Product Overview

The Epro PR6426/000-141 is a 32 mm eddy current sensor used to measure shaft displacement in large rotating machinery. Applications include steam and gas turbines, hydro turbines, industrial compressors, pumps, and fans, where engineers need to monitor shaft position without placing a contact probe against the rotating surface.

This model is part of the PR6426 sensor family, which measures both radial and axial displacement. In a turbine bearing housing, for example, the sensor can detect changes in the position of a shaft relative to its mounting point. In a compressor installation, displacement measurements can help maintenance personnel investigate changes in rotor behavior alongside vibration and other machinery-monitoring data.

The sensor operates as part of a complete measuring chain. Its sensing head interacts electromagnetically with a conductive target, and a compatible signal converter processes the resulting response into a usable displacement signal. The sensor and converter must be treated as a matched combination because their calibration determines the relationship between shaft movement and output voltage.

The PR6426 series has a nominal static measuring range of ±4.0 mm and a sensitivity of 2 V/mm when configured for the standard measurement range. The 32 mm head and associated mounting arrangement are intended for large-shaft applications, so the available installation clearance and target geometry must be checked before fitting the sensor.

For replacement work, the full designation PR6426/000-141 matters. Although related PR6426 models share the same basic measuring principle, the cable length, connector arrangement, and mounting configuration can differ between variants. These details should be matched to the existing installation rather than inferred from the shared series number.

Technical Specifications

Product Features

• 32 mm sensing head: Suits displacement-measurement installations involving large rotating shafts. The surrounding mounting arrangement must provide the required clearance from ferrous material.
• Non-contact measurement: Detects relative movement between the sensor head and a conductive target without mechanical contact, avoiding wear caused by a contacting measurement element.
• Radial and axial displacement monitoring: Supports measurements of shaft movement in different directions when installed with the appropriate orientation and monitoring inputs.
• Defined static measuring range: The nominal ±4.0 mm range allows the measuring chain to track shaft position over a comparatively broad displacement interval.
• 2 V/mm nominal sensitivity: Establishes the standard displacement-to-voltage relationship for the specified sensor and converter configuration.
• Industrial temperature capability: The stainless-steel sleeve and PTFE cable materials support use in machinery environments within the specified temperature limits.
• Low long-term drift: The PR6426 series specifies long-term drift below 0.3%, supporting consistent measurement over extended operating periods when the measuring chain is correctly installed and calibrated.
• Converter-based operation: Works with compatible signal-conditioning equipment that excites the sensor and converts its response into a displacement-related output.

Working Principle

The PR6426/000-141 measures displacement through changes in an electromagnetic field generated at the sensor head. A coil inside the probe is excited by a high-frequency signal from the compatible converter. When the field interacts with the conductive shaft surface, eddy currents form in the target and affect the coil’s electrical response.

As the shaft moves closer to or farther from the sensor, the strength of this interaction changes. The converter processes the resulting signal and produces an output related to the distance between the sensor and the target.

The measuring chain follows this path:

Conductive Shaft Surface → PR6426/000-141 Sensor → Compatible Signal Converter → Machinery Monitoring System

In actual machinery operation, the initial sensor gap determines the working point within the measurement range. The sensor must be positioned so that the expected shaft movement remains within the configured range during startup, normal operation, and relevant transient conditions.

The nominal center gap for the standard PR6426 configuration is approximately 5.5 mm. This is a configuration reference, not a universal mounting distance for every extended-range setup. The final adjustment must follow the instructions for the installed converter and the required measurement range.

Target material also affects calibration. The standard reference material is ferromagnetic steel, 42CrMo4. If the shaft material differs, the resulting measurement characteristics should be evaluated rather than assuming that the standard calibration remains unchanged.

The sensor measures relative displacement; it does not independently diagnose a bearing fault or determine whether shaft movement is acceptable. The monitoring system interprets the signal using the machine’s operating conditions, configured limits, and other available measurements.

