Product Overview

The Epro PR6424/104-021 16 mm Eddy Current Sensor is a non-contact displacement measurement probe designed for monitoring the condition and operating behavior of rotating machinery. It belongs to the PR6424 sensor family, which is commonly used in machinery protection and condition-monitoring systems for turbines, compressors, pumps, fans, and other critical industrial equipment.

The sensor operates according to the eddy current measurement principle. Instead of physically contacting a rotating shaft, it generates an electromagnetic field and detects changes in that field as the distance between the probe tip and a conductive target surface changes. The resulting measurement can be used to monitor shaft vibration, displacement, axial position, eccentricity, and other mechanical conditions.

A 16 mm sensing head provides a measurement arrangement intended for applications involving relatively large rotating shafts. When installed with a compatible signal converter and monitoring system, the probe can provide displacement information for machinery protection, predictive maintenance, and equipment diagnostics.

The PR6424 series is associated with a nominal sensitivity of 4 V/mm and a static measuring range of ±2.0 mm. Its typical center air gap is approximately 2.7 mm. These characteristics allow the sensor to detect small changes in shaft position and movement, helping maintenance teams identify abnormal mechanical behavior before it develops into a more serious equipment problem.

The PR6424/104-021 is identified by its complete ordering code. Although the general measurement characteristics are associated with the PR6424 family, cable length, connector arrangement, mounting configuration, and temperature limits should be checked against the exact variant documentation.

With a supplied weight of 0.2 kg, the sensor is a compact measurement component that can be installed near rotating machinery as part of an appropriate monitoring arrangement.

Technical Specifications

Note: The technical values above describe the PR6424 sensor family. Confirm the exact operating temperature, cable length, connector, mounting arrangement, and electrical compatibility for PR6424/104-021 before installation.

Function and Working Principle

The PR6424/104-021 uses electromagnetic induction to measure the distance between the sensor tip and a conductive target. This non-contact method is particularly useful for rotating machinery because it allows shaft movement to be measured without a mechanical connection to the rotating component.

1. Eddy Current Measurement Principle

When the sensor is energized by a compatible signal converter, an alternating electromagnetic field is generated at the probe tip.

When the probe is positioned near a conductive metal target, such as a ferromagnetic steel shaft, eddy currents are induced in the target surface. These currents affect the electromagnetic field produced by the sensor.

The strength of this interaction changes according to the distance between the probe and the target. The associated electrical response can therefore be used to determine the relative position of the shaft.

Because the measurement is non-contact, the sensor does not need to touch the rotating surface during normal operation.

2. Shaft Displacement Measurement

The sensor detects changes in the gap between its sensing tip and the shaft surface. As the shaft moves, the output signal changes accordingly.

This measurement can be used to identify radial shaft displacement, axial movement, and changes in shaft position.

The PR6424 series has a typical static measuring range of ±2.0 mm. Correct installation and adjustment of the initial air gap are important for maintaining the intended measurement range.

3. Vibration Monitoring

Rotating shafts may experience vibration because of imbalance, misalignment, bearing wear, looseness, or other mechanical conditions.

An eddy current probe positioned near the shaft can detect dynamic displacement as the shaft rotates. The resulting signal can be processed by a compatible monitoring instrument to evaluate vibration behavior.

The PR6424 family has a typical dynamic measurement range of 0–1,000 μm. This makes it suitable for machinery-monitoring arrangements where small changes in shaft movement are important.

4. Axial Position and Eccentricity Measurement

The sensor can also be used in suitable arrangements to monitor axial shaft movement and eccentricity.

Axial position measurement is useful for machinery where the shaft must remain within a defined operating position. Eccentricity measurement can help identify uneven shaft geometry or changes in the relationship between the shaft centerline and its rotating surface.

The exact measurement arrangement depends on probe orientation, target geometry, mounting position, and the connected monitoring equipment.

5. Signal Conversion and Monitoring

The sensor probe is part of a measurement chain rather than a complete standalone monitoring instrument. A compatible signal converter supplies the probe and processes its measurement response.

The resulting signal can be connected to a machinery protection or condition-monitoring system. That system can display measurements, compare them with configured limits, and generate alarms when abnormal conditions are detected.

Correct matching of the probe, extension cable, converter, and monitoring channel is essential for reliable measurements.

Role in Industrial Machinery Monitoring Systems

The PR6424/104-021 can serve as a sensing component within an industrial machinery protection system. Its measurements help operators and maintenance engineers understand the mechanical condition of rotating equipment.

Turbine Shaft Monitoring

Steam, gas, and hydro turbines operate under demanding mechanical and thermal conditions. Shaft vibration and displacement measurements provide information about the machine’s mechanical behavior.

