Microphone Voltage RMS

[T-Pope]

Hi,
I am using a Bruel and Kjaer 4994B microphone to record sound levels with with a cDAQ-9174 and a PCB Piezotronics signal conditioner. I don't have the sound and vibrations add-on to help me with this.
I want to use the data recorded by the microphone and convert it into decibels and other sound level readings. 
To do this I believe that I need to convert the output voltage into a RMS voltage.
I try to acquire voltage RMS from the microphone but LABVIEW returns an error message.

If anybody could help me with this it would be much appreciated

[Henrik_Volkers]

Adding the code and the Error number/message  REALLY helps 😉 

[simyfren]

I agree with Henrik_Volkers, it is too little information...

[T-Pope]

Yeah, sorry, that would be useful. 
Attached is the VI, it is very simple at the moment. I was planning to do decibel calculations in excel, a way to do it in LABVIEW to read to a file would be useful though if you had any tips.

The error returned when running the VI is:

Error -200431 occurred at DAQmx Create Channel (AI-Voltage-RMS).vi:4330001

Possible reason(s):

 Selected physical channel does not support the measurement type required by the virtual channel you are creating.

 Create a channel of a measurement type that is supported by the physical channel, or select a physical channel that supports the measurement type.

 Property: AI.MeasType

Requested Value: Voltage RMS

You Can Select: Current, Resistance, Strain Gage, Temperature:Built-in Sensor, Temperature:RTD, Temperature:Thermistor, Temperature:Thermocouple, Voltage, More:Voltage:Custom with Excitation

 Task Name: _unnamedTask<1>

[simyfren]

Try to change AI Voltage RMS to AI Voltage in a DAQmx Create Channel.

Simyfren

[T-Pope]

I did this originally and I do acquire the signal, however when trying to calculate decibels a RMS voltage/pressure is required. This is because the output of the microphone oscillates above and below 0v as expected, but the calculation for decibel uses log10 of the value. Therefore the input has to be a positive value.
I would like to get the VI to run as a continuous sound level meter.

[simyfren]

And what DAQ (physical) do you use?

Simyfren

[T-Pope]

I have:

NI cDAQ-9174 CompactDAQ
B&K 4944B microphone
PCB Piezotronics Signal Conditioner 482C
Is this the information you require?

[simyfren]

Yes, its strange that you cannot use Voltage RMS...

Simyfren

[T-Pope]

I agree, but I am new to LABVIEW so I could be omitting something simple
T