DMM_Frequency Domain Measurement Library

DMM_Frequency Domain Measurement Library VIs initialize, configure, measure and close user-configurable analog input pins and derive frequency domain measurements for the measured waveforms.

The DMM_Frequency Domain Meas Initialize VI creates a new NI-DMM driver session on the device specified by the DMM Resource Name control. The device uses the specified powerline frequency value to select a timebase for setting the Aperture Time property in powerline cycles (PLCs).

Note The default powerline frequency value is 50 Hz. Specify 60 Hz for North or South America.

The DMM_Frequency Domain Meas Configure and Measure VI configures the NI-DMM frequency or period measurement on the resource provided by the DMM Handle In control.

Note By default, the VI executes the measurement once it is configured. If you are using a trigger for your measurement, choose the Configure Only or Measure Only execution option to avoid automatic execution.

The DMM_Frequency Domain Meas Configure and Measure VI configures the measurement based on the following settings.

  • Function Settings—Specifies the desired function and range, and the resolution in digits for the measurement. Refer to Default Values and Automatic Range Coercion for more information about listed ranges.
    Note Range selections include AC Voltage Amplitude, which specifies the expected maximum amplitude of the input signal for frequency and period measurements. The minimum detectable peak-to-peak signal amplitude is 10% of the frequency voltage range specified for your DMM.
  • Execution Option Settings—By default, the Configure and Measure VI also executes the measurement. If you are using a trigger for your measurement, choose the Configure Only or Measure Only execution option to avoid automatic execution.
  • Configure and Measure—Configures the DMM according to the values provided on the front panel and executes the measurement.
  • Configure Only—Sets the configuration of the DMM but does not execute the measurement. This option can be useful to prepare a trigger and wait for a software or hardware event. This operation must be followed by a Measure Only operation.
  • Measure Only—Skips configuration to perform a DMM read. Formats the result into a string and outputs the effective execution settings to an output cluster. A Measure Only operation must be preceded by a Configure Only operation. If repeated, a DMM Measure Only operation uses the most recent DMM Configure Only configuration.
  • Timing & Trigger Settings—Specifies the aperture time, settle time, trigger source, trigger delay, and trigger slope options.

    • The DMM_Frequency Domain Meas Configure and Measure VI returns the following information.

  • Measurement—Returns a string format with units and automatic significant digits for the selected resolution as well as raw numeric values, units and out of range data for further analysis or limit comparison.
  • DMM execution settings—Output for debugging purposes. The output includes all execution settings used by the driver during the measurement.

    • The DMM_Frequency Domain Meas Close VI closes the NI-DMM session specified by DMM Handle In and releases the resource.

    Examples

    The following figure illustrates the minimum useful block diagram for this library.
    Figure 26. Minimum Use Case


    This example uses the DAQ Signal Voltage Generation library to generate voltage from an analog output device.

    Note Refer to the execution options settings information for each library to understand the differences the DAQ and DMM libraries for configuring repeated measurements.
    Figure 27. Repeated Measurement Use Case


    Default Values and Automatic Range Coercion

    To reduce the number of configuration parameters and accelerate development, the library VIs support a limited number of default values. Default values are statistically based on the best values for the most common DMM measurement use cases.

    Use the VI context help and block diagram comments to understand the impact of each parameter. Adjust the default values only when necessary for your application.

    Parameter Name Default Value
    Power Frequency 50 Hz
    Range and Function First main function in Auto Range for each physical quantity
    Resolution in Digits 5 1/2
    Execution Option Configure and Measure
    Aperture Time (s) -1 (Auto)
    Settle Time (s) -1 (Auto)
    AC Min Frequency 40 Hz
    Enable Trigger? False
    Trigger Source Immediate
    Trigger Delay (s) -1 (Auto)
    Slope Rising

    The listed range for each function include all possible ranges for all NI-DMM instruments. If you select a range that is not supported for your DMM, the upper supported range is automatically selected. Use the DMM » Execution Setting output to verify the actual execution values.

    DMM Trigger Methods

    If the physical signal is already active, a DMM can begin a measurement immediately when the read function executes within a Config and Measure VI when the Measure Only execution option is specified. Use the NI-DMM driver software to add software delays or specify a trigger delay to insert a user-defined delay before the measurement starts.

    The following figure illustrates a block diagram configured for immediate measurement with a delay based on a DAQ analog output signal.

    Note Refer to the execution options settings information for each library to understand the differences between the DAQ and DMM libraries when configuring repeated measurements.


    The DMM can start measurements using an external signal or internal TTL (X) channel configured as the HW Trigger Source. On a PXIe system, TTL (X) is connected to the PXI_Trigger(X) internal signal. For example, you can use a DAQ_6363/PXI_Trig0 as a start trigger by linking it to TTL 0 as the trigger source. When the read function executes inside the Configure and Measure VI, the DMM waits for the external signal and then waits for the duration of any specified trigger delay.

    This configuration uses only a parallel physical signal.

    The following figure illustrates a block diagram configured to use an hardware trigger source asynchronously.