Product Overview

The Epro PR6424/104-121 16 mm Eddy Current Sensor is a non-contact displacement and vibration sensor designed for monitoring the condition of rotating machinery. It belongs to the PR6424 sensor family associated with Emerson’s EPRO machinery protection and condition-monitoring solutions.

The sensor is designed to measure the movement of a conductive metal target without making physical contact with the rotating shaft. This measurement principle makes it particularly useful in applications where continuous monitoring of shaft vibration, radial displacement, axial position, and eccentricity is required.

In industrial facilities, rotating equipment such as steam turbines, gas turbines, compressors, pumps, and generators operates under changing mechanical and thermal conditions. Shaft movement can provide important information about machine condition. Excessive vibration, abnormal displacement, or changes in shaft position may indicate developing mechanical problems. A properly installed eddy current sensor provides measurement information that can be evaluated by a compatible monitoring system.

The PR6424 series uses a 16 mm sensing tip and is designed for applications requiring reliable non-contact measurement on suitable ferromagnetic targets. Its typical published performance includes a static measuring range of ±2.0 mm, sensitivity of 4 V/mm, and linearity within ±1.5%. These characteristics make the series suitable for machinery monitoring where accurate shaft-position and vibration measurements are important.

The PR6424/104-121 is identified as a specific model within this sensor family. However, the exact cable length, connector arrangement, mounting configuration, and associated accessories should be confirmed against the complete model label before installation or replacement. These details can vary between ordering configurations.

Technical Specifications

Note: The performance values above describe the PR6424 family. Confirm the exact PR6424/104-121 configuration before using cable, connector, mounting, or temperature details for an engineering installation.

Function and Working Principle

The PR6424/104-121 operates using the eddy current measurement principle. It generates an electromagnetic field at the sensor tip and detects changes in that field when a conductive target moves relative to the probe.

This method allows the sensor to measure shaft movement without mechanical contact.

1. Electromagnetic Field Generation

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

When the probe is installed near a suitable metallic shaft surface, this field interacts with the target material. The interaction depends on the distance between the sensor tip and the shaft.

2. Eddy Current Formation

The electromagnetic field induces small circulating electrical currents, known as eddy currents, in the conductive target.

As the distance between the probe and the shaft changes, the strength of the eddy currents changes. This affects the electrical characteristics of the sensor coil.

The sensor system detects these changes and uses them to determine the relative distance between the probe and the target.

3. Displacement Signal Conversion

The probe is normally used with a compatible signal converter. The converter processes the sensor’s electrical response and produces an output signal that represents the measured displacement.

For the PR6424 series, the published sensitivity is typically 4 V/mm when used with the specified measurement system and standard target material.

The resulting signal can be supplied to a machinery monitoring instrument, protection system, or compatible control platform for further analysis.

4. Shaft Vibration Measurement

When installed near a rotating shaft, the sensor detects the shaft’s movement relative to the probe. Repeated measurements can be used to evaluate vibration amplitude and changes in shaft position.

This information helps maintenance teams identify abnormal mechanical behavior, including excessive radial movement, changes in shaft orbit, and developing alignment or bearing-related problems.

5. Static Position Measurement

The sensor can also measure relatively slow changes in shaft position. This is useful for applications involving axial displacement, thermal expansion, and other changes in the mechanical position of rotating equipment.

The same measurement principle supports both dynamic vibration monitoring and static displacement measurement, provided the system is configured for the intended measurement task.

Role in Industrial Machinery Protection Systems

The PR6424/104-121 is intended to operate as part of a complete machinery measurement chain. The probe alone does not provide the entire monitoring and protection function. A compatible signal converter and monitoring equipment are required to process and interpret its measurement signal.

Shaft Vibration Monitoring

Shaft vibration is an important indicator of rotating machinery condition. The sensor provides non-contact displacement information that can be evaluated by monitoring equipment.

Changes in vibration amplitude or shaft movement may indicate imbalance, misalignment, looseness, bearing deterioration, or other mechanical conditions. The actual diagnosis requires analysis of the complete measurement data and operating conditions.

Axial Position Monitoring

In turbines and other large rotating machines, axial shaft movement must remain within the permitted mechanical range.

An eddy current probe installed at an appropriate measurement point can monitor axial displacement. The resulting signal may be used by a machinery protection system to identify abnormal shaft movement.

Eccentricity Measurement

Shaft eccentricity describes deviations between the shaft’s geometric center and its rotational center. The sensor can measure changes in the gap between the probe and the shaft surface.

This information can help engineers assess shaft condition during operation and investigate mechanical abnormalities.

Integration with Machinery Monitoring Equipment

The PR6424 series is designed for use with compatible EPRO signal converters and monitoring equipment. The complete system typically includes:

• PR6424 eddy current sensor.
• Compatible extension cable, where required by the configuration.
• Matching signal converter.
• Machinery monitoring or protection equipment.
• Control-system interfaces for alarms and operating data.

