Product Introduction
The Bently Nevada 991-06-70-03-01 is a Probe Vibration Transmitter designed for critical axial thrust monitoring in rotating machinery. As a thrust transmitter, it converts proximity probe signals into a 4-20 mA current loop output, enabling continuous condition monitoring. When a fault condition occurs, the Bently Nevada 991-06-70-03-01 responds within 100 µs by driving the output below 3.6 mA, alerting control systems instantly and preventing cascade failures.
Technical Specifications
The Bently Nevada 991-06-70-03-01 offers a precise measurement range and robust environmental tolerance. Key parameters include:
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Output Signal: 4-20 mAdc over specified full-scale range in 2-wire configuration.
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Loop Accuracy: Within ±1.5% of full scale (typical) from TEST signal input to 250 Ω loop resistance.
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Linear Range: 0.25 to 1.65 mm for Prox Out, suitable for 0.6-0-0.6 mm or 25-0-25 mils current loop linear ranges.
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Power Supply: Requires +12 to +35 Vdc input at the transmitter terminal.
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Maximum Loop Resistance: 1,000 Ω including cable at 35 Vdc.
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Current Limiting: 23 mA typical.
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Environmental Limits: Operating temperature -35°C to +85°C; storage -51°C to +100°C. Weight 0.43 kg.
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Mounting: DIN rail with clip and screw option (03).
Industry Applications
The Bently Nevada 991-06-70-03-01 is engineered for axial thrust monitoring in turbines, compressors, and large pumps. In a steam turbine application, the transmitter continuously measures thrust bearing displacement. If abnormal thrust occurs, the Not OK/Signal Defeat feature forces the output below 3.6 mA within 100 µs, triggering an alarm before damage progresses. This rapid response directly addresses common failure modes in thrust bearings, such as wipe or overload.
Maintenance & Reliability
To maintain the reliability of the Bently Nevada 991-06-70-03-01, verify loop power between +12 and +35 Vdc at the transmitter terminals. Inspect connections for corrosion or loose wiring semiannually. The non-interacting zero and span adjustments allow field recalibration without disconnecting wiring. Because the transmitter outputs a fault signal within 100 µs of a Not OK condition, routine functional testing of the defeat circuit is recommended every 12 months to confirm timely alert generation.
Troubleshooting & Common Issues
If the output current stays below 3.6 mA during normal operation, check for a valid Not OK signal defeat condition or a loop power supply below +12 Vdc. For erratic readings, verify the 3300 NSv proximity probe and extension cable integrity. Output stuck at 4 mA with no variation suggests a failed sensor or open loop. The Bently Nevada 991-06-70-03-01 restores normal output within 0.1 seconds after the fault clears, so transient faults will self-reset. For persistent issues, measure loop resistance; if it exceeds 1,000 Ω, reduce cable length or increase supply voltage.