Beginning Vibration Analysis - CTC

1 Beginning Vibration AnalysisConnection Technology Center, Rae BoulevardVictor, New York Collection20153 PortableRoute BasedPermanent, Continuous, On-lineLoop Power :00:0012:00:0024:00:0036:00:0048:00:0060 :00:00 time (minutes)Velocity (inches/second peak)AlertFaultPortable Data Collectors Route Based Frequency Spectrum time Waveform Orbits Balancing Alignment Data Analysis History Trending Download Data Upload Routes Alarms Smart algorithms20154 Permanent Monitoring Continuous Measurement Permanent Sensors Frequency Spectrum time Waveform Orbits Data Analysis History Trending Ethernet Connection Alarms Smart Algorithms20155 What s This ? Hz100 0 Hz 1 FFT, Frequency Spectrum,Power Hz100 0 Hz 1 Scaling X & Hz100 0 Hz 1 XYScaling X & Hz100 0 Hz 1 FREQUENCYAMPLITUDES caling X & Hz100 0 Hz 1 What is it ?How bad is it ?What s That ? 0 s 1 time 0 s 1 Scaling X & 0 s 1 Scaling X & 0 s 1 AMPLITUDES caling X & 0 s 1 What is it ?

2 How bad is it ?The X Scale2015 What is it ?Single Frequency2015181 Vrms0 Magnitude Hz100 0 HzPwr Spec 11V-1 Real sTime 1X:55 mV55 msFrequency & Time201519fHz= 1/tSectSec= 1/fHzFrequency & Time201520If: F = 1/T and T = 1/FThen: FT = 1FT = 1 Concept !201521FT = 1If: F increasesThen: t decreasesIf: T increasesThen: f decreasesSingle Frequency2015221 Vrms0 Magnitude Hz100 0 HzPwr Spec 11V-1 Real sTime 1X:55 mV55 msMultiple Frequencies2015231 Hz100 0 HzPwr Spec 11 Hz100 0 HzPwr Spec 11 Hz100 0 HzPwr Spec 11 Hz100 0 HzPwr Spec 1X:55 mVX:78 mVX:21 mVX:42 mVMultiple Waveforms2015241V sTime 78 11V sTime 21 11V sTime 42 11V sTime 55 155 Hz42 Hz21 Hz78 HzReal Life Waveform2015254V-4 Real sTIME 155 Hz + 78 Hz + 21 Hz + 42 Hz = Trouble !FFT Capabilities2015264V-4 Real sTIME 11 Vrms Hz100 0 HzFREQUENCY 1X:78 mVX:55 mVX:42 mVX:21 mVFFT separates & displays individual frequencies and the amplitude of each frequency.

3 Complex time waveform contains frequencies of 21, 42, 55, & 78 or Hz100 0 Hz 1 The FFT always has a defined number of lines or Bins. 100, 200, 400, 800, 1600, and 3200 lines are common spectrum has 800 lines, or the X scale is broken down into 800 Lowest Resolvable Frequency is determined by:Frequency Span / Number of Analyzer LinesThe frequency span is calculated as the ending frequency minus the starting number of analyzer lines depends on the analyzer and how the operator has set it , this is the value that can be measured by the cursorExample: 0 to 400 Hz using 800 linesAnswer = 400 / 800 = Hz / LineBandwidth201529 The Bandwidth can be defined by:(Frequency Span / Analyzer Lines) Window FunctionUniform Window Function = Window Function = Top Window Function = : 0 to 400 Hz using 800 Lines & Hanning WindowAnswer = (400 / 800) = Hz / LineResolution201530 The frequency resolution is defined in the following manner:2 (Frequency Span / Analyzer Lines) Window FunctionorResolution = 2 (Bandwidth)Example.

4 0 to 400 Hz using 800 Lines & Hanning WindowAnswer = 2 (400 / 800) = Hz / LineUsing Resolution201531 The analyst wishes to measure two frequency disturbances that are very close #1 = #2 = 30 hanning window and 800 lines will be frequency span is required to accurately measure these two frequency disturbances ?Using Resolution201532 Resolution Required = 30 - = HzResolution = 2 (Frequency Span / 800) = 2 (Frequency Span / 800) = 3 (Frequency Span) / 800400 = 3 (Frequency Span)133 Hz = Frequency SpanTherefore, the frequency span must be 133 Hz or less to measure the desired resolution of Sampling Time201533 Data sampling time is the amount of time required to take one record or sample of data. It is dependent on the frequency span and the number of analyzer lines being Nlines/ FspanUsing 400 lines with a 800 Hz frequency span will require:400 / 800 = secondsAverage & Overlap201534 Average On Overlap Percent 50% Overlap is the amount of old data that is usedTR#1TR#2TR#3TR#1TR#2TR#30% Overlap50% OverlapHow long will it take for 10 averages at 75% overlap using a 800 line analyzer and a 200 Hz frequency span?

