Why TEDS Microphone(GRAS 46BD_FV) Calibrated Sensitivity get wrong Value?

[Sam.Huang]

Hi all,

 I want to calibrated(GRAS 46BD_FV) sensitivity by standard calibrator(1K@94dB),when set up "AI voltage" per amplifier to PXI 4461 get right value and set up "TEDS AI Microphone" direct to PXI4461 get wrong value,if have somewhere mistake with the code, please someone help me for the matter. Thanks in advance!

[santo_13]

I see a bunch of misunderstandings,

1. The reference calibration for GRAS 46BD_FV is 249.8474Hz and not 1kHz (given in the TEDS summary, in the line next to sensitivity)
2. The waveform you get from DAQmx is already in Pascal and not V
3. You can directly use the Extract Single Tone VI to find the amplitude in Pascal peak (not V)
4. If you know the test stimulus dB SPL or Pascal, you can compare the measured Pascal and expected Pascal to calculate the sensitivity (V/Pa)
5. Both property nodes are redundant as the DAQmx task automatically configures these based on TEDS read made using the first VI in the execution

[Sam.Huang]

I appreciate for you prompt reply and modified redundant property, add extract signal tone.vi get value was same.

You mean that set up as "TEDS AI Microphone" get from DAQmx is 1.376 PA, but set up as "AI_Voltage" get value is 2.561 Pa.

However, calculated microphone sensitivity=2.561*(sqrt(2)/2)=1.8109 mV/Pa is approach TEDS EEPROM data with accurate+-0.08dB.

In other words, how to measured get right sensitivity by "TEDS AI Microphone"?

[santo_13]

Could you please elaborate on your goal?

BTW, in your VI, the measurements you make are still in Pascal and not in V because you already told DAQmx that you want the measurements in Pascal

Regarding why there is a small difference between the SVT VIs and the Extract Single Tone is due to the additional Hanning window applied in the SVT measurement.

[Sam.Huang]

Thank you again for your patience in the matter.
In general, DAQmx need get 1 Pascal,because of stimulus signal is 1k@94dB.
My purpose is how to measured microphone sensitivity with TEDS AI Microphone mode without amplifier.

[santo_13]

Please use the attached modified VI to measure Pascal rms from the Mic.

BTW, since the reference calibration frequency for Mic is 249Hz, there will be some difference in reading at 94dB SPL @ 1kHz, this expected difference can be obtained from the calibration report of the RefMic.

[Sam.Huang]

Thanks a lot ,I will try in next week.Have a nice day.

[Sam.Huang]

Try it with modified vi get value is same as screenshoot,for your refer, thanks!

[santo_13]

0.97207 Pascal RMS is close to 1 Pascal, the difference (-0.27dB) would arise from the offset stemming from the calibration frequency at 249Hz and not being 1kHz, please check your calibration report to understand the expected offset at 1kHz.

BTW, how are you generating the 1kHz 94dB SPL stimulus? how reliable is that 94dB SPL stimulus, is it calibrated?

[Sam.Huang]

Used to GRAS Sound calibrator(94&114dB SPL-1000Hz) ,as you said the value is approach spec.Actually I want to measured microphone sensitivity, might be set up AI_Voltage per amplifier not set up TEDS_AI_Microphone.Thanks!