Product Overview

The EPRO PR6424/015-021 16 mm Eddy Current Sensor is a non-contact displacement sensor designed for monitoring the condition and operating behavior of critical 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 shaft displacement and vibration measurements are required.

The sensor uses eddy current technology to measure the distance between its sensing tip and a conductive target, typically a ferromagnetic steel shaft. Because measurement takes place without physical contact, the sensor can monitor shaft movement without introducing mechanical wear between the probe and the rotating component.

The PR6424 series is designed for applications involving steam turbines, gas turbines, hydro turbines, compressors, pumps, fans, and other large rotating machines. It can measure radial and axial shaft displacement, shaft position, eccentricity, and speed-related signals when incorporated into a compatible monitoring system.

The PR6424/015-021 belongs to the 16 mm sensor family. Its sensing head has a nominal diameter of 16 mm, making it suitable for installations designed around this probe size. The series has a typical sensitivity of 4 V/mm and a static measurement range of ±2.0 mm. Its nominal center air gap is approximately 2.7 mm.

The supplied product weight is approximately 0.2 kg. This is consistent with the manufacturer’s reference weight of approximately 200 grams for the sensor with a 1-meter cable and without armor. Actual weight may vary with cable length and configuration.

For replacement projects, the complete model designation should be checked carefully. Probe dimensions, cable arrangement, connector configuration, extension cable, and signal converter compatibility all affect whether a replacement sensor can operate correctly in an existing machinery monitoring system.

Technical Specifications

Note: Temperature limits and cable arrangements should be checked against the exact sensor revision and complete order code. The table uses the December 2024 PR6424 specification sheet for the stated operating-temperature range.

Function and Working Principle

The PR6424/015-021 uses the eddy current principle to measure the distance between the sensor tip and a conductive metal target. It is commonly installed near a rotating shaft in machinery that requires continuous vibration and displacement monitoring.

1. Eddy Current Measurement Principle

The sensor generates an electromagnetic field around its sensing tip. When a conductive metal target approaches the tip, eddy currents are induced in the target surface.

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

With a compatible signal converter, the measured change can be converted into an electrical output representing the shaft-to-probe gap. The monitoring system can then use this signal to determine shaft position and dynamic movement.

2. Shaft Displacement Measurement

Shaft displacement is an important parameter in rotating machinery. Changes in shaft position may indicate mechanical movement, bearing condition changes, thermal expansion, or other operating conditions.

The PR6424 sensor provides non-contact measurement of the distance between its probe tip and the shaft surface. The resulting signal can be used by a machinery monitoring system to track shaft position over time.

3. Shaft Vibration Monitoring

Rotating shafts naturally experience some degree of vibration during operation. Excessive or abnormal vibration may indicate imbalance, misalignment, bearing deterioration, looseness, or other mechanical problems.

The PR6424 series can measure dynamic shaft movement within its specified measurement range. When paired with suitable monitoring equipment, the signal can be used to evaluate vibration trends and identify changes in machinery behavior.

4. Eccentricity Measurement

Shaft eccentricity describes the deviation between the shaft’s geometric center and its actual rotational center. Excessive eccentricity may contribute to uneven mechanical loading and vibration.

By measuring the gap between the probe and the shaft at the appropriate position, the sensor can provide information used to evaluate eccentricity. Correct probe positioning and suitable monitoring-system configuration are necessary for meaningful measurements.

5. Speed and Keyphasor-Related Measurement

The PR6424 family can also support speed and key-related monitoring applications when used with an appropriate target arrangement and signal-processing system.

A monitoring system can interpret periodic changes in the sensor signal to obtain rotational information. The exact installation geometry and processing configuration depend on the machinery monitoring design.

Role in Industrial Machinery Protection Systems

The PR6424/015-021 is generally used as a sensing element within a complete machinery protection or condition-monitoring system. It does not operate as a standalone display or monitoring controller.

A typical measurement chain includes the sensor probe, extension cable, signal converter, monitoring module, and plant control or supervisory system.

1. Sensor Probe

The PR6424 probe is installed near the rotating shaft with a specified mechanical gap. It detects changes in the distance between the probe tip and the target surface.

Correct installation is essential because probe position directly affects the measurement signal.

2. Extension Cable

The extension cable connects the sensor to the compatible signal converter. Cable length, connector type, shielding, and electrical characteristics must match the system requirements.

Using an unsuitable cable can affect measurement accuracy or prevent the sensor from operating correctly.

3. Signal Converter

A compatible converter conditions the sensor signal and produces an output suitable for monitoring equipment.

