Reference Clock and Timebase?

[RodosC]

Hello, 

I am building a Function Generator/Data Acquisition VI using DAQmx and I have a NI USB-6356 X-Series device. 

In LabVIEW NXG, I can use the 10 MHz Reference Clock as my deault sample clock. However, when selecting source, I can see that the "100 MHz Timebase" option showing.

Is there a way to actually use the 100 MHz timebase as the sample clock? I am using only a single device.

[Kevin_Price · Accepted solution]

Your device's spec sheet says the max sample rate for 1 channel of analog input is 1.25 MHz.  So you're not going to be able to sample at 10 MHz or 100 MHz.

Perhaps you're actually using the 10 MHz Ref Clock as the sample clock's *timebase* which can then be divided down to a rate of <= 1.25 MHz?   If so, the only advantage to using the 100 MHz clock as a timebase is that you get less quantization of possible sample rates.

(With 10 MHz, you can divide by 8 for 1.25 MHz sampling or divide by 10 for 1 MHz.  Only one discrete sample rate is available in between.  With 100 MHz, you can divide by 80 for 1.25 MHz sampling or divide by 100 for 1 MHz.  Then you have 19 discrete sample rates in between.)

-Kevin P

-Kevin P

[mcduff]

---

@Kevin_Price wrote:

Your device's spec sheet says the max sample rate for 1 channel of analog input is 1.25 MHz.  So you're not going to be able to sample at 10 MHz or 100 MHz.

Perhaps you're actually using the 10 MHz Ref Clock as the sample clock's *timebase* which can then be divided down to a rate of <= 1.25 MHz?   If so, the only advantage to using the 100 MHz clock as a timebase is that you get less quantization of possible sample rates.

(With 10 MHz, you can divide by 8 for 1.25 MHz sampling or divide by 10 for 1 MHz.  Only one discrete sample rate is available in between.  With 100 MHz, you can divide by 80 for 1.25 MHz sampling or divide by 100 for 1 MHz.  Then you have 19 discrete sample rates in between.)

-Kevin P

-Kevin P

---

The other thing that is confusing about this post, is that all the clocks you are interested in, the 10 MHz, 100 MHz, and sample clock are in a phase locked loop; they are basically the same clock. (You can't do better than the 50 ppm error with any of these clocks) These clocks can be shared among different devices such that multiple DAQs can be synchronized but the OP doesn't seem to be asking for that.

mcduff