Product Overview

The EPRO PR6424/008-121 16 mm Eddy Current Sensor is a non-contact displacement sensor designed for monitoring the condition and operating behavior 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 line of Emerson, the PR6424 series is used to measure shaft vibration, radial and axial displacement, shaft position, eccentricity, and rotational speed-related signals. Its non-contact measurement principle allows the sensor to monitor a rotating shaft without physically touching the target surface.

The PR6424/008-121 is identified as a 16 mm sensor-head model. It is intended for installation near a suitable ferromagnetic shaft surface, where changes in the distance between the probe and the shaft can be converted into an electrical measurement signal through a compatible signal-conditioning system.

Eddy current sensors are widely used in machinery monitoring because they can provide continuous measurements of shaft movement. These measurements help operators and maintenance engineers identify changes in vibration, rotor position, and machine operating conditions.

Typical applications include steam turbines, gas turbines, hydro turbines, compressors, pumps, fans, and other rotating equipment. In these installations, shaft displacement measurements can support machinery protection, condition assessment, and preventive maintenance.

The PR6424/008-121 should be selected according to its complete model configuration, including probe dimensions, cable arrangement, connector type, and compatibility with the signal converter. These details are important when replacing an existing sensor or integrating a new probe into an established machinery monitoring system.

Technical Specifications

Note: The technical performance values above describe the PR6424 16 mm sensor family. Confirm the exact cable length, connector, probe length, temperature limits, and other configuration details for the PR6424/008-121 before ordering.

Function and Working Principle

The EPRO PR6424/008-121 operates using the eddy current measurement principle. It generates an electromagnetic field at the sensor tip and measures changes caused by the presence and movement of a conductive target.

Unlike contact-based measuring devices, the probe does not need to touch the rotating shaft. This makes it suitable for continuous monitoring of machinery where physical contact would create friction, wear, or interference with normal operation.

1. Electromagnetic Field Generation

When the sensor is connected to a compatible signal converter, an alternating electrical signal energizes the probe coil. This produces an electromagnetic field around the sensing tip.

The sensor is positioned close to a conductive target, typically a suitable ferromagnetic steel shaft. The distance between the probe tip and the target is commonly called the air gap.

The measurement depends on the electromagnetic interaction between the sensor and the target surface.

2. Eddy Current Formation

When the electromagnetic field reaches the conductive shaft surface, circulating electrical currents known as eddy currents are induced in the target material.

These currents influence the electromagnetic characteristics of the probe coil. As the shaft moves closer to or farther from the sensor, the strength of this interaction changes.

The resulting electrical change is related to the distance between the probe and the target.

3. Signal Conversion

The probe is normally used with a compatible EPRO signal converter. The converter processes the probe’s electrical response and produces a conditioned output signal representing the measured displacement.

For the PR6424 family, the nominal sensitivity is 4 V/mm under the specified operating conditions.

The signal can then be supplied to a machinery protection or monitoring system for display, alarm processing, trend analysis, or equipment protection functions.

4. Shaft Vibration Measurement

During normal operation, a rotating shaft may move slightly because of mechanical vibration, imbalance, bearing conditions, misalignment, or changes in operating load.

The sensor continuously detects variations in the air gap. These variations provide information about shaft movement relative to the probe.

When two appropriately positioned probes are used, a monitoring system can obtain additional information about shaft movement in different directions.

5. Position and Eccentricity Monitoring

In addition to dynamic vibration, an eddy current sensor can measure static shaft position within its calibrated range.

This capability is useful for monitoring shaft displacement, rotor position, and eccentricity. Engineers can compare measurements with established operating baselines to identify changes that may require further investigation.

Role in Industrial Machinery Protection Systems

The PR6424/008-121 can serve as a sensing element within a larger machinery monitoring and protection system. It does not independently perform every monitoring or protection function. Instead, it supplies measurement information to compatible signal-conditioning and monitoring equipment.

1. Shaft Vibration Monitoring

Shaft vibration is an important indicator of rotating machinery condition. Changes in vibration may be associated with imbalance, misalignment, mechanical looseness, bearing problems, or other machine-related conditions.

The PR6424 sensor provides non-contact shaft displacement measurements that can be processed by a monitoring system.

2. Axial Displacement Monitoring

Axial shaft movement is important in turbines, compressors, and other machines where rotor position must remain within defined operating limits.

A suitable probe installation can measure axial movement relative to a target surface. The resulting signal can be evaluated by the monitoring system to identify abnormal changes in rotor position.

3. Radial Displacement Monitoring

Radial displacement measurements help monitor shaft movement relative to the machine’s bearing and housing arrangement.

These measurements are particularly relevant to large rotating machinery, where shaft motion can affect clearances, operating stability, and mechanical reliability.

4. Integration with Machinery Monitoring Equipment

The sensor requires compatible signal-conditioning equipment. Depending on the installed monitoring architecture, the processed signal may be connected to machinery protection equipment, vibration monitoring modules, or other measurement systems.

