description |
|---|---|
| Manufacturer | Bently Nevada (Baker Hughes) |
| Model | 991-01-XX-01-00 |
| Modification | MOD 284318-01 |
| Product Type | Thrust Transmitter (2-wire, loop-powered) |
| Input | Accepts one non-contacting 3300 NSv Proximity Probe and extension cable |
| Power Supply | +12 to +35 Vdc at transmitter terminals |
| Signal Output | 4 to 20 mAdc over specified full-scale range (2-wire configuration) |
| Loop Accuracy | Within ±1.5% of full-scale range |
| Maximum Loop Resistance | 1,000 Ω including cable at 35 Vdc |
| Current Limiting | 23 mA typical |
| Linear Range (Prox Out) | 0.25 to 1.65 mm (10 to 65 mils) |
| Prox Out Scale Factor | 7.87 mV/µm (200 mV/mil) ± 6.5% typical |
| Output Impedance (Prox Out) | 10 kΩ calibrated for 10 MΩ load |
| Frequency Response | 10 Hz to 1 kHz |
| Operating Temperature | -35°C to +85°C (-31°F to +185°F) |
| Storage Temperature | -51°C to +100°C (-60°F to +212°F) |
| Humidity | Up to 100% condensing (potted construction) |
| Mounting | 35 mm DIN-rail clips or bulkhead screws |
| Dimensions | Approx. 10 × 7.3 × 6 cm |
| Weight | Approx. 0.43–0.46 kg |
| Country of Origin | USA |
| Lifecycle Status | Active / Mature |
Part Number Breakdown (991-AXX-BXX-CXX-DXX):
991 – Thrust Transmitter Series
01 – Full-scale option: 0.6-0-0.6 mm (25-0-25 mils)
XX – System length: 5.0 m or 7.0 m
01 – Mounting: 35 mm DIN-rail clips
00 – Agency approval: Not required (00 = none; 05 = CSA/ATEX/maritime)
Modification Note: The MOD 284318-01 designation indicates an OEM-customized configuration of the standard 991 transmitter.
| Model | Description | Typical Application |
|---|---|---|
| 991-01-XX-01-00 (MOD 284318-01) (this model) | Thrust Transmitter, 25-0-25 mils, DIN-rail, no approvals | Standard OEM thrust monitoring |
| 991-01-XX-01-05 (MOD 284318-01) | Same configuration with CSA/ATEX hazardous area approvals | Hazardous area installations |
| 991-01-XX-01-00 (MOD 288865-01) | Alternate OEM modification of the 991 | Different OEM-specific configuration |
| 990 Vibration Transmitter | Companion vibration (not thrust) transmitter | Radial vibration monitoring for same machinery |
| 3300 NSv Proximity Probe | Required input sensor for the 991 | Shaft displacement measurement |
| 122115-01 Test Adapter | Signal isolation adapter for PROX OUT diagnostics | Required when using grounded, AC-powered test equipment |
| 02173006 | Bulk cable for 4–20 mA loop wiring | Field wiring for transmitter loop |
Q1: What is the primary function of the 991-01-XX-01-00?
It is a thrust transmitter that measures axial shaft displacement (thrust position) on small, non-critical machinery and converts it into a standard 4–20 mA signal for input to a PLC or DCS. It is specifically designed for OEMs of centrifugal air compressors with fluid-film thrust bearings.
Q2: What input sensor does the 991 require?
It accepts one 3300 NSv proximity probe and its matching extension cable. The NSv (narrow side view) design allows installation in tight spaces with minimal clearance, typical of centrifugal air compressors.
Q3: What is the difference between the 4–20 mA output and the PROX OUT?
The 4–20 mA loop signal is the primary process control output, proportional to thrust position. The PROX OUT (BNC coaxial connector) provides a non-isolated dynamic signal for machinery diagnostics. Important: When using grounded, AC-powered test equipment, the 122115-01 Test Adapter must be used to isolate and invert the PROX OUT signal—failure to do so can inject AC noise into the loop and cause false trips.
Q4: What does the "MOD 284318-01" designation mean?
It indicates an OEM-customized configuration of the standard 991 Thrust Transmitter. Bently Nevada offers several OEM-specific modifications (288865-01, 284318-01, etc.) tailored to different compressor manufacturers' requirements. These modifications may involve calibration curves, connector types, or firmware revisions.
Q5: What are the limitations compared to a full 3500 monitoring system?
The 991 is a transmitter, not a full monitor. It provides 4–20 mA trending and peak alarming but cannot perform gap alarms, phase measurement, Timed OK channel defeat, Danger Bypass, or Trip Multiply. PLCs connected to the 991 are not suitable for plant-wide diagnostic systems like System 1 or RulePaks.
The Bently Nevada 330105-02-12-05-02-00 is an 8 mm reverse-mount proximity probe from the 3300 XL series, engineered for non-contact vibration and position monitoring in space-constrained machinery.
The Bently Nevada 330130-085-00-00 is an 8.5-meter standard extension cable for the 3300 XL 8 mm Proximity Transducer System. It connects a 3300 XL proximity probe to its Proximitor® sensor, transmitting eddy-current displacement signals for vibration, axial position, and Keyphasor measurements on critical rotating machinery.
The Bently Nevada 21000-00-00-15-030-04-00 is a Proximity Probe Housing Assembly from the 21000 series, designed to provide a secure, environmentally sealed mounting interface for reverse-mount proximity probes on critical rotating machinery.
The Bently Nevada 330780-50-00 is a 5.0-meter Proximitor® Sensor for the 3300 XL 11 mm Proximity Transducer System. It receives signals from a 3300 XL 11 mm probe and its extension cable, conditioning them into a linear voltage output proportional to shaft displacement for radial vibration, axial thrust position, and Keyphasor measurement.
The Bently Nevada 21747-040-00 is a 4-meter Proximitor probe extension cable designed for the 3300 and 7200 Series Proximity Transducer Systems. It connects a proximity probe to its Proximitor sensor, transmitting high-frequency eddy-current displacement signals for vibration and shaft position monitoring on critical rotating machinery.
The Bently Nevada 330710-00-060-10-02-00 is a 3300 XL 11 mm Proximity Probe designed for non-contact vibration and position measurement on large, fluid-film bearing machinery. Its 11 mm tip provides a longer linear range compared to the standard 8 mm system, making it ideal for applications requiring greater measurement span, such as axial thrust position, differential expansion, and radial vibration on steam turbines, centrifugal compressors, and large pumps.
The Bently Nevada 330103-00-11-50-02-00 is a 3300 XL 8 mm proximity probe with a metric M10×1 thread and a 5.0-meter integral cable terminated with a miniature coaxial ClickLoc™ connector. This extended-reach configuration features a 110 mm overall case length and connects directly to a Proximitor® sensor without requiring an extension cable for short-run installations.
The Bently Nevada 990-10-XX-01-00 (MOD 165353-01) is a two-wire, loop-powered Vibration Transmitter designed for OEMs of centrifugal air compressors, small pumps, motors, and fans. It accepts input from a 3300 NSv proximity probe and its matching extension cable, conditioning the signal into a 4–20 mA output proportional to peak-to-peak vibration amplitude.
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