EPRO PR6423/002-031-CN CON041-CN Eddy Current Proximity Sensor – PR6423 Series

EPRO PR6423/002-031-CN + CON041-CN: Calibrated Eddy Current Measurement Chain for API 670 Machinery Protection

In critical rotating machinery — steam turbines, centrifugal compressors, boiler feed pumps, and gas expanders — shaft displacement and radial vibration are the primary indicators of mechanical degradation. A measurement gap of even 25 µm beyond the calibrated linear range can produce a DC bias error that masks a developing bearing fault or misalignment condition. The EPRO PR6423/002-031-CN eddy current proximity sensor, operating as a factory-matched system with the CON041-CN signal conditioner, delivers a calibrated, temperature-stable voltage output across the full operating range, providing the measurement fidelity that API 670 machinery protection architectures demand.

The PR6423 series employs a two-wire, driver-integrated eddy current topology. The sensor tip generates a high-frequency oscillating magnetic field — typically in the range of 1 MHz — which induces eddy currents in the conductive target (shaft). The impedance loading effect on the oscillator circuit is proportional to the gap distance. The CON041-CN proximitor conditions this impedance signal into a linear DC voltage output, nominally –24 VDC supply, with a standard sensitivity of 7.87 V/mm (200 mV/mil). This sensitivity figure is the calibration constant that ties the entire measurement chain together: it must remain stable across the operating temperature range of –35°C to +120°C to prevent false trips or missed alarms in the protection system.

The /002 suffix in the part number designates the sensor body diameter and coil geometry — a 5 mm tip diameter optimized for shaft targets with a nominal gap range of 0.25 mm to 2.25 mm. The /031 suffix specifies the integral cable length at 3.1 meters, a dimension that directly determines the system’s electrical characteristics. Eddy current systems are cable-length-sensitive: the distributed capacitance and inductance of the integral cable are part of the tuned oscillator circuit. Substituting a different cable length without recalibration will shift the sensitivity constant and introduce a systematic measurement error. The CON041-CN is factory-matched to this specific cable length, ensuring the published 7.87 V/mm sensitivity is maintained without field recalibration.

The -CN suffix designates the connector configuration for the Chinese market standard, ensuring mechanical and electrical compatibility with CN-type junction boxes and terminal assemblies commonly deployed in domestic power generation and petrochemical facilities. This eliminates the need for field-fabricated adapter assemblies, which are a common source of ground loops and signal noise in eddy current installations.

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Technical Parameters

Hardware Logical Analysis

The PR6423/002-031-CN operates on a self-oscillating LC circuit embedded in the sensor tip. The coil inductance (L) and the distributed capacitance of the integral cable form the resonant tank. When the conductive target enters the magnetic field, eddy currents dissipate energy from the tank circuit, reducing the oscillation amplitude. The CON041-CN demodulates this amplitude variation and applies a linearization algorithm to produce the final DC voltage output. The linearization is performed in analog hardware — not firmware — which eliminates the latency and potential failure modes associated with digital signal processing in the measurement path.

EMC Design: The sensor body is constructed with a grounded Faraday shield around the coil assembly. This shield intercepts capacitively coupled interference from adjacent high-voltage cables or variable frequency drives (VFDs) — a common noise source in turbine hall environments — and routes it to the machine frame ground rather than allowing it to modulate the oscillator circuit. The CON041-CN enclosure is designed to IEC 61000-4 immunity levels, with transient suppression on the supply and output lines rated to ±2 kV (1.2/50 µs waveform).

Thermal Stability: The sensitivity drift specification for the PR6423 series is ≤ 0.05% per °C across the operating range. For a turbine bearing housing that cycles between 40°C at startup and 95°C at full load, this translates to a maximum sensitivity shift of approximately 2.75% — well within the ±5% accuracy budget allocated by API 670 for the complete measurement chain. The CON041-CN incorporates a temperature-compensated reference voltage to maintain output accuracy independent of ambient temperature variation at the conditioner mounting location.