Before installation, engineers should verify probe compatibility, cable configuration, converter requirements, signal range, and system calibration.

5. Support for Predictive Maintenance

Continuous shaft measurements provide useful information for machinery condition assessment.

Maintenance teams can compare current measurements with historical trends and operating baselines. This can help identify developing changes before they lead to unexpected equipment shutdowns.

However, sensor readings should be evaluated together with operating conditions, other machine measurements, and appropriate diagnostic procedures.

Industrial Applications

The EPRO PR6424 16 mm Eddy Current Sensor is designed for demanding rotating machinery applications where non-contact shaft measurement is required.

1. Steam Turbines

Steam turbines operate at high rotational speeds and are important components in power generation and industrial energy systems.

Shaft vibration and displacement monitoring help operators assess rotor behavior and identify abnormal movement. Eddy current sensors can provide continuous measurements for machinery monitoring systems.

Typical monitoring applications include:

• Radial shaft vibration.
• Axial shaft displacement.
• Rotor position.
• Shaft eccentricity.
• Changes in operating vibration.

2. Gas Turbines

Gas turbines are used in power generation, industrial facilities, and mechanical drive applications. Their rotating assemblies operate under demanding mechanical and thermal conditions.

Non-contact displacement sensors can provide information about shaft movement and support the monitoring of turbine operating conditions.

3. Hydro Turbines

Hydroelectric generating units contain rotating equipment that requires long-term condition monitoring.

Eddy current sensors can be used to measure shaft movement and vibration, helping maintenance personnel assess changes in rotor behavior during different operating conditions.

4. Industrial Compressors

Compressors are widely used in petrochemical plants, refineries, natural gas facilities, and manufacturing operations.

Shaft vibration and position measurements can help identify changes in compressor operating conditions. Continuous monitoring is particularly important for critical compressors where unexpected shutdowns may affect production.

5. Pumps

Large industrial pumps are used in water treatment, chemical processing, power generation, and oil and gas facilities.

Where the monitoring system is designed for shaft displacement measurement, the PR6424 sensor can provide information about radial or axial shaft movement.

6. Industrial Fans

Large fans and blowers are common in power plants, ventilation systems, and industrial process facilities.

Monitoring shaft vibration can help maintenance teams identify developing mechanical problems and plan inspections or repairs.

Installation and System Integration

Correct installation is essential for accurate measurement and stable operation. The sensor must be installed with the correct mechanical clearance and connected to compatible signal-conditioning equipment.

1. Verify the Sensor Model

Before installation, confirm the complete model number PR6424/008-121.

The PR6424 series includes different probe lengths, cable configurations, mounting arrangements, and connector options. A probe with the same 16 mm diameter may not necessarily be a direct replacement for another model.

Check the existing sensor label, installation drawing, cable length, and connector arrangement.

2. Prepare the Mounting Position

The sensor should be installed in a suitable mounting location near the shaft target.

The mounting arrangement must provide mechanical stability and allow the probe to maintain the specified measurement gap during operation.

The surrounding structure should not interfere with the sensing field. Follow the manufacturer’s installation drawing for the required clearance from nearby ferromagnetic materials.

3. Set the Initial Air Gap

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

The actual installation gap should be set according to the applicable probe and converter instructions. Incorrect gap adjustment may cause the measurement to operate outside its calibrated linear range.

The initial gap should be verified during commissioning using the specified measurement procedure.

4. Connect the Sensor to the Signal Converter

The probe must be connected to a compatible EPRO signal converter.

The converter is responsible for processing the sensor response and producing the required measurement output. Confirm the supported probe type, cable arrangement, connector, and converter configuration before connecting the equipment.

Do not assume that every PR6424 sensor can be connected to every converter without checking the applicable compatibility information.

5. Cable Routing and Protection

The sensor cable should be routed to avoid unnecessary mechanical stress, sharp bends, and interference from high-power electrical conductors.

The PR6424 family uses PTFE-insulated cable. Cable handling should follow the manufacturer’s minimum bending-radius requirements for the specific cable construction.

Where cables are exposed to vibration, heat, or mechanical damage, suitable routing and protection should be provided.

6. Calibration and Commissioning

After installation, verify the sensor output and measurement behavior using the appropriate commissioning procedure.

Check the initial gap, signal stability, converter configuration, and monitoring-system input settings. Confirm that the measured values are consistent with the expected machine operating conditions.

Record the installation details and initial operating measurements to establish a reference for future maintenance.

Compatible System Components

A complete eddy current measurement system generally requires more than the sensor probe itself. The following components may be used depending on the monitoring architecture.

The exact components required depend on the existing machinery monitoring system. A replacement sensor should be checked against the original system configuration rather than selected solely by probe diameter.

Alternative Models and Replacement Considerations

The PR6424 family contains multiple sensor configurations. Some models may share the same 16 mm sensor-head diameter while differing in probe length, cable construction, connector, or other ordering details.

