EPRO PR6426/010-140 CON021/912-160 Eddy Current Sensor – PR6426 Series

EPRO PR6426/010-140 + CON021/912-160: Calibrated Eddy Current Measurement Chain for Rotating Machinery Protection

The EPRO PR6426/010-140 eddy current proximity sensor, paired with the CON021/912-160 signal conditioning transmitter, constitutes a factory-matched, two-component measurement chain purpose-built for continuous, non-contact monitoring of shaft radial vibration and axial displacement in high-speed rotating machinery. This sensor-transmitter combination is deployed across steam turbines, centrifugal compressors, gas expanders, and boiler feed pump trains where API 670 machinery protection compliance is mandatory and measurement chain integrity is non-negotiable.

The PR6426 series operates on the eddy current induction principle: a high-frequency oscillator (typically 1 MHz carrier) drives a coil wound within the sensor tip, generating an electromagnetic field that penetrates the target shaft surface. As shaft-to-sensor gap varies due to vibration or displacement, the induced eddy currents alter the coil impedance. The CON021 transmitter demodulates this impedance shift into a linear DC voltage or 4–20 mA current output proportional to gap distance, with a static sensitivity of 8 mV/µm across the calibrated measurement range. This architecture eliminates mechanical contact entirely, producing zero wear on the sensor element and enabling indefinite continuous operation without scheduled replacement intervals.

The integral 140 mm cable variant (suffix -140) is specified for installations where the sensor probe must be routed through tight bearing housing passages or where a short, rigid lead is required before transitioning to a CON011 extension cable. The CON021/912-160 transmitter accepts the PR6426 sensor signal directly and conditions it to a standard 4–20 mA output compatible with any DCS analog input card or dedicated machinery protection monitor.

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Technical Parameters

Hardware Logical Analysis

The PR6426/010-140 employs a differential impedance bridge topology within its oscillator circuit. The sensing coil forms one arm of the bridge; a reference coil — thermally co-located inside the sensor body — forms the opposing arm. This differential arrangement provides first-order temperature compensation: as ambient temperature shifts the coil resistance, both arms shift proportionally, and the bridge output remains stable. The result is a thermal drift coefficient below ±0.05% FS/°C across the rated operating range, which is critical in bearing housings where temperature gradients of 40–60°C between cold start and steady-state operation are common.

The CON021/912-160 transmitter incorporates a synchronous demodulator locked to the sensor’s carrier frequency. This architecture rejects out-of-band noise — including 50/60 Hz power line interference and switching transients from adjacent variable-frequency drives — with a common-mode rejection ratio exceeding 80 dB. The transmitter’s output stage is galvanically isolated from the sensor input circuit, providing 500 V AC isolation between the field-side sensor loop and the control-room 4–20 mA loop. This isolation is not incidental: in large turbine trains, ground potential differences between the bearing housing and the control cabinet can reach several volts, and without galvanic isolation, these potentials inject directly into the measurement signal as low-frequency noise indistinguishable from actual shaft motion.

The sensor probe tip geometry is machined to a tolerance of ±5 µm on the coil face flatness, ensuring that the electromagnetic field pattern is rotationally symmetric. Asymmetric field patterns produce a once-per-revolution (1X) artifact in the vibration spectrum that cannot be distinguished from genuine shaft bow or unbalance — a known failure mode in lower-grade proximity sensors. The PR6426 probe body is constructed from 316L stainless steel with a PEEK (polyether ether ketone) tip encapsulant, providing chemical resistance to turbine lube oil, seal gas condensate, and process hydrocarbons without dimensional change over service life.

EMC hardening is achieved through a combination of coaxial cable shielding (drain wire grounded at the transmitter end only, per API 670 §5.4 grounding requirements), ferrite bead suppression at the transmitter input terminals, and a metal enclosure with 360° shield termination at the cable gland. This configuration meets IEC 61000-4-3 radiated immunity at 10 V/m across 80 MHz–1 GHz, which covers the emission bands of most industrial wireless infrastructure and motor drive switching frequencies.

