Finally got it, but instructor wont like it!

I am 39 years old and my work has sent me to College on an Electrical Apprentice Program. I am in my 3rd semester and just now in "Introduction to PLC's"

I have a program at home called Trilogi that has an on screen simulator and it works well. With this program I completed my homework of "writing a working North/South, East/West Stoplight program that works by a simple ON switch...(No Road sensors or anything) Just timers...Well it works and work as per the instructions, other than my instructor has said "Any circuit that you design in this class that has a timer, will always need a reset (RST on the SLC-150 at school) coil for the timer". My Timer resets are simply a Relay coil at the end of the circuit that energizes NC contacts on relay coil rungs that activates the timers. Then when the circuit starts over, it kills the relay coil at the end... Works good, and I got it in 17 lines of logic.

Anyway, the circuit works correctly and it keeps on repeating, but I do not have a reset (RST) for any of the timers mainly because I have not figured out how to make a reset with this program...Anyway, I will show it to him. If he wont accept it without resets, then I can always write them even if I can't program them on my home computer.

BTW, I gave myself a big pat on the back, and I will not attempt to post it on this site simply because I see what everyone means by being able to learn it on your own.

Thanks for all the good reading guys!

A timer does not have to use a RESET instruction to be reset, if your logic is resetting the timer then do not worry about it.

It is difficult to read and instructors mind on what and how they want something...ask if unsure.

It's only rare that I need to use an explicit timer reset instruction, they don't often seem necessary on most AB and Siemens stuff I work on. I doubt your instructor will make anything of it but make sure you explain why your program does not need an explicit reset in your class write-up.

Expanding on what Ron said, if your instructor says you really need a reset you can simply put a contact from the reset switch in front of each timer in series with the current logic that turns it on. Then all timers would drop out when the reset is pressed, allowing your system to restart.

Unless he has asked you to use 'Retentative' timers, then normally you would need a dedicated reset function with this type.


You mentioned AB SLC150 as the PLC being used, and i'm sure something in the dimness of my mind is telling me that they only use RTO timers in its instruction set (but its been over 15 yrs since i last used one, so i'm probably way off!! )


Rob.

Kidblue said:

Unless he has asked you to use 'Retentative' timers, then normally you would need a dedicated reset function with this type.


You mentioned AB SLC150 as the PLC being used, and i'm sure something in the dimness of my mind is telling me that they only use RTO timers in its instruction set (but its been over 15 yrs since i last used one, so i'm probably way off!! )


Rob.

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Yes the SLC150 uses RTO's. And on each circuit that we have designed so far, may or may not have needed a specific "RST" coil for the timer...but we have been required to put them in. Even on the circuits that are not repeaters or sequencers. He wants them in...just because he said it is "a good practice to learn".

Anyway, Yes they can be reset by putting an interlock on to a relay line that activates the timer...for some reason, those interlocks will not work on the actual timer rung (on my program?)

Thanks again guys.

Guys, this is a SLC150 Brick. All timers in the SLC100 and SLC150 are retentive. There are no non-retentive timers available on this platform so Goldprospecor is right that an explicit reset has to be programmed.

Goldprospector: Welcome to the forum. I suggest that you rewrite the program in trilogi using retentive timers only. Then you will be emulating how the SLC150 works.

Alaric said:

Guys, this is a SLC150 Brick. All timers in the SLC100 and SLC150 are retentive. There are no non-retentive timers available on this platform so Goldprospecor is right that an explicit reset has to be programmed.

Goldprospector: Welcome to the forum. I suggest that you rewrite the program in trilogi using retentive timers only. Then you will be emulating how the SLC150 works.

Click to expand...

As far as I can tell, Trilogi does not have a retentive timer...None that I can find anyway.

sounds like some on needs to put a reset on the instructor, as he is "RETENTIVE".

regards.....kc

CaseyK said:

sounds like some on needs to put a reset on the instructor, as he is "RETENTIVE".

regards.....kc

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Use cascading timers! The first rung has to have an XIO controlling the timer and all of the others use XIC. Sorry if I'm missing something?

whiggins - as noted above this is a SLC150 - a different animal. As Alaric mentioned the timers are all RTO or RTF and the reset instuction (RST) MUST be used to get the timer back to a start.