A correctly installed eddy current probe can supply shaft movement data to a compatible monitoring system. This information can support alarm management, condition assessment, and maintenance planning.

Compressor Protection

Industrial compressors are often critical to continuous production. Changes in shaft vibration or position may indicate developing mechanical problems.

The sensor can be used in an appropriate monitoring arrangement to measure shaft displacement and provide information for compressor protection systems.

Pump Condition Monitoring

Large process pumps may operate continuously under changing load conditions. Monitoring shaft vibration and position can help maintenance teams identify abnormal movement, mechanical wear, or changes in operating behavior.

The probe should be selected and installed according to the pump shaft geometry and the measurement requirements of the monitoring system.

PLC and DCS Integration

A machinery monitoring system may communicate relevant measurements and alarm information to a plant PLC or distributed control system.

The PR6424 probe itself should not be treated as a direct PLC input device. Its signal must first be conditioned by a compatible converter or monitoring channel. Integration depends on the output interface provided by that equipment.

Industrial Applications

1. Steam Turbines

Steam turbines operate at high rotational speeds and require continuous monitoring of shaft behavior. Eddy current sensors can measure shaft vibration and displacement without physical contact.

Measurements can help identify changes in shaft movement associated with imbalance, misalignment, bearing conditions, or other mechanical issues.

2. Gas Turbines

Gas turbines are used in power generation and industrial process facilities. Their rotating assemblies require reliable condition-monitoring arrangements.

A PR6424 series probe can be used in a suitable installation to monitor shaft displacement and support machinery protection functions.

3. Hydro Turbines

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

Shaft displacement measurements can provide useful information about rotating assembly behavior and support long-term maintenance planning.

4. Industrial Compressors

Centrifugal and other large compressors are widely used in chemical processing, refining, gas transportation, and manufacturing.

Eddy current probes can be installed near appropriate shaft measurement locations to monitor vibration and position. The monitoring system can use this information to identify abnormal operating conditions.

5. Industrial Pumps

Large pumps used in water treatment, power generation, and process industries may require continuous vibration monitoring.

A non-contact displacement sensor can provide shaft movement information for compatible machinery-monitoring equipment.

6. Industrial Fans

Large industrial fans and blowers may experience imbalance, bearing deterioration, and mechanical vibration.

A suitable eddy current monitoring arrangement can help detect changes in shaft movement and support preventive maintenance activities.

Installation and System Integration

Correct installation is essential for accurate displacement measurements. The sensor must be positioned correctly relative to the shaft, and its electrical connections must match the connected converter and monitoring system.

1. Verify the Complete Model Number

Before installation, confirm that the probe is PR6424/104-021. Do not rely solely on the PR6424 family designation when selecting a replacement.

Different variants may have different cable lengths, connector arrangements, mounting details, and mechanical configurations.

2. Check the Target Surface

The PR6424 series is designed for measurement against suitable conductive targets, with ferromagnetic steel used as the reference material in its specifications.

The target surface should be appropriate for the measurement system. Surface material, finish, shaft geometry, and operating conditions can affect measurement performance.

3. Set the Initial Air Gap

The initial air gap is an important installation parameter. The PR6424 family specifies a nominal center air gap of approximately 2.7 mm.

The actual setup should follow the applicable probe and converter instructions. An incorrect gap can reduce the usable measurement range or result in an inaccurate output.

4. Confirm Probe Mounting

The sensor should be mounted securely using the correct mounting arrangement. The mounting thread and mechanical dimensions must be confirmed for the exact variant.

The probe tip must have adequate clearance from the shaft and surrounding metallic structures. Unintended metal near the sensing area may affect the electromagnetic field and measurement response.

5. Check Cable Routing

The sensor cable should be routed away from sources of electrical interference and mechanical damage.

Avoid excessive bending, sharp edges, and cable tension. The exact minimum bending radius depends on whether the cable is armored or non-armored and should be checked against the applicable cable specification.

6. Match the Signal Converter

The PR6424 probe must be paired with a compatible signal converter and monitoring channel.

Verify the probe type, extension cable arrangement, connector, and converter configuration. An incompatible converter or cable can produce incorrect measurements or prevent the sensor from operating properly.

7. Commission the Measurement Channel

After installation, verify the initial gap, output response, signal stability, and measurement direction.

Where possible, compare the channel reading with an appropriate reference measurement. Confirm that alarm limits and monitoring parameters are configured for the machinery and its operating conditions.

Compatible System Components

The PR6424/104-021 is normally used as part of a complete machinery-monitoring arrangement.

These components are examples of equipment used in a complete measurement system. They are not necessarily supplied with the sensor.

