View Full Version : Control Question!

16-11-2005, 03:49 PM
In our facility we utilize Allen Bradley PLC software. In specific RS5000 & RS 500. I noticed in the refrigeration industry they make there own logic & HMI platforms. We are considering utilizing our PLC to write the Logic for our air handlers (Positive air) for the facility (Milk Plant). Does anyone here or has anyone used Allen Bradley as a platform for there controls.



18-11-2005, 02:32 PM
There 's no reason why you cant use them.

I have Mitsibishi FX2n PLC's With E200 HMI's controlling large refrigeration plants and they work very well, we had a few teething problems trying to get the program right but running smoothly now.

Have a look at www.mrplc.com there may be some info there.

US Iceman
18-11-2005, 04:30 PM
There is no problem using a PLC to control the equipment. One thing I would caution you on is the control logic you write. The controls will do whatever you "tell" it to.

Any control logic written for the equipment should be checked to make sure it does exactly what you want. The general requirements are:

1) Basic control strategy
2) Alarms
3) Safeties

One other aspect to be aware of is control speed. By this I mean, how fast does the system react to control changes? PLC's and electronic controls can operate in milliseconds. Refrigeration systems are more tolerant of low speed changes. Any sudden change in suction pressure can cause very interesting things to happen.

My main point is this: any change you want to occur, should be done very slow to ensure the refrigeration system does not adversely react to the change.

Slow, stable control is better than fast reactions to a change in input value.

18-11-2005, 05:21 PM
In my opinini, you can do it faster, cheaper, more reliable with standard controllers, specific made for this task.
We use the Polygir for this. http://www.landisstaefa.co.uk/default.asp

20-11-2005, 08:32 AM
Hi balerjoe!
Certainly you can apply AB controller if you would want that nobody, except you, understand yours AHU control system:)

Otherwise better to use special configured controllers such manufacturers as Siemens, Honeywell,TAC,Trend, Carel, Regin and others...