The exact combination must be verified using the model number, cable configuration, converter type, and monitoring-system requirements.

Industrial Applications

The PR6424/104-121 is suitable for machinery-monitoring applications where non-contact measurement of shaft movement is required.

1. Steam Turbines

Steam turbines operate at high rotational speeds and under demanding thermal and mechanical conditions. Continuous shaft monitoring is important for evaluating machine stability and detecting abnormal movement.

The PR6424 sensor can be used at suitable measurement locations to monitor radial shaft vibration and displacement. Multiple sensors may be installed as part of a broader machinery protection arrangement.

2. Gas Turbines

Gas turbines are used in power generation and industrial processes. Their rotating assemblies require reliable monitoring because abnormal shaft movement can affect machine performance and mechanical safety.

Eddy current sensors provide non-contact measurement information that can be evaluated by the turbine’s monitoring system.

3. Industrial Compressors

Large compressors are widely used in petrochemical plants, refineries, gas-processing facilities, and manufacturing operations.

Shaft vibration and displacement monitoring can help maintenance teams evaluate compressor condition. The sensor can support continuous measurement when installed with a compatible converter and monitoring system.

4. Pumps and Rotating Process Equipment

Industrial pumps may operate continuously under changing flow, pressure, and load conditions. Shaft movement can provide useful information about mechanical condition.

The PR6424 series can be considered for suitable pump installations where the shaft dimensions, target material, operating temperature, and measurement requirements fall within the sensor system’s specifications.

5. Power Generation Equipment

Generators and other rotating equipment require monitoring to maintain stable operation. Shaft displacement measurements can support machinery condition assessment and help identify changes that require further inspection.

The sensor may be incorporated into a wider monitoring system that combines vibration, temperature, speed, and other operating measurements.

6. Industrial Fans and Blowers

Large fans and blowers are used in power stations, cement plants, steel production, and process industries. Monitoring shaft movement can help detect abnormal vibration and mechanical deterioration.

A properly configured eddy current measurement system can provide continuous shaft-displacement information for these applications.

Installation and System Integration

Correct installation is essential for accurate measurement. The probe position, target material, initial gap, cable arrangement, and signal converter configuration all influence measurement performance.

1. Verify the Complete Model Number

Before installation, confirm that the sensor is the correct PR6424/104-121 variant.

Check the model label, cable length, connector arrangement, mounting thread, and any associated extension cable. Do not assume that every PR6424 probe has an identical mechanical or electrical configuration.

2. Select a Suitable Measurement Location

Choose a measurement point that provides a stable view of the shaft surface. The target should be suitable ferromagnetic material and should meet the dimensional requirements of the sensor system.

The PR6424 series is designed for large-shaft applications, with a recommended shaft diameter of at least 80 mm in its published specifications.

Avoid installing the probe where nearby metal structures could interfere with the measurement field.

3. Set the Initial Air Gap

The initial gap between the sensor tip and the shaft must be adjusted according to the compatible converter’s calibration requirements.

The published PR6424 series reference value for the nominal center air gap is approximately 2.7 mm. The actual setup must follow the relevant sensor and converter documentation.

An incorrect air gap may reduce the available measurement range or cause the output to operate outside its intended linear region.

4. Secure the Probe Mechanically

Use the correct mounting hardware and ensure that the probe is securely installed. If the specific configuration uses an M18 × 1.5 mounting thread, verify that the mounting arrangement matches the equipment design.

The sensor should not be exposed to unnecessary mechanical stress. Cable routing should also prevent excessive pulling, vibration damage, or sharp bending.

5. Connect the Compatible Signal Converter

The probe must be connected to a compatible signal converter. The converter processes the probe response and generates the measurement output used by the monitoring equipment.

Confirm the sensor-converter combination before powering the system. Different sensor and converter configurations should not be mixed without verifying compatibility and calibration requirements.

6. Route and Protect the Cable

The sensor cable should be routed away from sources of electrical interference and excessive heat wherever possible.

Maintain the cable’s specified minimum bending radius. Avoid crushing, twisting, or sharply bending the cable near the sensor head or connector.

The exact cable length and connector arrangement for the /104-121 variant should be checked against the supplied product documentation.

7. Verify the Measurement Signal

After installation, confirm the initial gap and check the converter output. Verify that the measurement changes consistently when the shaft position changes under safe test conditions.

Compare the output with the monitoring instrument’s expected measurement range. Record the initial readings and configuration details for future maintenance.

Compatible System Components

A complete PR6424 measurement system requires compatible components that work together as a calibrated measurement chain.

The listed components are typical elements of an eddy current monitoring installation. They are not necessarily included with the sensor.

Alternative Models and Replacement Considerations

The PR6424/104-121 should be replaced only with a sensor that matches the original measurement and installation requirements.

