Product Overview

The Epro PR6426/000-020 is a 32 mm eddy current sensor used for non-contact shaft displacement measurement 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, compressors, pumps, and other large rotating equipment.

This version uses a non-threaded sensor sleeve and an 80 × 40 mm mounting plate. The mounting plate provides the reference surface for positioning the probe relative to the measuring target. Unlike threaded proximity probes that are adjusted by screwing them into a holder, the PR6426 is installed using its mounting plate and dedicated fixing arrangement.

The complete ordering code identifies a specific cable configuration. The PR6426/000-020 has a non-armored cable, an adapter plug, a total cable length of 6 m, and a LEMO cable connection. The 6 m cable length distinguishes this version from the PR6426/000-000, which uses a 4 m cable with the same basic mounting and connector arrangement.

This longer cable configuration is useful when the distance between the sensor mounting location and the signal conversion equipment requires additional routing length. It can simplify installation in large turbine or compressor housings where the sensor is positioned near the shaft but the monitoring electronics are located elsewhere in the machine room or control cabinet.

For example, in a centrifugal compressor, the PR6426/000-020 can be mounted near the rotor to measure changes in the shaft-to-probe distance. The measurement helps identify radial movement and changes in shaft position during operation. In a turbine, a similar arrangement can be used for axial displacement monitoring, depending on the available measuring surface and probe orientation.

The PR6426 has a nominal sensitivity of 2 V/mm and a standard static measuring range of ±4.0 mm. Its nominal center air gap is approximately 5.5 mm. These characteristics make it suitable for large-shaft measurement applications where the mechanical installation provides sufficient clearance around the sensing head.

The sensor uses a stainless-steel sleeve and PTFE cable construction. It operates in demanding machinery environments, but the actual temperature limits depend on the location being considered, including the sensor head, cable protection, and connector area.

The PR6426/000-020 is one part of a complete eddy current measuring chain. It must be matched with compatible signal conversion electronics, such as the CON series converters or supported monitoring equipment. The sensor, converter, target material, and installation gap must be considered together to obtain the intended measurement response.

Technical Specifications

Product Features

• 32 mm sensing head for large-shaft displacement measurement.
• Non-contact eddy current measurement technology.
• Standard static measuring range of ±4.0 mm.
• Nominal sensitivity of 2 V/mm.
• Approximately 5.5 mm nominal center air gap.
• 80 × 40 mm mounting plate for fixed installation.
• Non-threaded sensor sleeve configuration.
• Non-armored PTFE sensor cable.
• 6 m total cable length for installations requiring additional cable reach.
• LEMO connection with adapter plug.
• Stainless-steel sensor sleeve construction.
• Suitable for radial and axial shaft displacement measurement.
• Compatible with supported Epro signal conversion and machinery monitoring equipment.

Working Principle

The PR6426/000-020 measures displacement through changes in the electromagnetic interaction between its sensing coil and a conductive metal target.

The sensor operates with an excitation signal supplied by compatible conversion electronics. This signal generates an alternating electromagnetic field around the probe head. When the sensor is positioned near a metallic shaft, eddy currents develop in the target surface and affect the electrical characteristics of the sensing coil.

As the distance between the probe and the shaft changes, the strength of this interaction changes as well. The converter processes the resulting electrical variation and produces a signal corresponding to the displacement of the target.

The complete measurement arrangement follows this path:

PR6426/000-020 → 6 m Sensor Cable → LEMO Connection → Signal Converter → Machinery Monitoring System

In a compressor installation, the probe can be positioned beside the rotor with its sensing face directed toward the shaft surface. When the shaft moves radially, the clearance between the shaft and the probe changes. The converter translates this change into a displacement-related output that can be evaluated by the machinery monitoring system.

The nominal sensitivity of the standard PR6426 measuring chain is 2 V/mm. The static measuring range is ±4.0 mm, allowing the system to measure movement in both directions around its nominal operating position.

The initial measurement gap must be adjusted using the complete sensor and converter arrangement. The nominal center air gap is approximately 5.5 mm, but the final setting should follow the converter output and the specific measurement requirements rather than relying only on a mechanical distance measurement.

The target material also affects the response. The standard reference material is 42CrMo4 steel, equivalent to SAE 4140. If the actual shaft uses a different conductive material, the measuring chain may require adjustment to maintain the intended sensitivity and accuracy.

Role in a Machinery Protection and Condition Monitoring Architecture

The PR6426/000-020 functions as the displacement sensing element in an Epro machinery monitoring arrangement. It detects changes in shaft position and sends the corresponding sensor response to compatible conversion electronics.

