Program to manage 5 Compressors

Hello norimane;

The type of program you are trying to create is often refered to as a "lead lag" control, and it is very often used with multiple pumps, or in your case, compressors. You can search for lead lad control on the web, you will find a few discussions on the subject. 

For example have a look at this discussion (from another automation site):

http://www.plcs.net/dcforum/DCForumID5/1050.html

Note that you will have to create logical definitions of which pump will be lead (based on the running hours, or attained pressure...), determining the order of lag compressors (which one is the next to start) and have signals telling your program that a compressor has failed starting, or is out of the rotation (example: for maintenance), before you can even start programming the lead lag sequence.

Hope this helps,

Daniel Chartier

Hi

in water industry they often have two pumps - duty and standby.

Should fault occur the duty pump switches OFF and standby starts.

Any pump can be disabled for maintenance and then other pump starts at all times.

What they do is count start-ups and use sequence

1 - 1 - 2 - 1 - 1 - 2 - .....

i.e. 1st start command - use pump 1

2nd start command - use pump 1

3rd start command - use pump 2

4th start command - use pump 1

.....

This way pump 1 will wear quicker and require more frequent maintenance than pump 2.

The aim is to avoid even wear of both pumps which would cause them to break down

together or need service at the same time.

Another approach is to use run hours and make arrangement that will ensure some of devices

will accumulate much longer run time than others to ensure they will not need service at the same time.

Hi

ESTOP - you need a F (FAIL SAFE) PLC CPU and do e-stop routines in safety blocks

OR

have a separate safety PLC (i.e. Wieland) or just an e-stop relay which physically disconnects

peripherial 24V from your outputs.

standard PLC program and I/Qs are not to be used for safety (estops/guards/etc.)

the safe i/qs do check themserves and should they fail they do so in a safe manner.

PLC will need e-stop information for alarms and to abort the sequences.

if estop triggered you drop to manual and switch off all the outputs driving motive power.