Both the NI-9263 and NI-9264 C Series modules, as well as the USB-9263 and USB-9264, are specified to have 2 Ω output impedance. If the external devices attached to these NI DAQ devices have a very low internal resistance, the NI DAQ device will not output the expected 10 V. This is done intentionally to keep the card safe from an overvoltage condition.Learn more about the Output Impedance specification here: Specifications Explained: NI Multifunction I/O (MIO) DAQ.
Given the maximum current drive capability of the 9263 (1mA per channel), the minimum external resistance that is needed to generate 10 V is 10 kΩ. Therefore, when the external device contains less than 10 kΩ of resistance, the NI DAQ device will not output it's maximum voltage.You could optionally switch to using an NI-9269 C Series module. Because it has a smaller output impedance, the threshold at which it will produce 10 V should be covered by most external devices.You could also design a custom circuit which increases the resistance seen by the module. However, you would need to make sure that this still works for your external device.
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