SKF Condition Monitoring
Vibration SensorsVibration Sensors Power Supply Units Sensor Housings Cables and Connectors Accessories Installation/Mounting
Vibration SensorsTable of Contents
Introduction 1 The Critical Choice 1 Selection of Vibration Sensors ... 1 Piezoelectric Sensors .. 2 Choosing An Industrial Sensor .. 3 Primary Sensor Considerations .. 3 Environmental Requirements . 4 Electrical Powering Requirements . 5 Other Sensor Types 6
Vibration Sensor Descriptions
CMSS 786M Dual Sensor-Accelerometer and SEE Sensor, Piezoelectric . 7 CMSS 793T-3 Multifunction Sensor: Acceleration and Temperature ... 8 CMSS 797T-1 Low Profile, Industrial IsoRing Piezoelectric Accelerometer with Internal Temperature Sensor .. 9 CMSS 793L Low Frequency Piezoelectric Accelerometer .. 11 CMSS 797L Low Profile, Low Frequency, Industrial IsoRing Piezoelectric Accelerometer . 12 CMSS 793V Piezoelectric Velocity Transducer ...14 CMSS 797V Industrial IsoRing Velocity Accelerometer ... 15 CMSS 85 Series High Temperature Inductive Velocity Transducer 16 CMSS 603A-1 and CMSS 603A-3 Power Supply Units ..18
Vibration Sensor Installation Vibration Sensor Mounting Requirements
Vibration Sensor Installation Considerations ... 19
Mounting Requirements ... 22 Sensitivity Validation ... 23 Summary .. 23
Vibration Sensor Mounting Accessories
Mounting Hardware ... 24 CMSS 60139-4 Probe Tip (Stinger) . 24 CMSS 30168700 Threaded Mounting Stud (1/428 to 1/428) ...24 CMSS 30168701 Adaptor Stud (1/428 to M8) ... 24 CMSS 30168703 Adaptor Stud (1/428 to M6) ... 24 CMSS 30205300 Mounting Stud (1/428 to 10-32) 24 CMSS 910M Cementing Stud With 1/428 Male 24 CMSS 910F Cementing Stud With 1/428 Female ..24 CMSS 10876700 Captive Screw .. 24 Magnetic Mounting Hardware . 24 CMSS 908-RE Rare Earth Magnetic Base Flat Bottom ... 24 Magnetic Bases For Curved Surfaces 25 CMSS 908-MD Medium Duty Magnetic Base 25 CMSS 908-HD Heavy Duty Magnetic Base 25 Quick Connect/Disconnect Sensor Mounting Pads 25 CMSS 910QDP-1 Stud Mounting Pad . 25 CMSS 910QDP-2 Cement Mounting Pad 25 CMSS 910QDB-1 Sensor Base 25 CMSS 50042300 Case Mounted Transducer Housing . 26 70003010 Mounting Kit for Seismic Transducers 27 CMSS 30266101 Vibration Sensor Housings .. 28
Hazardous Area Information i
Area General Information . 29 Agency Approvals 29
Vibration SensorsTable of Contents
Piezoelectric Materials for Vibration SensorsThe Technical Advantages of Piezoceramics Versus Quartz ... 30 Sensors Solutions for Industrial Cooling Towers and Process Cooler Fans 31 Accelerometers Measure Slow Speed Rollers and Detect High Frequencies .. 32
Glossary Conversion Charts Sensor Selection Checklist
33 39 40
Vibration Sensors Introduction / Selection IntroductionDespite the advances made in vibration monitoring and analysis equipment, the selection of sensors and the way they are mounted on a machine remain critical factors in determining the success of any monitoring program. Money saved by installing inferior sensors is not a prudent investment since the information provided about the machine of interest often is not accurate or reliable. Poor quality sensors can easily give misleading data or, in some cases, cause a critical machine condition to be completely overlooked. approach necessitates the parameter. Such an approach can be classified as Multi-Parameter Monitoring.
