Order Analysis

[rladr]

I'm using the order analysis tool kit to measure displacement magnitude and phase trigered by an analog keyphasor. Rotating speed range is 0-10krpm. Magnitude and phase is lost below about 2500 rpm. My question/request is for a solution to get magnitude and phase below 2500 rpm. Thanks! 

[johnsold]

I do not have the toolkit, so this is just a guess. At 2500 rpm you get one reading every 24 ms or at about 42 Hz. If you are not reading enough data to get a full cycle, that might cause loss of data.

Lynn

[rladr]

Lynn,

Thank you for your reply. You hit the nail on the head, that's is the error recieved. You mention full cycle, so what is a full cycle? 24ms? Ultimately I want to get data down to at least 500 rpm, with 100 rpm or less being ideal. Bently Nevada's ADRE system can acquire magnitude and phase at 100 rpm, so it can be done. I'm seeking a solution using Labview and NI4472 hardware. Thanks again!

[R^2]

Have you checked your time outs. If your VI's are counting the pulses/waveform/cycles and it has a time out to free up the system in the case of a sensor failure then you my need to increase that time out to get enough data to return a valid measurement. Look at your Hardware setup / read and your data analysis tool kit the time out could be in either place. 

[johnsold]

Do the math:  At 100 rpm one cycle (= one revolution) is 100/60 = 1.67 revolutions/second or one cycle every 600 ms. So your acquisition process needs to accumulate 600 ms of data to assure that you have one complete cycle at 100 rpm.

Lynn

[preston_johnson]

Are you running the acquisition in continious mode?

Are you using the resampling functions of the order analysis tools?

There are some excellent examples in the Sound and Vibration Measurement Suite,

for example the "log data (analog tach)"  is a good example for setting up continius data acquisition, and it displays speed. 

a more complete example is the " Order tracking magnitude and phase (Analog tach)"  which calculates magnitude and phase. 

with continious data acquisition, we can tract speeds below 100 RPM. 

Hope this helps

[rladr]

I'm using Labview 7 and Order Analysis version2.1 with a NI4472 card to acquire displacement and keyphasor signals. Data is continuously acquired at 20kS/s. I'm inputting waveforms and speed profile into OAT Convert to Even Angle Signal.vi then that output to OAT Order Magnitude and Phase.vi Once rotative speed drops below about 2500 rpm the magnitude and phase measurements drop out. It just isn't apparent to me how to get measurements at lower speeds. I have current versions of Labview Development Suite available but would like to get this working in LV7 if possible. Any guidance would be appreciated.

[preston_johnson]

Why do you need it to work in LV 7, that version is over 10 years old.....

1)  make sure the resampling, tachometer VIs, and the order magnitude and phase VIs are reset on first call, the NOT reset on subsequent calls.  There is a reset input to each of these VIs.  They have internal memory that needs to be reset on first call.  We automatically take care of this in later versions of the toolkit. 

2) make sure you are continiously acquiring data (use a separate configure and start DAQ VI outside the loop, read DAQ inside the loop, and stop DAQ vi outside the loop

3) lengthen the block size you are reading, the tachometer VI needs one or two pulses to work.  I suspect your problem is with the reset input. 

Hope this helps. 

[rladr]

Preston,

You were correct about the reset. I added a reset at First Call and NOT reset for subsequent calls to my top level vi. I'm now getting filtered data down to about 300 rpm or so. However, phase values on some channels, at slow roll speeds will--for lack of a better term--run away. That is, the values will rapidly increase to a 6 or 7 digit number. Ever see this before?

[preston_johnson]

are you also using the same 4472 for the speed sensor measurement?  in other words, are you simultaneously measuring speed and vibration?  if not, there will be drift in the phase measurement as you experience