Product Overview

The Epro PR6424/016-121 16 mm Eddy Current Sensor is a non-contact displacement sensor designed for monitoring the operating condition of rotating machinery. Manufactured under the EPRO product line associated with Emerson, it belongs to the PR6424 series of 16 mm eddy current sensors. The sensor is designed for applications where accurate measurement of shaft movement, vibration, and position is important for machinery protection and condition monitoring.

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 continuously monitoring high-speed rotating equipment, including turbines, compressors, pumps, and industrial fans.

The PR6424/016-121 is identified by its 16 mm sensor head diameter. It is intended for use in machinery monitoring systems that measure radial and axial shaft displacement, shaft vibration, position, eccentricity, and speed-related signals. These measurements can help maintenance teams identify abnormal machine conditions before they develop into serious mechanical problems.

The PR6424 series uses an eddy current measurement principle and provides a nominal sensitivity of 4 V/mm with a specified linearity of up to ±1.5%. Its static measurement range is ±2.0 mm, while its dynamic measurement range extends from 0 to 1,000 μm. The nominal center air gap is approximately 2.7 mm.

The sensor is normally used as part of a complete measurement chain that includes a compatible signal converter and the required connecting components. The converter processes the sensor signal and provides an output suitable for machinery monitoring equipment.

For industrial maintenance and replacement projects, verifying the complete model number, cable configuration, connector type, and converter compatibility is essential.

Technical Specifications

Note: Electrical performance values are based on PR6424 series specifications. The exact cable, connector, thread, and mounting configuration should be confirmed against the PR6424/016-121 product label and applicable variant documentation.

Function and Working Principle

The PR6424/016-121 operates using the eddy current principle. It generates an electromagnetic field at the sensor tip and measures changes in that field when a conductive target moves relative to the probe.

The resulting signal represents the distance between the sensor and the target surface. When used with a compatible signal converter, this measurement can be processed into an electrical output for monitoring and protection equipment.

1. Non-Contact Displacement Measurement

The sensor is installed near a rotating shaft with a carefully adjusted clearance between the probe tip and the target surface.

As the shaft moves, the distance between the shaft surface and the probe changes. The sensor detects these variations without contacting the shaft.

This arrangement is useful for measuring shaft movement in large rotating machines where continuous mechanical contact would be unsuitable.

2. Eddy Current Measurement Principle

The sensor produces a high-frequency electromagnetic field around its sensing tip. When a suitable conductive target approaches the tip, eddy currents are induced in the target material.

These currents influence the electromagnetic characteristics of the sensor coil. Changes in the target distance therefore produce measurable changes in the sensor’s electrical response.

A compatible signal converter processes this response and converts it into a usable measurement signal.

The target material is important. PR6424 specifications identify ferromagnetic steel as the standard target material, so the target surface and material properties must be considered during installation and calibration.

3. Shaft Vibration Monitoring

Rotating machinery naturally experiences some degree of mechanical movement. However, excessive shaft vibration may indicate imbalance, misalignment, bearing deterioration, looseness, or other mechanical problems.

The PR6424 sensor can measure dynamic shaft displacement within its specified operating range. When installed at appropriate measurement locations, it provides information that can help monitoring systems identify changes in vibration behavior.

4. Shaft Position Measurement

In addition to dynamic vibration, the sensor can measure static shaft displacement within its specified range.

This capability is useful for monitoring shaft position, axial movement, and other mechanical changes that may affect the operating condition of turbines and compressors.

5. Signal Conversion

The sensor is one part of a complete measurement system. Its output must be processed by a compatible signal converter before being connected to the relevant monitoring equipment.

The converter establishes the appropriate measurement characteristics and provides an output that can be interpreted by machinery protection or condition-monitoring systems.

The correct converter model and connection arrangement must be confirmed for the specific sensor variant.

Role in Industrial Machinery Monitoring Systems

The Epro PR6424/016-121 can serve as a measurement element in machinery protection and condition-monitoring installations. It provides information about shaft movement that can be used by monitoring equipment, control systems, and maintenance personnel.

Turbine Protection

Steam and gas turbines operate at high rotational speeds and require continuous monitoring of critical mechanical parameters.

Eddy current sensors can measure shaft displacement and vibration at designated monitoring positions. These measurements help operators identify abnormal shaft movement and assess the mechanical condition of the turbine.

Compressor Monitoring

Industrial compressors operate under changing pressure, temperature, and load conditions. Shaft vibration and position measurements can provide important information about mechanical performance.

The PR6424 sensor can be installed at suitable measurement points to monitor shaft behavior and support maintenance decisions.

PLC and Monitoring-System Integration

A compatible signal converter can provide a measurement output for machinery monitoring equipment or an appropriate control-system input.

