Bently Nevada 3300/45 Dual Differential Expansion Monitor

The Bently Nevada 3300/45 Dual-Channel Differential Expansion Monitor is a dual-channel monitor designed for the legacy Bently Nevada 3300 Monitoring System.
It is specifically engineered to measure Differential Expansion, defined as the relative axial movement between the turbine shaft and the casing.

This parameter is critical for large steam turbines during startup and shutdown, where thermal expansion rates differ between rotating and stationary components. Accurate monitoring helps prevent rotor-to-casing contact, mechanical stress, and potential turbine damage.

Technical Specifications

1. Input & Signal Processing

Transducer Input
Accepts signals from non-contacting proximity probes, including:

• 8 mm Proximitor System

• 11 mm Proximitor System

• 25 mm Proximitor System

• 50 mm Proximitor System

Measurement Modes

The monitor supports multiple configuration methods depending on the mechanical design:

Standard Single Composite

• Uses one probe to measure a tapered collar or ramp surface

• Common in compact turbine designs

Dual Complementary

• Uses two probes to increase measurement linearity

• Provides redundancy for critical protection systems

Accuracy

• ±0.33% of full-scale (typical)

• Reference temperature:
  +25°C (+77°F)

2. Outputs

Recorder Outputs

User-programmable signal formats:

• +4 to +20 mA

• 0 to -10 Vdc

• +1 to +5 Vdc

Buffered Outputs

• Front panel: Coaxial connectors

• Rear panel: Terminal block connections

• One output per channel

Output Impedance

• 100 Ω

3. Alarms & Display

Display

• Dual vertical bargraph LCD indicators

• Real-time differential expansion visualization

Alarm Setpoints

Bi-directional alarm configuration:

• Alert Alarm

• Danger Alarm

• Digitally adjustable thresholds

OK Indicator

The OK LED monitors the health status of:

• Monitor electronics

• Connected transducers

• Field wiring integrity

Ordering Information

Order Format

3300/45-AXX-BXX-CXX-DXX-EXX

A — Full-Scale Range Option

B — Transducer Input Option

C — Alarm Relay Option

D — Agency Approval Option

E — Safety Barrier Option

Engineering & Installation Guide

Tapered Collar Configuration

When a single probe is installed on a tapered collar:

• The collar angle must be accurately configured in the monitor

• This ensures correct linear conversion from displacement to expansion

Incorrect angle configuration will directly affect measurement accuracy.

Cold vs. Hot Zero Reference

Differential expansion monitoring follows a standard baseline method:

Cold condition:

• The system is zeroed during machine startup

• Shaft and casing temperatures are stable

Hot condition:

• The monitor tracks expansion as thermal growth occurs

• Real-time displacement is calculated relative to the cold reference

This method is standard practice for steam turbine protection systems.

Relay Voting Strategy (Recommended for Critical Turbines)

For high-integrity protection systems:

AND voting logic (2-out-of-2) is recommended.

This configuration ensures:

• A single probe failure will not trigger a false trip

• Both channels must confirm an alarm condition

This approach is widely used in turbine protection architectures.

Probe Linearity Considerations

Large-range proximity probes require precise mechanical setup.

Important differences:

25 mm and 50 mm probes

• Have a wider measurement range

• Require specific initial gap settings

• Exhibit different linear regions compared to standard 8 mm probes

Improper probe gapping may result in:

• Reduced measurement accuracy

• Non-linear output response

• False alarm conditions