Cable Sensitivity and System Matching: The integral cable is not a passive conductor — it is a tuned element. The /031 designation (3.1 m) sets the cable capacitance at approximately 310 pF (assuming 100 pF/m for the specified cable type). This capacitance is factored into the CON041-CN’s oscillator compensation network. Field extension cables (CON021 series) can be added between the sensor integral cable and the conditioner, but only within the specified maximum total cable length, and only using EPRO-specified extension cable types with the correct characteristic impedance.

System Integration Benefits

• Direct API 670 Compliance Path: The PR6423/CON041 system meets the transducer performance requirements of API 670 Fifth Edition, simplifying the documentation burden for machinery protection system certification on new installations and retrofits.
• Drop-in Compatibility with EPRO MMS6000 and Bently Nevada 3500 Racks: The –24 VDC supply and 7.87 V/mm output are the standard interface parameters for both monitoring platforms, enabling direct substitution without rack reconfiguration or I/O card replacement.
• Deterministic Analog Output: The DC voltage output has no protocol overhead, no scan cycle latency, and no firmware dependency. The monitoring rack receives a real-time analog signal with a propagation delay determined only by the conditioner’s analog filter bandwidth (DC to 10 kHz, –3 dB), not by a communication stack.
• Diagnostic Transparency via Gap Voltage: The DC output voltage at the nominal operating gap (typically –10 VDC at 1.0 mm gap) serves as a continuous health indicator for the sensor-target interface. A slow drift in the gap voltage — without a corresponding change in vibration amplitude — indicates shaft centerline migration, bearing wear, or thermal growth, providing actionable data for condition-based maintenance scheduling.
• Hazardous Area Compatibility: With appropriate Zener barriers or galvanic isolators (consult EPRO for ATEX/IECEx certification documentation), the PR6423/CON041 system can be deployed in Zone 1 and Zone 2 classified areas, covering the majority of oil and gas processing environments.
• Multi-Parameter Measurement from a Single Sensor: A single PR6423 installation simultaneously provides radial vibration (AC component, filtered above 1 Hz), shaft average centerline position (DC component), and eccentricity (slow-roll vector at 1× running speed). This data density reduces the total sensor count required per bearing journal compared to velocity-based vibration transducers.
• Long Service Life in Harsh Environments: The absence of moving parts, the IP67-rated sensor body, and the high-temperature cable insulation (rated to 120°C continuous) result in a mean time between replacement (MTBR) that typically exceeds 10 years in well-maintained installations, reducing lifecycle maintenance costs.
• Standardized Calibration Traceability: Each PR6423/CON041 system is factory-calibrated against EPRO’s reference standard, with calibration data traceable to national metrology standards. This traceability is a requirement for machinery protection systems on assets covered by insurance or regulatory inspection programs.

Quality Assurance & Global Logistics

Every PR6423/002-031-CN + CON041-CN unit supplied by siemensplc.com is sourced through verified distribution channels with full supply chain traceability. Incoming units undergo a structured inspection protocol: visual examination of the sensor tip, cable jacket, and connector body for mechanical damage; label verification against the EPRO part number and date code; and packaging integrity assessment to confirm the factory seal has not been compromised.

Where test equipment is available, sensor-conditioner pairs are functionally verified as a matched system prior to dispatch: supply voltage is applied at –24 VDC, and the output voltage is measured at a known gap distance against a steel target to confirm the sensitivity constant is within the published tolerance band. Units that do not meet the specification are quarantined and returned to the supply chain — they are not offered for sale.

All units are shipped with original EPRO manufacturer documentation. Calibration certificates and certificates of conformance are available upon request and are provided as standard for orders destined for regulated industries (nuclear, offshore, power generation under grid operator requirements).

Logistics operations are based in Xiamen, China — a major export hub with direct access to international express carriers (DHL Express, FedEx International Priority, UPS Worldwide Express) and consolidated freight services. Standard export documentation — commercial invoice, packing list, certificate of origin — is prepared for every shipment. For time-critical plant shutdowns, same-day dispatch is available for in-stock units on orders confirmed before 14:00 CST. Transit times to major industrial centers: Europe 3–5 business days (DHL Express), North America 4–6 business days (FedEx IP), Southeast Asia 2–3 business days, Middle East 4–5 business days.

A 12-month warranty covers manufacturing defects from the date of shipment. In the event of a verified quality issue, replacement units are dispatched on a priority basis to minimize plant downtime exposure.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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