What is a digital input?

Hi,

I know what analog inputs are, but what are examples of digital inputs.

pxs

Don't know how you learned about analog inputs without learning about digital ones, because these are the simpler ones. Digital means only two states: on and off (or 1 and 0 or true and false). Think of switches!

Regards,

Digital inputs - in the world of PLC's - are not to be mistaken for (digital) communication as e.g. RS232.

In PLC terms, a digital input is - as jvdcande states - a "Examine if closed" input. The PLC will determine if a signal is present at the digital input terminal or not. E.g. a "START" push button.

Actually, I see the term "discrete I/O" replacing the older term "digital I/O". Either term represents the fact that there are only two discrete states, which can be represented by the digits 0 or 1 as stated above.

I avoid the term "examine if closed" because that is Allen Bradley specific.

"discrete" is used in relation to the sampling of a signal over time. The "discrete" means that the actual value of a signal between samples is unknown.

"digital" means that a signals amplitude is sampled and quantisezed into a finite numberset. That could be 0-1 for a 1-bit (boolean) value, and 0-4095 for an 12-bit (analog) value.

Apart from that, "digital" is freely used everywhere when it is actually meant to be "boolean". Have anyone ever seen a boolean input card ?