# Timer in plc

Discussion in 'Homework Help' started by anhnha, Dec 25, 2013.

1. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
Please help me understand this exercise. The goal is to create a signal "output" as in the picture. Both timers are ON-DELAY with time base =0.1s.
The set values for timer 000 and timer 001 are 20s and 10s respectively.
I don't understand why the output of timer 000 has the shape like that. Why doesn't it start with 1 level as the tim 001 relay is normally closed relay?

File size:
29.4 KB
Views:
83
2. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,995
1,117
As you can see first timer 000 start to count this 20s.
After this 20s timer 000 is "ON" so he open "normally closed contacts" and shorts "normally open contact " So the output relay is OFF.
But at the same time timer001 start to count up to 10s. And after this 10s he opens "normally closed contacts" and shorts "normally open contact ". So Timer 000 is "OFF" so timer000 NC contract is "ON" again and Output relay is ON also.

Last edited: Dec 25, 2013
anhnha likes this.
3. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
Got it. My confusion was from the starting point of examination. I started with the system in that state for a long time.
Is the pulse in timer 001 very short?
And for example, if we need to create a waveform of output as in the picture, is there any clue to use timers like that?

Here is what I guess so far.
Output is the inversion of Timer 000 and therefore first we need to create a pulse tim 000. And to make the pulse we need to use two timers arranged as in the picture.
I think I understand how to analyse it right now but don't really get a clear picture how to design one.

4. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,995
1,117
I think that I don't understand something.Isn't your circuit already work as showed in this time chart?

5. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
Yes, I think it works. My confusion is about how to design. For example, we are assigned to design a circuit that create the output like that, what is the steps to design? I think I am okay with analysis but the designing is confusing.

6. ### strantor AAC Fanatic!

Oct 3, 2010
4,302
1,989
With a time base of .1 and values of #10 & #20, your timers are set to 1sec and 2sec, not 10sec & 20sec.
Are you getting this from a textbook, or did you witness this in real world testing? You are right, the initial condition of the output of timer 000 should be OFF. If you witnessed something else in testing, then I suspect you are experiencing some user error. If reading from a textbook, textbook error.

Are you using Omron PLC? That looks like Omron instructions to me.

7. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
Thanks, that is correct! I ignored that because I thought it is not so important with the problem here.
I took first course PLC programming this semester and this is what my lecturer wrote in blackboard. I don't found in in my book.
I am afraid that is what I got after getting help not my initial thought!
To be honest, I am totally new to PLC and I have just learned some basic concepts.
Just curious, how did you know it is from Omron? I guess it is from the addresses.

8. ### strantor AAC Fanatic!

Oct 3, 2010
4,302
1,989
Addresses, and TIM instruction. I work with a lot of PLC brands/platforms, and everybody has their little quirks. Most PLCs have a prefix for every type of address, like M500.01, or D205.12. For physical I/O, most use a I o a O, sometimes X and Y. Omron chooses to use nothing. 0.00 is the first input and 100.00 is the first output, and that's something you just have to remember. Also, most use TMR or something similar for timer, TON, TOF, etc. Omron's "tim" is cute, like "little Timmy." And then there's the "#" to denote "binary" as they call it, which really isn't binary, and "&" to denote decimal which really isn't decimal.

anhnha likes this.
9. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,995
1,117
steps by step ?
First you draw a time chart for the output relay.
As as see from you time chart you what output relay to be "ON" (energized) but after some time (20s) you want to TURN-OFF (de-energized) the output relay for about 10s, and then energized is again.
So as you can see we will need a timer relay.
So we built this circuit and see how it works:

But this circuit will not met all our requirements. We need to de-energized TD1 after 30s. And after some thought we decided to add another timer that will be energized after 20 by TD1. And after another 10s TD2 will energized and de-energized TD2.

But this circuit also don't work as we expect. We create some kind of astable multivibrator.

We again need some change. The simplest change is to add NO TD2 contact parallel with NO TD1 contact on TD2 ladder.

I hope I don't make any stupid.
I work with a TOYODA PLC and Siemens S7.

File size:
6 KB
Views:
63
File size:
8.8 KB
Views:
70
• ###### 12.PNG
File size:
9.4 KB
Views:
65
anhnha likes this.
10. ### atferrari AAC Fanatic!

Jan 6, 2004
2,674
785

Nice confusion strantor...

11. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
Jony, your steps seem logic but I can't understand it all right now.

First, can you explain if the following would work?
I wonder why you didn't use this.

File size:
19.1 KB
Views:
57
12. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,995
1,117
Well it seems to me that you understand these stuff very well.

Yes your circuit will work, so good job for you.
And why my version is so complicated? I don't know. I simply overlook that possibility because my intention was to end up with the same circuit you post in your first post.

anhnha likes this.
13. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
Oh, I was not sure that it is okay.