Hi,
If I understand correctly, the USB-1608FS can use an external clock for sampling but I don't know how.
I currently acquire 6 analog signals at 32768Hz. At the same time, I am applying a lower frequency sine or square signal to the thing I'm measuring. Because it is a different device (a DDS function generator), I have to play some tricks to get the timing between the 1608 and the function generator as close as possible. I capture a TTL signal from the generator and then find the edges to figure out the timing. e.g., if the generator is programmed at 16Hz, the data from the 1608 will appear to be, say, 15.95Hz. The compounding of this difference can have a significant impact of my experiment.
The generator has a second channel that can go to about 20MHz and is derived from the same DDS. Can I use it as an external clock? If so, what frequency would I use to get the 1608 to sample at 32768Hz? This would ensure perfect timing.
Many thanks,
John.
- Job Title: Owner
- Industry: Analytical instrumentation
- Application: Nanoparticle characterization
20 months ago
JohnnyMalaria
Hillsborough, NC
Answers
When using the internal clock, not all requested clock rates are possible since we divide down an on-board crystal. On a USB-1608FS, when requesting 32768 Hz, we return the actual rate as 18 odd Hz higher (32786). Note this does not account for crystal tolerances. You can provide your own external clock source (to the SYNC pin), to achieve exactly the rate you desire. Your clock signal would need to be 32768, and any/all channels will be sampled at this rate. You must specify, in your application software, that you will be using an external clock. Note that not all application programs support this. In general, if you are creating your own application, it is possible. But menu-driven software generally does not give you this option.
20 months ago
Measurement Computing
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