Display structure vibration frequency using MAX

[jmperez]

I have to display the structure vibration frequency using MAX, how can I perform the impact test if I'm using an impact hammer and accelerometer?

[<Mike Ross> mross@smpcorp.com]

Hola imperez,

You cannot do what you say using MAX. These are the functions of MAX:

>>Quoted from MAX front page>>
What is Measurement & Automation Explorer?

Measurement & Automation Explorer (MAX) provides access to all your National Instruments DAQ, GPIB, IMAQ, IVI, Motion, VISA, and VXI devices. With Measurement & Automation Explorer, you can:

Configure your National Instruments hardware and software

Add new channels, interfaces, and virtual instruments
Execute system diagnostics

View devices and instruments connected to your system

Schedule updates to your National Instruments software
>>end quote>>

Presumably, you want to use some version of LabVIEW software (please confirm).

In this case you should look at
example code. This can be found under Find Examples of the startup page for LabVIEW.

Pick the Search Tab then select Analog from the list. A good VI to begin with might be Aquire N Scans Digital Trig.vi. This VI will acquire voltage information from your accelerometer for the period of time you specify, at the rate you specify, and begin when a trigger signal is received.

There are many other VIs that can monitor you accelerometer.

You will also need to address the issue of signal conditioning. The signal from the accelerometer must be sent to the acquiring hardware through a connection interface. (This is when the software called MAX is used.)

You must describe the type of computer you are using, and the signal conditioning hardware.

Also, we must know the requirements to operate the accelerometer and the parrameters of its output.

Best regards,

Mike

[Filipe A.]

Hello;

MAX is an application Software that is used maily to do some basic resources tests on your board, as well as to do some simple data acquisition.

In case you need a more advanced application, you will need to use a programming environment and to program the application yourself. I suggest LabVIEW as your programming environment for that application.

Regards
Filipe A.
Applications Engineer
National Instruments

[jmperez]

Hello Filipe A:

Thank you very much for your answer.

I use LabVIEW 6.1 version, but LabVIEW is new for me and I can't use it properly yet. Is possible to use any DAQ solutions (or any modification) to display the structure vibration frequency to perform the impact test if I'm using an impact hammer and accelerometer?

I connected the accelerometer output to one channel(CHANNEL 0) input of the amplifier (NEXUS by Brüel&Kjaer) and the amplifier output to the input (CHANNEL 0) of SCXI-1140. The hammer output is connected to the NEXUS input (CHANNEL 1) and the amplifier output to the input (CHANNEL 1) of SCXI-1140 (CHANNEL 1).

Best regards,

Jesús Miguel Pérez

[<Mike Ross> mross@smpcorp.com]

Jesus Miguel,

To use Acquire N Scans Digital Trig.vi you should become familiar with the description of this VI. (I know it is hard to comprehend. I also find it hard to read.) It explains the function of the VI, how to connect the signals, and what the controls of the front panel do. There are step by step instructions for you to follow.

I suggested this VI because it can do the following:

It can start and stop acquisition based on an external signal (for example the same signal that starts and stops the hammer).

It will acquire the signal from the sensor into a buffer and create an array of values that you can then analyse using other tools in LabVIEW.

You must tell the VI how to acquire the data. You must know the frequency of vibrations that interest you.

I would use an oscilloscope to examine the vibrating system first, although you could do this with LV using a continuous analog input VI (use search examples to find). or you could use an oscilloscope from the DAQ solutions.

Suppose you see that your vibration is 1MHz. Then you must sample the signal according to Nyquist. If you want only to accurately gauge frequency then you must scan at a rate at least two times this frequency. If you wish to look closely at the shape of the 1MHz vibration you must sample at at least ten times the signal frequency. You need to know the duration of the vibration. Will you strike the structure once and sample the ringing as the system disipates energy? You need to decide how long to sample this data. The number of scans to acquire is the sample rate times the time of acquisition. Pretrigger scans allows you to sample data prior to the trigger.

The output of this VI is a screen representation of the data (waveform graph), and a "bundle" containing the data and t0 and dt (the intial time of the graph and the increment of time between data). You can strip off (unbundle) the t0 and dt and use only the array that remains for analysis purposes. What exactly do you wish to do with the results of this acquisition? FFT?

One of your main concerns will be signal conditioning. You must know the characteristics of the output from the accelerometer amplifier. In MAX you will prepare a channel to sense a signal of this type. Then you can enter the channel name in the channels control of the VI. You should review the requirements of you DAQ card so that you know the levels of input that can be allowed. You must not exceed the limits or you can damage the DAQ card. Unfortunately, I have never used SCXI so I will be of little help in that regard.

Typically you want to condition your input from the sensor system so that it uses the entire range of input resolution. For example, if you have 24 bit resolution from 0V to 10V, you would not want your input to vary from 0V to 1V. You would only have 1/24bits of resolution in this range. Gain can be set using SCXI tand MAX to prepare the channel properly.

Most importantly, you must start using the equipment and software. Once you have conditioned the signal so that the DAQ system is protected from damage, you should begin by trying out VI's to familiarize yourself with the system.

Stay in contact and ill try to be helpful,

Mike

Jesus Miguel wrote>>
I have to display the structure vibration frequency using MAX, how can I perform the impact test if I'm using an impact hammer and accelerometer

I looked VI Adquire N Scans Digital Trig.vi but I didn't know how to
use it. I connected the accelerometer output to one channel (CHANNEL 0)
input of the amplifier (NEXUS by Br�el&Kjaer) and the amplifier output
to the input (CHANNEL 0) of SCXI-1140. The hammer output is connected
to the NEXUS input (CHANNEL 1) and the amplifier output to the input
(CHANNEL 1) of SCXI-1140 (CHANNEL 1).

I use LabVIEW 6.1 version, but LabVIEW is new for me and I can't use it properly yet. Is possible to use any DAQ solutions (or any modification) to display the structure vibration frequency to perform the impact test if I'm using an impact hammer and accelerometer?

I connected the accelerometer output to one channel(CHANNEL 0) input of the amplifier (NEXUS by Br�el&Kjaer) and the amplifier output to the input (CHANNEL 0) of SCXI-1140. The hammer output is connected to the NEXUS input (CHANNEL 1) and the amplifier output to the input (CHANNEL 1) of SCXI-1140 (CHANNEL 1).
end quote>>