Section 4 — Measurement Types and their Uses
52
Demodulation
The demodulation process looks for repetitive patterns created by
impact events that lie embedded within a time waveform. The process
works by extracting the low amplitude, high frequency impact signals
and then tracing an 'envelope' around these signals to identify them as
repetitions of the same fault. The resulting spectrum, with the low
frequency data removed, will now clearly show the high frequency
impact signals and harmonics.
Demodulation is also useful as an early warning device as it detects
bearing tones before they are visible in a normal spectrum.
The high frequency signals that demodulation aims to extract are very
localized, therefore extra care must be taken to ensure the
accelerometer is set up correctly. Ensure that the:
•
Accelerometer is mounted close to the signal source.
•
Accelerometer is well coupled, using either stud mounting or a
very strong magnet on bare metal. A handheld probe or stinger
is NOT recommended.
•
Accelerometer mounting is consistent between visits, otherwise
trend plots of overall RMS values will be meaningless.
The bandwidth you select determines which range of frequencies the
demodulation process will use. If possible, your instrument will suggest a
suitable demodulation bandwidth using the machine's default RPM
when configuring a demodulation recording.
For most standard speeds (above 1000 RPM), a bandwidth of 2 - 10 kHz
will typically be recommended and automatically selected when you
open the
Bandwidth
window (
Bandwidth
after selecting a
measurement type of
Demod
).
Summary of Contents for SCOUT100-Ex
Page 18: ...Section 1 Introduction 7 Installation Control Drawing for Hazardous Locations ...
Page 20: ...Section 1 Introduction 9 Installation Control Drawing GE2214VBX for ATEX Hazardous Locations ...
Page 21: ...Section 1 Introduction 10 IECEx ATEX Declaration of Conformity ...
Page 40: ...Section 2 Instrument Fundamentals 29 Viewing hint labels Accessing more detailed help ...
Page 44: ...Section 2 Instrument Fundamentals 33 Using the advanced options ...
Page 54: ...Section 3 Sensors 43 Selecting the appropriate voltage for your tachometer and machine ...
Page 85: ...Section 4 Measurement Types and their Uses 74 Selecting the required parameter settings ...
Page 111: ...Section 4 Measurement Types and their Uses 100 Using the keypad to enter measurements ...
Page 116: ...Section 4 Measurement Types and their Uses 105 Example of tracked measurement ...
Page 120: ...Section 4 Measurement Types and their Uses 109 Saving multi channel measurements ...
Page 124: ...Section 5 Set Measurement Options 113 Spectral lines submenu ...
Page 164: ...Section 8 Send and Receive Information 153 Transferring recordings to Ascent ...
Page 194: ...Section 9 Working with Routes 183 Linear Speed ...
Page 241: ...Section 11 Balancing Rotors 230 Splitting a weight ...
Page 247: ...Section 12 Balancing Walkthrough 236 Taking an initial reading ...