There are a number of ways to find a resonant frequency of a part like an automotive inlet manifold. Here are three different types of popular test technique. But which one should you use and why? Continue reading
We were asked the following question…
I want to perform some cylinder head and inlet manifold vibration analysis, what should I do?
First we need to consider sensor selection Continue reading
The relationship between sample rate and maximum frequency that can be analysed (called bandwidth) is a factor of 0.4. Or to look at it another way the sampling rate is 2.5 times the maximum analysis frequency.
The value of 10,000 Hz is multiplied by 2.5 to allow for an anti-alias filter during the capture of the data. An anti-alias filter is set to 0.4 of the sample rate, thus the bandwidth or frequency content that can be studied is 0.4 of the sample rate.
For example, when looking to study a frequency up to 10,000 Hz what sample rate should be used?
So we multiply by 2.5…
10,000 Hz x 2.5 = 25,000 Hz
So the sample rate should be 25,000 samples per second to allow frequencies of up to 10,000 Hz to be studied.
James Wren (Prosig UK) explains how to store FRFs, coherence and/or time series data in modal hammer testing using Prosig’s P8000 & DATS software.
James Wren (Prosig UK) explains how nodes, components & structures are used in modal hammer testing using Prosig’s P8000 & DATS software.
Put the wax on the shaker top. Place the accelerometer in the axis you wish to calibrate with positive up and cable connected to P5000 with the relevant transducer class chosen.
Go to Single Channel Calibration screen.
Click on the Tone tab.
With P5000 armed turn on the shaker and monitor the sine wave on the real-time monitor and check Signal Quality as being GOOD.
With a GOOD sine wave click the Calculate button. It is recommended to click Calculate three times.
Check to see the Sensitivity change from what was originally entered when setting up the channel transducer information to the new calculated value. The calculated value should be close to the original.
DC Cal Offset is for DC level accelerometers.
Requested Excitation is for non IEPE (ICP) accelerometers such as capacitive.
After calculating the new sensitivity click on the Use button to make the change in the Transducer Sensitivity Acquisition Setup file.
NOTE: To achieve a GOOD signal reading place the shaker on a flat surface and avoid touching during operation. Make sure the surface the shaker is sitting on does not come in contact with other sources of vibrations or electrical conductance.
Justin Foster (Prosig UK) explains how to set up the DATS software to switch off the P8000′s cooling fans during data capture. This can be important to reduce noise during capture of audio data.
James Wren (Prosig UK) steps through how to calibrate a strain gauge for use with a Prosig P8000 system.
A DATS user asked…
We are using the third octave band filter at very low frequencies (~1Hz) and I noticed that the response of the filter could introduce very significant errors for short or transient signals. Looking a bit more in details at the function, the help says:
“For audio work ISO standards use a reference frequency of 1kHz not 1Hz”
Does that implies that for non-audio work, a reference frequency of 1Hz should be applied? If yes, is it possible to change this reference frequency in the dats function?
Dr Mercer replied…
Essentially there is no problem and no need to change the reference frequency provided you use Base 10 mode and not Base 2. Base 10 is the ANSI S1.11-2004 preferred scheme. Continue reading