Description

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This system, manufactured by EPRO (now owned by Emerson) in Germany, is model PR6423/010-040 with a CON021 preamplifier. It is an 8mm eddy current displacement sensor system used for non-contact displacement and vibration measurement in rotating machinery.

　　I. System Composition

Sensor Probe PR6423/010-040

Probe head diameter 8mm, M8 mounting thread

Cable length 4 meters (010 indicates 1.0 meter standard configuration, 040 indicates 4 meter cable length option)

The probe coil generates a high-frequency alternating magnetic field at the head, inducing eddy current effect when close to the metal surface being measured. The coil impedance changes with the gap.

Material: Stainless steel sleeve, PTFE cable, withstand voltage 2 bar (approximately 200 kPa)

Preamplifier CON0 21

Protection Rating IP20

Connects to the sensor via LEMO connector

Provides a high-frequency excitation signal to the probe and converts probe coil impedance changes into a standard DC voltage output.

Output voltage linear range: -4V to -20V (when the supply voltage is -24V), maximum range: -1V to -22V

Reference voltage: -12V (symmetrical measurement range at both ends), internal resistance: 100kΩ, response time: 15µs

　　II. Technical Parameters

Measurement range: Static ±0.5mm (±0.02mm) 0 inches), dynamic 0 to 250 micrometers (0 to 10 milliinches)

Sensitivity: 8 volts per millimeter (203.2 mV per mil), linearity error ≤ ±1%

Rated air gap (center): Approx. 1.5 mm (0.06 inches)

Long-term drift: <0.3%

Temperature error: <2% per 100 Kelvin (API compliant)

Operating temperature range: Sensor and cable -35°C to +200°C, connector -35°C to +150°C

Maximum Surface velocity: 2500 m/s

Shaft diameter requirement: ≥25 mm

Vibration and shock resistance: 5g at 60 Hz (25°C)

Measured material: Ferromagnetic steel, reference material is 42CrMo4 steel

Linearity error: ≤1.0% when using CON021

Temperature drift: 0.200 mV per 100 Kelvin, sensitivity ≤2% per 100 Kelvin

Time drift: Maximum 0.3%

Power supply voltage error: ≤0.2% per volt

Explosion-proof rating: Eex ib IIC T6/T4, intrinsically safe, with ATEX/IEC Ex/CSA certification

　　III. Working principle

The high-frequency oscillating current in the preamplifier flows into the probe coil through the extension cable, generating an alternating magnetic field at the probe head. When the measured metal object approaches this magnetic field, an induced current, i.e., eddy current, is generated on the metal surface. The magnetic field generated by the eddy current is opposite to the direction of the coil’s magnetic field, changing the effective impedance of the coil. The impedance change is proportional to the distance from the probe to the surface of the metal conductor. The preamplifier electronics convert the coil impedance change into a voltage output, the magnitude of which varies with the distance between the probe and the surface of the measured object. The sensor and preamplifier assembly has been linearly calibrated using 42CrMo4 calibration material before leaving the factory; no further calibration is required during installation, only adjustment of the air gap to the desired gap voltage.

　　IV. Installation and Calibration Requirements:

Installation Method: Secure to the bearing housing using an M10×1 thread. A 12–15 N·m torque wrench is recommended for tightening; avoid overloading.

Air Gap Calibration:

Insert a 0.8mm standard calibration clip between the probe and the measured shaft surface.

After powering on, adjust the mounting bolts to stabilize the preamplifier output at -12V ±0.1V, which is the effective measurement zero point.

After calibration, tighten the lock nut and apply high-temperature threadlocker (such as Loctite 243) to prevent loosening.

Connection Specifications:

Sensor ↔ Preamplifier: Achieve quick and reliable connection via the LEMO connector (IP20 protection). Do not use non-original components; otherwise, sensitivity deviation may reach 20%–40%.

Preamplifier ↔ Control System: Power supply (24V DC) and output signal (-4V~-20V) are connected via screw terminals. Strictly adhere to polarity during wiring to avoid damaging the circuit.

　　V. Application Scenarios

Widely used in the MMS3000 and MMS6000 turbine monitoring and protection systems, and also for monitoring shaft vibration and displacement in rotating machinery such as compressors, gearboxes, fans, and pumps. Complies with international standards such as API 670, DIN 45670, and ISO 10817-1. Suitable for equipment condition monitoring and fault prevention in industries such as power, petrochemicals, steel, and rail transportation.

　　VI. Installation Precautions

When installing the probe, ensure the sensor is perpendicular to the surface being measured. The natural frequency of the support should be at least 10 times the machine speed. The diameter of the shaft being measured should be at least three times the diameter of the probe, i.e., greater than 24 mm. The surface being measured should be smooth, with a roughness requirement of 0.4 to 0.8 micrometers for vibration measurement and 0.4 to 1.6 micrometers for displacement measurement. Sufficient distance must be maintained between the two probes to avoid magnetic field interference. During installation, adjust the probe position using the DC voltage (gap voltage) output from the preamplifier, typically adjusted to the midpoint of the linear range corresponding to -10V DC. A non-conductive medium space must be left around the probe head.

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EPRO PR6423/00R-010 CON021
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