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RustyCas

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Reply with quote  #1 
Does the actual line frequency show up in signatures of motors that operate on drives? For instance, will you see any 60 or 120 Hz for a motor on a drive running at 56 Hz?
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jvoitl

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Reply with quote  #2 
Negative.  The line is rectified to a well filtered DC bus and then transistors turn on and off creating the AC output from the bus to the motor.  No chance of line voltage showing up on the output.
Noknroll

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Reply with quote  #3 
Rusty,
you're example you would see 112Hz, (in pkv anyway).
Edwin

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Reply with quote  #4 
And if you see the line freq, it means the rectifier and/or filtering is bad. It will be more likely you would see 6 times line frequency on a three phase power supply.
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James.

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Reply with quote  #5 
What I sometimes see is the 'VFD pulse frequency '.

2x inverter output frequency 'VFD pulse frequency' = (max inverter speed / max turning speed) x actual speed x 2

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Walt Strong

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Reply with quote  #6 
I have an older model Sears variable speed bench grinder. It has a slider switch to control speed. I have no idea what kind of electronics are inside, but I assume they are relatively crude and cheap. It produces a substantial 60 Hz vibration frequency. I have not used the grinder for grinding in a long time. I have used it for vibration training and recently to develop a balancing program. Time synchronous averaging can really make the 60 Hz vibration frequency disappear!

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MachDiag

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Reply with quote  #7 
On VFD machinery, I find it's not too unusual to see 2xLF occurrences in the spectral data that is dependent on drive speed.  Here, changes in the drive speed, create predictable changes in the collected data. 

Capture 1.JPG                                              VFD Bypassed, 2xLF Sidebands of 120 Hz

Capture 2.JPG                        
   Drive set at 60 Hz, 1776 RPM, 2xLF Sidebands of ~120 Hz

Capture 3.JPG                                    
   Drive set for 1705 RPM, 2xLF Sidebands of 115.33 Hz

Capture 4.JPG                         
   Drive set for 1423 RPM, 2xLF Sidebands of 96.04 HzSaveSaveSaveSaveSaveSaveSaveSaveSaveSave

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