Product Overview

The EPRO PR6424/017-121 16 mm Eddy Current Sensor is a non-contact displacement measurement probe designed for monitoring the operating condition of rotating machinery. Manufactured under the EPRO product line associated with Emerson, the PR6424 series is used in machinery protection and condition-monitoring systems where accurate measurement of shaft vibration, displacement, position, and eccentricity is required.

Unlike contact-based measurement devices, an eddy current sensor measures the distance between its sensing tip and a conductive target without physically touching the rotating shaft. This non-contact measurement principle makes it suitable for continuous monitoring in demanding industrial environments, including power generation, oil and gas processing, and heavy manufacturing.

The PR6424 series uses a nominal 16 mm sensor head and is designed for applications involving relatively large rotating shafts. Typical monitored equipment includes steam turbines, gas turbines, hydro turbines, compressors, pumps, and industrial fans.

The sensor operates by generating an electromagnetic field at its sensing tip. When a suitable metallic target approaches the probe, eddy currents are induced in the target. The resulting change in the probe’s electrical characteristics is used to determine the distance between the sensor and the target surface.

When connected to a compatible signal converter and monitoring system, the PR6424 sensor can provide measurement information for machinery protection, vibration analysis, and predictive maintenance.

The PR6424/017-121 is identified as a 16 mm eddy current sensor. Its supplied listing weight is 0.2 kg. Because the detailed configuration of the suffix can determine cable and connection arrangements, the complete model number should be checked when purchasing a replacement.

Technical Specifications

Note: The technical values above describe the published PR6424 family specifications. Confirm the exact cable, connector, thread, and configuration for PR6424/017-121 using the product label and applicable ordering documentation.

Function and Working Principle

The PR6424/017-121 uses the eddy current principle to measure the distance between the probe tip and a conductive metallic target. This allows the sensor to monitor shaft movement without direct mechanical contact.

1. Electromagnetic Field Generation

An electrical signal supplied by a compatible signal converter energizes the sensor coil. The coil generates a high-frequency electromagnetic field around the sensing tip.

When a conductive target is positioned within the effective measuring area, the electromagnetic field interacts with the target material.

2. Eddy Current Induction

The alternating electromagnetic field induces circulating electrical currents, known as eddy currents, in the metallic target.

The strength and distribution of these currents depend on the distance between the sensor and the target, as well as the target’s material and electrical properties.

As the shaft moves closer to or farther away from the probe, the interaction between the electromagnetic field and the target changes.

3. Distance Measurement

The change in the sensor’s electrical characteristics is processed by a compatible signal converter. The converter produces an output related to the distance between the probe tip and the target surface.

For the PR6424 family, the published sensitivity is 4 V/mm, with a linearity specification of up to ±1.5% under the specified operating conditions.

This relationship allows the system to measure both static shaft position and dynamic shaft movement.

4. Shaft Vibration Monitoring

When a rotating shaft vibrates, its distance from a stationary sensor changes continuously. The probe detects these variations and provides a signal representing the shaft’s relative movement.

The monitoring system can use this information to identify abnormal vibration patterns, changes in shaft position, and developing mechanical problems.

5. Position and Eccentricity Measurement

The sensor can also monitor shaft position and eccentricity. These measurements are useful during machine startup, shutdown, and normal operation.

By observing changes in shaft position, maintenance personnel can identify operating conditions that may require further inspection or corrective action.

Role in Industrial Machinery Protection Systems

The PR6424/017-121 is intended to function as part of a complete machinery monitoring arrangement rather than as a standalone display or controller.

A typical measurement system consists of a sensor probe, a compatible extension cable, a signal converter, and a monitoring or protection instrument.

1. Shaft Relative Vibration Measurement

In rotating machinery, shaft vibration is an important indicator of mechanical condition. Excessive vibration may be associated with rotor imbalance, misalignment, bearing problems, looseness, or other mechanical abnormalities.

An eddy current probe positioned near the shaft can continuously measure changes in the gap between the probe and the shaft surface.

The resulting signal can be processed by a monitoring instrument to display vibration values and support alarm or trip functions when the complete system is appropriately configured.

2. Axial Displacement Monitoring

Axial movement can affect the operating condition of turbines, compressors, and other large rotating machines.

A properly installed displacement sensor can monitor axial shaft movement relative to a suitable reference surface. The measurement can help identify abnormal rotor movement and provide information for machinery protection.

The probe orientation, target surface, measuring range, and system configuration must be selected for the specific machine.

3. Shaft Position Monitoring

Shaft position measurements provide information about the relative location of the rotating shaft.

These measurements can be used during commissioning, startup, shutdown, and routine operation. Changes in shaft position may indicate thermal movement, mechanical changes, or abnormal operating conditions.

4. Machinery Condition Monitoring

Continuous measurement data can be collected by machinery monitoring equipment and used to evaluate operating trends.

Maintenance personnel can compare current measurements with established baseline values to identify developing problems before they result in unplanned equipment shutdowns.

