# Sampling Rate

Could someone clarify sampling rate units?  I've seen it reported as "points/sec" How does this translate to hertz/sec? If someone can answer that would be great, if you can provide me with a source it would be fantastic

• Hi ecarenzo,

I have updated the tags for better visibility. Can you let us know which instrument model and which detector you are asking about?

Regards

James

• Hello James Jenkins: Thank you for replying.  My question is rather generic in that different vendor request that you select a sampling rate of X points/sec other hertz/sec. I recall that Waters HPLC systems request that you input a sampling rate of points/sec where as Thermos Ultimate 3000 systems (via Chromeleon CDS) request a hertz/sec value for sampling rate.  QC chemists get a methods developed on one type of HPLC system and then have to scramble around to try to interpret what the setting would be for another type of HPLC system. I specifically want to know what 2 points/sec would be in hertz/sec. I think it is one for one, meaning points/sec = hertz/sec, but not 100% sure.

Any help would be very helpful

Thanks

• Hi ecarenzo,

As the information that james_jenkins has posted suggested, the sampling rate can be specified as Hertz (abbreviated Hz) or samples per second. These are two different terms for the same thing, so there is no conversion factor between the two. (OK, you could say the conversion factor between the two is 1, but that's like saying the conversion factor between kilometers per hour and kph is 1.) Saying "hertz/sec" is just wrong, unless the specification indicates the rate at which the sampling rate is changing per second.

You may find it useful to refer to the Wikipedia article about Hertz. Start at http://wikipedia.org and type "Hertz" in the search area.

• Dear ecarenzo:

Very simply, Hz is in units of 1/sec.  Frequencies as calculated in sine waves(e.g. sin(wt)), etc. are in terms of radians/sec, so when we talk about frequency in Hertz, we divide omega (w above) by 2*pi.  The same sine with frequency specified in Hertz is
then sin(2*pi*f*t) where f is frequency in Hertz (the inverse of seconds).  Thus, the term Hertz/sec doesn't make much sense (1/(s^2)) unless we are discussing acceleration.

What often gets confused are the sample period (in units of time) and the sample rate (in units of Hertz), and these are inverses of each other. 1 Hz = 1 sample/sec <=> sample period = 1 second, 10 Hz = 10 samples/sec <=> sample period = 0.1 second.

Another confusing point is that people tend to think of chromatographic peak times in terms of minutes, but filters and sample periods are calculated in terms of samples per second.

I hope that helps a bit.