Product Overview

The Epro PR6426/000-030+CON021/916-120 is an extended-range eddy current measurement assembly combining a PR6426 32 mm sensor with a CON021 signal converter. The system is used for non-contact shaft displacement measurement in large rotating machinery, particularly where the required measuring range exceeds that of a standard PR6426 measurement configuration.

The assembly consists of two matched components. The PR6426/000-030 detects changes in the distance between its sensing head and the metallic target, while the CON021/916-120 processes the sensor response and converts it into a displacement-related electrical output. The converter’s /916-120 designation identifies the 12 mm extended measuring range for the PR6426 sensor family.

The sensor uses a non-threaded sleeve and an 80 × 40 mm mounting plate. Its 32 mm sensing head is suitable for installations around large turbine and compressor shafts, where a fixed mounting arrangement is required to maintain the probe position relative to the measuring surface.

The /000-030 sensor configuration includes an 8 m non-armored cable, an adapter plug, and a LEMO connector. This cable arrangement is useful when the probe is installed close to the rotor but the signal converter is located farther away in a machine instrumentation panel or monitoring cabinet.

The main distinction between this assembly and the previously described PR6426/000-030+CON021 combination is the converter’s measuring range. The standard CON021 configuration and the CON021/916-120 are not interchangeable in terms of measurement characteristics. The latter is configured for a 12 mm extended measuring range, with a nominal measuring-chain sensitivity of approximately -1.33 V/mm and a specified linearity error of ≤ ±1.5%.

This extended range can be useful in applications involving large shaft displacement, axial movement, or installations where a wider measurement window is required. For example, on a large steam turbine, the assembly can monitor axial rotor movement across a wider displacement interval than a standard-range arrangement. In a centrifugal compressor, it can be applied to suitable shaft position measurement points where the mechanical installation and monitoring requirements call for extended-range measurement.

The CON021 is a panel-mounted converter with a self-locking LEMO sensor connection and screw-terminal connections for its supply and output. The processed measurement signal can be connected to compatible machinery monitoring equipment for displacement evaluation and alarm processing.

An important consideration is that the PR6426 sensor and CON021 converter form a matched measuring chain. Their adjustment, sensor identity, and target material must be considered together. When replacing an existing assembly, the converter’s type plate and measuring range should be checked rather than selecting a converter solely because it belongs to the same CON021 family.

Technical Specifications

PR6426/000-030 Eddy Current Sensor

CON021/916-120 Eddy Current Signal Converter

Complete Assembly

Product Features

• Complete eddy current measurement assembly with sensor and signal converter.
• 32 mm PR6426 sensing head for large rotating machinery.
• CON021/916-120 configured for a 12.0 mm extended measuring range.
• Measuring-chain sensitivity of approximately -1.33 V/mm.
• Linearity error of ≤ ±1.5%.
• Approximately 1.5 mm initial air gap for the extended-range configuration.
• 80 × 40 mm sensor mounting plate.
• Non-threaded stainless-steel sensor sleeve.
• 8 m non-armored PTFE sensor cable.
• LEMO connection with adapter plug.
• Panel-mounted CON021 signal converter.
• Self-locking sensor input connection.
• Screw-terminal power and output connections.
• Frequency response up to 20 kHz (-3 dB).
• Suitable for static displacement and dynamic shaft movement measurements.
• Compatible with supported Epro machinery monitoring arrangements.

Working Principle

The PR6426/000-030 and CON021/916-120 operate as a matched eddy current measuring chain. The sensor detects the distance between its sensing face and a conductive metallic target, while the converter controls the excitation circuit and processes the resulting electrical response.

Inside the PR6426 probe, a sensing coil generates a high-frequency electromagnetic field. When this field reaches the metallic shaft surface, eddy currents develop within the target material. The resulting interaction changes the electrical characteristics of the coil.

As the shaft moves toward or away from the probe, the electromagnetic coupling changes. The converter detects this variation and converts it into a voltage signal corresponding to the measured displacement.

The complete measurement path is:

Rotating Shaft → PR6426/000-030 → 8 m Sensor Cable → CON021/916-120 → Displacement Output → Machinery Monitoring System

The /916-120 converter configuration extends the measuring range to 12 mm. Its nominal measuring-chain sensitivity is approximately -1.33 V/mm. This is lower than the sensitivity of a standard-range PR6426 measuring chain because the same output variation represents a wider displacement interval.

For example, on a steam turbine, the probe can be installed at an axial measurement point to monitor rotor movement during startup, load changes, and normal operation. The wider measurement interval allows the monitoring system to track larger changes in shaft position without using the standard 4 mm or 8 mm measuring configuration.

The initial air gap is approximately 1.5 mm for the 12 mm extended-range arrangement. Correct positioning is essential because the sensor must operate within the converter’s calibrated measurement window. The final adjustment should be performed using the complete sensor and converter combination.

The target material also influences the measurement response. The standard reference material is 42CrMo4 steel, equivalent to SAE 4140. If the actual shaft material differs, the calibration characteristics must be considered when configuring the measuring chain.

The CON021/916-120 therefore does more than amplify the probe signal. Its specific calibration establishes the extended measurement range, sensitivity, and linearity characteristics of the complete sensor assembly.

