Magnitude energy Vs Spectral Energy

[berryc]

We currnetly use ENTEK software and take magintude readings and Spectral readings in Velocity and Accerlation. I've always assumed the energy from the spectral reading is the area under the spectra for the Fmax stated, but I'm unsure of the parameters for the magnitude energy reading, (it's labelled as 0-200Hz for V and 1-1000Hz for Acc), but is there a related lines of resolution?

Cheers

Craig

 

[electricpete]

I suspect the magnitude that you're talking about is an "analog overall" - which comes directly from time waveform by rms calaculation (square all time samples, add the squares, divide by number of samples, then take the square root).

The way our Entek/Odessy is set up, this analog overall is displayed in data pane when cursor is on magnitude. When you put your cursor on spectrum, the level displayed is the max peak of the spectrum. To get the digital overall related to Fmax which you describe (in my software setup), we have to go to the spectrum window and look at bar graph on right side.

 

[berryc]

Electricpete,

Excellent, that now makes a lot more sense. Does the TWF that the analog overall is derived from have any resolution parameters? and what effect will the use of HP filters have on it? (i'm assuming none as the spectral conversion is done after the fact).

Cheers

Craig Berry
New Zealand

 

[electricpete]

Resolution parameters - the time resolution is of course determined by the sample rate... which is automatically set somewhere around 2.5*Fmax to ensure Nyquist criteria is met.

I've never given much thought to the D/A resolution (how small a change in ips can be digitally represented).

I'm not sure about what you said about filtering.

I know one case where filtering does affect the analog overall (magnitude) - that is spike energy. Here we put the signal through a hi-pass filter, then we envelope detect (time domain), then we find the analog overall based on the filtered/enveloped time waveform.

I believe that in all other cases what you said is true... the filter does not affect the analog overall/magnitude.

 

[berryc]

Electricpete

With regards to the High Pass Filters, we have moved away from using the "Smart HP" and "overall" filters as it cuts off relevent info for slower speed machines (we insted use 0.36Hz, & 5.3Hz H.P filters in Velocity, and 0.18Hz(?) and 2.67Hz H.P filters in Accelartion). The problem is when using the lower HP filters (on output bearings of gearboxes) I get a huge swing in magnitude readings (from the varying skislope) which makes the trend data less useful, is there any advantage of using the lower HP filters in this case?. I am temped to revert back to the more sensible overall filters for magnitude (leaving the HP filters for spectra) but have reached resistance from my co-workers.