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The SVT Gain VI measures the amplification between the amplitude of the identified tone in the input signal and the reference amplitude. The SVT Gain VI identifies the tone with the highest amplitude as the fundamental tone unless you wire a value to the expected fundamental frequency [Hz] terminal. You must connect the amplitude of the excitation tone to the amplitude input terminal regardless of whether you use the output of the acquisition device or an external source. The following figure shows the required connection.

The accuracy of this measurement is dependent on the absolute amplitude accuracies of the output channel and the input channel. When generating and acquiring the signal with an NI PXI-4461, the expected measurement uncertainty is less than 0.3 dB.