Racheting relay

MikeS

Member
Join Date
Mar 2007
Location
Eugene, Oregon
Posts
4
Got a simple one that I forgot how to do......old age kicking in. I'm using a SLC 5/03... I have a hyd ram that needs to cycle back and forth all day long....I'm stuck with using a common pressure switch to tell it to stop and reverse the stroke.
When the ram bottoms out and the hyd. pressure rises, it sends a signal to the plc to change direction.
In the old days it was a ratching relay that did the trick.
Any help would appreciated.
Thanks.
 
I'm sure their are alot of ways to do that in a plc.. but

Does the ram require a delay in either direction?
Either extended. or reversed.. and are their any limit inputs on the return..?

Whats the travel time to open and close?

Are there 2 outputs required..? one to open one to close?
 
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Search the forum for "Flip Flop" and you'll find a zillion ways to do it. If you'd rather not weed through the search results, HERE'S a popular method for AB.

🍻

-Eric
 
I had problems using a single pressure switch to determine end of travel in one application. The stiction of the hydraulic cylinder required the application of a bit of pressure just to get it moving. The pressure lowered as the piston traveled from one end to the other. The pressure then rose when the piston reached the opposite end. The distinction between the break-away pressure and the final end pressure was too fine to tune out by setting of the pressure sensor. We had to introduce a time delay after the beginning of movement longer than the initial break-away pulse. After that we could wait for the pressure to rise again. It was fairly reliable. Of course we then implemented a flip-flop much as the others here have suggested.
 
very simple ron.. I'm not sure how it will ever count if it never outputs and reaches the pressure limit.

unless you use S:1/15 (first pass) bit to set the counter to 1 to start with :)

and don't forget to clear the counter when it reaches max.
 
I see says the blind man... :)

some reason I tidy up too much lol

just wasn't sure how it would get started without something to set the first count
 
this "counter flip-flop" idea was first proposed (I'm pretty sure) by our distinguished colleague Alaric ...

the idea is to "flip-flop" (reverse the status) of a certain bit each time the "input condition" becomes true ... what use the programmer then makes of the bit's status is another piece of the puzzle ... our original poster hasn't told us much about how the machinery actually works (single-action vs. double-action vs. maintained-action vs. momentary-action, etc.) so the method offered here should just be considered a starting point - not a full-blown detailed "solution" ...

and resetting the counter isn't necessary ... the value will just "roll-over" (without generating an "overflow" fault) and the status of the bit will reverse just fine ...

of course, as robo77 has mentioned, details such as how to properly treat the direction at "power up" and after a "power cycle" should be carefully considered as part of the final answer ...

and as Bernie says, the actual mechanical characteristics of the machinery also have to be considered in writing the program ...
 
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thanks Ron.. I shall not reset my counter in the future.. lol one line of code un-needed :)

ya posted a few QQ's but we shall see what he does with the info and the direction he takes.
 
Another consideration is the ram safety regulations on an E-Stop I cannot recall if it requires a maintianed position or a release all pressure return home, However this can be implemented using either progamming idea previously mentioned
 
to tell the truth, I was just caught up in the "magic of the moment" in finally having a real-live honest-to-goodness application for a flip-flop ... when you get a slow, straight, right-down-the-middle pitch like that, you just take a swing at it and think later ...
 

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