Selection of Vibration SensorsThe three parameters representing motion detected by vibration monitors are displacement, velocity, and acceleration. These parameters can be measured by a variety of motion sensors and are mathematically related (displacement is the first derivative of velocity and velocity is the first derivative of acceleration). Selection of a sensor proportional to displacement, velocity or acceleration depends on the frequencies of interest and the signal levels involved. Figure 1 shows the relationship between velocity and displacement and acceleration. Sensor selection and installation is often the most critical determining factor in accurate diagnoses of machinery condition. DISPLACEMENT SENSORS Eddy current probes are non-contact sensors primarily used to measure shaft vibration, shaft/rotor position and clearance. Also referred to as displacement probes, eddy current probes are typically applied on machines utilizing sleeve/journal bearings. They have excellent frequency response with no lower frequency limit and can also be used to provide a trigger input for phase-related measurements. SKF monitors also have the ability to take the output of an accelerometer and double integrate to obtain a relative displacement; however, except in very special cases, it is inadvisable because of significant low frequency instability associated with the integration process. Eddy current probe systems remain the best solution for shaft position measurements. (Please refer to SKF Condition Monitoring publication CM2004 for guidance on the selection, application and installation of Eddy Current Probe Systems.) VELOCITY SENSORS Velocity sensors are used for low to medium frequency measurements. They are useful for vibration monitoring
The Critical ChoiceThe various rotating machine operating conditions concerning temperature, magnetic field, g range, frequency range, electromagnetic compatibility (EMC) and electrostatic discharge (ESD) conditions and the various parameters measured in the multi-parameter approach necessitates the need for a variety of sensors. Without a proper sensor to supply the critical operating information, the machine can be operating in a most hazardous condition to both the machine as well as the personnel operating the machine. SKF in partnership with one of the worlds leading industrial sensor manufacturers has developed and can provide the epitome of industrial sensors, accelerometers and velocity transducers for your critical machine monitoring. The key to proper machine monitoring however is the proper choice of sensor for the particular installation. Without the proper sensor, the best instrumentation and software available will not provide the definitive information on which to make a sound engineering determination regarding the mechanical operating condition or deficiencies of the machine. The ability to monitor more than one machine parameter with the same sensor can give added insight to machine performance at a more economical cost than using separate sensors for each (ESD) conditions and the various parameters measured in the multi-parameter approach necessitates the (ESD) conditions and the various parameters measured in the multi-parameter
CONSTANT VELOCITYtio n
D is pl ac em en t
Displacement Frequency Frequency Frequency
Figure 1. The relationship of acceleration and displacement and velocity.
2and balancing operations on rotating machinery. As compared to accelerometers, velocity sensors have lower sensitivity to high frequency vibrations. The mechanical design of the velocity sensor; an iron core moving within a coil in a limited magnetic field, no clipping of the generated signal occurs, but smooth saturation. In an accelerometer with ICP electronics, sensor resonance excitation can cause saturation and clipping of the electronic circuit generating false low frequency components. Integrating to velocity from the acceleration signal leads to large low frequency components. Resonance damping circuits between sensor element and amplifier can minimize that effect.
Vibration Sensors Introduction / SelectionTable 1. Electromagnetic Velocity Sensors vs. Piezoelectric Velocity Sensors.
Characteristic Flat Frequency Response 201,500 Hz 25,000 Hz Phase Fidelity 25,000Hz Reduced Noise at Higher Frequencies Linearity Mounting in Any Orientation Temperature Limitation EMI* Resistance Mechanical Durability
Coil and Magnet Velocity Sensor
Piezoelectric Velocity Sensor
Yes No Acceptable No Good Sensor Dependent > +707F (+375C) Acceptable Good
Yes Yes Excellent Yes Good Yes +248F (+120C) Excellent Excellent
*EMIElectro Magnetic Interference
Traditional velocity sensors are of a mechanical design that uses an electromagnetic (coil and magnet) system to generate the velocity signal. Recently, hardier piezoelectric velocity sensors (internally integrated accelerometers) have gained in popularity due to their improved capabilities and more rugged and smaller size design. A comparison between the traditional coil and magnetic velocity sensor and the modern piezoelectric velocity sensor is shown in Table 1. The electromagnetic (Inductive) velocity sensor does have a critical place in the proper sensor selection. Because of its high temperature capability it finds wide application in gas turbine monitoring and is the sensor of choice by many of the major gas turbine manufacturers. The high temperature problems for systems using accelerometers can also be solved by splitting sensor and electronics (charge amplifiers). The sensor can have high temperature ranges up to +1,112F (+600C). Some methods of investigating bearing defects and gear problems may require a higher frequency range and because the signals are generated by impact, the sensitivity should be lower. By the same means if the user is using the SKF Enveloping Te