Assignment

[timske]

Hey guys, i have an assignment for TAFE and im stuck. I have tried searching but in all honesty i don't know what im looking for so it mkaes it hard. I have a very basic knowledge, this is only my first course on PLC's.

Problem is as follows:

When a switch (s1) is closed, it activates a timer (t1) for 12 seconds. During which if S2 is closed while (t1) is still running it will activate an output (O1). I can't get O1 to activate till after the timer stops.

Am i better to use a Count Down Timer?


Any information would be greatly appreciated.

 

[Steve Bailey]

It sounds to me like you're using the timer's "Done" status to allow the output to be turned on. You should be using the timer's "Timing, but not yet Done" status.

Since you haven't bothered to tell us what model PLC you're using I can't be any more specific than that. On the other hand, even if you had told us what model PLC you're using I wouldn't have been more specific.

 

[timske]

Thanks, ill have a read of that.

 

[Lancie1]

What is TAFE? What brand of PLC software are you using in this assignment? (It makes a difference in what timer contacts are available and how to write the program.)

 

[Dua Anjing]

Technical and Further Education.
Typically they offer courses between High School and University. Trade apprenticeships, Technician etc.

 

[timske]

TAFE is as DUA Anjing said.

The program im using is omron CX-P.

 

[Lancie1]

If you are using the Omron TIM Timer, then you only have one timer contact, which goes ON when Set Value is reached. So put a "normally closed" version of the T1 (TIM contact) in series with your Normally Open S2 Switch contact, to allow Output to stay on until timer times out.

Instruction: TIM - Timer

®Property of Omron Corporation 1999-2002 All rights reserved.

Variations: None.

Purpose:
A timer is activated when its execution condition goes ON and is reset (to SV) when the execution condition goes OFF. Once activated, TIM decrements the Present Value (PV) in units of 0.1 second from the SV.

If the execution condition remains ON long enough for TIM to time down to zero, the Completion Flag for the TC number used will turn ON and will remain ON until TIM is reset (that is, until its execution condition goes OFF).

The timer number N must be between 0000 and 4095.
The set value S must be between 0000 and 9999.

Operand Data Areas:
N: Timer Number T, ,IR
S: Set Value CIO, W, H, A, T, C, D, E, E?_, @D, @E, @E?_, *D, *E, *E?_, #, DR, ,IR

Availability: All PLCs.

®Property of Omron Corporation 1999-2002 All rights reserved.

 

[Lancie1]

I tried what you said and it worked!

My only problem now is that, with the normally closed contact in series with the t/1 'on' contact. Once the timer has finished it stays activated. Therefore the output stays on until i reset the timer.

The Normally Closed contact MUST BE the Timer T/1 'ON' Contact!

 

|                        Timer T1  |

|  Switch S1             +------+  |

|-----| |----------------|12 sec|--| 

|                        +------+  |

|                                  |

| Switch S2    Timer T1   Output 1 |

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

Is there anyway i can have it so that:

- once the timer starts and s1 closes an output is activated (it should only activate when s1 closes AND the timer is running.

If S1 controls T1, then nothing happens until S1 is closed, so it controls everything. You do not have to keep re-activating it.

Is there a way so that: Once this output is activated the timer resets so that the output attached to the timer contact and normally closed switch turns off?

Wait, is there another part to this assignment? I thought you only had to keep the Output on until the timer times to 12 seconds, then it goes off.

To reset everthing, turn off S2 or S1 or both.

If you want to make things automatic, you can add an interposing relay (flag relay or interlock) to seal in a certain condition.

 

[Lancie1]

Perhaps you need to re-state the original problem or assignment. Either you left out something before, or you are done!

1. Switch S1 turns on and starts Timer T1.
2. If Switch S2 turns on, Output 1 is energized.
3. When T1 reaches 12 seconds, Output 1 goes off.
4. ??? What Else ???

 

[timske]

sent you a PM lancie. Thanks again

 

[Lancie1]

Okay, here is a LogixPro version that works. It is set up to convert directly to a Omron CX program--that's why the extra relay on Rung 0 that would not be needed for the Allen-Bradley because of the Timer Timing bit being available.

PLC ASSIGNMENT

- A switch (S1) senses when a truck enters the road.
- Another switch (S2) senses when the same truck leaves the road.
- If the switches (S1 & S2) are activated in less than 12 seconds (TIM 1) of each other, the speed limit has been exceeded.
- The Speed camera is to be activated and the signal shall stay ON for 0.5 of a second (Timer TIM 2).

 



|      S2-Truck   Timer                 Speed     |



|      Leaves      T1                   Exceeded  |



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



|   |                    |                        |

|   |                    |                        |

|   |  Speed     Timer   |                        |

|   |  Exceeded   T2     |                        |

|   +---| |-------|/|----+                        |

|                                                 |

|                                                 |

|     S1-Truck   Relay                            |



|     Enters      R0                              |



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



|  |                         |                    |

|  |                         |                    |

|  | Relay R0      S2        |   +-------------+  |



|  +------| |------|/|-------+---| Timer T1    |--|



|                                +-------------+  |



|                                                 |



|                                                 |



|    Speed Exceeded              +-------------+  |



|----------| |-------------------| Timer T2    |--|



|                                +-------------+  |



|                                                 |

 

[timske]

Nothing seems to be coming up on my screen in your previous post #11.

Just your 2 lines of text and a quote.

Thanks heaps Lancie!

 

[Lancie1]

Check again. The previous post timed out before I could correct the arrangement. Do not swap positions with rungs 1 and 2, because it will not work then.

 

|       S2-Truck                     Speed Exceeded, |

|       Leaves      Timer T1         Activate Camera |

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

|  |                             |                   |

|  |                             |                   |

|  |                             |                   |

|  | Speed Exceeded,             |                   |

|  | Activate Camera    Timer T2 |                   |

|  +------| |-----------|/|------+                   |

|                                                    |

|                                                    |

|       S1-Truck                           Relay     |

|       Enters                              R0       |

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

|  |                             |                   |

|  |                             |                   |

|  |                 S2-Truck    |                   |

|  |   Relay R0       Leaves     |    +----------+   |

|  +----| |------------|/|-------+----| Timer T1 |---+

|                                     +----------+   |

|                                                    |

| Speed Exceededed                                   |

| Activate Camera                     +----------+   |

|---------| |-------------------------| Timer T2 |---|

|                                     +----------+   |

|                                                    | 

 

[timske]

It would have taken me a long time to get to that answer!. Thanks heaps lancie, ill give you some feedback once i get it tested.