Role in a Machinery Protection and Condition Monitoring Architecture

The PR6426/000-030+CON021/916-120 functions as a complete displacement measurement channel within a rotating machinery monitoring system. It combines the physical sensing element and the calibrated signal conversion stage, allowing shaft movement to be monitored through a compatible protection or condition monitoring platform.

A typical measurement architecture is:

Rotating Shaft → PR6426/000-030 → 8 m LEMO Cable → CON021/916-120 → Monitoring Input → Machinery Protection System

The 12 mm measuring range is particularly relevant when the monitoring point requires a wider displacement window than a standard configuration can accommodate. In turbine applications, axial shaft movement can change during different operating conditions, making the selection of an appropriate measuring range important.

The converter output can be connected to compatible monitoring inputs, where displacement trends and configured alarm limits are evaluated. The actual alarm and shutdown functions depend on the connected protection system and its configuration.

Because the sensor and converter are adjusted together, the converter type plate should retain the corresponding sensor identification. Replacing only the converter without checking the original sensor and measuring-chain configuration can introduce measurement errors.

Industrial Applications

Installation and Maintenance

1. Verify the Complete Model: Confirm that the assembly includes PR6426/000-030 and CON021/916-120. Check the sensor cable length, LEMO connection, mounting plate, and converter type plate.
2. Inspect the Sensor Assembly: Examine the 32 mm sensing head, non-threaded sleeve, cable, adapter plug, and mounting plate for mechanical damage before installation.
3. Select the Measuring Position: Determine whether the application requires axial or radial shaft displacement measurement. Position the sensor face toward the appropriate measuring surface.
4. Check the Target Material: Confirm that the shaft material matches the standard 42CrMo4 reference material or that the measuring chain has been adjusted for the actual target material.
5. Inspect the Measuring Surface: Check the shaft track for scratches, corrosion, deposits, and irregularities that could affect the electromagnetic measurement.
6. Set the Initial Air Gap: Position the probe according to the 12 mm extended-range configuration. The nominal initial air gap is approximately 1.5 mm. Use the calibrated measurement arrangement when setting the final position.
7. Secure the Mounting Plate: Fix the 80 × 40 mm mounting plate firmly to the machine structure. Check that the sensor cannot shift under vibration or thermal movement.
8. Route the 8 m Cable: Keep the non-armored cable away from rotating components, sharp edges, and excessive mechanical tension. Avoid tight bends and protect the cable from unsuitable temperature conditions.
9. Connect the LEMO Interface: Insert the sensor connector into the CON021/916-120 input and ensure that the self-locking connection is fully engaged.
10. Wire the Converter: Connect the DC supply and output terminals according to the converter wiring arrangement. Verify polarity, grounding, and the receiving equipment’s input requirements before energizing the circuit.
11. Check the Extended-Range Output: Verify that the converter responds across the intended 12 mm measurement interval. Confirm the signal direction, sensitivity, initial position, and output behavior before connecting the channel to active protection logic.
12. Record the Measuring-Chain Configuration: Document the sensor serial number, converter type plate information, target material, initial air gap, cable routing, output configuration, and final commissioning measurements.

Compatible System Components

Recommended Related Models

Key Advantages

• Complete sensor and converter measurement assembly.
• 32 mm sensing head for large rotating machinery.
• 12 mm extended measuring range.
• Approximately -1.33 V/mm measuring-chain sensitivity.
• Linearity error of ≤ ±1.5%.
• 8 m cable for installations with greater distance between the probe and converter.
• LEMO sensor connection with adapter plug.
• Panel-mounted converter with screw-terminal power and output connections.
• Suitable for wider-range axial and radial shaft displacement measurement.
• Integration with compatible machinery monitoring and protection systems.

Technical FAQs

What is the measuring range of the CON021/916-120?

The CON021/916-120 is configured for a 12.0 mm extended measuring range when used with the PR6426 sensor family. Its nominal measuring-chain sensitivity is approximately -1.33 V/mm, with a specified linearity error of ≤ ±1.5%. This differs from the standard-range CON021 configuration and should be considered when selecting a replacement converter.

How does the /916-120 version differ from CON021/916-160?

Both converters are intended for PR6426 extended-range measurement, but they have different measuring intervals. The /916-120 supports 12 mm with a linearity error of ≤ ±1.5%, while the /916-160 supports 16 mm with a linearity error of ≤ ±2.0%. The correct version depends on the required displacement range and the mechanical installation.

Why is the initial air gap different from the standard PR6426 configuration?

The extended-range converter changes the calibration and sensitivity of the complete measurement chain. For the 12 mm /916-120 configuration, the nominal initial air gap is approximately 1.5 mm. This differs from the nominal center gap used in standard-range arrangements. The probe must therefore be positioned according to the extended-range installation procedure rather than the standard PR6426 setting.

Can the PR6426/000-030 sensor be connected to a different CON021 converter?

A PR6426 sensor can be used with different supported CON021 measuring-range configurations, but the sensor and converter must be treated as a matched measurement chain. The converter calibration, sensor identification, target material, and required displacement range all affect the measurement response. Replacing the /916-120 with a standard or differently ranged converter without checking the complete configuration can produce incorrect displacement readings.