Introduction to EMERSON PR9268/202-000
Product Description
The EMERSON PR9268/202-000 is a rugged, high-precision eddy-current proximity sensor designed for industrial machinery condition monitoring and rotational speed/target position measurement. As a flagship model in Emerson’s PR9268 series—specialized for harsh industrial environments—this sensor excels at non-contact detection of metallic targets, making it ideal for applications such as turbine speed monitoring, motor shaft position sensing, and bearing condition analysis in industries like power generation, oil and gas, petrochemical, and heavy manufacturing.
The model designation “PR9268/202-000” encodes key attributes: “PR9268” denotes the product series (eddy-current proximity sensors), “202” specifies a 2mm nominal sensing distance and 2-wire DC current output configuration, and “000” references standard calibration and no optional accessories. Unlike inductive sensors with limited precision, the PR9268/202-000 uses eddy-current technology to deliver sub-millimeter accuracy, even in extreme conditions (high temperature, vibration, oil contamination)—critical for protecting expensive rotating machinery from catastrophic failure. Its robust stainless-steel housing and hermetic sealing ensure long-term reliability in environments where dust, moisture, and chemical exposure are common.
Typical use cases include:
- Measuring the rotational speed of gas turbine shafts in power plants (to prevent overspeed).
- Detecting the position of motor rotors in electric vehicles or industrial pumps (for synchronization).
- Monitoring bearing wear in centrifugal compressors (by tracking shaft displacement relative to the bearing housing).
- Providing speed feedback for variable-speed drives (VSDs) in conveyor systems or manufacturing lines.
Technical Parameters
- Sensor Technology: Eddy-current (inductive proximity), non-contact detection of ferrous/non-ferrous metallic targets.
- Sensing Range:
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- Nominal sensing distance: 2mm (for ferrous targets, e.g., carbon steel); 1mm (for non-ferrous targets, e.g., aluminum).
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- Operating distance range: 0.5mm to 3mm (adjustable via calibration).
- Output Configuration:
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- Type: 2-wire DC current output (4–20mA), proportional to target distance (linear output).
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- Load resistance: 0–500Ω (at 24V DC supply).
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- Output linearity: ±1% of full scale (4–20mA corresponds to 0.5mm–3mm distance).
- Target Requirements:
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- Material: Ferrous (carbon steel, stainless steel) or non-ferrous (aluminum, copper) metals.
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- Minimum target size: 10mm × 10mm (flat surface) or φ8mm (cylindrical shaft, for speed measurement).
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- Target surface finish: Ra ≤ 6.3µm (roughness) to ensure consistent eddy-current generation.
- Electrical Specifications:
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- Power Supply: 18–30V DC (24V DC nominal); reverse polarity protection (up to 30V DC).
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- Power Consumption: ≤20mA (no-load current).
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- Frequency Response: 0–10 kHz (supports speed measurements up to 60,000 RPM for 1-pulse-per-revolution targets).
- Environmental Ratings:
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- Temperature Range: Operating: -40°C to +125°C (-40°F to +257°F); Storage: -55°C to +150°C (-67°F to +302°F).
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- Vibration Resistance: 10–2000 Hz, 20g peak (IEC 60068-2-6); Shock Resistance: 100g peak (11ms duration, IEC 60068-2-27).
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- Protection Rating: IP67 (dust-tight, waterproof to 1m depth for 30 minutes); IP68 optional (with specialized cable).
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- Chemical Resistance: Resistant to mineral oils, diesel fuel, and mild acids (per ISO 10882-1); compatible with industrial cleaning agents.
- Mechanical Specifications:
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- Housing Material: 316L stainless steel (corrosion-resistant for offshore/marine applications).
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- Housing Diameter: 18mm (M18 thread for easy mounting).
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- Cable: 2m PTFE-insulated cable (high-temperature resistant); optional 5m or 10m lengths.
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- Weight: 120g (sensor head) + 30g (2m cable).
- Certifications:
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- Industrial: CE (EN 61000-6-2/4, EMC compliance), UL 61010-1 (safety for electrical equipment), RoHS 2.0.
