Product Overview

The Epro PR6426/010-020 is a 32 mm eddy current sensor used for non-contact measurement of shaft displacement in critical rotating machinery. It belongs to the PR6426 sensor family used in turbine, compressor, pump, and fan monitoring applications, where engineers need to track the position and movement of a rotating shaft without introducing mechanical contact at the measurement point.

In a steam turbine, a sensor installed near a bearing can measure the shaft’s position relative to the stationary machine structure. In an industrial compressor, displacement measurements help maintenance personnel examine rotor movement during startup, changes in operating load, and investigations into abnormal vibration. Depending on the sensor arrangement, the measurement can be used to monitor radial or axial shaft displacement.

The PR6426/010-020 performs the sensing function within a larger measurement chain. Its electromagnetic field interacts with the conductive shaft surface, and changes in the distance between the sensor head and the target alter the sensor’s electrical response. Compatible signal-conditioning electronics process that response into a measurement signal for the machinery monitoring system.

The complete model designation matters when replacing an installed probe. Although PR6426 variants share the 32 mm sensor-head format, that common dimension does not establish that their cable arrangements, connections, or measuring-chain configurations are interchangeable. The /010-020 suffix should therefore be retained when identifying the required spare part.

For maintenance engineers, the main considerations are the mounting position, target material, initial gap, cable routing, and compatibility with the installed signal converter. These factors determine whether the sensor can deliver meaningful displacement readings under the machine’s actual operating conditions.

Technical Specifications

Product Features

• Non-contact shaft measurement: Detects changes in the distance between the probe and a conductive target without a contacting element rubbing against the rotating shaft.
• 32 mm sensor-head format: Suited to PR6426 installations where the mounting arrangement and target geometry accommodate this probe configuration.
• Displacement measurement capability: Supports shaft-position monitoring in applications where radial or axial movement needs to be evaluated during machine operation.
• Defined standard measuring characteristics: The PR6426 family specifies a nominal sensitivity of 2 V/mm and a static measuring range of ±4.0 mm for the standard measuring configuration.
• Low long-term drift: The family specification lists long-term drift below 0.3%, a useful characteristic for installations where displacement readings are recorded and compared over extended operating periods.
• Industrial construction: A stainless-steel sleeve and PTFE cable form part of the sensor construction, with operating limits determined by the applicable sensor and cable specifications.
• Converter-based signal processing: The sensor works with compatible electronics that excite the probe and convert its response into a signal suitable for monitoring equipment.
• Variant-specific identification: Retaining the complete /010-020 designation helps prevent confusion with other PR6426 probes that share the same nominal head diameter.

Working Principle

The PR6426/010-020 operates through electromagnetic coupling between its sensing coil and a conductive target. When the sensor is excited by compatible electronics, an alternating electromagnetic field forms around the sensing head. Eddy currents develop in the target, affecting the electrical response of the sensor coil.

As the shaft moves relative to the fixed probe, the gap between the sensing head and the target changes. The corresponding electrical response is processed by the signal-conditioning equipment to produce a measurement related to the shaft’s position.

The measurement path is:

Conductive Shaft Target → PR6426/010-020 Sensor → Compatible Signal Converter → Machinery Monitoring System

For the standard PR6426 measuring configuration, the nominal sensitivity is 2 V/mm and the static measuring range is ±4.0 mm. These characteristics apply to the specified standard measuring chain; the exact performance of an installed channel depends on the compatible converter, calibration, and target conditions.

The initial gap establishes the sensor’s operating point. If the probe is mounted too close to the shaft, available travel in one direction may be limited. If it is positioned too far away, the sensor may operate outside the intended measurement region. Correct adjustment is therefore essential before the channel is returned to service.

The material of the measured surface also affects the electromagnetic response. Ferromagnetic steel, specifically 42CrMo4, is the standard reference target for the PR6426 family. When the actual shaft material differs, the effect on calibration should be assessed rather than assuming that the same displacement-to-signal relationship will remain unchanged.

Once the signal reaches the monitoring system, engineers can compare displacement readings with machine speed, load, vibration, and operating history. The sensor supplies measurement data; identifying a mechanical fault requires interpretation of that data in the context of the machine’s operating condition.

