I have a spec for the analog input section of a data logger which reads as below :
Just wanted to check what does the term Bandwidth denote here ... I cannot use this logger to capture signals with frequency above 50 kHz ? Is it normally one tenth of the Maximum sampling rate so as to get full information on the waveform.
Please explain what you mean by "capture signals".
jremington:
Please explain what you mean by "capture signals".
I will be using this logger to record the pressure variations in the hydraulic lines of a mobile equipment and generally I do not know the actual maximum frequency that may occur while measuring.
So the general trend ( OK, trend is to generalize - lets call it my preference ) is to select a logger that has the highest frequency response.
So by capture signals what i meant was to record or data log a parameter like pressure. And here I am presented with two spec and one reads 500ks/sec and other reads 50kHz.
Trying to understand that ... suppose I capture ( record ) a sine wave of 50kHz for 1 second at the maximum sample rate of 500ks/sec, then I will have 500,000 samples representing 50,000 sine wave pattern. Is that right ??
Extending this further what will happen if I try the above with a 60kHz sine wave ??
generally I do not know the actual maximum frequency that may occur while measuring.
Then it would be an excellent idea to determine that, before you buy measuring equipment.
Sorry, but you still haven't answered the important question of what you mean by "capture signals".
If you want to know the details of the signal waveform, then, as you say, the sample frequency must be at least 10x the signal frequency.
However, if you only want to measure signal frequency, then the minimum required sample rate is twice the maximum expected signal frequency.
In that case you also need a low pass filter between the source and the input that prevents or severely diminishes any signal with frequency higher than half the sample frequency from reaching the input, or you will have "aliasing" artifacts. Sharp spikes in the input have very high frequency components.
Nyquist criteria and capturing 10x for profiling the signal - understood.
I want to be able to see the profile of the capture and not just its frequency. And mostly we are called by clients in case of any problem only and at that time deciding on exact frequency is a real challenge.
My primary query was on the specs of the particular data logger which said it has a maximum of 500ks/sec sample rate and 50kHz bandwidth - is it in line with the 10x criteria ?
Looks to be so.
is it in line with the 10x criteria ?
Yes.