NI9234 IEPE compatibility with PCB 130A24

[temirk]

Hi,

I am planning to use NI9234 with PCB Piezotronics 130A24 (datasheet). Following the NI article here on compatibility I tried to check compliance but I am not sure.

For PCB 130A24:

Constant Current Excitation: 2-20mA

Output Bias Voltage: 9 - 14 VDC

Sensitivity: 10 mV/Pa

Dynamic Range (High): 150dB re 20uPa

Dynamic Range (3% Distortion Limit) > 143dB re 20uPa

For Dynamic Range (High); 150dB corresponds to 632Pa so using the formula:

Excitation_max = [High End Measurement Range] * Sensitivity + High-end Bias Voltage

gives me 632*10mV + 14 = 20.32 which is above NI-9234's 19V IEPE compliance voltage.

However for 3% Distortion value; 143dB corresponds to 282.5Pa which gives me 16.825V and that is within the compliance range of NI-9234.

Can anybody please advise me regarding NI-9234's compatibility with PCB 130A24 microphone?

Best,

Temir

[santo_13]

Your calculations seem about right, as long as you're operating a dB SPL that requires not more than 19V excitation, you're good.

As you described, if your application requires to use the Mic at or less than 143dB SPL, you're good to use NI 9234.

Calculating for max. dB SPL that is supported for 19V excitation at 10mV/Pa results in 147.95 dB SPL.

[temirk]

Thanks for prompt response Santhosh. So if I understand it correctly as long as the input signal is below 147.95 db SPL; NI 9234 should be good to go right?

Will the DAQ just saturate if the observed signal is above 147.95? Is there some chance of damaging the microphone or the DAQ itself in such a scenario?

Best,

Temir

[santo_13 · Accepted solution]

I don't think there will be any damage, as the DAQ is the one sourcing current up to the compliance voltage when a signal above 147.95 dB SPL is picked up by the mic, the mic will increase its internal resistance to convert it into an equivalent voltage at a constant current. Since the DAQ will not go above 19V, the constant current would drop since it hit the compliance voltage.

Since the DAQ has the upper hand to control the current and voltage across Mic, neither Mic nor the DAQ will be damaged. The worst case might be that for the duration of signal above 147.95 dB SPL, the Mic might receive lesser than the configured constant current and might turn off and recover once the signal is below.