Product Overview

The Epro PR6424/018-121 16 mm Eddy Current Sensor is a non-contact displacement sensor designed for monitoring the operating condition of critical rotating machinery. It belongs to the PR6424 sensor family developed for industrial machinery protection and condition-monitoring applications.

Manufactured under the EPRO product range associated with Emerson, the PR6424 series is used in applications involving steam turbines, gas turbines, hydro turbines, compressors, pumps, and fans. It measures the relative movement between the sensor tip and a conductive shaft surface without requiring direct mechanical contact.

In rotating equipment, shaft vibration and displacement can indicate changes in bearing condition, alignment, mechanical balance, or operating stability. Continuous measurement helps monitoring systems identify abnormal movement and provides information for machinery protection and maintenance decisions.

The PR6424/018-121 has a nominal sensor head diameter of 16 mm. Its eddy current measuring principle allows it to detect changes in the distance between the probe and a suitable ferromagnetic target. When connected to a compatible signal converter and monitoring system, the sensor can provide measurement information for shaft displacement, vibration, position, eccentricity, and speed-related monitoring.

The PR6424 family has a published sensitivity of 4 V/mm and a linearity specification of up to ±1.5%. Its static measurement range is ±2.0 mm, while its dynamic measurement range is specified from 0 to 1,000 μm. These characteristics make the sensor suitable for applications requiring continuous monitoring of rotating machinery.

The sensor is typically installed near the rotating shaft, with a carefully adjusted air gap between the probe tip and the target surface. Correct installation, suitable target material, and compatibility with the signal converter are essential for accurate measurement.

Technical Specifications

Note: The technical performance values above describe the PR6424 16 mm sensor family. Exact cable length, connector arrangement, temperature rating, and mechanical configuration should be verified for the complete PR6424/018-121 part number.

Function and Working Principle

The PR6424/018-121 uses the eddy current principle to measure the distance between its sensing tip and a conductive target. This non-contact method is particularly useful for monitoring rotating shafts because the sensor can measure shaft movement without physically touching the rotating component.

1. Eddy Current Measurement Principle

The sensor generates an electromagnetic field at its probe tip. When a conductive metallic target approaches the sensing area, eddy currents are induced in the target material.

These currents affect the electrical characteristics of the sensor coil. The resulting change in impedance is related to the distance between the probe tip and the target surface.

A compatible signal converter processes this change and converts it into a usable measurement signal. The monitoring system can then interpret the signal as shaft displacement or vibration.

Because measurement does not require mechanical contact, the sensor can continuously monitor rotating machinery without introducing friction between the probe and shaft.

2. Shaft Displacement Measurement

Shaft displacement refers to the movement of a rotating shaft relative to a defined reference position. Changes in shaft position may occur because of bearing movement, thermal expansion, mechanical loading, or other operating conditions.

The PR6424 sensor measures the distance between the probe and the shaft surface. When installed in an appropriate monitoring arrangement, this measurement can be used to assess shaft position and movement.

Static displacement measurement is useful for monitoring shaft position and clearance-related changes. Dynamic measurement is used to observe movement associated with shaft vibration.

3. Vibration Monitoring

Rotating machinery naturally produces some vibration during operation. However, excessive or changing vibration may indicate mechanical problems.

The PR6424 sensor provides a non-contact measurement of shaft movement. A compatible monitoring system can use this signal to evaluate vibration behavior and identify changes that may require inspection.

Typical monitoring applications include turbine shaft vibration, compressor rotor movement, and pump shaft displacement.

4. Position and Eccentricity Monitoring

The sensor can also be used to monitor shaft position and eccentricity.

Eccentricity describes the deviation of a rotating shaft or rotor from its ideal geometric center. Excessive eccentricity can contribute to uneven movement, vibration, and mechanical loading.

By measuring the gap between the probe and target surface, the sensor provides information that can be used by a monitoring system to evaluate shaft position and eccentricity.

5. Speed and Keyphasor-Related Measurement

Eddy current sensors can also support speed-related monitoring when installed with a suitable target arrangement. Changes in the measured gap caused by a shaft feature or reference target can provide information for speed and rotational reference measurements.

The actual function depends on the target geometry, installation arrangement, signal converter, and monitoring equipment.

Role in Industrial Machinery Protection Systems

The PR6424/018-121 is a sensing component rather than a complete machinery protection system. It normally works with compatible signal-conditioning equipment and monitoring hardware.

Signal Converter Integration

The probe produces a measurement response that must be processed by a compatible signal converter. The converter conditions the sensor signal and provides an output suitable for monitoring equipment.

The complete measurement chain typically includes:

• PR6424 eddy current probe.
• Compatible extension cable, where required.
• Matching signal converter.
• Machinery monitoring or protection system.
• Monitoring software or operator interface.

Compatibility between the probe, cable, and converter is essential. Different sensor configurations may require different cable lengths, connectors, or converter types.

