Product Overview

The Epro PR6426/000-000 is a 32 mm eddy current sensor used for non-contact measurement of shaft displacement in large rotating machinery. It belongs to the PR6426 sensor family and is intended for monitoring radial and axial shaft movement, including shaft position, eccentricity, and displacement in steam turbines, gas turbines, hydro turbines, compressors, pumps, and industrial fans.

The PR6426/000-000 has a mounting-plate configuration rather than a conventional threaded probe body. Its 80 × 40 mm mounting base is secured to the machine structure using two mounting points. This arrangement is particularly useful when the installation requires a fixed probe position near a large rotating shaft.

The complete ordering designation also identifies its cable and connection arrangement. The /000-000 configuration uses a non-armored cable, a supplied adapter plug, and a 4 m total cable length with a LEMO connector. These details matter when replacing an existing sensor because the mounting arrangement and connector configuration must match the installed measurement chain.

In a centrifugal compressor, for example, the sensor can be positioned near the shaft to detect changes in the radial clearance during operation. The resulting displacement measurement helps the machinery monitoring system identify abnormal shaft movement, mechanical instability, or changes in rotor operating conditions.

The sensor has a nominal sensitivity of 2 V/mm and a static measuring range of ±4.0 mm. Its nominal center air gap is approximately 5.5 mm. This relatively large measuring range makes the PR6426 suitable for applications involving large shaft displacement measurements, particularly on shafts with diameters of 200 mm or greater.

The sensor uses a stainless-steel sleeve and PTFE cable construction. Its operating temperature range is -35 to 175°C, with short-term temperature excursions up to 200°C for less than four hours. The cable itself has a maximum temperature rating of 200°C.

The PR6426/000-000 operates as part of an eddy current measuring chain. It must be paired with compatible signal conversion electronics or supported monitoring equipment. Correct target material selection, probe clearance, mounting rigidity, and converter calibration are all necessary to obtain the intended measurement performance.

Technical Specifications

Product Features

• 32 mm sensing head for large-shaft displacement measurement.
• Non-contact eddy current operating principle.
• Static measuring range of ±4.0 mm.
• Nominal sensitivity of 2 V/mm.
• Approximately 5.5 mm nominal center air gap.
• Designed for ferromagnetic steel targets, with 42CrMo4 as the standard reference material.
• 80 × 40 mm mounting plate with two fixing points.
• Non-threaded sensor mounting configuration.
• Non-armored PTFE cable.
• 4 m total cable length.
• Supplied adapter plug with LEMO connector arrangement.
• Stainless-steel sensor sleeve.
• Operating temperature range of -35 to 175°C.
• Short-term temperature excursion capability up to 200°C.
• Suitable for radial and axial shaft displacement monitoring.
• Compatible with supported Epro signal converters and machinery monitoring systems.

Working Principle

The PR6426/000-000 uses electromagnetic induction to measure the distance between its sensing face and a conductive metallic target.

Inside the sensor, an excitation signal generates an alternating electromagnetic field around the sensing coil. When the probe is positioned near a ferromagnetic steel shaft, eddy currents are induced in the target surface. These currents influence the electrical characteristics of the sensor.

As the shaft moves, the distance between the sensing head and target changes. This changes the electromagnetic interaction and produces a corresponding change in the sensor’s electrical response.

The complete measurement process follows this arrangement:

PR6426/000-000 → Sensor Cable → LEMO Adapter Connection → Signal Converter → Monitoring System

For example, when the sensor is installed beside a compressor shaft, radial movement changes the air gap between the shaft and probe. The compatible converter processes this change and generates a displacement-related output for the machinery monitoring system.

The nominal sensitivity is 2 V/mm. Within the specified measuring configuration, a displacement change of 1 mm corresponds to a nominal output change of 2 V.

The initial probe position is important because the standard static measuring range is ±4.0 mm around the nominal operating point. The center air gap is approximately 5.5 mm, and the final installation position should be adjusted using the complete sensor and converter measuring chain.

The target material also affects measurement characteristics. The standard calibration reference is ferromagnetic 42CrMo4 steel, corresponding to SAE 4140. If the actual shaft material differs, the measurement chain must be evaluated and adjusted for the target material.

Because the PR6426/000-000 does not physically contact the rotating shaft, it can continuously monitor displacement without introducing friction or mechanical wear at the sensing interface.

Role in a Machinery Protection and Condition Monitoring Architecture

The PR6426/000-000 acts as the displacement measurement element in an Epro machinery monitoring arrangement. Its function is to detect shaft movement and deliver the corresponding measurement information to compatible signal conversion electronics.