Before replacing a sensor, check:

• Complete probe model number.
• Sensor-head diameter and mechanical dimensions.
• Probe length and mounting thread.
• Cable type and total cable length.
• Connector arrangement.
• Signal converter compatibility.
• Nominal air gap and measurement range.
• Target shaft material and surface condition.
• Temperature and environmental requirements.
• Monitoring-system configuration and calibration.

A sensor with the same diameter is not automatically interchangeable. Differences in electrical characteristics or cable configuration may affect measurement accuracy and system operation.

Key Advantages

Non-Contact Measurement

The PR6424 measures shaft movement without physical contact. This avoids mechanical wear between the sensor and rotating target during normal operation.

Continuous Shaft Monitoring

The sensor can provide continuous displacement measurements when connected to a compatible monitoring system.

High Measurement Sensitivity

The PR6424 family has a nominal sensitivity of 4 V/mm, supporting detailed measurement of shaft movement within its specified range.

Static and Dynamic Measurement

The sensor family supports both static displacement and dynamic shaft vibration measurements, allowing different aspects of rotating machinery behavior to be monitored.

Industrial Machinery Applications

The 16 mm probe design is intended for critical rotating machinery, including turbines, compressors, pumps, and fans.

Integration with EPRO Monitoring Systems

The sensor can be incorporated into a compatible EPRO measurement arrangement using the appropriate signal converter and monitoring equipment.

Support for Condition Monitoring

Continuous shaft measurements can help maintenance teams establish operating baselines, identify changes, and plan inspections according to equipment condition.

Technical FAQs

1. What is the EPRO PR6424/008-121?

The PR6424/008-121 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 sensor-head diameter is 16 mm, as specified in the product listing.

3. What is the measurement principle?

It uses the eddy current principle. The sensor generates an electromagnetic field, and changes in the conductive target’s distance affect the probe’s electrical response.

4. What is the sensitivity of the PR6424 series?

The nominal sensitivity is 4 V/mm, equivalent to approximately 101.6 mV/mil, under the specified operating conditions.

5. What is the static measurement range?

The PR6424 16 mm sensor family has a static measurement range of approximately ±2.0 mm.

6. What is the dynamic measurement range?

The published dynamic measurement range is 0 to 1,000 μm. The actual usable range depends on the measurement setup and operating conditions.

7. What is the nominal air gap?

The nominal center air gap is approximately 2.7 mm. The actual installation setting should follow the applicable sensor and converter documentation.

8. Which materials can be measured?

The PR6424 family is specified for ferromagnetic steel targets, with 42CrMo4 steel identified as the standard target material in the technical documentation.

9. Does the sensor work without a signal converter?

The probe is normally used with a compatible signal converter. The converter processes the probe response and supplies the measurement signal to the monitoring system.

10. Where is the PR6424/008-121 commonly used?

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

11. What is the product weight?

The supplied product listing weight is 0.2 kg. The PR6424 family specification sheet also lists approximately 200 grams for the sensor with a 1-meter cable without armor.

12. Can another PR6424 model replace the PR6424/008-121?

Not automatically. The replacement must match the required probe length, cable configuration, connector, converter compatibility, and measurement requirements.

Procurement and Maintenance Recommendations

When purchasing the EPRO PR6424/008-121, verify the complete model number and confirm that the probe matches the existing machinery monitoring installation.

The PR6424 family includes several configuration options. A difference in cable length, armor, connector, or probe dimensions may affect installation even when two sensors share the same 16 mm diameter.

For replacement projects, compare the original sensor label and installation documentation with the proposed replacement. Confirm that the signal converter supports the selected probe and that the required cable arrangement is available.

During maintenance, inspect the probe body, cable, connector, mounting thread, and installation position. Check for mechanical damage, contamination, loose connections, or signs of cable deterioration.

It is also useful to retain initial measurement values and calibration records. Comparing current readings with historical baselines can help maintenance personnel identify changes in machine behavior.

For critical turbines and compressors, sensor replacement should be performed according to the machinery protection system’s maintenance procedures. After replacement, verify the measurement signal and alarm configuration before returning the machine to normal operation.

Conclusion

The EPRO PR6424/008-121 16 mm Eddy Current Sensor is designed for non-contact shaft displacement and vibration measurement in critical industrial rotating machinery. Its operating principle allows it to detect changes in the distance between the probe and a conductive shaft target without physical contact.

With a 16 mm sensor head, nominal series sensitivity of 4 V/mm, static measurement range of ±2.0 mm, and dynamic range of 0–1,000 μm, the PR6424 family supports machinery monitoring applications involving turbines, compressors, pumps, and fans.

For industrial maintenance and replacement projects, the complete sensor configuration must be verified. Probe dimensions, cable arrangement, connector type, signal converter compatibility, and installation gap should all be checked to ensure reliable measurement and proper integration into the existing machinery protection system.