Another school assignmet problem (timer)

goldprospector · Jun 12, 2006

Hello again, I am the old guy who's work is sending him to school for a degree in Elect. Tech.
I am in my Intro to PLC class and working with a SLC 150 @ school but and working on assignments at home.
The assignment is a pump that comes on and stays on for 3 minutes, easy enough...



 

ON/OFF RLY 1

 

----||----------------------( )---

 



 

RLY1 PUMP

 

----||----------------------( )---

 

TMR |

 

----||---

 



 

PUMP TMR rt=3min

 

----||----------------------( )---

But once the pump turns off...it must remain off for 3 minutes not matter what.
Am I correct in assuming that,in rung #4, an OFF delay timer is the way to go? If so, there was a link posted on here a while back about using an ON Delay as an OFF Delay,(since my home program don't have Off Delay's) but I really don't understand how this works, here is the link
http://www.plctalk.net/qanda/showpo...427&postcount=5

Any help in explaining how simulating Off delay logic with an On Delay would apply to this circuit would be greatly appreciated.

chavak · Jun 12, 2006

Hi,

You need to use two timers (altough one timer can be used because your on/off time limit is the same)

Think the timer complete signal as an event, which trigger the motor on enable and motor off signals.

Tip: Do a self holding of the pump energise rung, and break it with the timer done event.

Work on this, put more effort - the victory is yours
_________

rsdoran · Jun 12, 2006

I have not dealt with an SLC 100 or 150 for a long time so had to find the manual: http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1745-um001_-en-p.pdf

According to that manual the SLC150 has RTO; Retentive ON Delay and RTF; Retentive OFF Delay. Section B, Chapter 6, page 1. Page 3 shows examples of how to use compare instructions for the accumulated value. You could use one timer set for 6 minutes and disable the pump after 3 minutes then reset the timer at 6 minutes...I think, I did not look real hard at the instruction.

Steve Bailey · Jun 12, 2006

There is no need for an Off-delay timer in this assignment. You can do it with two TON intructionss. You will use the TON instruction far more often than the TOF, so you should make sure you thoroughly understand it.

If the NO contact you've labeled 'TMR' is supposed to represent the timer's 'Done' bit, the logic you posted won't keep the pump running for three minutes.

goldprospector · Jun 12, 2006

rsdoran said:
I have not dealt with an SLC 100 or 150 for a long time so had to find the manual: http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1745-um001_-en-p.pdf

According to that manual the SLC150 has RTO; Retentive ON Delay and RTF; Retentive OFF Delay. Section B, Chapter 6, page 1. Page 3 shows examples of how to use compare instructions for the accumulated value. You could use one timer set for 6 minutes and disable the pump after 3 minutes then reset the timer at 6 minutes...I think, I did not look real hard at the instruction.

Yes I understand that a SLC 150 has an Off Delay, but my program at home does not. It is called Trilogi 5.33

goldprospector · Jun 12, 2006

Steve Bailey said:
There is no need for an Off-delay timer in this assignment. You can do it with two TON intructionss. You will use the TON instruction far more often than the TOF, so you should make sure you thoroughly understand it.

If the NO contact you've labeled 'TMR' is supposed to represent the timer's 'Done' bit, the logic you posted won't keep the pump running for three minutes.

When I run the simulation with the posted logic in the program call Trilogi 5.33, the pump actually does stay on for the full length of the "TMR" coil.

Steve Bailey · Jun 12, 2006

When I run the simulation with the posted logic in the program call Trilogi 5.33, the pump actually does stay on for the full length of the "TMR" coil.

That would make it the equivalent of the 'TT' bit in the SLC.

Lancie1 · Jun 12, 2006

Any help in explaining how simulating Off delay logic with an On Delay would apply to this circuit would be greatly appreciated.

Basically, use the first (Time On) timer to start a second timer, called PUMP OFF TIME. Do it similar to this, EXCEPT CHANGE THE TIMES TO 3 MINUTES. I set them at 6 seconds to test the program:

goldprospector · Jun 12, 2006

Steve Bailey said:
That would make it the equivalent of the 'TT' bit in the SLC.