The converter must match the probe’s electrical characteristics and configuration. A sensor and converter should not be assumed compatible merely because they belong to the same PR6424 product family.

4. Machinery Monitoring Module

The monitoring module receives the conditioned signal and evaluates machinery operating parameters. Depending on the installed system, it may provide vibration, displacement, position, or alarm information.

5. Plant Control and Supervisory System

Monitoring data can be transferred to a plant control system, operator interface, or asset-management platform. Operators and maintenance personnel can use this information to review machinery conditions and investigate abnormal operating trends.

Industrial Applications

The EPRO PR6424/015-021 is designed for non-contact measurement in critical rotating machinery. Its applications include the following equipment types.

1. Steam Turbines

Steam turbines operate under demanding mechanical and thermal conditions. Shaft vibration and displacement monitoring are important for evaluating machine behavior and identifying potential mechanical problems.

The PR6424 series can be installed at suitable measurement locations to monitor radial or axial shaft movement as part of a complete turbine protection system.

2. Gas Turbines

Gas turbines operate at high rotational speeds and require reliable machinery monitoring. Shaft displacement and vibration measurements can provide useful information about rotor behavior.

The sensor can be used in appropriately designed monitoring arrangements where its temperature, pressure, installation, and electrical specifications are satisfied.

3. Hydro Turbines

Hydro turbine installations require monitoring of rotating components, including shafts and associated bearing systems.

Non-contact displacement measurement can help maintenance personnel observe shaft movement and identify changes in operating behavior.

4. Industrial Compressors

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

Shaft vibration and displacement monitoring can help identify abnormal mechanical conditions. The PR6424 sensor can provide measurement signals for suitable compressor monitoring systems.

5. Industrial Pumps

Critical pumps used in power generation, chemical processing, and other industrial operations may require continuous condition monitoring.

The sensor can be used to measure shaft movement in applications where the mechanical installation and target material meet the probe requirements.

6. Industrial Fans

Large industrial fans and blowers may experience vibration due to imbalance, bearing problems, or mechanical looseness.

A suitable eddy current monitoring arrangement can provide shaft movement information for condition assessment and maintenance planning.

Installation and System Integration

Correct installation is essential for reliable measurements. Probe position, mounting arrangement, target material, cable routing, and converter compatibility all affect system performance.

1. Confirm the Probe Model

Before installation, verify the complete model number PR6424/015-021. Do not select a replacement solely by the 16 mm head diameter.

Different PR6424 configurations may have different cable lengths, connectors, mounting arrangements, and converter compatibility.

2. Check the Mounting Arrangement

The PR6424 series uses a threaded mounting arrangement in applicable configurations. Confirm the exact mechanical drawing and thread specification for the supplied probe before preparing the mounting location.

The probe should be secured firmly and positioned so that it does not contact the rotating shaft during operation.

3. Set the Initial Air Gap

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

The actual installation gap must be established according to the manufacturer’s procedure and the compatible converter’s requirements. Incorrect positioning can reduce the available measurement range or cause the signal to operate outside its intended linear region.

4. Verify the Target Material

The published specification identifies ferromagnetic steel as the target material, with 42CrMo4 steel as the standard reference.

Different shaft materials or surface conditions may affect sensor response. Verify the target material and calibration requirements before commissioning.

5. Connect the Extension Cable and Converter

Use the correct extension cable and signal converter for the exact probe configuration.

Check connector compatibility, cable length, shielding, grounding, and cable condition. Avoid unnecessary cable extensions or substitutions that have not been approved for the measurement system.

6. Protect the Cable During Installation

The sensor cable should be routed away from hot surfaces, moving components, sharp edges, and sources of electrical interference.

Observe the manufacturer’s minimum cable bending radius. Avoid excessive pulling, twisting, or bending that could damage the cable or internal conductors.

7. Commission the Measurement System

After installation, verify the initial gap, signal output, converter settings, and monitoring-channel configuration.

Check that the output changes correctly as the shaft-to-probe distance changes within the permitted measurement range. Confirm alarm and protection settings in the monitoring system before placing the machinery into normal operation.

Compatible System Components

The PR6424/015-021 is part of a measurement chain. The following components may be used in a compatible EPRO machinery monitoring installation.

The components listed are examples of equipment used in PR6424 measurement systems. They are not automatically included with the sensor. Confirm the exact converter and cable combination using the applicable manufacturer documentation.

Alternative Models and Replacement Considerations

The PR6424/015-021 belongs to the EPRO 16 mm eddy current sensor family. When replacing an existing probe, engineers should verify the complete configuration rather than selecting another sensor based only on its diameter.