System Integration Benefits

• Direct 4–20 mA loop compatibility: The CON021 output connects without signal conditioning to any standard DCS analog input card (Emerson DeltaV, Honeywell Experion, ABB 800xA, Yokogawa CENTUM VP), eliminating the need for intermediate signal converters and the associated failure points.
• API 670 machinery protection monitor compatibility: The 4–20 mA output and sensor impedance characteristics are matched to Bently Nevada 3500/40M and 3500/42M monitor cards, as well as EPRO MMS6000 series modules, enabling drop-in replacement without reconfiguration of trip setpoints.
• Factory-matched calibration traceability: The sensor and transmitter are calibrated as a pair against a NIST-traceable displacement standard. The calibration certificate documents the actual sensitivity curve (mV/µm vs. gap) for the specific unit pair, not a nominal curve — this matters when the protection system’s trip setpoint is set to ±125 µm (5 mil) per API 670 alarm levels.
• Deterministic frequency response: The measurement chain bandwidth is flat (±3 dB) from DC to 10 kHz, covering all relevant vibration frequencies for machinery operating up to 60,000 RPM (1,000 Hz fundamental), including sub-synchronous instability modes in fluid-film bearings and blade-pass frequencies in centrifugal stages.
• Galvanic isolation for ground loop elimination: The 500 V AC isolation between sensor and output loop prevents ground-loop currents from corrupting vibration data — a common source of spurious alarms in plants where multiple earthing systems coexist.
• Redundant installation support: The compact M8 probe body diameter allows dual-sensor installation in standard API 670 proximity probe brackets (two sensors at 90° X-Y orientation) without bracket modification, supporting full redundant vibration monitoring per API 670 §6.2.
• Diagnostic transparency via loop current monitoring: The 4–20 mA loop current can be monitored by the DCS for sensor health: a reading below 3.6 mA or above 21 mA indicates a wiring fault or sensor failure, enabling the control system to generate a sensor fault alarm distinct from a process alarm — improving diagnostic resolution without additional hardware.
• Interoperability with keyphasor systems: When used alongside a PR6424 keyphasor sensor, the PR6426/CON021 measurement chain provides the raw vibration signal for synchronous analysis (1X, 2X vector tracking, Bode plots, polar plots) in machinery diagnostic software such as System 1 or Machinery Health Manager.

Quality Assurance & Global Logistics

Every EPRO PR6426/010-140 + CON021/912-160 unit dispatched from our Xiamen, China facility undergoes a structured pre-shipment verification protocol. Units are sourced exclusively from authorized EPRO distributors or verified OEM-surplus channels with documented chain of custody. Upon receipt, each unit is subject to visual inspection of the probe tip, coaxial connector, and transmitter housing for mechanical damage; label and serial number verification against manufacturer documentation; and a functional impedance check of the sensor coil (nominal 100 Ω ±10% at 1 kHz) to confirm coil integrity before packaging.

Original manufacturer packaging is preserved where available. For units sourced from surplus, anti-static packaging with desiccant is applied, and the sensor tip is protected with a machined aluminum cap to prevent coil face damage during transit. Traceability documentation — including distributor invoice, serial number record, and available calibration data — is provided on request at no additional charge.

Logistics from Xiamen port covers all major industrial destinations: DHL Express (3–5 business days to Europe, North America, Southeast Asia), FedEx International Priority, and sea freight for bulk orders. Export documentation including commercial invoice, packing list, and HS code classification (HS 9031.80 — instruments for measuring or checking) is prepared in-house. L/C (Letter of Credit), T/T (Telegraphic Transfer), and PayPal are accepted. All shipments carry a 12-month warranty from the date of dispatch, covering manufacturing defects and premature failure under normal operating conditions.

Contact Information

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