Key Technical Specifications
- Sensor Compatibility: 5mm & 8mm Proximity Probes
- Supply Voltage: -24V DC Nominal (±10%)
- Output Signal: Scaled Voltage (-2V to -18V Typical)
- Frequency Response: 0 to 10 kHz (-3dB)
- Operating Temp: -40°C to +77°C (-40°F to +170°F)
- Mounting: DIN Rail or Panel Mount
- Cable Length: 5m or 9m Standard (System Dependent)
- Isolation: 500V RMS Input-to-Output
- Compliance: API 670, CE, UL
Product Introduction
A dead Proximitor doesn’t just give you bad data; it gives you no data, and your 3500 rack will happily sit there blind while your turbine shakes itself to pieces. The Bently Nevada 18745-03 is the front-line translator that takes the raw, messy eddy current signal from your probe and turns it into a clean, scaled voltage the monitor can actually understand. It’s the unsung hero of the vibration loop, and when it fails, you don’t get a graceful degradation; you get a trip or a missed fault.Field engineers keep this specific module in the cabinet because it handles both 5mm and 8mm probes, which saves you from stocking two different part numbers for the same skid. The -24V DC supply is standard, but the internal regulation is what matters; it rejects the nasty ground loops and EMI that live in every motor control center. Just remember: this is an analog front-end. If your cable is shorted or the probe is grounded to the shaft, no amount of module magic will fix it. Check the physical loop first.
Quality SOP & Tech Pitfalls
The Lab Report:
We don’t ship blind. Every Bently Nevada 18745-03 gets a full bench validation. We hook it to a calibrated 5mm/8mm simulator and verify the output voltage matches the gap curve within ±1%. We check the -24V supply rail for ripple and verify the isolation barrier with a megger. Then we do a 24-hour burn-in at elevated temp to catch infant mortality. If it’s out of spec, it’s scrap.The Engineer’s Warning:
The #1 way you kill this module is by wiring it backwards or shorting the output to ground while powered. The internal FETs are tough, but they aren’t invincible. Always verify your -24V supply polarity before plugging in the connector. Also, don’t mix cable types. If your system is set up for 9m cables and you slap on a 5m cable without recalibrating the Proximitor, your gap voltage will be wrong, and your monitor will trip on startup. Photograph the old module’s DIP switches or jumpers before you pull it.
Installation & Configuration Guide
- Pre-Installation: ⚠️ VERIFY SUPPLY VOLTAGE. Ensure your -24V DC is clean and within ±10%. Take a photo of the old module’s DIP switch/jumper settings and cable connections. Check the probe and extension cable for shorts to ground with a multimeter.
- Removal: Disconnect the probe and output cables. Release the DIN clip or remove panel nuts. Pull the module straight out. Inspect the backplane connector for bent pins or corrosion.
- Installation: Copy DIP/Jumper settings exactly. This is critical for 5mm vs 8mm selection and cable length compensation. Slide the Bently Nevada 18745-03 into the slot until it seats firmly. Reconnect the probe first, then the output cable, then the power.
- Power-On & Testing: Apply -24V DC. Verify the LED indicator (if equipped) or check the monitor’s “OK” status. Measure the output voltage with a DMM; it should be between -9V and -11V for a mid-range gap. If it’s pegged at -2V or -18V, you have a probe/cable fault or a bad gap setting.
Compatible Replacement Models
| Model | Compatibility Tier | Notes |
|---|---|---|
| 18745-03 | ✅ Drop-in Replacement | Exact match. Verify sensor size (5mm/8mm) jumper setting. |
| 330180-50-00 | ⚠️ Software Compatible | 3300 XL 8mm Proximitor. Same function, different form factor. Requires 3300 XL rack or adapter. |
| 18745-02 | ✅ Drop-in Replacement | Older revision. Functionally identical for most 3500 apps. Check cable length setting. |
| 330100-00-00 | ❌ Hardware Mod Required | 3300 XL 5mm Probe. Not a Proximitor. Different component entirely. Do not substitute. |
Frequently Asked Questions (FAQ)
Can I use this with a 11mm probe?
No. The Bently Nevada 18745-03 is specifically calibrated for 5mm and 8mm sensors. An 11mm probe requires a different Proximitor (like the 330180-90-00). Using the wrong one will give you completely wrong gap voltages and false trips.What if my output voltage is stuck at -18V?
That usually means the probe is open-circuit or the gap is way too large. Check the probe connection at the junction box and the Proximitor. If the cable is good, your probe might be damaged or the target surface is non-conductive.Is this module hot-swappable?
In a 3500 system, yes, but I don’t recommend it unless you have to. The transient can sometimes glitch the monitor channel. If you can schedule a 30-second channel disable, do it. It’s safer for the module and the monitor.How do I know if it’s the Proximitor or the probe?
Swap the Proximitor with a known-good unit from another channel. If the problem follows the module, it’s the Proximitor. If it stays on the channel, check the probe, extension cable, and target surface. 90% of the time, it’s the cable or probe, not the module.Does this work with the 3300 XL system?
The 18745-03 is a 7200-series module. It can work in 3300 XL racks if the backplane supports it, but the 330180-50-00 is the native 3300 XL part. Verify your rack manual before mixing families.What’s the max cable length?
Standard is 5m or 9m. If you need longer, you must use the correct Proximitor model designed for extended cable and adjust the DIP switches. Don’t just splice in extra cable; the capacitance will kill your frequency response.