Machinery Monitoring System Integration

After signal conditioning, measurement data can be delivered to a machinery monitoring system. Depending on the system architecture, the information may be used for:

• Shaft vibration monitoring.
• Radial displacement measurement.
• Axial position monitoring.
• Shaft eccentricity analysis.
• Rotational speed measurement.
• Machinery alarm and protection functions.

A monitoring system can compare measured values with configured limits and provide alarms when operating conditions exceed defined thresholds.

Maintenance and Diagnostic Applications

Continuous shaft measurement helps maintenance teams understand the operating behavior of critical rotating machinery. Historical measurement data can support trend analysis and help identify gradual changes.

For example, increasing shaft vibration may indicate a developing mechanical issue. A sudden change in shaft position may require inspection of bearings, supports, or other mechanical components.

The sensor itself does not independently diagnose every mechanical fault. Reliable interpretation requires suitable monitoring hardware, operating history, and engineering analysis.

Industrial Applications

The Epro PR6424 16 mm sensor family is designed for critical rotating machinery where non-contact shaft measurement is required.

1. Steam Turbines

Steam turbines operate at high rotational speeds and require continuous monitoring of shaft movement and vibration.

The PR6424 sensor can be installed near the turbine shaft to measure radial displacement and support vibration-monitoring functions. These measurements help operators evaluate mechanical stability and identify abnormal shaft behavior.

Typical monitoring points include bearing locations and other positions specified by the turbine monitoring design.

2. Gas Turbines

Gas turbines operate under demanding thermal and mechanical conditions. Continuous monitoring of shaft movement is important for machinery protection and condition assessment.

The PR6424 series can support non-contact shaft displacement and vibration measurement when the selected sensor configuration is suitable for the installation environment.

Temperature limits, probe mounting, cable routing, and converter compatibility must be verified for the specific turbine application.

3. Hydro Turbines

Hydro turbines are used in power generation and may require long-term monitoring of shaft position and vibration.

The PR6424 sensor can provide displacement measurements that help monitor rotor movement and mechanical stability.

Monitoring data can be incorporated into a wider condition-monitoring strategy to support inspection planning and maintenance activities.

4. Industrial Compressors

Large compressors are used in petrochemical facilities, refineries, gas-processing plants, and other industrial environments.

Shaft vibration and displacement are important operating parameters for these machines. The PR6424 sensor can monitor shaft movement without physical contact and provide information to a compatible machinery protection system.

5. Pumps and Fans

Large industrial pumps and fans often operate continuously in demanding production environments. Monitoring shaft movement can help maintenance teams identify changes in mechanical condition.

The sensor can be used in suitable installations to measure shaft displacement and vibration, supporting condition monitoring and preventive maintenance.

Installation and System Integration

Correct installation is essential for accurate measurements and reliable long-term operation.

1. Confirm the Probe Configuration

Before installation, verify the complete PR6424/018-121 part number. Check the sensor head, cable arrangement, connector type, mounting thread, and any supplied accessories.

Do not assume that all PR6424 probes have identical cable lengths or connection arrangements. The suffix may identify a particular configuration that must be matched to the signal converter and installation requirements.

2. Select a Suitable Mounting Position

The probe should be installed at the measurement location specified by the machinery monitoring design.

For shaft vibration measurement, the probe is commonly positioned near a bearing or another designated monitoring point. The mounting arrangement must provide sufficient mechanical stability and allow the required clearance between the probe and shaft.

The sensor should not contact the rotating shaft during normal operation.

3. Adjust the Air Gap

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

The actual installation gap must be established using the manufacturer’s recommended procedure and compatible signal-conditioning equipment.

Incorrect gap adjustment can reduce measurement accuracy or cause the sensor to operate outside its linear measuring range.

4. Verify the Target Surface

The PR6424 family is specified for ferromagnetic steel targets, with 42CrMo4 identified as a standard reference material.

The target surface should be suitable for eddy current measurement. Material differences, surface conditions, and shaft geometry can affect the measurement response.

Engineers should confirm that the actual shaft material and dimensions are consistent with the sensor’s specifications.

5. Install the Cable Correctly

Cable routing should protect the sensor connection from mechanical damage, excessive bending, heat, and electrical interference.

Follow the minimum bending radius and cable installation requirements for the exact configuration. Avoid placing the sensor cable alongside high-power conductors where this may introduce unwanted electrical interference.

Protect connectors from contamination and ensure that all connections are secure.

6. Connect the Signal Converter

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

The converter must match the probe configuration. Incorrect combinations of probe, extension cable, or converter may produce inaccurate readings or prevent normal operation.

After wiring, check the measurement signal and confirm that the installed air gap is within the recommended operating range.

7. Commission the Monitoring System

During commissioning, verify sensor output, signal stability, shaft clearance, and the response of the monitoring system.

Record the initial measurement values and relevant installation information. These records provide a useful baseline for future condition monitoring and maintenance.

Compatible System Components

A complete PR6424 measurement system requires compatible sensing, signal-conditioning, and monitoring components.