5 75% Overlap ?201535 10 Averages 75% Overlap 800 Lines 200 HzAverage #1 = 800 / 200 Average #1 = 4 secondsAverage #2 - #10 = (4 x )Average #2 - #10 = 1 second eachTotal time = 4 + (1 x 9)Total time = 13 secondsFilter Windows201536 Window filters are applied to the time waveform data to simulate data that starts and stops at zero. They will cause errors in the time waveform and frequency spectrum. We still like window filters !201537 Window ComparisonsReal TimeNo Window201538 Window ComparisonsReal TimeHanning Window201539 Window ComparisonsReal TimeFlat Top WindowWindow Filters201540 Hanning (Frequency) Window Factor Amplitude Accuracy 18% Flat Top (Amplitude) Window Factor Amplitude Accuracy 1% Uniform (Impacts) Window Factor Amplitude Accuracy 56% Force Exponential Force/Expo Set up Requires Channel 1 Input Force (Hammer) Requires Channel 2 Response (Sensor) Response/Force (Channel 2/Channel 1) Normalizes data based on response to forceFilter Windows201541 Use the Hanning Window for normal Vibration monitoring (Frequency) Use the Flat Top Window for calibration and accuracy (Amplitude) Use the Uniform Window for bump testing and resonance checks (No Window)The Y Scale2015 How bad is it ?

6 Amplitude201543 Acceleration = g s rms. or peakVelocity = inch/s rms. or peakDisplacement = mils peak to peakNote: 1 mil = inchesPk Pk (Peak Peak)2015441V-1 Real sTime 12 VPk-Pk0 Magnitude Hz100 0 HzPwr Spec 1 mVX:55 VThe Peak - Peak value is expressed from the peak to peak peak to peak value is measured in the time - Peak. = 2 VPk (Peak)2015451V-1 Real sTime 11 VPeak0 Magnitude Hz100 0 HzPwr Spec 1 mVX:55 mVThe time wave has not changed. The Peak value is expressed from zero to the largest positive or negative peak peak value is measured in the time = 1 VRMS (Root Mean Square)2015461 Vrms0 Magnitude Hz100 0 HzPwr Spec 11V-1 Real sTime 1X:55 mVThe time wave has not changed. The rms. value is expressed from zero to of the peak amplitude for a single rms. value is calculated for the a periodic time wave, the rms. value must be calculated in the FFT. It will represent the overall energy of the = 707 mVUnit Comparison2015472 Vrms0 Magnitude Hz100 0 HzPwr Spec 12 VPeak0 Magnitude Hz100 0 HzPwr Spec 12 VPk-Pk0 Magnitude Hz100 0 HzPwr Spec 11V-1 Real sTime 11V-1 Real sTime 11V-1 Real sTime 1X:55 mVX:55 mVX:55 mVRMSPeakPeak - PeakChanging Units201548 Many times it is necessary to change between / 2 = PeakPeak x = RMS (Peak / = RMS)RMS x = Peak (RMS / = Peak)Peak x 2 = Pk-Pk201549 Convert the UnitPeak - PeakRMS 2x 2x Units (EU)201550 Engineering units are used to give meaning to the amplitude of the of the default volts , it is possible to incorporate a unit proportional to volts that will have greater meaning to the.

7 100 mV / g20 mV / Pa1 V / in/s200 mV / mil50 mV / psi10 mV / fpm33 mV / %10 mV / VEU s the Hard Way201551 Sometimes we forget to use EU s, or just don t understand how to set up the analyzer. The measurement is in volts!There is no immediate need to panic if ????You know what the EU is for the sensor you are : An accelerometer outputs 100 mV / g and there is a 10 mV peak in the frequency is the amplitude in g s ?Answer = 10 mV / 100 mV/g = gThree Measures201552 Acceleration Velocity DisplacementConverting Measures201553In many cases we are confronted with Acceleration, Velocity, or Displacement, but are not happy with we have taken the measurement in acceleration, but the model calls for we have taken the data in displacement, but the manufacturer quoted the equipment specifications in do we change between these measures ?Converting Measures201554 Velocity = Acceleration / 2f Displacement = Velocity / 2f Displacement = Acceleration / (2f)2 Where: Acceleration = g s Multiply acceleration in g s by ( inches/second 2)/g Multiply acceleration in g s by (9807 mm/second 2)/g Velocity = inches/second or mm/second Displacement = inches or mm f= frequency in Hz.

