Analog output settling time specification

[Jason_S]

The spec sheets for several of the analog output devices do not seem to list the step change used to measure the settling time. For example

NI PCI-6713

NI PCI-6733

Questions:

1) Does "settling time" include the slew portion of the step change?

2) If 'yes,' what magnitude step changes are used to measure settling time?

Thanks

[iCan'tBerrPuns]

Hello Jason_S,

To answer your two questions:

• It does not seem to be clear within the specifications because the two specifications are listed separately. Simply, the answer to your question is, yes the “settling time” does include the slew portion of the step change.
• The magnitude of the step change will be dependent on the type of load you are using within your application. Why do you need to know what magnitude of step change is used to measure the settling time within the specifications for the products?

Regards

[Jason_S]

Hi Gabby,

The magnitude of the step change should not, under normal circumstances, be dependent on the load. If I tell my AO to go from -5 V to 5 V, the output had best be 5 V when it gets done. (I would believe that the settling time might depend on the load.)

Regardless, if you read NI's own glossary (here) you'll see that the settling time should have a step size

"Settling Time – The amount of time required for a signal to be accurate to within the specified accuracy and to remain within that range of accuracy. The amount of time to settle depends on the voltage step the analog output channel is generating. Thus, the specification will indicate the voltage step, and the amount of time required to settle to within a specified accuracy."

It seems however, that most of the AO specifications do not, in fact, have a step size, making me wonder if some default step size was assumed. One needs to know the step size in order to make any definitive decisions about whether or not the settling time is sufficiently small for a given application.

Fortunately, I don't have a specific problem, right now. I'm teaching students how to go about understanding the specifications.

Thanks,

Jason

[iCan'tBerrPuns]

Hello Jason_S,

Firstly, I would like to apologize for the incorrectness of my previous post. I said, “The magnitude of the step change will be dependent on the type of load you are using within your application,” when I meant to say, the settling time will be dependent on the type of load you are using within your application. Meaning, even though the settling time is specified a certain way, it is indeed dependent on the step change used, as you mentioned.

From the glossary that you attached a link to in your last post, I found a sentence that mentions what magnitude of step size is used to calculate the settling time. Underneath the definition of “Settling-Time-to-Full-Scale Step”, the step size used to calculate settling time is described as follows, “National Instruments specifies how long it takes a worst-case step (from minus full scale to plus full scale) to settle to different accuracies.” So it seems like the magnitude of the step is the full scale of a specific module. I am not entirely sure if this is the definitive step change used within NI’s specifications. I will continue to look into this to see if I can get a definitive answer.

Thank you for your patience.