The sensor is therefore an important measurement component in predictive maintenance and machinery protection systems.

Industrial Applications

The EPRO PR6424 series is designed for critical rotating machinery where non-contact shaft measurement is required.

1. Steam Turbines

Steam turbines operate at high rotational speeds and are exposed to significant thermal and mechanical loads.

The PR6424 sensor can be used in suitable turbine monitoring arrangements to measure shaft vibration, displacement, and position. These measurements help operators evaluate rotor behavior during startup, steady-state operation, and shutdown.

2. Gas Turbines

Gas turbines require continuous monitoring of rotating components to support reliable operation.

Eddy current sensors can provide shaft displacement information for machinery protection systems. Changes in vibration or shaft position can be evaluated alongside other operating parameters to help identify abnormal conditions.

3. Hydro Turbines

Hydro turbines are used in hydroelectric power generation and may operate under varying load conditions.

The PR6424 sensor can support shaft vibration and displacement monitoring when installed with compatible monitoring equipment. Continuous measurement helps maintenance teams assess rotor behavior and identify changes that may require inspection.

4. Industrial Compressors

Large centrifugal and other industrial compressors rely on accurate rotor alignment and stable operating conditions.

Non-contact displacement sensors can monitor shaft vibration and relative movement. This information can help detect developing mechanical issues and support condition-based maintenance programs.

5. Industrial Pumps

Large pumps used in power plants, petrochemical facilities, and water-treatment installations may require continuous shaft monitoring.

The PR6424 sensor can be incorporated into a suitable monitoring system to measure shaft movement and provide information about the mechanical condition of the rotating assembly.

6. Industrial Fans

Large industrial fans and ventilation equipment can experience imbalance, misalignment, and vibration during operation.

A properly installed eddy current probe can measure shaft movement and provide data for vibration monitoring and maintenance analysis.

Installation and System Integration

Correct installation is essential for obtaining reliable measurements from the PR6424/017-121. Probe positioning, target material, cable routing, and signal-converter compatibility all influence measurement performance.

1. Confirm Sensor Configuration

Before installation, verify the complete model number, including the /017-121 suffix.

Check the sensor’s cable arrangement, connector type, mounting thread, and compatibility with the existing measurement system. Do not assume that every PR6424 probe has an identical cable or connector configuration.

2. Select the Correct Target Surface

The PR6424 family is designed to measure suitable ferromagnetic targets. The published standard target material reference is 42CrMo4 steel.

The target surface should be suitable for eddy current measurement and should meet the manufacturer’s requirements for material, geometry, and surface condition.

Material differences can affect sensor calibration and measurement accuracy. Where a non-standard target material is used, confirm the required calibration procedure.

3. Set the Initial Air Gap

The published nominal center air gap for the PR6424 family is approximately 2.7 mm.

The actual installation gap should be established according to the sensor and converter documentation. Correct positioning helps ensure that the sensor operates within its intended linear measurement range.

An incorrect initial gap may reduce measurement accuracy or cause the output to operate outside the specified range.

4. Secure the Probe

Install the sensor using the appropriate mounting arrangement. Ensure that the probe is firmly supported and cannot move because of machine vibration.

The sensing tip must be positioned correctly relative to the shaft. Avoid contact between the probe and rotating components.

For threaded installations, use the specified mounting hardware and follow the manufacturer’s tightening and adjustment instructions.

5. Connect the Signal Converter

The PR6424 probe must be paired with a compatible signal converter and system components.

The converter provides the electrical interface and processes the sensor response into a usable measurement signal. Confirm the converter model, cable type, total cable length, and connector arrangement before connecting the probe.

Do not assume compatibility based solely on the 16 mm probe diameter or PR6424 series name.

6. Route and Protect the Cable

The sensor cable should be routed away from sources of excessive heat, mechanical damage, and electrical interference.

Maintain the manufacturer’s specified minimum bending radius. Avoid sharp bends, pulling forces, or repeated movement that could damage the cable or connector.

Where the installation requires additional mechanical protection, select suitable cable routing and protection arrangements.

7. Verify Measurement Performance

After installation, confirm the initial gap, sensor connection, converter configuration, and monitoring-system response.

Check the measurement output under appropriate operating conditions and compare it with expected values. Record the installation position and baseline measurements for future maintenance.

Compatible System Components

A complete PR6424 measurement arrangement requires more than the probe itself. The following components may be used depending on the monitoring architecture and the specific sensor configuration.

The probe, extension cable, and converter should be treated as a matched measurement chain. Replacing only one component without checking the complete system may result in incorrect readings or incompatibility.

Alternative Models and Replacement Considerations

The PR6424 family includes different probe configurations. A replacement should not be selected solely because it has the same 16 mm sensing-head diameter.