Before selecting a replacement, compare:

• Sensor head diameter.
• Complete catalog number.
• Static and dynamic measurement ranges.
• Sensitivity and linearity.
• Nominal air gap.
• Target material and shaft diameter.
• Mounting thread and probe length.
• Cable length and connector arrangement.
• Operating temperature.
• Compatible signal converter.
• Monitoring-system input requirements.

A probe with the same diameter is not necessarily a direct replacement. Different variants may have different cable assemblies, calibration characteristics, and converter requirements.

Key Advantages

Non-Contact Measurement

The eddy current principle allows the sensor to measure shaft movement without physical contact. This avoids the mechanical wear associated with contact-based measurement methods.

Continuous Shaft Monitoring

The sensor can provide displacement information for machinery monitoring systems during normal equipment operation.

Suitable for Critical Rotating Machinery

The PR6424 family is designed for applications involving turbines, compressors, pumps, fans, and other large rotating machines.

High Measurement Sensitivity

The published series sensitivity of 4 V/mm supports measurement of relatively small changes in the gap between the probe and the target.

Static and Dynamic Measurement Capability

The series supports both static shaft-position measurement and dynamic vibration measurement within its specified operating range.

Industrial Sensor Construction

The series uses a stainless-steel sleeve and PTFE cable construction in documented configurations. Exact materials and environmental ratings should be confirmed for the individual model.

Integration with Machinery Monitoring Systems

When paired with a compatible signal converter, the sensor can provide measurement information for machinery monitoring and protection equipment.

Technical FAQs

1. What is the Epro PR6424/104-121?

The Epro PR6424/104-121 is a 16 mm eddy current sensor used for non-contact measurement of shaft displacement and vibration in rotating machinery.

2. What is the main function of this sensor?

Its main function is to detect the relative movement between the sensor tip and a conductive shaft surface. The resulting measurement can be used for shaft vibration, radial displacement, axial position, and eccentricity monitoring.

3. What is the sensor head diameter?

The supplied product specification identifies a 16 mm sensor head diameter, consistent with the PR6424 series.

4. What is the measuring range of the PR6424 series?

The published static measuring range is ±2.0 mm. The recommended dynamic measurement range is approximately 100–1000 μm peak-to-peak. The actual usable range depends on the complete measurement system and installation conditions.

5. What is the sensitivity of the sensor?

The typical PR6424 series sensitivity is 4 V/mm, with published linearity of approximately ±1.5%.

6. Does the sensor require a signal converter?

Yes. The probe is normally used with a compatible signal converter that processes the sensor response and provides a measurement output for monitoring equipment.

7. What material should the sensor measure?

The PR6424 series is designed for suitable ferromagnetic targets. Its published standard reference material is 42CrMo4 steel. Calibration should use the appropriate target material and system documentation.

8. Can this sensor measure shaft vibration?

Yes. When correctly installed and connected to a compatible converter, it can measure dynamic shaft displacement associated with vibration.

9. Where is the PR6424 series commonly used?

Typical applications include steam turbines, gas turbines, hydro turbines, compressors, pumps, fans, generators, and other large rotating machines.

10. Can the PR6424/104-121 replace another PR6424 sensor?

Not automatically. Confirm the complete model number, cable and connector configuration, mounting dimensions, converter compatibility, and calibration requirements before using it as a replacement.

Procurement and Maintenance Recommendations

When purchasing the Epro PR6424/104-121, verify the complete model number on the sensor label. The PR6424 family includes different ordering configurations, and the suffix can identify important differences in cable and connection arrangements.

For replacement projects, compare the existing sensor with the proposed unit before installation. Confirm the sensor head diameter, mounting thread, cable length, connector type, and compatible signal converter. These details are particularly important in machinery protection systems where sensor calibration and measurement accuracy affect alarm and shutdown functions.

For used or refurbished sensors, inspect the sensing tip, threaded sleeve, cable jacket, and connector. Look for signs of mechanical damage, corrosion, contamination, or cable deterioration. Where possible, request electrical testing or a functional verification using the appropriate converter.

During routine maintenance, inspect the probe mounting, cable routing, connector condition, and signal stability. Record baseline measurements and investigate significant changes rather than relying only on visual inspection.

The sensor should be installed and commissioned according to the equipment manufacturer’s instructions. Correct initial-gap adjustment and compatible signal conditioning are essential for reliable measurement performance.

Conclusion

The Epro PR6424/104-121 16 mm Eddy Current Sensor is designed for non-contact shaft displacement and vibration monitoring in critical rotating machinery. Based on the published PR6424 family specifications, it offers a static measuring range of ±2.0 mm, sensitivity of 4 V/mm, and linearity of approximately ±1.5%.

Its applications include turbines, compressors, pumps, generators, and industrial fans. For reliable operation, the sensor must be correctly mounted, adjusted to the required air gap, and connected to a compatible signal converter and machinery monitoring system.

When sourcing or replacing the PR6424/104-121, confirm the complete model configuration, cable and connector details, and converter compatibility to ensure that the sensor matches the requirements of the installed machinery protection system.