Understanding Temperature Sensors in Machinery Monitoring

Devices

Portable balancer & Vibration analyzer Balanset-1A

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Vibration sensor

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Optical Sensor (Laser Tachometer)

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Balanset-4

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Magnetic Stand Insize-60-kgf

$55.05

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Reflective tape

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Dynamic balancer “Balanset-1A” OEM

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Definition: What is a Temperature Sensor?

Temperature sensor in machinery monitoring context is a device that measures the temperature of bearings, motors, process fluids, or equipment surfaces, providing critical information for detecting overheating, lubrication problems, excessive friction, and abnormal operating conditions. While vibration monitoring detects mechanical defects, temperature monitoring provides complementary information about thermal condition, making the combination of vibration and temperature more powerful than either alone.

Temperature sensors are essential components of comprehensive condition monitoring programs because many machinery failures are preceded by temperature increases—bearing failures from friction, motor windings from overload, seals from rubbing. Early detection through temperature trending enables intervention before catastrophic failures occur.

Common Types for Machinery

1. RTD (Resistance Temperature Detector)

Most accurate and stable:

• Principle: Platinum wire resistance changes with temperature
• Common Types: Pt100 (100Ω at 0°C), Pt1000
• Accuracy: ±0.1-0.5°C typical
• Range: -200 to +600°C
• Stability: Excellent long-term
• Cost: Moderate to high
• Applications: Critical bearing monitoring, precision measurements

2. Thermocouple

Wide range and rugged:

• Principle: Junction of dissimilar metals generates voltage proportional to temperature
• Types: Type K (most common), Type J, Type T, Type E
• Accuracy: ±1-3°C typical
• Range: -200 to +1300°C (type dependent)
• Cost: Low
• Applications: High-temperature monitoring, exhaust, furnaces

3. Thermistor

• Principle: Semiconductor resistance highly temperature-sensitive
• Sensitivity: Very high (large resistance change per °C)
• Accuracy: ±0.1-1°C
• Range: Limited (-50 to +150°C typical)
• Cost: Low
• Applications: Consumer equipment, some industrial

4. Infrared (Non-Contact)

• Principle: Detects thermal radiation from surface
• Advantage: No contact required
• Range: -50 to +1000°C+
• Accuracy: ±2-5% of reading
• Applications: Spot checks, thermal imaging surveys

Bearing Temperature Monitoring

Measurement Locations

• Embedded in bearing housing (near bearing outer race)
• Surface-mounted on bearing cap
• In oil drain (for oil lubricated bearings)
• Multiple locations for large bearings

Normal Temperature Ranges

• Ambient + 20-40°C: Normal operating temperature
• Ambient + 50-60°C: Acceptable maximum for most bearings
• > Ambient + 70°C: Indicates problem, investigate
• > 90-100°C absolute: Alarm condition for most bearings

Trending and Alarms

• Establish baseline temperature for each bearing
• Alert on 10-15°C rise from baseline
• Alarm on 20-25°C rise or absolute limit
• Trip (shutdown) on 30-40°C rise or critical absolute

Integration with Vibration Monitoring

Complementary Information

• Vibration: Detects mechanical defects early
• Temperature: Confirms severity, indicates friction/lubrication issues
• Together: More reliable diagnosis than either alone

Diagnostic Patterns

• High Vibration + Normal Temp: Mechanical issue (unbalance, misalignment)
• High Vibration + High Temp: Bearing defect with friction (advanced stage)
• Normal Vibration + High Temp: Lubrication problem, alignment causing friction
• Both Increasing: Progressing bearing failure

Installation Best Practices

Sensor Placement

• As close to heat source as possible (bearing)
• Good thermal contact with measured surface
• Avoid air gaps (use thermal paste if needed)
• Protected from ambient temperature variations

Wiring

• Use correct wire type for sensor (compensating cable for thermocouples)
• Avoid running near high-current or high-voltage cables
• Proper termination and connection
• Shield and ground if needed

Applications

Bearing Monitoring

• Early detection of lubrication problems
• Bearing defect confirmation
• Overload detection
• Most common temperature monitoring application

Motor Protection

• Winding temperature (embedded RTDs)
• Bearing temperature
• Frame temperature
• Overload and cooling system adequacy

Process Equipment

• Pumps (bearing, seal, casing temperatures)
• Compressors (discharge temperature, bearing)
• Gearboxes (oil sump temperature)

Temperature sensors are essential companions to vibration sensors in comprehensive machinery monitoring programs. The combination of vibration analysis detecting mechanical defects and temperature monitoring confirming thermal condition, friction issues, and lubrication adequacy provides more complete equipment health assessment than either technology alone, enabling early detection of diverse failure modes in rotating equipment.

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