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- Hazardous Environments: ATEX Zone 2 (II 3G Ex nA IIC T4 Ga), IECEx (Ex nA IIC T4 Ga) for use in explosive atmospheres.
Usage Methods
1. Installation
- Mounting Preparation:
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- Select a mounting location where the sensor axis is perpendicular to the target surface (maximum tilt angle: ±5° to avoid measurement errors). For rotational speed applications, position the sensor 2mm (nominal) from the target (e.g., a gear tooth or shaft keyway).
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- Use the M18 thread on the sensor housing to secure it to a mounting bracket or machinery frame. Tighten with a 24mm wrench (torque: 15 Nm) to prevent vibration-induced loosening.
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- Ensure the target surface is clean and free of oil, grease, or debris—contaminants can reduce eddy-current coupling and degrade measurement accuracy. Use a solvent (e.g., isopropyl alcohol) to clean the target before installation.
- Cable Routing:
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- Route the PTFE cable away from high-voltage cables (e.g., 480V motor wiring) and sources of electromagnetic interference (EMI) such as VFDs. Use cable glands (IP67-rated) to secure the cable to the machinery frame and prevent water ingress.
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- Avoid bending the cable beyond its minimum bend radius (10mm for the 2m PTFE cable) to prevent conductor damage. For extended cable lengths (optional 5m/10m), use a shielded cable and ground the shield at the sensor end to minimize noise.
2. Wiring and Connection
- Power and Output Wiring:
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- The PR9268/202-000 uses a 2-wire configuration: Connect the brown wire to the positive (+) terminal of the 18–30V DC power supply, and the blue wire to the negative (-) terminal. The 4–20mA output is measured across the load resistor (0–500Ω) in series with the power supply.
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- For condition monitoring systems (e.g., Emerson’s CSI 6500 Machinery Health Monitor), connect the sensor’s output to the analog input channel of the monitor. Configure the monitor to map the 4–20mA signal to the target distance range (0.5mm–3mm) via the monitor’s software.
- Polarity Protection:
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- The sensor includes reverse polarity protection, but incorrect wiring (e.g., swapping brown and blue wires) will prevent it from operating. Use a multimeter to verify the power supply polarity before connecting the sensor.
3. Calibration and Testing
- Zero-Point Calibration:
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- Position the target at the minimum sensing distance (0.5mm) and adjust the sensor’s calibration potentiometer (accessible via a small hole in the sensor head) until the output current is 4mA.
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- Move the target to the maximum sensing distance (3mm) and re-adjust the potentiometer until the output current is 20mA. Repeat this process twice to ensure linearity.
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- For automated calibration, use Emerson’s PR9268 Calibration Tool (part no. CT-PR9268), which provides a precision target and digital current meter to verify output linearity (±1% of full scale).
- Functionality Testing:
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- Verify speed measurement by rotating the target (e.g., a shaft with a single pulse tooth) at a known speed (e.g., 1000 RPM). Use an oscilloscope to measure the output current frequency—1 pulse per revolution should produce a 16.67 Hz signal (1000 RPM = 16.67 revolutions per second).
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- Test environmental resilience by subjecting the sensor to a water spray (IP67 test) or high temperature (125°C) in a thermal chamber. Monitor the output current to ensure it remains stable (no drift >0.1mA) during testing.
4. Operation and Maintenance
- Real-Time Monitoring:
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- Integrate the sensor with a machinery health monitoring system (e.g., Emerson’s AMS Asset Monitor) to track target distance, speed, or displacement in real time. Set up alarms for abnormal conditions (e.g., “trigger alert if output current >18mA” = target distance <0.8mm, indicating potential bearing wear).
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- For rotational speed applications, monitor the output frequency to detect overspeed (e.g., turbine speed exceeding 110% of rated) and trigger a shutdown via a connected PLC.
- Maintenance:
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- Monthly: Inspect the sensor head for physical damage (e.g., dents, corrosion) and clean the target surface with a dry cloth to remove oil or dust buildup.
