NI 5421/5422/5441
Output Impedance
The NI 5421/5422/5441 Analog Output path is designed to have an output impedance of 50 Ω from the Output Enable relay looking back towards the Main DAC. There is a selectable 25 Ω resistance that can be switched into the Analog Output path between the Output Enable Relay and the CH 0 SMB connector for applications requiring a 75 Ω impedance. Most applications use a load impedance of 50 Ω, but applications such as video testing, require 75 Ω. Refer to the following figure.
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If the load impedance is a high impedance (~1 MΩ), you may see output levels up to twice the selected output value for a matched input/output impedance. These levels can be as high as 24 Vpk-pk for the High-Gain Amplifier path. Normally, the output levels increase as the load impedance increases. The NI 5421/5422/5441 can compensate for different load impedance values. Refer to CH 0 Connector for more information.
You can select an output impedance of 50 Ω or 75 Ω. Refer to the niFgen Configure Output Impedance VI or the niFgen_ConfigureOutputImpedance function for more information.
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Note The NI 5421/5422/5441 uses mechanical relays to switch between the 50 Ω/75 Ω switch states. When you change a setting that results in a relay to switch, the bouncing of electromechanical relays on the NI 5421/5422/5441 interrupts the output signal for up to 10 ms. |