# Understanding sampling rate and frequency of logic analysers

Below shown is the screenshot of the GUI for Saleae logic analyser http://www.saleae.com/logic

I would like to know what is the meaning of "number of samples to collect" and "sample rate" ? As per my understanding, sample rate is how often samples are collected. Here it is shown 16MHz. so that means in one second, there are 16 mega samples collected. But then what is this "1 M samples" ? Is it 1 million samples per second (but then what is 16MHz) ?

Or is it like this

1. in one second, we sample 16 Mega times
2. and in each of this 16 Mega sample, we will take 1 Million samples ?

Please correct me. I am so much confused.

The leftmost setting it the total number of samples per capture while the rightmost option selects the sampling rate.

1M samples, @16MHz : will gather 1M samples total with a rate of 16M samples per second. That means that the capture duration will be (1/16)=0.0625 second (1M/16M)

16M samples, @16MHz : will gather 16M samples total with a rate of 16M samples per second. That means that the capture duration will be (16/16)=1 seconds (16M/16M)

32M samples, @16MHz : will gather 32M samples total with a rate of 16M samples per second. That means that the capture duration will be (32/16)=2 seconds (32M/16M)

Choosing a different sampling rate

5M samples, @1MHz : will gather 5M samples total with a rate of 1M sample per second. That means that the capture duration will be (5/1)=5 seconds (5M/1M)

• Does this mean that 16M samples, @16MHz has a capture duration of 1 second and after 1 second, the measurement will stop ? Mar 22 '14 at 22:32
• @robomon Yes, that is why I wrote in the reply for 16M/16M that the duration will be 1sec Mar 22 '14 at 22:33

The 16 MHz refers to the sample rate while the 1 MHz is the actual number of samples taken. At a rate of 16 million samples per second, it takes 1/16 of a second to accumulate 1 million samples. Thus there is a tradeoff between sample rate and the number of samples. For a fixed sample rate, the sampling time is proportional to the number of samples.