Description
Key Technical Specifications
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Model Number: 3500/25-02-01-05
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Manufacturer: Bently Nevada (Baker Hughes)
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Channels: 2 independent (software-configurable for keyphasor or speed input)
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Input Type: Eddy current pickups (Proximitor), magnetic pickups (variable reluctance), TTL/CMOS digital pulses
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Input Frequency Range: 0-25 kHz (covers 0-150,000 RPM at 60 pulses/rev)
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Output Signal: Digital pulse train to 3500 framework (via rear transition module)
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Supply Voltage: 24V DC (±10%, intrinsically safe power supply required for Zone 0/1)
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Operating Temperature: 0°C to +65°C (rack-mounted)
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Storage Temperature: -40°C to +85°C
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Electrical Isolation: 500Vrms (channel-to-rack, per IEC 60664-1)
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Hazardous Area Rating: Ex ia IIC T4 Ga (05 suffix denotes intrinsic safety for Zone 0/1)
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Dimensions: 119mm x 25mm x 102mm (WxHxD, 3500 half-height slot)
- Weight: 0.16kg
Field Application & Problem Solved
In the field, rotating machinery in hazardous areas (refinery compressor buildings, chemical plant turbine skids) demands phase reference signals that are both precise and explosion-proof. The biggest challenge with older keyphasor modules is their lack of intrinsic safety—forcing costly explosion-proof enclosures or risky installations in Zone 0/1. This 2-channel module solves that by combining redundant phase reference with 05-certified intrinsic safety. You’ll find it on catalytic cracker compressors (synchronizing vibration plots in flammable vapor zones), hydrogen reformer turbines (tracking rotor phase in H2-rich environments), or offshore platform generators (providing phase data in potentially ignitable atmospheres). Its core value is twofold: dual channels eliminate single-point failures (critical for 24/7 ops), and intrinsic safety removes the need for bulky enclosures—saving $10k+ per installation in a Gulf Coast refinery. The 0-25kHz range also handles high-speed rotors (e.g., 30,000 RPM gas turbines), while the -18V to -2V output integrates directly with 3500/42M monitors. For example, in a Texas chemical plant, it prevented a shutdown by providing backup phase data when a magnetic pickup failed—all while meeting ATEX Zone 1 requirements.
Installation & Maintenance Pitfalls (Expert Tips)
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Ignoring Intrinsic Safety Wiring: The 05 suffix requires intrinsically safe (IS) cabling (Belden 8761 or equivalent) and barriers. Using standard cable bypasses the IS rating—risk of ignition in Zone 0/1. Verify barrier ratings match the -24V supply (max 250mW power).
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Wrong Pickup Air Gap: Magnetic pickups need 0.5-1.5mm gap; eddy current probes need 1-2mm. Set too wide, and you lose signal at low speeds; too tight, and you risk rubbing (dangerous in explosive areas). Use a non-ferrous feeler gauge—neversteel.
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Reversed Signal Polarity: If the keyphasor signal is inverted (rising vs. falling edge), phase data flips 180°. Verify polarity with a scope: the 3500/25 expects a positive-going pulse at TDC. Swap pickup wires if needed—this mistake caused a 6-hour outage in a Louisiana refinery.
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Mismatched Pulse Wheel Teeth: The module assumes a standard pulse wheel (1 tooth/rev for speed, 60 teeth/rev for phase). If the wheel has 30 teeth, you’ll get double the frequency—adjust the 3500 configuration to “teeth per rev” to fix scaling.
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Skipping IS Barrier Testing: Intrinsically safe barriers degrade over time. Test them annually with a multimeter—check voltage/current limits. A failed barrier in a West Virginia plant nearly caused an arc flash.
Technical Deep Dive & Overview
The 3500/25-02-01-05 is a dual-channel keyphasor module for Bently’s 3500 Machinery Protection System, engineered for hazardous-area use. It acts as a signal conditioner: raw pulses from shaft-mounted pickups (magnetic/eddy current) are amplified, filtered (to remove EMI), and converted to digital signals via Schmitt triggers. Each channel handles 0-25kHz inputs—enough for 150,000 RPM at 60 pulses/rev. The 05 suffix adds intrinsic safety (Ex ia IIC T4 Ga) via galvanic isolation and power limitation, ensuring no spark energy exceeds 250mW in Zone 0/1. Redundant channels mean if one fails, the other takes over—critical for compressor trains. It interfaces with 3500 racks via rear transition modules (e.g., 3500/92), sending phase data to processors (3500/42M) for FFT analysis. In short, it’s the “explosion-proof metronome” for hazardous-area machinery—keeping vibration data in sync without compromising safety.
