sample analogue input at preselected intervals

[alanled]

Hi a little help on this one would be great. I have an analogue input which only needs to be sampled at preselected intervals for example, the analogue input is rising from 0 upto a maxumum of 300 and needs to be sampled every 15 (amount selected on the sample interval selector) when 300 is reached it would stop. Could I use a pulse counter for this?

[AdnanZ]

That doesn't make sense. What kind of signal is your analog input? How many samples are you trying to acquire? Where exactly do you get the 0-300 count from?

[alanled]

Im sorry, I should have explained it a little better, I have a 0-10v analogue input (LVDT) which i will scale to the LVDT stroke length say, 300mm  (10v equals 300mm) every 15mm i need to take a sample from two other 0-10v analogue inputs and plot them against the LVDT stroke length, I hope this explains things, thanks for your help.

[AdnanZ]

I don't think you should try to implement this logic while you are sampling since every thing will be software timed and you won't get accurate data. I would recommend sampling all analog inputs till the LVDT signal reaches 10V, and then do the processing in software. Hope that makes sense; post back if you have any questions.

[alanled]

This is a very slow process, it would take 2 hours to travel from 0mm (0v) to 300mm(10v) and taking a single sample from 2 inputs every 15mm I would need to scale the input I think because the samle interval (15mm) has to be able to be changed.

[Coq_Rouge]

The sampling theory belongs to the time domain. In your project you have to set your sampling speed high enough to be sure you get the movement resolution you need. If you need some signal processing you also have to take this into consideration an increase the sampling rate. As an example. If you in your setting find a samplearte equal to 1 pr second to be adequate. You could of course use a sample rate equal to 1 pr sec. But you can remove a great deal of noise ( and then increase accuracy) by increasing the samplerate to say 100 pr sec, and then present a new value every second based on the average value of 100 samples