8 (cycles/second)201555 Converting MeasuresAcceleration (g s)Velocity (inch/s)Displacement (inch)x 2(Pi)f 2(Pi)fx 2(Pi)fx 2(Pi)f (inch/s)Acceleration (inch/s2)Acceleration (inch/s2)Standard Measures201556 Converting MeasuresAcceleration (g s)Velocity (mm/s)Displacement (mm)x 9807 2(Pi)f 2(Pi)fx 2(Pi)fx 2(Pi)f 9807 Velocity (mm/s)Acceleration (mm/s2)Acceleration (mm/s2)Metric MeasuresAcceleration Velocity201557 Example: Find the equivalent Peak velocity for a 25 Hz Vibration at 7 mg l o c i t y= (g x ) / (2 f )Ve l o c i t y = ( x ) / ( x 25)Ve l o c i t y = inches / second RMS Answer = x = inches / second PeakVelocity Displacement201558 Example: Find the equivalent peak-peak displacement for a 25 Hz Vibration at in/s Peak ?Displacement = Velocity / (2 x f )Displacement = / ( x 25)Displacement = inches PeakAnswer = x 2 = inches Peak Peakor mils Peak - PeakAcceleration Displacement201559 Example.

9 Find the equivalent Peak-Peak displacement for a 52 Hz Vibration at 15 mg (g x ) / (2 x f )2 Displacement= ( x ) / ( x 52)2 Displacement= inches = ( x ) 2 = inches Peak-Peakor mils Peak - PeakRadians, Degrees, or Time20156000900180027003600 2 3 22 3600= 2 Radians3600/ 2 Radian020156100900180027003600 2 3 22 0 Radians, Degrees, or TimeRadians, Degrees, or Time20156200900180027003600 2 3 22 Period (seconds/cycle)0 Sensors201564 DisplacementFrequencySpeedAccelerometers 201566 IEPE Integrated Amplifier Industrial Charge Mode External Amplifier High TemperatureAccelerometerRequirements and Applications201567 Requirements Functionality Durability Affordability Applications Trending Alarming Diagnostics Remember One sensor does not fit all applications Fit, Form & FunctionAccelerometer Advantages201568 Measures casing Vibration Measures absolute Vibration Integrate to Velocity Double integrate to Displacement Easy to mount Large range of frequency response Available in many configurationsAccelerometer Disadvantages201569 Does not measure shaft Vibration Sensitive to mounting techniques and surface conditions Difficult to perform calibration check One accelerometer does not fit all applicationsMass & Charge201570 Relative movement between base & mass creates shear in ceramic producing a charge Accelerometer Parameters/Specifications201571 SpecificationValueAlternate ValueSensitivity100 mV/g +/ 5%Frequency Response +/ 3dB30 900,000 15,000 HzFrequency Response +/ 10%60 420,000 7,000 HzFrequency Response +/ 5%120 240,000 4,000 HzDynamic Range+/ 80 g peakResonant Frequency1,560,000 CPM26.

10 000 HzTypical AccelerometerFrequency Response201572 FrequencyAmplitude+/- 3dB+/- 10%Transmission RegionThe usable frequency range of the accelrometer based on acceptable amplitude limitsAmplificationRegionThe natural frequency is excited causing gain around resonanceIsolationRegionPhase between sensor & machine is shifted by 180 degrees and signal rolls off to zero+/- 5%Accelerometer Mounts201573 Realistic Mounting201574 Sensitivity, Range & Application201575 Sensitivity Range OutputApplication10 mV/g+/- 500 g+/- 5 VAC50 mV/g+/- 100 g+/- 5 VAC100 mV/g+/- 50 g+/- 5 VAC500 mV/g+/- 10 g+/- 5 VACA 10 mV/g accelerometer will have a dynamic range of +/- 500 g s, and a dynamic output of +/- 5 volts are typically used for machinery that is generating high amplitude vibrations. With the large dynamic range, they are much less likely to become saturated as a result of the high amplitude vibrations. Sensitivity, Range & Application201576 Sensitivity Range OutputApplication10 mV/g+/- 500 g+/- 5 VAC50 mV/g+/- 100 g+/- 5 VAC100 mV/g+/- 50 g+/- 5 VAC500 mV/g+/- 10 g+/- 5 VACA 50 mV/g accelerometer will have a dynamic range of +/- 100 g s, and a dynamic output of +/- 5 volts are typically used for general purpose machinery measurements, and are sometimes offered as standard sensors for data , Range & Application201577 Sensitivity Range OutputApplication10 mV/g+/- 500 g+/- 5 VAC50 mV/g+/- 100 g+/- 5 VAC100 mV/g+/- 50 g+/- 5 VAC500 mV/g+/- 10 g+/- 5 VACA 100 mV/g accelerometer will have a dynamic range of +/- 50 g s, and a dynamic output of +/- 5 volts 90% of all Vibration Analysis and data collection is accomplished with a 100 mV/g sensors are also available with a +/- 80g dynamic range for measuring larger signal.