Before selecting a replacement, compare:

• Complete sensor model and suffix.
• Probe head diameter.
• Sensor body and mounting dimensions.
• Thread type and installation length.
• Integrated cable length and connector type.
• Extension cable specifications.
• Signal converter compatibility.
• Sensitivity and measurement range.
• Target material and shaft diameter.
• Operating temperature and environmental conditions.
• Monitoring module input configuration.

A probe with the same 16 mm diameter may still be unsuitable if its cable or electrical configuration differs from the original installation.

Key Advantages

Non-Contact Measurement

The eddy current principle allows the sensor to measure shaft displacement without physical contact with the rotating component. This avoids mechanical contact wear at the sensing interface.

Suitable for Critical Rotating Machinery

The PR6424 series is designed for machinery such as turbines, compressors, pumps, and fans, where shaft movement monitoring is important.

High Measurement Sensitivity

The published sensitivity of 4 V/mm supports the measurement of relatively small changes in probe-to-target distance when used with a compatible converter.

Static and Dynamic Measurement

The sensor supports both static shaft-position measurement and dynamic displacement measurement within the specified operating range.

Industrial Construction

The stainless-steel sleeve and PTFE-insulated cable are designed for industrial sensor installations, subject to the applicable environmental and temperature limits.

Integration with Machinery Monitoring Systems

When paired with the appropriate extension cable, converter, and monitoring equipment, the sensor can contribute to continuous machinery condition monitoring.

Technical FAQs

1. What is the EPRO PR6424/015-021?

It is a 16 mm eddy current displacement sensor designed for non-contact measurement of shaft displacement, vibration, position, and eccentricity in rotating machinery.

2. What is the sensor head diameter?

The sensor head diameter is 16 mm.

3. What is the measurement range of the PR6424 series?

The published static measurement range is ±2.0 mm. The dynamic measurement range is 0 to 1,000 μm.

4. What is the sensitivity of this sensor?

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

5. What is the nominal air gap?

The nominal center air gap is approximately 2.7 mm. The final installation gap should follow the manufacturer’s setup procedure and compatible converter requirements.

6. What material can the sensor measure?

The published specification identifies ferromagnetic steel as the target material, with 42CrMo4 steel as the standard reference.

7. What is the weight of the PR6424/015-021?

The supplied product weight is 0.2 kg. The manufacturer’s reference value is approximately 200 grams for the sensor with a 1-meter cable and without armor.

8. Does the sensor require a signal converter?

A compatible signal converter is normally required to condition the probe signal for use by a machinery monitoring system. The converter must match the exact probe configuration.

9. Where is the PR6424 sensor commonly used?

It is commonly used in steam turbines, gas turbines, hydro turbines, compressors, pumps, fans, and other critical rotating machinery.

10. Can another PR6424 model replace the PR6424/015-021?

Not automatically. The probe suffix may identify differences in cable and electrical configuration. Confirm the complete model, mounting details, cable arrangement, and converter compatibility before substitution.

Procurement and Maintenance Recommendations

When purchasing the EPRO PR6424/015-021, verify the complete part number and confirm that it matches the existing machinery monitoring system. The 16 mm probe diameter alone is not sufficient to establish compatibility.

For replacement projects, check the sensor cable, connector, extension cable, signal converter, and monitoring-channel configuration. If the original installation uses a specific converter or cable length, the replacement should be checked against those requirements before ordering.

For used or surplus sensors, request clear photographs of the probe head, threaded body, cable, connector, and model identification. Inspect the cable for cuts, crushing, excessive bending, or signs of heat damage. Where possible, request electrical testing or verification with a compatible converter.

During maintenance, inspect the probe mounting arrangement and cable routing. Confirm that the sensor remains securely positioned and that the installed air gap has not changed. Review monitoring trends and investigate unexpected changes in shaft displacement or vibration.

For critical rotating equipment, replacement work should follow the plant’s machinery protection procedures. Incorrect sensor installation or calibration can produce misleading measurements and may affect the reliability of machinery protection functions.

Conclusion

The EPRO PR6424/015-021 16 mm Eddy Current Sensor is designed for non-contact shaft displacement and vibration measurement in critical industrial rotating machinery. With a 16 mm sensing head, 4 V/mm sensitivity, ±2.0 mm static measurement range, and approximately 2.7 mm nominal center air gap, it provides measurement capability for suitable turbine, compressor, pump, and fan monitoring applications.

The sensor is typically used with a compatible extension cable, signal converter, and machinery monitoring module. For maintenance and replacement projects, confirming the complete model suffix, cable configuration, converter compatibility, and installation requirements is essential for reliable operation.