振动分析和仪器的艺术达芬奇.ppt
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1、优秀精品课件文档资料,The Art of Instrumentation & Vibration Analysis,Back to the Basics Forward to the Future,Our Objective,The objective of Condition Monitoring is to provide information that will keep machinery operating longer at the least overall cost. What it is NOT: Establish new measured point records
2、Means to show analytical brilliance The answer to every problem!,Back to the Basics,Vibration Simple Harmonic Motion Oscillation about a Reference Point Modeled Mathematically as,Back to the Basics,Back to the Basics,Basic Signal Attributes Static Slowly Changing Temperature,Basic Signal Attributes
3、Dynamic Sensor must respond in fractions of a Second Vibration, Amperage, Pressure,Back to the Basics,Dynamic Signal Fundamentals Amplitude Frequency Timing Shape,Amplitude Proportional to the severity of vibratory motion Expressed as Peak to Peak Zero to Peak RMS,Frequency Determined by the recipro
4、cal of the Period CPS or Hz RPM Orders,Timing, or Phase Represented by the time delay between two signals Leading Lagging,Signal Shape Waveform Simple Complex Pattern Recognition,Peak and RMS Comparison,Relationships of Acceleration, Velocity and Displacement,The Big Picture,Sensor(s),Cables,Signal
5、Conditioning,Data Acquisition & Storage,Communications,Remote Analysis and Diagnostics,Displacement Sensors,Elements Probe, matched extension cable, Driver,Displacement Sensors,How it Works: The tip of the probe contains an encapsulated wire coil which radiates the drivers high frequency as a magnet
6、ic field. When a conductive surface comes into close proximity to the probe tip, eddy currents are generated on the target surface decreasing the magnetic field strength, leading to a decrease in the drivers DC output. This DC output is usually 200mV/mil or in a similar range.,Displacement Sensors,P
7、ros and Cons Pros Measures Displacement Rugged Cons Limited Frequency Range (0-1000Hz) Susceptible to electrical or mechanical runout Installation Issues,Velocity Sensors,Pros and Cons Pros Measures Velocity Easier Installation than Displacement Cons Limited Frequency Range (0-1000Hz) Susceptible to
8、 Calibration Problems Large Size,Acceleration Sensors,Pros and Cons Pros Measures Accel. Small Size Easily Installed Large Frequency Range (1-10,000 Hz) Cons Measures Acceleration (requires Integration to Vel.) Susceptible to Shock & Requires Power,Machine Speed Sensors,Displacement Probes Active or
9、 Passive Magnetic Probes Optical Permanent Stroboscopes Laser Tach,Voltage or Current?,Current Output Accelerometers 4-20 mA Output Proportional to Dynamic Signal and/or Overall Voltage Output Accelerometers Preferred in U.S. Generally 100mV per g Sensitivity,AC and DC Signal Components,Signals have
10、 both AC and DC AC considered the “Dynamic” Signal DC is the “Static” Signal Displacement Probes Set “Gap” for DC Accelerometers “Bias” voltage is DC,AC and DC Signal Components,How AC and DC work together: AC signal “rides” the DC bias (VB) Affects the Dynamic Range of the Sensor.,Power Circuit for
11、 Accelerometers,“Strips off” DC Voltage,Grounds,A Potential Problem Source Ground Loops Caused when two or more grounds are at different potentials Sensors should be grounded only at the sensor, not the monitoring rack!,Sensor Cables,Coaxial with BNC Connectors Long Coaxial can become antennas! Twis
12、ted, Shielded Pair Teflon Shield ground at only one end!,Sensor Cables,Driving Long Cables Under 90 feet, cable capacitance no problem Cable Capacitance specd in Pico-farads per foot of cable length Over 90 feet or so, CCD must supply enough current to charge the cable as well as the sensor amplifie
13、r. May result in amplifier output voltage becoming “Slew Rate Limited”,Sensor Cables,Output of Sinusoid looks like this:,Whats Happening? The + part of the signal is being limited by the current available to drive the cable capacitance. In the part of the sin wave, the op-amp must “sink” the current
14、 being discharged by the cable capacitance.,Sensor Cables,Practical Effect: Signal distortion produces harmonics May lead to vibration signals being misinterpreted. To calculate the maximum frequency for a length of cable:,Signal Conditioning,Gain Integration (Hardware) AC/DC Coupling Anti-Aliasing
15、Filter(s) Sample and Hold Circuit,Signal Gain Circuit,X1 and X10 are Common Gain is simply amplification of a Signal Careful Should know your vibration level and the ADC input range first! 100mV/g accel; +-5V input range = +-50 gs Can “Clip” Signal,Signal Integration,Best to Integrate as close to si
16、gnal source as possible Reduces noise,AC/DC Coupling,Normally, Systems are AC coupled Means that there is a DC blocking Capacitor that only allows AC signal through to the system MAARS Innovation DC Switch that allows AC and DC to work on the same data channel without contaminating phase Allows use
17、of same channel to record data for shaft centerline (DC) and Transient data (AC),Anti-Aliasing Filters,What are they and why do I need them? Because “false Frequencies” are displayed when Aliasing is present in a system. The maximum frequency component a sampled data system can accurately handle is
18、its Nyquist limit. The sample rate must be greater than or equal to two times the highest frequency component in the input signal. When this rule is violated, unwanted or undesirable signals appear in the frequency band of interest.,Aliased Signals,In old western movies, as a wagon accelerates, the
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