my data acquisition problem:noise and transducer rocking

[fenny]

Thanks to Otis and Dan, I 've finally got DAQmx installed and run, But I still have some problems with my application:

1>, before my transducer was connected, when I check my board with "traditional NI-DAQ devices test panels", the board acquired noise of-0.02to 0.03volts firts" and then the value dropped to "-0.004-0.005volts", but if I check it with" NI-DAQmx devices", the board sensed noise of" -0.02 to 0.03 volts", why inconsistent for the same board?

2> when I check my board with my transducer turned-on( dispalcemnet transducer, need to push the handle to turn on), the reading is about"-0.3 to 0.2", this is the result without input signal. seems that "pushing down" the handle of the transducer rocking the tested surface and induced vibration of my tested surface.

3> when i check my testing system with transducer turned on and with my signal input (by inducing vibration of the tested surface), my acquired data reading is only about"0.06 maximum",

4> it seems my input signal is too little compared with the system noise or transducer induced vibration.

5>the frequency domain analysis indicated that the noise frequency is wide with some three main peaks of frequencies higher than my expected signal frequency.

Due to the previous reason or some other causes, my acquired data just did not show up any consistency.

I want to know if there are any measures that I can take to get better testing results.

thanks!

[fenny]

it seems that Triggering does not work for DAQmx.

when I set the trigger level to be beyound the maximum of the data range. the program acquired the data (0), immediately after start.

I 'm thinking Triggering just does not work, or useless.

as I understand, if the triggering level is higher than the data range, the program should wait for a triggering and should bot be triggered at all. or the response should be slower than when i set the triggering level lower than the maximum of the data.

I need the program to wait for me to generate the vibration.

[Otis]

Hi fenny,

Are you using any signal conditioning on this device?  It looks like your signal is still pretty small.  If you have a small signal and a lot of noise then the data you are getting will be useless.

It sounds like you are trying to do analog triggering.  Make sure that you are inserting the analog trigger line into APFI 0.  Try looking at this Example Program:  M Series: Analog Input Acquisition with an Analog Start Hardware Trigger

Keep in mind that if you are trying to do analog triggering that you need a 625X or a 628X device.  If you don't have one of these devices. Then you will need to use a software analog trigger.  Essentially all that is would be to look at the values returned in a continuous acquisition, and once they go past a certain level, then you would begin displaying the data that you have acquired.

Regards,