A typical measurement arrangement is:

Rotating Shaft → PR6426/000-020 → 6 m Sensor Cable → Signal Converter → Monitoring Rack → Machinery Protection System

In a turbine monitoring installation, the PR6426/000-020 can be used at a suitable axial or radial measurement point. Its output is processed by the associated converter before being transferred to the monitoring equipment.

The monitoring system evaluates shaft displacement against configured operating limits. Depending on the application, the measurement can be used for condition trending, alarm generation, or machinery protection.

The 6 m cable configuration is relevant when planning the physical layout of the measuring chain. Cable routing must account for the distance between the probe and converter, machine movement caused by thermal expansion, and the need to keep the cable away from rotating components.

Industrial Applications

Installation and Maintenance

1. Verify the Complete Ordering Code: Confirm that the sensor is PR6426/000-020. Check the non-threaded sleeve, mounting plate, non-armored cable, adapter plug, 6 m cable length, and LEMO termination.
2. Inspect the Mounting Plate: Check the 80 × 40 mm mounting plate and its fixing arrangement for deformation, contamination, or damage before installation.
3. Select the Measuring Position: Position the sensor according to the required radial or axial measurement direction and the available shaft measuring surface.
4. Maintain the Required Clearance: The PR6426 requires at least 80 mm of free space around the sensor head for its standard measuring range. Insufficient clearance can reduce the available measuring range and increase linearity error.
5. Check the Measuring Surface: Inspect the shaft track for scratches, corrosion, and surface irregularities. A surface finish of approximately 0.41–0.76 μm is recommended for the measuring track.
6. Confirm Target Material: Verify that the target material matches the standard 42CrMo4 reference material or the material used to adjust the measuring chain.
7. Adjust the Mounting Distance: Use the mounting plate as the reference surface. The nominal distance from the mounting plate to the measuring target at the center position is approximately 39.5 mm.
8. Secure the Mounting Screws: Tighten the mounting screws according to the installation requirements and bend the anti-twisting safety plate after fixing to prevent the screws from loosening.
9. Route the 6 m Cable Correctly: Install the non-armored cable without twisting or excessive tension. Allow sufficient cable length for machine thermal expansion and maintenance access.
10. Protect the LEMO Connection: Push the LEMO connector into its matching socket until it locks. Do not twist the connector when connecting or disconnecting it. Protect the adapter connection with the supplied shrink sleeve.
11. Verify the Complete Measuring Chain: Check the sensor response through the compatible converter and confirm that the initial gap and output correspond to the required measuring range.
12. Document the Installation: Record the sensor position, target material, mounting distance, cable route, LEMO connection, converter type, and measurement settings for future maintenance.

Compatible System Components

Recommended Related Models

Key Advantages

• Non-contact shaft measurement without mechanical contact or wear.
• 32 mm sensing head for large-shaft monitoring applications.
• ±4.0 mm standard static measuring range.
• 2 V/mm nominal sensitivity.
• Fixed mounting-plate arrangement for PR6426 installations.
• 6 m non-armored cable for installations requiring additional cable reach.
• LEMO connection with adapter plug.
• Stainless-steel sensor sleeve and PTFE cable construction.
• Suitable for demanding turbine and compressor monitoring applications.
• Compatible with supported Epro converters and machinery monitoring systems.

Technical FAQs

What is the difference between PR6426/000-020 and PR6426/000-000?

Both models use a non-threaded sleeve, an 80 × 40 mm mounting plate, a non-armored cable, an adapter plug, and a LEMO cable end. The difference is the total cable length. The PR6426/000-000 has a 4 m cable, while the PR6426/000-020 has a 6 m cable. The longer version is suitable when the distance between the sensor mounting point and the conversion equipment requires additional cable reach.

Does the 6 m cable affect the sensor’s measuring sensitivity?

The standard nominal sensitivity remains 2 V/mm when the sensor is used with the correctly matched converter and measuring chain. Cable length is a configuration parameter, not a change to the specified static measuring range. The complete sensor and converter arrangement should nevertheless be checked to ensure that the selected cable configuration matches the intended system.

How should the PR6426/000-020 be mounted relative to the shaft?

The PR6426 uses its 80 × 40 mm mounting plate as the installation reference. At the nominal center position, the distance from the mounting plate to the measuring target is approximately 39.5 mm. The probe also requires at least 80 mm of free space around the sensor head for the standard measuring range. The final position should follow the installation drawing and the connected converter’s adjustment procedure.

Can the PR6426/000-020 be used with a CON021 signal converter?

The PR6426 family is compatible with supported CON series signal converters, including the CON021. The sensor and converter should be matched and adjusted as one measuring chain. Before installation, verify the connector arrangement, cable configuration, target material, and converter version to ensure that the measurement system operates within its specified range.