Required recomendations and/or advice


Thread Starter

Laura Montiel

I am working in a revamp that includes substitution of Siemens SIMATIC TI545 PLC (APT programming) with a Modicon Quantum (140 CPU 534 14). This is in a compressed air plant that has 5 Centac model 3C7OM4 centrifugal compressors. Each compressor has a dedicated TI545 PLC, it has a pneumatic system for flow air control that includes a PIC, CV for the bypass and the inlet valve. For the vibrations it has a Bently Nevada 9000 Series Vibration Monitor Model 24717-01.

It has been required that one Quantum PLC controls 3 compressors + a chiller and a second one for the other 2 and in a future 3rd compressor. Two PLCs for controlling 6 air compressors. The pneumatic system will be eliminated (this control will be done by the new PLC) and the vibration monitor will remain.

My personal opinion is to use one PLC to control one compressor (how it is done now), nevertheless, it will be done how I described. Maybe I am wrong about considering 1 PLC for 1 compressor or maybe my arguments about my point are not strong enough. I need some advice on how this change can impact the performance of the compressors or control or any recommendations.

P.D. my written English is not very good, if my message is not clear be free to ask any point.

Thomas Hergenhahn

Hello Laura,

I'm not quite sure what you need in the first place: support for your 1 PLC per compressor point of view? Or help on how to migrate from Siemens to quantum?

A PLC for 3 compressors certainly has the disadvantage that 3 compressors are halted whenever the PLC is nonfunctional, be it for program changes or failure.
On the other hand, there may be applications where a common (centralized) control can do new things, e.g. distributing the load amonng the compressors or run the most economic one for partial loads.
Dear Laura,

For 1 PLC to control 3 compressors it's having some drawback of PLC failure causing the 3 compressors stopped. I Have done some using PLC to control air compressor. shall you require further information. feel free to contact me at [email protected]

I would not see a problem with running 3 or more compressors from 1 PLC. If you don't want to risk all compressors shutting down because of PLC failure, put in 2 dual redundant PLCs.

I would imagine that 1 TI545 was used per compressor because the APT programming language is so hungry for memory!

Paul Darby
[email protected]

Laura Montiel

Hi Thomas Hergenhahn,

Yes! Technical basis on why 1 PLC per compressor is better, the disavantages you name don't seem to worry maintenance. Also for the startup and during tests in some cases the other compressor could be shutdown. Anyway the centralized control you mention will be a good thing to implement.

About migrating from Siemens to Quantum I made a printout of the program to study the APT language which I'm not familiar with.

Thank you for your answer,

Laura Montiel

Thank you for your answer.At this point this was my doubt, for further information I will contact.


Matthew Hyatt

You may want to consider small standalone PIC devices, cheaper than PLCs, can perform all the functions you require and easily programmed in C.

I would not use 1 PLC to control several compressors, too much risk for a multiple machine shutdown if the PLC fails.