Voltage offset at analog output on USB-6351 after power on

[user6351]

Hello,

recently we discovered that our USB-6351 is "generating" some voltage offset (between 60mV and 160mV) at its analog outputs some 20 seconds after power on. It doesn't matter whether the card is connected to the PC or not. As soon as some software (we tried LabView, DAQExpress and our own software using the DAQmx C API) accesses at least one of the analog outputs this voltage offset disappears on all analog outputs and does not reappear, until we turn the card off and back on. The driver version seems to have no impact on the behavior (tried DAQmx versions 20.1 through 23.8). It looks like the card does not load its calibration data until the analog outputs are accessed.

As we are seeing this behavior on all our DAQ cards, is this a known issue or is it even intended behavior?

Thanks in advance.

[santo_13]

As per the specification, it could be +/-5mV but not more significant.

What voltage are you generating on the other AO channels? What if you just generate 0V on the other channels?

[ZYOng]

Analog Output maintains its last value. Did you set the value to zero before you closed the task?

How Can I Reset to Zero My Analog Output Value After I Stopped My Application?

[user6351]

As far as I can tell at least USB DAQ cards do not maintain their analog output value across PC reboots or power resets. The issue appears only after power on of the DAQ card, before any task has accessed the analog outputs. Regardless of that the output value has been set to zero before closing the task at all times.

[user6351]

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@santo_13 wrote:

As per the specification, it could be +/-5mV but not more significant.

What voltage are you generating on the other AO channels? What if you just generate 0V on the other channels?

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The voltage generated on the other analog outputs doesn't have any impact, the voltage offset error disappears as soon as a DAQmx task accesses the analog outputs (calling DAQmxCreateAOVoltageChan seems to be enough to make the voltage offset disappear). The voltage offset drops to something smaller +/- 1mV then.

Edit: The analog output channel passed to DAQmxCreateAOVoltageChan doesn't matter, the offset disappears on all analog outputs simultaneously.

[user6351]

Anybody any idea what might be causing this?

[AnalogKid2DigitalMan]

Are you using power supplies from NI or a different make/model?

-AK2DM

[user6351]

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@AnalogKid2DigitalMan wrote:

Are you using power supplies from NI or a different make/model?

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We're using the power supplies from NI, I haven't tested other power supplies yet.

[AnalogKid2DigitalMan]

I asked just to make sure they have enough current capacity, the manual stated that use of an improper supply could cause erratic behavior.

I am not sure what is going on then 😞

-AK2DM

[AnalogKid2DigitalMan]

Are there loads on the AO channels when this is being measured?

Wondering if it is leakage current in the output channels.

-AK2DM