Depending on the system architecture, the measurement may be used for:

• Displaying shaft vibration values.
• Monitoring shaft displacement.
• Generating alarms when configured limits are exceeded.
• Recording long-term machinery trends.
• Supporting maintenance and diagnostic procedures.

The sensor itself is not a PLC input module. Correct signal conditioning and interface hardware are required between the probe and the monitoring or control system.

Condition-Based Maintenance

Continuous measurement data can help maintenance teams evaluate changes in machine behavior over time.

Instead of relying exclusively on fixed maintenance intervals, operators can use vibration and displacement trends to identify equipment that may require inspection.

This approach can support more informed maintenance planning and help reduce the risk of unexpected machinery downtime.

Industrial Applications

The PR6424 series is designed for critical rotating machinery applications. Its 16 mm sensing head and non-contact measurement principle make it suitable for installations where shaft displacement and vibration measurements are required.

1. Steam Turbines

Steam turbines operate under demanding mechanical and thermal conditions. Monitoring shaft vibration and displacement is important for evaluating rotor behavior and identifying abnormal operating conditions.

The PR6424 sensor can be installed at appropriate measurement positions to provide non-contact shaft movement measurements.

2. Gas Turbines

Gas turbines require reliable monitoring because excessive vibration or shaft displacement can affect equipment stability and service life.

Eddy current sensors can provide measurements for machinery protection and condition-monitoring systems, helping operators observe changes in rotor behavior.

3. Hydro Turbines

Hydro turbines operate with large rotating assemblies and may experience changes in mechanical loading during operation.

Shaft displacement monitoring can help identify abnormal movement and provide useful information for equipment maintenance.

4. Industrial Compressors

Compressors are widely used in chemical processing, petrochemical production, power generation, and manufacturing.

The PR6424 sensor can be used to measure shaft vibration and position in suitable compressor monitoring installations. These measurements can support the detection of mechanical changes associated with imbalance, misalignment, or bearing-related problems.

5. Industrial Pumps

Large industrial pumps often operate continuously and may be critical to production processes.

Shaft vibration and displacement measurements can help maintenance personnel evaluate pump operating conditions and identify potential mechanical deterioration.

6. Industrial Fans

Large fans and ventilation systems may operate under changing load conditions. Monitoring shaft movement can provide additional information about mechanical stability and equipment condition.

The sensor can be considered for suitable fan monitoring applications where its measurement range and installation requirements are met.

Installation and System Integration

Correct installation is essential for obtaining reliable measurements from an eddy current sensor. Probe position, target material, air gap, cable arrangement, and signal-converter compatibility all influence measurement performance.

1. Confirm Sensor Compatibility

Before installation, verify the complete PR6424/016-121 model number and confirm that it is compatible with the intended signal converter and monitoring system.

Do not assume that every PR6424 variant has identical cable lengths, connectors, or electrical configurations.

The sensor, extension cable, and converter should be treated as a coordinated measurement system.

2. Prepare the Mounting Location

The sensor should be installed at a mechanically stable location near the shaft or target surface.

The mounting arrangement must prevent unwanted probe movement during operation. Vibration of the sensor housing itself can affect measurement accuracy and should be minimized.

Follow the manufacturer’s installation requirements for threaded mounting, locking hardware, and mechanical clearance.

3. Set the Initial Air Gap

The distance between the probe tip and the target surface is an important installation parameter.

The PR6424 series has a nominal center air gap of approximately 2.7 mm. The actual installation gap must be established according to the manufacturer’s calibration and converter requirements.

Incorrect gap adjustment may cause measurement errors or reduce the available linear operating range.

4. Verify Target Material

The target material should match the sensor’s specified measurement characteristics.

The PR6424 series identifies ferromagnetic steel as its standard target material. Differences in material composition, surface condition, and geometry may influence the measurement response.

Verify the target material and shaft characteristics before commissioning.

5. Route and Protect the Cable

The sensor cable should be routed carefully to avoid excessive bending, abrasion, heat exposure, and mechanical damage.

Keep the cable away from sources of electrical interference where required by the installation design. Maintain the specified minimum bending radius and use suitable cable protection in areas exposed to vibration or mechanical contact.

6. Connect the Signal Converter

Connect the sensor to the specified compatible signal converter using the correct cable and connector arrangement.

Incorrect connections or mismatched converter configurations may result in inaccurate readings or failure to obtain a valid measurement signal.

Check the converter’s sensor compatibility, calibration requirements, supply arrangements, and output configuration before energizing the system.

7. Commission and Verify Measurements

After installation, verify the initial gap, sensor mounting stability, cable connections, and converter configuration.

Check that the measurement output changes consistently when the target distance changes. Confirm that the monitoring system displays plausible shaft position and vibration values.