Role in the Machinery Monitoring Architecture

The PR6426/000-141 occupies the sensing stage of a machinery-monitoring chain. It measures the relative position of a shaft and supplies the corresponding electrical response to a compatible converter or integrated monitoring interface.

For a turbine, this arrangement can provide shaft-position information near a bearing location. On a large compressor, the same measurement principle can be used to observe changes in rotor displacement during operation. The sensor’s mounting orientation and monitoring channel determine which displacement direction is measured.

The complete chain must be calibrated as a unit. Replacing the probe while retaining the existing converter requires verification of the sensor type, connection arrangement, and calibration compatibility before the recorded measurements can be treated as comparable with previous data.

Industrial Applications

Installation and Maintenance

1. Verify the complete model number: Confirm PR6426/000-141 from the installed identification marking and maintenance records. Do not select a replacement solely because it belongs to the PR6426 series.
2. Check converter compatibility: Verify that the existing signal converter or monitoring interface supports the sensor and its measurement configuration. Confirm the required input characteristics and calibration before connection.
3. Confirm the target material: Check the shaft material against the sensor’s specified target requirements. The standard reference material is ferromagnetic steel, 42CrMo4.
4. Prepare the mounting location: Inspect the bracket and mounting surface to ensure that the sensor can be positioned securely and aligned with the intended measurement point.
5. Adjust the initial air gap: Set the sensor-to-target distance according to the applicable converter instructions. Use the nominal center gap of approximately 5.5 mm only where the standard measuring configuration applies.
6. Check surrounding clearance: Ensure that nearby ferrous components do not interfere with the sensing field. Follow the applicable installation drawing for the required clearance around the sensor.
7. Inspect the sensor head: Examine the stainless-steel sleeve and sensing surface for dents, deformation, or other mechanical damage that could affect installation or measurement.
8. Inspect the cable route: Check the cable for cuts, crushed sections, abrasion, and exposure to temperatures beyond its specified limit. Maintain the required bending radius for the actual cable construction.
9. Verify the connection arrangement: Match the cable and connector to the installed converter. Do not assume that the connection arrangement is identical across all PR6426 variants.
10. Check the measurement output: Use the approved commissioning procedure to confirm that the converter output changes in the expected direction when the target position changes.
11. Validate the operating measurement: Compare the displacement reading with the expected machine behavior and configured monitoring limits. Investigate abnormal signals before changing protection settings.
12. Record commissioning details: Document the full sensor designation, converter identification, initial gap, cable configuration, and test results so that future maintenance can reproduce the correct installation.

Compatible System Components

The correct component combination depends on the complete sensor suffix, cable and connector arrangement, measuring range, and converter configuration. Shared series identification alone is not sufficient to establish direct interchangeability.

Recommended Related Models

Key Advantages

• Non-contact measurement of shaft displacement.
• Nominal static range of ±4.0 mm in the standard measuring configuration.
• Nominal sensitivity of 2 V/mm with compatible signal conditioning.
• Stainless-steel sleeve and PTFE cable construction.
• Integration with compatible converters and machinery monitoring equipment.

Technical FAQs

What should be checked when replacing a PR6426/000-141 with another PR6426 variant?

Check the complete article number, cable and connector arrangement, mounting configuration, and compatibility with the installed signal converter. The shared 32 mm head diameter does not establish that two variants are electrically or mechanically interchangeable.

How does the sensor’s initial gap affect shaft-displacement readings?

The initial gap establishes the sensor’s operating point within the measuring range. If it is set incorrectly, the expected shaft movement may extend beyond the usable range or produce an unsuitable output operating point.

Can the PR6426/000-141 measure displacement on any metallic shaft?

No. The measuring response depends on the target material and calibration. The standard reference material is ferromagnetic steel, 42CrMo4. Different shaft materials may require a specific compatibility assessment.

Why must the sensor and signal converter be checked as a complete measuring chain?

The converter excites the sensor and processes its electrical response into a displacement-related output. The calibration and measuring range depend on the selected combination, so an apparently compatible replacement may still require configuration and verification before its readings can be used for machinery monitoring.