Overview
Hardware Specifications
| Parameter | Specification |
|---|---|
| Model | Bently Nevada 3500/50 |
| Part Number | 134938-01 |
| Brand | Bently Nevada |
| Product Type | 2-Channel Tachometer Module |
| System | 3500 Machinery Protection System |
| Operating Temp | -30 deg C to +65 deg C with standard I/O; 0 deg C to +65 deg C with Internal Barrier I/O |
| Storage Temp | -40 deg C to +85 deg C |
| Humidity | 95%, non-condensing |
| Number of Channels | 2 |
| Input Type | Proximity probes or magnetic pickups |
| Input Signal Range | +10.0 V to -24.0 V |
| Input Impedance | 20 kOhm standard; 40 kOhm TMR; 7.15 kOhm Internal Barrier |
| Events per Revolution | 0.0039 to 255 |
| Maximum Full-Scale Speed | 99,999 RPM |
| Maximum Input Frequency | 20 kHz |
| Accuracy Below 100 RPM | +/- 0.1 RPM |
| Accuracy at 100 to 10,000 RPM | +/- 1 RPM |
| Accuracy at 10,000 to 99,999 RPM | +/- 0.01% of true shaft speed |
| RPM/Min Accuracy | +/- 20 RPM/min |
| Recorder Output | +4 to +20 mA proportional to full-scale range |
| Buffered Outputs | Buffered transducer outputs available at I/O module |
| Power Consumption | 5.8 W typical |
| Front Panel Indicators | OK, TX/RX, Bypass |
Bently Nevada TSI Signal Processing
The 3500/50 processes rotational signals from proximity probes or magnetic pickups and derives shaft-speed information from detected events. Therefore, correct transducer installation and signal conditioning directly affect tachometer measurement quality.
The module supports up to 255 events per revolution and accepts input frequencies up to 20 kHz. In addition, the specified full-scale range reaches 99,999 RPM, allowing the module to process high-speed rotating equipment signals.
For eddy-current probe installations, technicians should verify probe gap voltage before commissioning. A nominal -10 VDC gap target is commonly used for Bently Nevada proximity probe systems, subject to the applicable probe and monitor configuration.
The tachometer measurement can support rotor-dynamics monitoring by providing rotational reference information. The module also provides conditioned Keyphasor-related signals through the 3500 rack architecture where the configured I/O arrangement supports this function.
Frequently Asked Questions
Q: What transducer types can the 3500/50 accept?
A: The module accepts proximity probe or magnetic pickup signals. The supplied specification defines an input range of +10.0 V to -24.0 V.
Q: What is the maximum speed and input frequency supported?
A: The specified maximum full-scale speed is 99,999 RPM, while the maximum input frequency is 20 kHz.
Q: What should technicians verify when installing an eddy-current probe?
A: Verify probe polarity, cable termination, shielding, signal routing, and gap voltage before commissioning. A -10 VDC gap target is commonly used for Bently Nevada eddy-current probe systems, subject to the applicable configuration.
Field Installation Guidelines
- Install the module in the designated 3500 rack slot according to the applicable rack configuration.
- Confirm the I/O module type before connecting field transducers.
- Route tachometer signal cables separately from high-current power and switching circuits.
- Maintain consistent signal polarity between the transducer, field wiring, and I/O termination.
- For eddy-current probes, verify mechanical probe clearance and gap voltage before applying operating speed.
- Connect cable shields according to the approved site grounding architecture and Bently Nevada installation documentation.
- Inspect terminal connections for secure mechanical engagement before commissioning.
- Verify the OK, TX/RX, and Bypass LEDs after energization.
- Confirm the configured speed range and alarm setpoints before placing the machinery protection channel into service.
- Where magnetic pickups are used, verify the generated pulse signal at the expected operating speed.
- Do not assume hot-swap capability unless the installed 3500 rack and system documentation explicitly permit module replacement under energized conditions.
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