Hi guys,

I'm currently working on a project which uses the above mentioned PLC as a controller.
Basically the system is made up of a compressor, dryer, an input timer and a start/stop push button.

The sequence of operation is as follows;

1. User sets the on-time for compressor.
2. User pushes start button to start the compressor.
3. Compressor runs based on the time input.
4. 2 minutes before the timer expires, the dryer will kick in.

My problem lies in step 4. I somehow am not able to figure out a way to turn the dryer on 2 minutes before the time expires. Note that the dryer has to turn on 2 minutes before the timer expires no matter how many minutes the timer is set.

Can anybody familiar with Siemens LOGO! PLC help me with my predicament please?

Thanks in advance.

 

I'm not familiar with that controller but why not just do something like this:

1. User is prompted for the on-time for compressor.
1a. Goto 1 if user entered a time less than 3 minutes etc.
2. User pushes start button to start the compressor.
3. Compressor starts.
4. Wait for (input - 2mins).
5. The dryer kicks in.
6. Wait for 2mins.
7. Shut off compressor and dryer.

__________________
Inside every little problem, is a big problem trying to get out.

 

Thanks for your reply.

That's what I'd do if i was programming with C but this language is very primitive its basically PLC language. I'm restricted to high or low states and a bunch of relays and timers. Can't define variables and stuff. I'm at a loss now as I can't even extract any information out of the timer until the expiry time. Upon expiry the timer will output a high logic state.

 

Hello guys,
Although late but I managed to design and simulate it and here is the answer in the attachment.
The user setting time is 50s.

Attached Thumbnails