Hi frequency mic doesn't work with 6062e card

[EHP]

I am attempting to measure and record sound fields with the ACO Pacific PS9200KIT (

http://www.acopacific.com/PS9200kit.html) and a National Instruments NIDAQ-6062E data acquisition card, but am having problems.

Specifically, the connections are as follows:

(ACO Mic) -> (ACO Pre-Amp) -> (ACO Power Supply) -> (NI BNC-2110 Connector Block) -> (NI-DAQ 6062E Card) -> (Laptop)

When attempting to acquire a signal using either National Instrument's Signal Express software or the MATLAB Data Acquisition Toolbox, the result seems to be DC-saturated. That is, no signal other than some arbitrary DC level (not zero) can be observed.

I read the article on the use of 'bias resistors':

https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

but I don't see any way to implement these with the 4012 preamp.

Do you all have any recommendations on how to remedy this problem?

[rpurser]

I can't remember -- does this device support AC coupling?  You may need to set the channels to AC coupling mode.  This is a property on the Channel object off the main analog input object.

-Rob

[Hani R]

Hi EHP,

The Developer Zone article you mentioned has a lot of useful information on how to properly ground your signal.  The document describes the use of bias resistors to ground a floating signal source (when trying to measure differentially).  If you notice, there is a switch under each analog input channel of the BNC-2110 that is labeled FS-GS.  Setting the switch to FS will essentially ground your floating signal source the way bias resistors would on a different terminal block.  The manual for the BNC-2110 describes this functionality well. 

Just a few questions for you so we can assist you further.  Are you setting up your input as a differential or single ended measurement?  Is your signal source floating (not connected to building ground)?  What range of DC values are you getting? 

Keep me posted on your results.

[EHP]

I've tried every possible configuration I could think of using the 'Test Panels' option from the MAX device menu:


With the BNC-2110 switch in the Grounded Source (GS) position, I tried:
1. Input configuration = Differential


2. Input configuration = RSE


3. Input configuration = NRSE



With the BNC-2110 switch in the Floating Source (FS) position, I again tried:
4. Input configuration = Differential


5. Input configuration = RSE


6. Input configuration = NRSE


As you can see, the signal climbs to +10V and stays there in every case.  Incidentally, if I plug the mic directly into my sound card it seems to work well enough, except for a DC offset present in the data.  I can show you some of that data if you like.

The manufacturer says that the mic is a floating source, the preamp has a single-ended output and approximately 14VDC is present at the output of the power supply.

Apparently the 6062E does not support AC coupling, but correct me if I am wrong on that.

Thoughts?

Ed

[mallorim]

Hi EHP,

If I understand your issue, your analog input is ramping up to 10 V in a test panel, regardless of the setting you select. You believe that the signal you are trying to measure has a DC offset, possibly to due to the DC Power supply. This offset may or may not be the cause of the incorrect values you are measuring, and you are therefore interested in finding a way to AC couple the signal. Is this a correct assessment? If not, could you please clarify?

With regards to the PCI-6062E, you are correct in that your card does not support AC coupling.  Some of our DAQ cards and our Dynamic Signal Acquisition (DSA) cards include internal circuitry that adds a capacitor in series with the signal to remove any DC component. Since your card lacks this internal hardware, you could provide the AC Coupling yourself by adding a small external capacitor.

Your PCI-6062E card has the maximum/minimum voltage specification of +/- 10 V. If the voltage is out of specifications, as a 14 V offset provided by the power supply would be, then the card will not display the voltage correctly. Could you please confirm whether this is the case (perhaps by using a DMM)?

You also mentioned that the data seemed to be correct when the mic was plugged into your sound card, just with a DC offset. I would appreciate if you could post the screenshots that you had volunteered as well as any of the associated settings related to these results.

Thanks-

Mallori M

[EHP]

Mallori,

Your assessment is correct, though I don't know whether AC coupling is the answer to the problem or not.  I placed a meter across the terminals of the power supply output and momentarily observed a small (< 1 Volt) DC level which quickly decayed to zero.

Below is a spectrogram of a 3-second time sample that I recorded with the mic plugged into the sound card (through the power supply).

The signal starting near 2 seconds is a ringing telephone.

Note the constant level at zero Hz.  This appears in the spectrogram even if the mic is not plugged into the power supply.

Ed

[rpurser]

Are you running single ended or differential?

-Rob

[EHP]

Rob,

The sound card recording was performed with the Matlab Data Acquisition Toolbox, which only provides a channel configuration option of 'AC-Coupled'.  'Single Ended' and 'Differential' are not available.

Ed

[rpurser]

You should be able to set the InputType.  Here's an example: 

Create the connection to the device

ai = analoginput('nidaq','Dev1')

Display Summary of Analog Input (AI) Object Using 'DAQCard-6062E'.

  Acquisition Parameters:  1000 samples per second on each channel.
                           1000 samples per trigger on each channel.
                           1 sec. of data to be logged upon START.
                           Log data to 'Memory' on trigger.

      Trigger Parameters:  1 'Immediate' trigger(s) on START.

           Engine status:  Waiting for START.
                           0 samples acquired since starting.
                           0 samples available for GETDATA.

AI object contains no channels.

Get a list of all properties for the device

Note InputType in the list -- default is differential

get(ai)

        BufferingConfig = [64 30]
        BufferingMode = Auto
        Channel = [0x1 aichannel]
        ChannelSkew = 2e-006
        ChannelSkewMode = Minimum
        ClockSource = Internal
        DataMissedFcn = @daqcallback
        EventLog = [1x0 struct]
        InitialTriggerTime = [0 0 0 0 0 0]
        InputOverRangeFcn = []
        InputType = Differential
        LogFileName = logfile.daq
        Logging = Off
        LoggingMode = Memory
        LogToDiskMode = Overwrite
        ManualTriggerHwOn = Start
        Name = nidaqmxDev1-AI
        Running = Off
        RuntimeErrorFcn = @daqcallback
        SampleRate = 1000
        SamplesAcquired = 0
        SamplesAcquiredFcn = []
        SamplesAcquiredFcnCount = 1024
        SamplesAvailable = 0
        SamplesPerTrigger = 1000
        StartFcn = []
        StopFcn = []
        Tag = 
        Timeout = 1
        TimerFcn = []
        TimerPeriod = 0.1
        TriggerChannel = [1x0 aichannel]
        TriggerCondition = None
        TriggerConditionValue = 0
        TriggerDelay = 0
        TriggerDelayUnits = Seconds
        TriggerFcn = []
        TriggerRepeat = 0
        TriggersExecuted = 0
        TriggerType = Immediate
        Type = Analog Input
        UserData = []

        NIDAQMX specific properties:
        ExternalSampleClockSource = PFI2
        ExternalScanClockSource = PFI7
        HwDigitalTriggerSource = PFI0

get(ai,'InputType')

ans =

Differential

Get a list of possible settings for InputType

set(ai,'InputType')

[ NonReferencedSingleEnded | SingleEnded | {Differential} ]

Set InputType to SingleEnded

set(ai,'InputType','SingleEnded')

get(ai,'InputType')

ans =

SingleEnded

[EHP]

Oh, sorry Rob.  I thought you were referring to the sound card measurement.  I did in fact try both 'Single Ended' and 'Differential' configurations with 6062E and the Data Acquisition Toolbox.  The results were similar to those obtained with the Test Panels above.

Ed