07-15-2012 10:11 PM
I am a graduate student doing my research thesis on Sound signal analysis for online control and monitoring in machining process. I have 377A12 condensor microphone, BNC-2120 as by DAQ and labview 2010.
I am setting up the experiment for my research. Could you please share and guide me for setting up the experiment. I would like to know if you could provide me with the guidelines of the above microphone connection with BNC and also labview setting. I have gone through the manuals and labview guideline but i am not able to get the proper signal. The signal i obtained is not remaining in fixed centerlines. It keeps on moving towards the maximum voltages setting and then stops sensing the signals.
Please guide me in this regards as soon as possible.
UNB graduates students
07-17-2012 12:39 PM
As far as setting up the hardware, it should be just a matter of connecting the output of the microphone to an analog input BNC connector on the BNC-2120 block. The fact that you are getting incorrect readings in LabVIEW could be caused by a number of factors.
Is the hardware detected properly in Measurement & Automation Explorer (MAX)?
Have you tried getting a measurement with a MAX test panel? What DAQ card do you have connected in your PC (what is the BNC-2120 interfacing with)?
Are you using a LabVIEW example as code for your test? If not, I would recommend first trying a simple example program such as Cont Acq & Graph Voltage - Int Clk which can be found in the Example Finder by navigating to Hardware Input and Ouptut >> DAQmx >> Analog Measurements >> Voltage.
Please also make sure that you are providing the necessary bias and excitation voltages to the microphone (as per the manual for that device). Can you try displaying the signal on an oscilloscope and see if you get the right readings?
07-17-2012 06:12 PM
Thank you very much for prompt response.
I have already performed all the recommendation sent by you. The hardware is detected properly in Measurement and Automation Explorer.
I have also checked my microphone with oscilloscope and working fine.
While measuring the sound signal, the graph indicator shows the signals. However, the signal line in Y axis does not remain in fixed scaled value...It starts to measure the voltage from minimum voltage and start to increase...It keeps on increasing until it reach the maximum voltages of the DAQ setting, i.e 10V.....
The open circuit sensitivity @ 251.2Hz of the 1/4" pressure microphone is 0.32mV/Pa, polarization Voltage, External is 0 volts, capacitance is 4pF. I am using BNC cable to connect the microphone through the recommended external power supply to BNC-2120 analog input AI0. i have the switch to BNC, and to FS.
I even tried changing the switch to FS to GS and so on.....but the signal keeps on changing in the graph indicator from lowest to the maximum setting of the DAQ setting.....
So please advice me on this.
07-17-2012 08:38 PM
07-18-2012 10:45 AM
The DAQ card i am using is PCI-6036E. I have set it for RSE. The card has been already configured and a lot of experiments have been conducted by my earlier friends using that configuration. For my experiments, as you suggested, i have performed the setting and aquired the signal. Present problems is that the sensed voltages keeps on fluctuating even in idle condition.....
Thank you for your response.
07-18-2012 04:38 PM
I want to verify/clarify some details about the situation. The measurement that you described above (where the reading fluctuates until it reaches 10 V), is this what you see when testing with a MAX test panel as well as a LabVIEW example program, such as the one I mentioned in my previous post?
Have you tried any of the other analog inputs? (AI1, AI2 etc..)
Can you try to simply output a sine wave from the function generator on the 2120 and input that signal into each of the analog inputs. I want to make sure that all the analog inputs are functioning properly.
Do you have any other sensor or instrument that you can try to hook up to the BNC-2120?
If you have another card (another DAQ card that will interface with the 2120) to which you could try to hook up the BNC-2120 and the microphone, that would also be very helpful.
07-18-2012 06:30 PM
The reading doesnot fluctuates during the testing with a MAX test panel as well as a LabView example program.
I have tried with all the analog inputs and the fluctuations are same.
I haven't tried with the sinewave output function generator. But one of my friends is also doing experiments on the same set up with different sensors and he is getting good result.
Regarding spare cards, i have to find it out from other department. If i get one, i shall perform my testing and inform you accordingly...
I shall reconfirm the testing with the sinewave output function generation soon and see the difference.
07-19-2012 02:38 PM
You mentioned that the readings do not fluctuate when using a MAX test panel as well as a LabVIEW example program. Is this correct? If that is the case, then this would suggest that the program that you have set up is not properly displaying the data.
You also mentioned that a friend has been able to get proper measurements with the same hardware set up, but using a different sensor. Is everything the same in your friend's set up as far as NI hardware and peripherals go (i.e. same 2120 board, same BNC cable etc.)? If that is the case, then we can rule out the possibility that the hardware is causing any issues and it will not be worth it to try another card.
Since you verified that the microphone is working properly with the oscilloscope, then I would have to conclude that there is something going wrong with the set up in software. Please continue with the function generator test. Can you also confirm that your first statement is true (that the readings look good when using a MAX test panel and a LabVIEW example program)?