Think there is an analog signal source and we are recording it with a data logger. Sampling rate isn't important in here. We know the analog signal is 0 mV when time 0 and goes to 1000mV in 1000 milliseconds. It increases linearly like this. 1 mV for each millisecond. What we can say about its frequency?
To take up the questions from the comments:
(1) What exactly do you mean by "what can we say about its frequency?"
I'm not sure if this signal have measurable frequency. But the question can be answered in any way.
You will probably receive more helpful answers if you provide some more detail about your application or what you are trying to achieve by measuring the "frequency" of a "ramp".
I'm trying to find my analog signal source's frequency.
(2) what do you mean by "frequency is free from sampling rate?"
Its clear, I don't want to get limited by sampling rate. If you say that I can't get true frequency of an analog signal with slow sampling rates, forget it. Think there is no any limitation.
(3) What happens with the signal after the 1000ms. Does it drop to 0 Volt? Does it grow linearly until infinity?
Infinity or not. Its never important. I stop data acquiring after 1 second.
(4) add a sketch of the graph, where the time ranges over a wider time than 0ms-1000ms.
(5) specify if you're looking for the spectrum of the analog or the discrete signal. They are not the same.
I said there is an analog signal source and we are recording it with a data logger. It's in time domain. I didn't get what you said. It's analog signal by itself.