Before replacing a PR6424/017-121, check:

• Complete model number and suffix.
• Sensor head diameter and mechanical dimensions.
• Mounting thread and installation length.
• Cable length and cable construction.
• Connector and extension-cable arrangement.
• Signal-converter compatibility.
• Measurement sensitivity and linearity.
• Static and dynamic measuring ranges.
• Target material and initial air gap.
• Operating temperature and environmental requirements.

A probe with the same nominal diameter may have a different cable configuration or electrical specification. Always compare the complete measurement system before approving a substitute.

Key Advantages

Non-Contact Measurement

The eddy current measuring principle allows the probe to monitor shaft movement without physical contact. This is suitable for continuous monitoring of rotating equipment.

High Measurement Sensitivity

The PR6424 family has a published sensitivity of 4 V/mm, supporting measurement of small changes in the distance between the sensor and the target.

Shaft Vibration Monitoring

The probe can detect dynamic shaft movement and provide measurement information for vibration analysis and machinery protection.

Static Position Measurement

The sensor can also measure static displacement within its specified range, supporting shaft-position and eccentricity monitoring.

Industrial Operating Temperature Range

The published PR6424 family operating temperature range is -35°C to +180°C, subject to the applicable installation and cable limitations.

Compact 16 mm Sensing Head

The 16 mm sensing head supports installation in suitable machinery-monitoring locations where probe access and mounting space must be considered.

Integration with Machinery Monitoring Systems

When paired with a compatible converter and monitoring instrument, the sensor can form part of a complete machinery protection and condition-monitoring arrangement.

Technical FAQs

1. What is the EPRO PR6424/017-121?

The PR6424/017-121 is a 16 mm eddy current displacement sensor used for non-contact monitoring of shaft vibration, displacement, position, and eccentricity in rotating machinery.

2. What is the sensor head diameter?

The nominal sensor head diameter is 16 mm.

3. What is the measurement principle?

The sensor uses electromagnetic induction. Its sensing coil generates an electromagnetic field, and the interaction with a conductive target changes according to the distance between the probe and the target surface.

4. What is the sensitivity of the PR6424 series?

The published family sensitivity is 4 V/mm, equivalent to approximately 101.6 mV/mil, with a linearity specification of up to ±1.5%.

5. What is the static measurement range?

The published static measurement range is ±2.0 mm.

6. What is the dynamic measurement range?

The published dynamic measurement range is 0–1,000 μm.

7. What material should be used as the measurement target?

The PR6424 family is designed for ferromagnetic steel targets. The published standard target material reference is 42CrMo4 steel.

8. What is the nominal center air gap?

The published nominal center air gap is approximately 2.7 mm. The final installation gap must follow the applicable sensor and converter documentation.

9. Which machines can use the PR6424 sensor?

Typical applications include steam turbines, gas turbines, hydro turbines, compressors, pumps, and industrial fans.

10. Does the sensor work independently?

No. It is normally used with a compatible extension cable, signal converter, and machinery monitoring system. The complete measurement chain must be checked for compatibility.

11. What is the weight of the PR6424/017-121?

The supplied product weight is 0.2 kg. The published PR6424 family specification lists approximately 200 grams for the sensor with a 1-meter cable, excluding armor.

12. Can another PR6424 model replace the PR6424/017-121?

Not automatically. Check the full model suffix, mounting dimensions, cable configuration, connector, converter compatibility, and measurement requirements before selecting a replacement.

Procurement and Maintenance Recommendations

When purchasing the EPRO PR6424/017-121, verify the complete model number and compare it with the identification label on the installed probe. The suffix is important because different configurations may have different cable lengths, connector arrangements, and mechanical details.

For replacement projects, confirm the compatibility of the probe, extension cable, and signal converter as a complete system. A sensor that appears mechanically similar may not produce the correct measurement signal when connected to an incompatible converter.

For used or refurbished equipment, inspect the sensing tip, threaded sleeve, cable insulation, connector, and identification label. Check for physical damage, corrosion, bent mounting hardware, and signs of cable stress. Where possible, request suitable electrical or functional test information.

During routine maintenance, inspect the probe mounting position and cable routing. Ensure that the cable is not exposed to excessive heat, vibration, sharp edges, or mechanical tension. Check that the probe remains securely installed and that the monitoring system continues to produce stable readings.

Maintain records of the initial air gap, converter configuration, baseline measurement values, and replacement history. These records help maintenance teams compare operating trends and identify changes in sensor performance.

Conclusion

The EPRO PR6424/017-121 16 mm Eddy Current Sensor is designed for non-contact measurement of shaft vibration, displacement, position, and eccentricity in critical rotating machinery. Its PR6424 family specifications include 4 V/mm sensitivity, ±2.0 mm static measurement range, 0–1,000 μm dynamic measurement range, and a nominal center air gap of approximately 2.7 mm.

When integrated with a compatible signal converter and machinery monitoring system, the sensor can support continuous equipment monitoring and condition-based maintenance. For procurement and replacement, verifying the complete model number, cable configuration, mounting details, and system compatibility is essential to maintaining reliable measurement performance.