Role in the Machinery Monitoring Architecture

The PR6426/010-020 occupies the sensing stage of a shaft-displacement measurement channel. It detects relative movement between the shaft and the stationary sensor mounting point, while compatible electronics process the response for the receiving monitoring equipment.

In a turbine installation, the measurement channel may be used to observe shaft movement near a bearing. In a compressor, displacement readings can be reviewed alongside vibration and operating data to help investigate changes in rotor behavior.

The sensor and converter must be treated as parts of a coordinated measuring chain. Replacing the probe without checking the converter configuration can introduce differences in calibration or signal interpretation, even when the replacement fits the existing mounting arrangement.

Industrial Applications

Installation and Maintenance

1. Verify the full model designation: Confirm PR6426/010-020 against the installed probe and maintenance records. Do not select a replacement based only on the PR6426 family name or sensor-head diameter.
2. Check signal-converter compatibility: Confirm that the existing electronics support the replacement sensor and intended measuring configuration. Verify the complete measuring chain before connecting the probe.
3. Inspect the shaft target: Examine the measurement surface for damage, deposits, or other conditions that could affect the sensing response. Confirm that the target material is appropriate for the installed calibration.
4. Prepare the mounting arrangement: Inspect the bracket, mounting thread, and fixing points. The probe must remain stationary relative to the machine structure so that holder movement does not distort the displacement reading.
5. Set the initial gap: Adjust the distance between the sensing head and target according to the applicable installation procedure. Use the correct procedure for the installed sensor-converter combination rather than estimating the gap from the head diameter.
6. Check surrounding metal clearance: Inspect nearby ferrous components that may influence the electromagnetic field. Confirm that the probe’s installation meets the required clearance conditions.
7. Inspect the sensing head: Check the sleeve and sensing area for impact damage, deformation, or contamination. Verify that the probe can be secured without mechanical stress on the sensing assembly.
8. Examine the cable route: Look for abrasion, cuts, crushing, or excessive bending. Keep the cable away from moving parts and heat sources beyond the applicable cable temperature limits.
9. Verify the connection arrangement: Confirm that the cable and connector match the receiving electronics. Do not assume that all PR6426 variants have identical cable terminations.
10. Check the measurement response: Follow the approved commissioning procedure to confirm that changes in target position produce the expected sensor response. Investigate abnormal readings before placing the channel into normal service.
11. Validate monitoring-channel scaling: Check the receiving system’s configured measurement range, engineering units, and alarm limits. Ensure that the channel settings correspond to the installed sensor and converter combination.
12. Record commissioning details: Document the complete model designation, converter identification, initial gap, cable arrangement, and commissioning results. These records simplify subsequent inspections and replacement work.

Compatible System Components

Component compatibility must be verified for the actual sensor and monitoring configuration. A shared PR6426 family designation does not, by itself, establish that a particular converter, cable, or connection assembly can be substituted directly.

Recommended Related Models

Key Advantages

• Non-contact measurement of relative shaft displacement.
• 32 mm sensor-head configuration for compatible PR6426 installations.
• Defined sensitivity and measuring characteristics in the standard configuration.
• Stainless-steel sleeve and PTFE cable construction.
• Integration with compatible machinery monitoring equipment.

Technical FAQs

What should be checked before using the PR6426/010-020 as a replacement for another PR6426 probe?

Compare the complete model designation, cable termination, connector arrangement, mounting requirements, and converter compatibility. The same head diameter does not establish direct interchangeability.

Does the PR6426/010-020 measure shaft vibration as well as displacement?

The sensor detects changes in the relative position between the sensing head and target. Dynamic changes in that position can contribute to vibration measurements when the sensor, converter, and monitoring channel are configured for the intended measurement.

Why does the initial gap matter when commissioning this sensor?

The initial gap establishes the sensor’s operating point within the calibrated range. Incorrect positioning can reduce the available measurement travel or place the channel outside its intended linear operating region.

What information is useful when investigating an unexpected change in displacement readings?

Review the sensor mounting, initial gap, cable and connector condition, converter configuration, target material, and monitoring-channel scaling. Compare the readings with machine speed, load, and other condition-monitoring data before deciding whether the change represents actual shaft movement.