Hi!
I have a digital transmitter from which I fetch and save values from. I wonder how I know if I must apply this theorem or not?

 

You have to explain in more detail why you think this is a concern.

 

I want to make sure that the sample time that I use gives me values that are true to reality (and not "aliased"?).

 

The Nyquist theorem does not apply to digital data.
If the recording clock is synchronized to the data then all you need is one sample per data point.
That is how UART, SPI, I2C, etc. work.

If you need to capture rise time and fall time, that is a different matter.

 

Could you explain "If the recording clock is synchronized to the data then all you need is one sample per data point." ?

I am using a RS485/usb converter to acquire the digital values in Lab veiw.

 

What does the digital transmitter transmit? Is it some value that originally was analog?

 

It transmits pressrue values. The manual says that the electronics measure and converts outpt sign. from the pressrue dependent sensor bridge to dig. values. The dig. value is conv. to analog for the current loop.

 

The Nyquist theorem is applicable when the analog signal is changing faster than you can sample and you are interested in frequency information.

If the analog signal is not periodic and changing randomly (i.e. noisy signal) you can take multiple samples and compute the average value.

 

If the samples I fetch are of digital values and the fastest that I can recieve each of them is about 10 Hz - can aliasing occur ?

 

If the samples I fetch are of digital values and the fastest that I can recieve each of them is about 10 Hz - can aliasing occur ?

For any analog signal frequency components above 5Hz, yes.