Simple explanation of positive edge?

Hello Folks,

OK, while going through a program at work yesterday, I came accross this symbol -]p[-, and found out it was for positive edge? That it reads the signal faster, am I getting this right? When it scans, it picks up the signal on the front edge. Why/what is a typical application for this? Be easy on me, I'm new.
Thanks guys.

Rembrant

It's a "one-shot". That means that the bit will be true for one program scan, and one program scan only. The positive edge part means it activates on the off to on "transistion" of the bit. The |N| function would one-shot on the on to off transistion. They work like this:

There's a |P| for input 0. When you turn on input 0, the |P| is true for only one scan of the ladder program, then is false again--even if input 0 is still on. The only way the |P| will be true for a scan again is for input 0 to turn off, then on again.

They're called oneshots, transistion contacts, leading and trailing edge contacts, among other things, I'm sure.

Also known as a differentiated input or diff up. A diff down is available in most PLCs also.
Typical application is to set a latch. Also quite often used to move data from a live register/data memory to another section of the register area, if the PLC does not have differentiated functions available.
Typically I use differentiated functions to increment a channel by one each time a meter pulses the input. If my PLC did not have these functions then I would use a diff up relay to achieve the same purpose.
Commonly used to pulse a shift register, counter, do a math function etc.
beerchug

One-shot usage

Also commonly used to prevent 'sticky fingers' - the operators that insist on holding the pushbuttons longer than one intended.
Trigger the one shot with the button, do a routine, then the operator must release the button and re-press it before the next cycle can initiate.