Starting System Self-Calibration

Calibrating the system moves RTG from the Inactive state to the System Self Calibration state, and back again to the Inactive state on completion.

Ensure you initialized the instruments in the RTG User Interface that you want to calibrate in Initializing Instruments and Opening a New Session in the RTG Software.
NI recommends that you perform self-calibration of the system before starting the target generation.
Note Invoke this functionality with gRPC. Refer to the rtg_api_service.proto file, installed with the software, for more information.
Note You can perform self-calibration on individual VST instruments instead of the entire system. In the instrument tree, right-click an initialized instrument and select Start Self Calibration.
  1. Perform a self-calibration in NI MAX of the VST if the self-calibration was not recently performed. Refer to the VST documentation for information about performing self-calibration on the instrument.
  2. Create a loopback connection between the test fixture’s output and input as shown in the following figure.
    Figure 1. Test Fixture Loopback Connection


    Note You can skip the loopback cabling if you added the Agile Attenuator to the system.
  3. Click Start System Self Calibration to start the calibration process on all initialized instruments.
    Figure 1. Calibration Pane


    Calibration Status
    Minimum Time Delay (s) Indicator
    External Time Delay (s) Field
    Offset Frequency (Hz) Field
    Minimum Attenuation (dB) Indicator
    External Attenuation (dB) Field
    Target Common Attenuation (dB) Field
    Self Calibration/Abort System Self Calibration Button

    The process takes several minutes to complete.

    Note You can click Abort System Self Calibration to return to the Inactive state before calibration completes. During some phases of system self-calibration, clicking Abort System Self Calibration may not result in immediate moving to the Inactive state. The RTG receives the Abort System Self Calibration call, but waits until that phase of calibration completes before moving to Inactive.
    When calibration completes, the following occur:
    • Software updates the calibration results for the minimum time delay and minimum attenuation on the calibration pane for each instrument configured as part of the system.
    • Software updates the status on the calibration pane for each instrument configured as part of the system.
    • The RTG returns to the Inactive state.
  4. Click Calibration under each initialized instrument to access the Calibration pane. Update the following settings to manually account for any offset, attenuation, and delay not included in the system self-calibration:
    • External Time Delay
    • External Attenuation
    • Offset Frequency
    • Target Common Attenuation

Saving and Using Stored Calibration Data

You can save self-calibration data so that future RTG sessions with the same frequency and reference level settings can skip the full calibration process.

RTG self-calibration features the following default behavior:

  • The RTG software does not save calibration data to disk by default. This is to prevent potentially storing sensitive information, such as center frequencies, unless explicitly configured by the user.
  • The RTG software will not perform a new calibration if it finds stored calibration data that matches the current center frequency and reference level.

Saving and using stored self-calibration data provides the following benefits:

  • Calibration time is greatly reduced. The procedure will take at least 30 seconds to allow for the VST temperature to settle and samples this over a minimum of 30 seconds.
  • No loopback cabling requirements.
Note The RTG software does not have a way to inform the user of valid existing calibration data. The user must either already know that valid calibration data exists on disk and will be used, or must connect the system into loopback to be safe.

In either case, RTG self-calibration—whether performing a new calibration or loading existing calibration data—is performed using the same API functions or user interface buttons.

You can configure how the RTG software handles calibration data through the API and soft front panel.

Soft Front Panel

To configure the calibration options for a VST, click the Options menu and select for each applicable VST:

  • Select Enable Save Calibration Data to configure RTG software to write the calibration data to disk for future use.
  • Select Enable Overwrite Calibration Data to configure RTG software to perform a new calibration regardless of whether data already exists for the frequency and reference level.

API

Use the option string in the API to save and/or use calibration data. Refer to Configuring RTG with the INI File or Through an Option String.