Siemens LOGO! PLC: need help

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.

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.

tamubarak

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.

Just gave this a go and got it, the user time is interchangeable and the drier will come on for last 2 mins no matter what the comp time is set for.
View attachment 65900

konzen said:

this language is very primitive its basically PLC language.

Click to expand...

hated Logo and Siemens products in general. FB circuits are quite ugly. Overlapping wires...!!?
What connects to what? I know, editor keeps rubber bending them every time you touch component but still.
This is not the way to code. Btw, Logo also supports ladder (which suffers from similar problems but is usually more readable).