Using Digital Output or +5 Volt Lines on the NI 651x

Issue Details

• I am using either the +5 Volt line or digital output lines on my NI 651x to perform a digital output task. I'm not seeing any response when measuring the terminals though. Why is this happening?
• Do I need to provide an external supply to out the digital outputs on my PXI-651x card?

Solution

Yes. The NI 651x series does not internally generate the voltage used to drive digital outputs. To operate the DO lines or use the +5 V pins, you must provide an external power supply between +5 V and +30 V. According to page 3-3 of the NI 651x User Manual :
 

Additional Information

The NI 651x family uses 24 V industrial logic levels. This means:

• A logic low typically pulls the line near 0–4 V (depending on load).
• A logic high rises to the voltage of your external supply, typically 11–30 V.

If you require a low state to reach closer to a true 0 V level, you may use a Pull-down resistor to ensure the line returns fully to ground when the output transistor is off.
These devices are designed for industrial applications, and proper external wiring is required for safe and correct operation.