Product Overview

The Epro PR6426/000-111 is a 32 mm eddy current sensor used for non-contact displacement measurement in critical rotating machinery. It belongs to the PR6426 sensor family, which is commonly applied to steam turbines, gas turbines, hydro turbines, compressors, pumps, and fans. The sensor measures changes in the distance between its sensing face and a conductive metal target, allowing shaft position and movement to be monitored while the machine is running.

In a large turbine, the rotor can move axially as thrust conditions change, while radial displacement may develop alongside bearing wear, imbalance, or changes in rotor dynamics. A probe installed at the appropriate measurement point detects variations in the shaft-to-sensor gap. The resulting signal can be processed by compatible monitoring equipment to track shaft displacement and identify changes from the machine’s established operating pattern.

The 32 mm sensing head is intended for installations involving large rotating shafts. The PR6426 family supports a static measuring range of ±4.0 mm under its standard configuration, making it suitable for applications that require more displacement travel than a narrow-range proximity measurement may offer. Actual measurement performance depends on the target material, initial air gap, mounting geometry, and associated signal-conversion equipment.

The PR6426/000-111 should be treated as one component of a complete measurement chain. The probe must be matched to compatible conversion equipment and the receiving monitoring channel. When replacing an existing sensor, the complete order code, cable arrangement, connector interface, and converter configuration need to be checked rather than relying on the shared PR6426 family designation alone.

For maintenance engineers, the value of shaft-displacement measurement lies in the information it adds to machinery condition assessment. A gradual change in rotor position may call for a different investigation from an abrupt signal deviation. Comparing the displacement trend with vibration, bearing temperature, and operating load helps establish whether further mechanical inspection is warranted.

Technical Specifications

Product Features

• Non-contact displacement sensing: Measures the changing gap between the probe and a conductive shaft without physical contact.
• 32 mm sensing head: Suited to large-shaft measurement arrangements that meet the required mounting and target-clearance conditions.
• Wide static measuring range: Supports displacement measurement up to ±4.0 mm under the standard PR6426 configuration.
• Dynamic shaft monitoring: Captures changes in shaft position within the bandwidth of the complete measurement chain.
• Converter-based signal processing: Works with compatible electronics to make the probe response available to monitoring equipment.
• Industrial sensor construction: Uses a stainless-steel sleeve and PTFE cable in the specified sensor assembly.
• Continuous condition assessment: Supplies shaft-displacement data that can be compared with other machinery measurements.
• Integration with monitoring systems: Can be incorporated into a compatible machinery monitoring or protection arrangement.

Working Principle

The PR6426/000-111 measures displacement through 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, changing the electrical response of the sensor according to the distance between the sensing face and the shaft surface.

A compatible signal converter processes the response into an electrical measurement signal. In a typical installation, the signal path is:

Rotating Shaft → PR6426/000-111 Sensor → Compatible Signal Converter → Machinery Monitoring System

As the shaft moves toward the probe, the gap decreases. When it moves away, the gap increases. Within the configured linear region, the electrical response changes in relation to the displacement. The monitoring system can then display the measurement, store operating trends, and compare readings against configured alarm thresholds.

The standard PR6426 configuration has a static measuring range of ±4.0 mm and a nominal sensitivity of 2 V/mm for the specified reference target. The actual output characteristics depend on the selected converter and measurement mode. The probe and converter therefore need to be configured as a matched measuring chain, particularly where the application requires a specific output range.

Target material affects the measurement relationship. The standard reference target is ferromagnetic steel, grade 42CrMo4. A shaft made from a different material may produce a different response at the same physical gap because its electrical and magnetic properties influence eddy current behavior. Material compatibility should be considered during system selection and commissioning.

The initial air gap establishes the sensor’s operating point. If the probe is positioned too close to or too far from the shaft, the expected movement may extend beyond the intended linear measuring region. Correct adjustment leaves sufficient measurement travel for the anticipated shaft displacement in both directions.

The sensor itself does not determine whether a machine should stop. It supplies displacement data to the connected monitoring or protection equipment, which evaluates the signal according to its configured thresholds and operating logic.

Role in a Machinery Condition Monitoring System

The PR6426/000-111 serves as the measurement point between the rotating shaft and the electronic monitoring system. It detects changes in the shaft-to-probe gap, while compatible conversion equipment processes the response into data that can be interpreted by plant personnel or protection logic.

Rotating Shaft → PR6426/000-111 → Signal Converter → Monitoring Channel → Alarm or Protection Logic

Industrial Applications

Installation and Maintenance

1. Verify the complete model code: Confirm that the sensor is PR6426/000-111 and that its connection arrangement matches the intended measuring system.
2. Inspect the mounting location: Check that the probe can be secured at the required measurement point with suitable alignment to the shaft surface.
3. Set the initial air gap: Follow the applicable installation procedure to establish the correct starting position for the selected measuring configuration.
4. Check target-material compatibility: Confirm that the shaft material is compatible with the measurement calibration, particularly when it differs from the standard 42CrMo4 reference material.
5. Maintain the required clearance: Observe the specified clearance around the probe to reduce interference from nearby ferrous structures.
6. Verify converter compatibility: Match the sensor interface, converter configuration, and required output characteristics before commissioning.
7. Inspect the cable assembly: Check for abrasion, damaged insulation, loose connections, or signs of excessive heat exposure.
8. Protect cable routing: Keep the cable away from sharp edges, excessive bending, moving components, and sources of electrical interference.
9. Validate the measurement output: Confirm that the signal corresponds to the expected initial gap and selected converter configuration before enabling the monitoring channel.
10. Investigate abnormal readings: Check probe alignment, the target surface, cable connections, converter settings, and machine operating conditions if the signal changes unexpectedly.
11. Apply machinery safety procedures: Follow the required isolation and site safety measures before accessing the sensor near rotating equipment.
12. Record commissioning data: Document the model, target material, initial gap, converter configuration, and baseline readings for future trend comparisons.

Compatible System Components

Recommended Related Models

Key Advantages

• Measures shaft displacement without contacting the rotating surface.
• Supports a standard static measuring range of ±4.0 mm.
• Supplies measurement data to compatible machinery monitoring equipment.
• Supports continuous observation of shaft position in critical rotating machinery.
• Helps engineers assess displacement trends alongside vibration and operating conditions.

Technical FAQs

What should be verified when selecting a replacement for the PR6426/000-111?

Check the complete order code, sensor connection, cable arrangement, target material, and compatibility with the installed converter. Sensors within the same PR6426 family should not be assumed interchangeable solely because they share the same head diameter.

Can the PR6426/000-111 monitor both axial and radial shaft movement?

The PR6426 family can be used for either measurement direction, depending on the probe’s mounting position. The installation must align with the intended shaft movement, and the monitoring channel must be configured for the corresponding measurement.

Why does the shaft material matter when commissioning this sensor?

Eddy current response depends on the electrical and magnetic properties of the target. The standard reference material is 42CrMo4 ferromagnetic steel. If the actual shaft material differs, the measurement response may change and must be considered when validating the measuring chain.

What checks are useful when the displacement reading changes suddenly?

Review the shaft’s operating conditions alongside the sensor mounting, initial air gap, cable connections, target surface, and converter status. Comparing the reading with vibration and bearing-temperature data can help determine whether the change reflects actual rotor movement or a measurement-system issue.