Product Overview

The Epro PR6426/000-121 is a 32 mm eddy current sensor used for non-contact measurement of shaft displacement in critical rotating machinery. It belongs to the PR6426 family, which is used to monitor axial and radial shaft movement, shaft position, eccentricity, and related rotor behavior. Typical applications include steam turbines, gas turbines, hydro turbines, large compressors, pumps, and industrial fans.

In a turbine bearing housing, the shaft may shift as thrust loads change or the rotor reaches its normal operating temperature. A sensor installed near the shaft measures the changing gap between its sensing face and the conductive metal surface. The resulting signal can be processed by compatible monitoring electronics to track displacement and help engineers identify changes in the machine’s operating condition.

The 32 mm sensing head is intended for applications involving large shafts. The PR6426 family supports a standard static measuring range of ±4.0 mm, with a nominal sensitivity of 2 V/mm when used with the specified reference target and measuring chain. This makes the family suitable for installations where shaft-position changes need to be measured over a wider range than conventional small-displacement probes allow.

The PR6426/000-121 is associated with CON031 converter configurations in product listings. The probe and converter must be treated as a matched measuring chain, since the connector arrangement, calibration, and output characteristics determine whether the signal can be used correctly by the monitoring system. When replacing a sensor, confirm the full order code and the installed converter interface rather than relying on the shared PR6426 designation alone.

For maintenance teams, the useful information is not just a single displacement reading but how that reading changes with machine load, temperature, and operating time. A gradual shift may point to a different investigation than a sudden signal deviation. Reviewing the trend alongside vibration and bearing-temperature data provides a more complete picture of the machine’s condition.

Technical Specifications

Product Features

• Non-contact shaft measurement: Detects changes in the distance between the probe and the rotating metal surface.
• 32 mm sensing head: Suited to large-shaft displacement measurement where the installation geometry meets the probe’s requirements.
• Wide static measuring range: The standard PR6426 configuration supports measurement up to ±4.0 mm.
• Displacement and position monitoring: Supplies data for observing axial or radial shaft movement, depending on probe placement.
• Converter-based signal processing: Works with compatible electronics to convert the probe response into usable measurement data.
• Industrial construction: The PR6426 family uses a stainless-steel sleeve and PTFE cable.
• Dynamic measurement capability: Supports shaft-motion monitoring within the bandwidth of the complete measuring chain.
• Machinery monitoring integration: Can be incorporated into a compatible monitoring or protection arrangement.

Working Principle

The PR6426/000-121 operates using the eddy current principle. Its sensing circuit generates an electromagnetic field that interacts with the conductive metal shaft. This interaction produces eddy currents in the target, and the sensor’s electrical response changes as the gap between the probe and the shaft changes.

A compatible converter processes this response into an electrical signal representing displacement. The typical measurement path is:

Rotating Shaft → PR6426/000-121 Sensor → Compatible Signal Converter → Machinery Monitoring System

When the shaft moves toward the sensing face, the gap decreases. When it moves away, the gap increases. Within the configured linear measuring region, the change in gap produces a corresponding change in the signal. The monitoring equipment can then display the displacement, store operating trends, and compare measurements with configured alarm limits.

For the standard PR6426 measuring configuration, the static range is ±4.0 mm and nominal sensitivity is 2 V/mm for the specified reference target. The final output depends on the converter and measuring mode. The sensor should therefore be commissioned with compatible conversion electronics rather than connected to an arbitrary input channel.

The target surface also influences the result. The standard reference material is 42CrMo4 ferromagnetic steel. Different electrical and magnetic properties can change the relationship between physical gap and output, so target-material compatibility matters when setting up the measuring chain.

The initial air gap determines the sensor’s operating point. The probe must be positioned so that expected shaft movement remains inside the usable linear region. An incorrect starting gap can limit available travel in one direction or produce misleading readings when the shaft moves under load.

The probe supplies displacement data but does not independently decide when a machine should trip. Alarm and shutdown actions depend on the connected monitoring or protection equipment and its configured logic.

Role in a Machinery Condition Monitoring System

The PR6426/000-121 acts as the sensing element in a shaft-displacement channel. It detects the changing distance between the probe and the shaft, while compatible conversion equipment and monitoring electronics process the signal for operational assessment.

Rotating Shaft → PR6426/000-121 → CON031-Compatible Measuring Chain → Monitoring Channel → Alarm or Protection Logic

Industrial Applications

Installation and Maintenance

1. Verify the full order code: Confirm that the sensor is PR6426/000-121 and check that the installed converter supports the specific sensor configuration.
2. Inspect the mounting point: Ensure the probe can be secured and aligned with the intended shaft measurement surface.
3. Set the initial air gap: Follow the applicable installation procedure to position the sensor within the intended measuring range.
4. Check target-material compatibility: Confirm that the shaft material matches the measuring-chain calibration or that any required adjustment has been accounted for.
5. Maintain the required clearance: Observe the specified clearance around the sensing head to minimize interference from nearby ferrous structures.
6. Verify converter compatibility: Confirm the CON031 configuration, connector arrangement, and output requirements before commissioning.
7. Inspect the cable assembly: Check for abrasion, damaged insulation, loose connections, and signs of excessive heat exposure.
8. Protect cable routing: Avoid sharp edges, excessive bending, moving parts, and sources of electrical interference.
9. Validate the measurement signal: Confirm that the output matches the expected initial gap and converter settings before enabling the monitoring channel.
10. Investigate unexpected readings: Check the probe alignment, target surface, cable connections, converter status, and machine operating conditions if the signal changes unexpectedly.
11. Follow machinery safety procedures: Apply the required isolation and site safety measures before accessing the sensor near rotating equipment.
12. Document commissioning settings: Record the sensor model, target material, initial gap, converter configuration, and baseline readings for later trend comparisons.

Compatible System Components

Recommended Related Models

Key Advantages

• Measures shaft displacement without contact with the rotating surface.
• Supports a standard static measuring range of ±4.0 mm.
• Supplies measurement data to compatible monitoring electronics.
• Supports continuous assessment of shaft position in critical rotating machinery.
• Helps maintenance teams compare displacement trends with other operating measurements.

Technical FAQs

What should be checked before replacing a PR6426/000-121?

Verify the complete order code, sensor connection, cable arrangement, target material, and converter compatibility. A matching 32 mm head diameter alone does not establish that another PR6426 variant can be installed without further checks.

What does the ±4.0 mm measuring range mean?

It is the standard static measuring range of the PR6426 family. The usable range in an actual installation depends on the selected measuring configuration, the initial air gap, and the associated conversion electronics.

Why must the probe be calibrated for the target material?

Eddy current response depends on the electrical and magnetic properties of the conductive target. The standard reference material is 42CrMo4 steel. A different shaft material can affect the relationship between the physical gap and the electrical output.

Can this sensor provide a machine trip signal directly?

The sensor measures displacement and supplies a corresponding response to the connected electronics. Alarm and trip functions depend on the compatible monitoring or protection equipment and its configured logic.