A typical measurement arrangement is:

Rotating Shaft → PR6426/000-000 → Extension / Connection Cable → Signal Converter → Machinery Monitoring Rack → Protection System

In a steam turbine installation, multiple eddy current sensors can be positioned around the rotor to monitor different displacement directions. The PR6426/000-000 can be assigned to a suitable measurement point where its 32 mm sensing head and ±4.0 mm range meet the installation requirements.

The converter processes the sensor response and supplies the resulting measurement signal to the monitoring system. The monitoring equipment evaluates the shaft position or displacement against configured operating limits and can generate alarms or protection actions when abnormal movement is detected.

The sensor itself performs the measurement. Alarm evaluation and machinery shutdown functions are handled by the connected monitoring and protection equipment.

Industrial Applications

Installation and Maintenance

1. Verify the Complete Model: Confirm that the replacement is PR6426/000-000 rather than another PR6426 configuration. Check the mounting plate, cable protection, adapter plug, and connector arrangement.
2. Inspect the Mounting Plate: Check the 80 × 40 mm mounting base and its two fixing points for damage, deformation, or contamination before installation.
3. Select a Suitable Mounting Position: Position the sensor close to the intended measurement point while maintaining the required clearance from surrounding ferrous materials.
4. Maintain the Required Free Space: Keep at least 80 mm clearance from ferrous material around the sensor head as specified for the PR6426 measuring arrangement.
5. Check the Target Surface: Ensure that the shaft measurement track is smooth and free from scratches, corrosion, and other surface irregularities that could affect the output signal.
6. Confirm Target Material: Check whether the shaft material matches the standard 42CrMo4 reference material. If another material is used, the complete measuring chain must be adjusted accordingly.
7. Adjust the Initial Air Gap: Set the probe position using the connected signal converter and the required measurement configuration. The nominal center air gap is approximately 5.5 mm.
8. Protect the Non-Armored Cable: Route the cable away from moving machinery, sharp edges, high-temperature surfaces, and locations where mechanical damage may occur.
9. Observe Cable Bending Limits: Maintain a minimum bending radius of 25 mm for the non-armored cable to avoid damaging the internal conductors.
10. Inspect the LEMO Connection: Check the adapter plug and connector contacts for contamination, loose connections, or physical damage before connecting the measurement chain.
11. Verify Measurement Performance: After installation, check the converter output and confirm that the sensor operates within the intended linear measuring range.
12. Record the Installation Configuration: Document the mounting position, target material, initial air gap, cable routing, connector arrangement, and converter settings for future inspection and replacement.

Compatible System Components

Recommended Related Models

Key Advantages

• Non-contact measurement avoids mechanical wear at the shaft interface.
• 32 mm sensing head accommodates large-shaft monitoring applications.
• ±4.0 mm static measuring range supports substantial shaft displacement measurements.
• 2 V/mm nominal sensitivity for displacement-related signal processing.
• Mounting-plate configuration provides a fixed installation arrangement.
• 4 m non-armored cable with LEMO connection.
• Stainless-steel sleeve and PTFE cable construction.
• Suitable for elevated-temperature rotating machinery environments.
• Integrates with compatible Epro signal converters and monitoring systems.

Technical FAQs

What does the PR6426/000-000 ordering code specify?

The complete designation identifies the sensor’s mechanical and cable configuration. The first group specifies a non-threaded sensor, non-armored cable, and an 80 × 40 mm mounting plate. The second group specifies an included adapter plug, a 4 m total cable length, and a LEMO cable end. These details are important when selecting a replacement for an existing installation.

Is the PR6426/000-000 suitable for monitoring large compressor shafts?

Yes. The PR6426 family is intended for large-shaft displacement measurements, with a standard minimum shaft diameter of 200 mm. Its ±4.0 mm static measuring range and 2 V/mm nominal sensitivity make it suitable for monitoring radial or axial shaft movement when the mounting geometry and target material meet the measurement requirements.

Does the 4 m cable include the LEMO adapter connection?

The ordering configuration specifies a total cable length of 4 m and an adapter plug with a LEMO cable end. The sensor arrangement also includes a short sensor cable section and the adapter connection. When replacing the complete assembly, the connector arrangement and total cable configuration should be checked rather than selecting a cable based only on its nominal length.

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

The sensor’s electrical response depends on the target material, initial air gap, and associated conversion electronics. The sensor and converter are adjusted together to establish the required sensitivity and measuring range. Using an incompatible converter or changing the target material without recalibration can result in inaccurate displacement readings.