Record the initial operating readings as a reference for future machinery-condition assessments.

Compatible System Components

The PR6424/016-121 is normally used as part of a complete eddy current measurement system. The following components may be required depending on the installation.

The components listed above are system elements, not necessarily accessories included with the sensor. Confirm the actual supply scope before ordering.

Alternative Models and Replacement Considerations

The PR6424 product family includes multiple probe variants. Although they may share a 16 mm sensing head diameter and similar measurement principles, differences in cable arrangement, probe length, connector configuration, and converter compatibility can affect replacement suitability.

Before replacing a sensor, compare:

• Complete model number and suffix.
• Sensor head diameter and probe length.
• Thread type and mounting dimensions.
• Integrated cable length.
• Connector and adaptor configuration.
• Armored or non-armored cable arrangement.
• Signal converter compatibility.
• Measurement range and calibration requirements.
• Target material and installation air gap.

A sensor with the same 16 mm head diameter is not necessarily a direct replacement. Always verify the full configuration.

Key Advantages

Non-Contact Measurement

The PR6424 uses eddy current technology to measure shaft movement without physical contact. This makes it suitable for continuous monitoring of rotating machinery.

16 mm Sensor Head

The 16 mm sensing head is designed for applications requiring a larger probe diameter within the PR6424 sensor family.

High Measurement Sensitivity

The specified sensitivity of 4 V/mm supports the measurement of small changes in target distance when used with the appropriate converter.

Static and Dynamic Measurement

The series supports both static displacement and dynamic vibration measurements within its specified ranges.

Industrial Temperature Capability

The PR6424 series is designed for industrial operating environments, with a published sensor temperature range of -35°C to +180°C. The temperature limits of the complete cable and measurement system should also be checked.

Turbomachinery Monitoring

The sensor is intended for applications involving turbines, compressors, pumps, and fans, where shaft movement measurements are important for machinery protection.

Condition-Monitoring Support

Measurement data can help operators identify changes in shaft behavior and support predictive and condition-based maintenance strategies.

Technical FAQs

1. What is the Epro PR6424/016-121?

The Epro PR6424/016-121 is a 16 mm eddy current displacement sensor used for non-contact measurement of shaft movement, vibration, position, and related mechanical parameters in rotating machinery.

2. What is the sensor head diameter?

The specified sensor head diameter is 16 mm.

3. What is the measurement principle?

It uses electromagnetic eddy current technology. Changes in the distance between the sensor tip and a conductive target influence the sensor’s electrical response.

4. What is the sensitivity of the PR6424 series?

The published sensitivity is 4 V/mm, with a specified linearity of up to ±1.5%.

5. What is the static measurement range?

The PR6424 series has a static measurement range of ±2.0 mm.

6. What is the dynamic measurement range?

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

7. What is the nominal center air gap?

The nominal center air gap is approximately 2.7 mm. The actual installation gap must follow the applicable sensor and converter calibration instructions.

8. Which machines can use this sensor?

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

9. Does the sensor connect directly to a PLC?

It is generally used with a compatible signal converter. The converter provides a suitable output for the machinery monitoring system or control-system interface.

10. What should be checked before purchasing a replacement?

Confirm the complete model number, sensor dimensions, cable length, connector type, mounting thread, and compatible signal converter. Also verify the unit’s condition and the supplier’s testing and warranty information.

Procurement and Maintenance Recommendations

When purchasing the Epro PR6424/016-121, verify the full catalog number rather than relying only on the PR6424 series name. Different variants may have different probe lengths, cable configurations, and connector arrangements.

For replacement projects, compare the existing sensor with the proposed replacement before installation. Check the probe label, mounting thread, cable length, connector, and signal converter requirements.

For used or surplus units, request clear photographs of the sensor head, cable, connector, and identification label. Confirm whether the supplied product includes the required cable or other connection accessories.

During maintenance, inspect the probe mounting, cable insulation, connector condition, and mechanical clearance. Look for signs of abrasion, loose mounting hardware, excessive heat exposure, or cable damage.

It is also useful to retain initial measurement readings and installation details. Comparing current readings with historical data can help maintenance teams identify changes in machinery behavior and plan inspections more effectively.

Conclusion

The Epro PR6424/016-121 16 mm Eddy Current Sensor is designed for non-contact shaft displacement and vibration measurement in critical rotating machinery. Its PR6424 series specifications include 4 V/mm sensitivity, linearity of up to ±1.5%, a static measurement range of ±2.0 mm, and a dynamic measurement range of 0–1,000 μm.

With applications in turbines, compressors, pumps, and industrial fans, the sensor can provide important measurement information for machinery protection and condition monitoring. For reliable operation, correct probe installation, air-gap adjustment, cable configuration, and signal-converter compatibility must be verified before commissioning.