LOL we have not gotten to "TT" in the class yet.

goldprospector · Jun 12, 2006

I finally got it, this works on my Home software and will work on the SLC 150 as long as I put resets on the RTO's.



   ON/OFF     TMR1     TMR2        PUMP

----||---------|/|------|/|--------(out)

   pump  |

----||--- 

 

   pump                             TMR1

----||-----------------------------(tmr)

   TMR1   TMR2   |

----||-----|/|---

 

   TMR1                             TMR2

----||-----------------------------(tmr)

Thanks for the bit of info Chavak

Steve Bailey · Jun 12, 2006

Now I'm confused. I don't see how both your first and second posts could work.

In your second, the NO and NC contacts labeled 'TMR1' and 'TMR2' behave like standard timer 'Done' bits. By that I mean the a NO 'TMR1' contact is false until the 'TMR1' timer function has been enabled for a period greater than or equal to its preset.

For your first to work, the NO 'TMR' contact would have to be true as soon as the 'TMR' timer function is enabled and then go false when the preset is reached.

goldprospector · Jun 12, 2006

Steve Bailey said:
Now I'm confused. I don't see how both your first and second posts could work.

In your second, the NO and NC contacts labeled 'TMR1' and 'TMR2' behave like standard timer 'Done' bits. By that I mean the a NO 'TMR1' contact is false until the 'TMR1' timer function has been enabled for a period greater than or equal to its preset.

For your first to work, the NO 'TMR' contact would have to be true as soon as the 'TMR' timer function is enabled and then go false when the preset is reached.

I am not sure how to explain it other than when I run the Simulate function of the software...and close the "ON/OFF" contact, the Pump run for the excact length that TMR is specified, when the Pump turns on...it will not start back until the specified time on TMR2.
This fulfills the direction on the assignment...I wish I knew more about logic so I could see where you are coming from...The only thing I have to go by is my eyes seeing the simulation work correctly. Thanks for challenging me though, it will keep me thinking.

goldprospector · Jun 12, 2006

Steve Bailey said:
Now I'm confused. I don't see how both your first and second posts could work.

In your second, the NO and NC contacts labeled 'TMR1' and 'TMR2' behave like standard timer 'Done' bits. By that I mean the a NO 'TMR1' contact is false until the 'TMR1' timer function has been enabled for a period greater than or equal to its preset.

For your first to work, the NO 'TMR' contact would have to be true as soon as the 'TMR' timer function is enabled and then go false when the preset is reached.

This is the way that I see it, when the pump comes on, it activates the TMR1 in rung #2, when TMR1 reaches its count, the NCTO contact in rung one turns off, thereby fulfilling that part of the circuit.
Next the TMR1 holding contact in rung #2 keeps the timer held on, which keeps TMR2 in rung #3 energized for the alotted time of TMR2. Also when TMR2 energizes, it open TMR2 NC contact in rung #1 thereby not letting the pump run again for the alotted time.

That makes sense to me...but again, I am a newbie and I have an instructor that has worked with the SLC150 for the last 30 years and no other types of logic...So I am using his terminology in the way he explains things to us.

chavak · Jun 13, 2006

I guess you understand the logic. To make things clear study this logic - I do not know how Trilogi's timer contacts work, but in SLC it is like this (more or less same as Lancie's logic)

Jimmie_Ohio · Jun 13, 2006

All of the replies so far are fine and dandy for SLC500, but not the SLC100.

The SLC100 uses retentive timers ONLY, both on and off delay. As an aside, this antique also has a limit of only 32 timers, believe it or not!

Therefore, any further help really needs to address timer circuits with separate and distinct reset rungs. Likewise, I believe the only bits available from the timer is the "done" bit, no TT, no EN, etc... Otherwise, your SLC500 sample designs will not work on the SLC100.

Another school assignmet problem (timer)

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