These components are not necessarily included with the sensor. Confirm the complete system requirements before ordering replacement parts.

Alternative Models and Replacement Considerations

The PR6424 family includes different probe configurations. A replacement should be selected according to the complete model number and the requirements of the existing measurement system.

A similar sensor diameter does not guarantee direct replacement compatibility.

Before substituting another model, compare:

• Complete sensor part number.
• Probe diameter and mechanical dimensions.
• Mounting thread and installation length.
• Cable length and cable construction.
• Connector and extension cable arrangement.
• Signal converter compatibility.
• Sensitivity and linearity.
• Static and dynamic measurement ranges.
• Target material requirements.
• Operating temperature limits.
• Monitoring-system input requirements.

For critical machinery, replacement selection should follow the original equipment documentation and the machinery monitoring system’s approved configuration.

Key Advantages

Non-Contact Measurement

The eddy current measuring principle allows the sensor to measure shaft movement without physical contact with the rotating surface.

Continuous Shaft Monitoring

The sensor supports continuous measurement of shaft displacement and vibration when integrated with compatible monitoring equipment.

High Measurement Sensitivity

The PR6424 family has a published sensitivity of 4 V/mm, supporting the measurement of small changes in probe-to-target distance.

Suitable for Critical Rotating Machinery

The sensor family is designed for applications involving turbines, compressors, pumps, and fans.

Static and Dynamic Measurement

The published static range of ±2.0 mm and dynamic range of 0 to 1,000 μm support different shaft-position and vibration-monitoring requirements.

Industrial Construction

The stainless steel sleeve and PTFE cable construction support use in demanding industrial installations within the specified environmental limits.

Integration with Machinery Monitoring Systems

When paired with compatible signal-conditioning equipment, the sensor can supply measurement information for industrial monitoring and protection systems.

Technical FAQs

1. What is the Epro PR6424/018-121?

The PR6424/018-121 is a 16 mm eddy current sensor designed for non-contact measurement of shaft displacement and vibration in rotating machinery.

2. What is the sensor head diameter?

The nominal sensor head diameter is 16 mm.

3. What is the measurement principle?

It uses eddy current technology. The sensor generates an electromagnetic field, and changes in the conductive target’s distance affect the electrical characteristics of the sensing coil.

4. What is the sensitivity of the PR6424 series?

The published sensitivity is 4 V/mm, equivalent to approximately 101.6 mV/mil.

5. What is the linearity specification?

The PR6424 family has a published linearity specification of up to ±1.5%.

6. What is the static measurement range?

The published static measurement range is ±2.0 mm.

7. What is the nominal air gap?

The nominal center air gap is approximately 2.7 mm. The actual installation gap should be adjusted according to the manufacturer’s procedure.

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

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

9. Does the sensor require a signal converter?

Yes. The probe is normally used with compatible signal-conditioning equipment that processes the sensor response into a usable measurement signal.

10. What machinery can use this sensor?

Typical applications include steam turbines, gas turbines, hydro turbines, compressors, pumps, fans, and other critical rotating machinery.

11. What is the weight of the PR6424/018-121?

The supplied product listing weight is 0.2 kg. The PR6424 family specification also gives an approximate weight of 200 grams for the sensor with a 1-meter cable and without armor.

12. Can another PR6424 model replace this sensor?

Not automatically. The complete part number, cable configuration, connector, converter compatibility, and mechanical dimensions should be checked before selecting a replacement.

Procurement and Maintenance Recommendations

When purchasing the Epro PR6424/018-121, verify the complete part number and compare it with the sensor installed in the existing machinery monitoring system.

For replacement projects, confirm the sensor head diameter, mounting thread, cable arrangement, connector type, and compatibility with the existing signal converter. These details are important because an incorrect probe or cable configuration may prevent the measurement system from operating correctly.

For used or surplus equipment, inspect the sensor tip, threaded sleeve, cable insulation, connectors, and identification markings. Check for damaged threads, bent components, cracked insulation, or signs of contamination.

During maintenance, keep the probe and connector area clean. Inspect cable routing and mounting hardware, and verify that the sensor has not moved from its original installation position. Periodically check the signal response and compare measurement trends with the established baseline.

For critical rotating machinery, sensor replacement and commissioning should follow the plant’s machinery protection procedures. Correct installation and signal verification help maintain the reliability of the overall monitoring system.

Conclusion

The Epro PR6424/018-121 16 mm Eddy Current Sensor is designed for non-contact shaft displacement and vibration measurement in critical rotating machinery. Its eddy current technology, 4 V/mm sensitivity, ±1.5% linearity specification, and ±2.0 mm static measurement range make it suitable for integration into industrial machinery monitoring applications.

Used with a compatible cable, signal converter, and monitoring system, the sensor can support shaft vibration, position, eccentricity, and speed-related measurements. For maintenance and replacement projects, verifying the complete model number and connection configuration is essential to ensure correct system compatibility.