Alternative Models and Replacement Considerations

The PR6424 family includes different sensor variants. A replacement should be selected according to the exact mechanical and electrical configuration rather than the 16 mm head diameter alone.

Before selecting a replacement, compare:

• Complete model number and suffix.
• Sensor head diameter.
• Mounting thread and mechanical length.
• Cable length and cable construction.
• Connector type and pin arrangement.
• Sensitivity and linearity.
• Static and dynamic measuring ranges.
• Operating temperature limits.
• Target material and shaft geometry.
• Compatible signal converter.
• Monitoring channel configuration.

A probe with the same nominal diameter may still have a different cable or electrical configuration. Replacing only the sensor without checking the complete measurement chain can result in incorrect readings or unreliable monitoring.

Key Advantages

Non-Contact Measurement

The eddy current principle measures shaft displacement without requiring direct mechanical contact. This is particularly valuable for high-speed rotating machinery.

Sensitive Displacement Detection

The PR6424 family has a typical sensitivity of 4 V/mm and a static measuring range of ±2.0 mm, supporting the detection of relatively small changes in shaft position.

Dynamic Vibration Measurement

The sensor can detect dynamic shaft movement within the specified measurement range, providing information for vibration-monitoring applications.

Industrial Machinery Applications

The PR6424 series is intended for demanding rotating machinery applications, including turbines, compressors, pumps, and fans.

Compact Sensing Head

The 16 mm sensor head supports installation in suitable machinery measurement locations where probe access and mounting space must be considered.

Stainless Steel Sensor Sleeve

The stainless steel sleeve provides a durable mechanical housing for the sensing assembly in suitable industrial installations.

Condition-Monitoring Integration

When paired with a compatible converter and monitoring system, the sensor can contribute to machinery protection, alarm management, and predictive maintenance strategies.

Technical FAQs

1. What is the Epro PR6424/104-021?

The PR6424/104-021 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 supplied product description identifies a 16 mm sensor head diameter.

3. What measurement principle does it use?

It uses the eddy current principle. An electromagnetic field interacts with a conductive target, and changes in the interaction are used to determine the distance between the sensor and the target surface.

4. What is the typical sensitivity of the PR6424 series?

The PR6424 family has a typical sensitivity of 4 V/mm, with a specified linearity of up to ±1.5%.

5. What is its static measuring range?

The typical static measuring range is ±2.0 mm. The actual usable range depends on the initial air gap and the complete measurement configuration.

6. Can it measure shaft vibration?

Yes. When installed and connected to a compatible converter and monitoring system, it can measure dynamic shaft displacement used for vibration monitoring.

7. What equipment is it commonly used with?

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

8. Does the sensor connect directly to a PLC?

It should not be assumed to connect directly to a standard PLC input. The probe normally requires a compatible signal converter or monitoring channel to condition its measurement signal.

9. What is the supplied weight?

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

10. Can another PR6424 model replace the PR6424/104-021?

Not automatically. Check the full model number, cable length, connector, mounting arrangement, measurement characteristics, and converter compatibility before selecting an alternative.

Procurement and Maintenance Recommendations

When purchasing the Epro PR6424/104-021, confirm the complete model number and inspect the sensor label. The 16 mm head diameter identifies the general sensor family but does not establish that every PR6424 variant has the same cable and connection configuration.

For replacement projects, compare the original probe with the proposed unit. Pay particular attention to cable length, connector type, mounting thread, sensor dimensions, and compatibility with the installed signal converter.

For used or surplus equipment, request clear photographs of the sensor head, mounting section, cable, connector, and identification label. Check for damaged insulation, bent mounting components, corrosion, and signs of mechanical impact.

During maintenance, inspect the probe mounting and cable condition. Keep the sensing area free from unintended metallic objects and verify that the probe has not shifted from its commissioned position.

Measurement readings should be reviewed in the context of machine operating speed, load, temperature, and historical trends. Changes in vibration or shaft position should be investigated alongside other machinery information rather than evaluated in isolation.

Maintaining accurate records of sensor model numbers, installation gaps, converter settings, and alarm limits can simplify future troubleshooting and replacement work.

Conclusion

The Epro PR6424/104-021 16 mm Eddy Current Sensor is designed for non-contact measurement of shaft displacement and dynamic movement in industrial rotating machinery. Its PR6424 family characteristics include a typical sensitivity of 4 V/mm, a static measuring range of ±2.0 mm, and a nominal center air gap of approximately 2.7 mm.

When installed with a compatible signal converter and machinery monitoring system, the sensor can support vibration monitoring, shaft-position measurement, machinery protection, and condition-based maintenance. Accurate identification of the complete model number and verification of cable, connector, mounting, and converter compatibility are essential for reliable operation.