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- Quarterly: Verify calibration by measuring the output current at known target distances (0.5mm = 4mA, 3mm = 20mA). Recalibrate if drift exceeds ±0.2mA.
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- Annually: Replace the cable if signs of wear (e.g., cracked insulation, exposed conductors) are detected. Test the sensor’s vibration resistance using a shaker table to ensure it meets IEC 60068-2-6 standards.
System Introduction
The EMERSON PR9268/202-000 operates as a critical sensing node in industrial machinery health monitoring systems, integrating three core functional layers to enable reliable condition monitoring and protection:
1. Sensing Layer
The sensor uses eddy-current technology to detect metallic targets: When power is applied, the sensor’s coil generates an alternating magnetic field. This field induces eddy currents in the target, which in turn create a secondary magnetic field that opposes the original field. The strength of this interaction depends on the target’s distance from the sensor—closer targets increase eddy-current generation, reducing the coil’s impedance and changing the sensor’s output current (4–20mA, proportional to distance). This non-contact design eliminates mechanical wear, making the sensor ideal for high-speed rotating machinery.
2. Signal Conversion Layer
The sensor’s internal electronics convert the coil’s impedance change into a linear 4–20mA current output. This analog signal is robust to electrical noise (common in industrial environments) and can be transmitted over long distances (up to 100m) without degradation—critical for monitoring machinery in remote locations (e.g., offshore oil platforms). The 2-wire configuration simplifies wiring and reduces installation costs compared to 3-wire sensors.
3. Integration Layer
The PR9268/202-000 integrates seamlessly with Emerson’s machinery health management ecosystem:
- Condition Monitoring Systems: Connect to the CSI 6500 or AMS Asset Monitor to analyze trends (e.g., gradual increases in shaft displacement indicating bearing wear) and predict maintenance needs.
- PLCs/DCS: Send speed or position data to a PLC (e.g., Emerson’s DeltaV DCS) to enable closed-loop control (e.g., adjusting VFD speed based on sensor feedback).
- Safety Systems: Trigger emergency shutdowns via safety PLCs if abnormal conditions are detected (e.g., turbine overspeed, excessive shaft vibration).
Example System Integration:
In a combined-cycle power plant, the PR9268/202-000 monitors the rotational speed of a gas turbine shaft:
- The sensor is mounted 2mm from a gear tooth on the turbine shaft (1 tooth = 1 pulse per revolution).
- It generates a 4–20mA current signal proportional to the tooth’s distance (stable at 10mA during normal operation, 20mA if the tooth is too close).
- The signal is transmitted to a CSI 6500 monitor, which converts the current to a speed reading (e.g., 3000 RPM = 50 Hz signal).
- If the speed exceeds 3300 RPM (110% of rated), the monitor sends a signal to the plant’s safety PLC, triggering a turbine shutdown to prevent damage.
Related Models in the Series
- EMERSON PR9268/102-000: 2mm → 1mm nominal sensing distance variant, ideal for applications with limited space (e.g., small motor shafts, compact pumps).
- EMERSON PR9268/302-000: 2mm → 3mm nominal sensing distance model, designed for large targets (e.g., turbine rotors, large-diameter shafts) requiring longer detection ranges.
- EMERSON PR9268/204-000: 2-wire 4–20mA → 4-wire voltage output (0–10V) variant, compatible with legacy systems that use voltage inputs (e.g., older PLCs).
- EMERSON PR9268/202-001: IP67 → IP68-rated variant with a specialized cable (waterproof to 10m depth), suitable for submersible applications (e.g., marine propeller speed monitoring, underwater pumps).
- EMERSON PR9268/202-002: ATEX Zone 1/IECEx-certified variant (Ex ia IIC T4 Ga), designed for hazardous environments (e.g., oil refineries, chemical processing plants with explosive atmospheres).
- EMERSON PR9268/202-003: High-temperature variant with an extended operating range (-40°C to +150°C), optimized for applications like exhaust gas recirculation (EGR) systems in automotive or power generation.
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