I have been around industrial automation for 24 years and I cannot believe that I still don't fully understand a "One Shot". Could someone explain that to me , and also an example of a "Real World" situation .
Thanks , in advance. Have a great Thanksgiving.
I find it hard to believe that after programming PLC's for 24 years, you've never understood the value or importance of a One-Shot. It's not an esoteric high-level concept like Modbus or communication protocols.
Let me guess, after 24 years, you've also never managed to understand the function of SET or RESET coils either? I only presume because one-shots are essential in the proper functionality of SET and RESETs. Perhaps you meant you have been programming for 2.4 years? Still considerably longer than I've been a controls engineer, and I'm not still fumbling with the basics. For someone who takes their skills or profession seriously, it's an embarrassment of an admission to not know this essential functionality, and you probably should have tried Google before throwing up your hands in defeat on this forum and wasting the time of others.
Regardless, although you receive
no compassion from me for your laziness, I will still provide an answer to your post as their may be noobie amateurs who will stumble across the same question, and THEY deserve an answer (inexperience is an excuse I can accept):
One-shots are essential any time you have logic where you want to output a single action based on conditions which
need to be met, but when you don't necessarily want to HOLD that output true the entire time the conditions solve:
"Debounce" for holding a pushbutton down is a good example (as another commentor mentioned, you could have a pushbutton held down for 100 PLC scans, and you wouldn't want to register 100 presses for each time that rung evaluates).
A practical application I implemented just yesterday involved putting a valve state in either AUTO or MANUAL. The operator can switch between AUTO and MANUAL at his command, but they also wanted the valve to automatically switch to AUTO based on certain conditions. If I
did not use a one-shot for this logic, the rung would HOLD the valve in AUTO the entire time the conditions were true, and therefore the operator would be unable to put the valve back into manual. Therefore, a one-shot was appropriate because you want to initiate the change in state, but not maintain that state forever.
If it still doesn't make sense to you, there are some great jobs in the Amazon delivery field of work these days! 24 years is far too long to struggle with a simple concept. If nobody around you is telling you to change your profession, then I am your only
true friend.