Suggestions for project with mostly PID processing


Thread Starter

Jose Rodriguez

PAC Suggestions. I have small project for a continuous process with a very tight budget that does not allow the luxury of going to a full scale DCS of the majors (Honeywell, Emerson, etc). This is for small pilot plant for a lab with following IO count and loop count.

Controllers: 15 (Mostly single loops, 2 Cascade and 1 Ratio control)
Analog Inputs: 32 (Includes indicators and ai for controllers)
Analog Outputs: 15 (Includes HIC and output of controllers)
Digital Outputs: 5
Digital Inputs: 10

I'm exploring the option of using a PAC for this and communicate via OPC to the HMI of our choice.

I've seen the Opto 22 SnapPAC, AB CompactLogic, Toyo (automation direct) DL205, etc...

Any experiences with this kind of small project with a DCS type of requirements, using PAC, PLC, PC based controls is appreciated.


I don't know what a PAC is, but Honeywell's HC-900 is custom made for what you're trying to do. It's a hybrid controller, process-capable with PID, cascade or ratio control, rack mounted modular I/O with ethernet ModbusTCP suitable for any OPC client.

They have an HMI panel if needed, but it'll run blind, stand-alone. I run 4 of them with the honeywell panel, because the panel is so easy to configure - same software as the controller, just add a tag to one of the screen templates. Our sister plant runs them with Wonderware HMI over OPC. The hardware is durable & reliable, it even has steel racks, not plastic. I've lost one AI card, probably due to lightning, in 5 years.

I am budgeting for another, so I have the link:


William Sturm

I think it could work with any of the controllers that you mention.  I have definitely have used both the Koyo and Opto 22 for process controls.  I'm sure the CompactLogix would work fine as well. 

The Opto 22 has higher level math and analog instructions than the Koyo.  The Koyo will work well, it is just closer to assembly language.  You load registers, process them one instruction per box, and store them back to memory.  You also have to convert between data types, such as float, int, and BCD.  It is quite easy, once you understand the process.

The A-B and the Opto22 both have subroutines, while the Koyo does not.  It is just a big ladder file and a sea of memory.

Have you looked at EZAutomation?  You might be surprised what they have to offer.  I have not used one yet, but I would like to.  They make very nice MMI panels and even build the PLC into the back of the panel, if you like.  They have analog I/O, 32 bit math, floating point, subroutines, PID, and Ethernet.  You get a lot of PLC for the money.

Bill Sturm
Abbeytronics LLC

Go the Compact Logix.

It has 1 huge advatage and that is the PID tuner. Make sure you get the version of RS5000 that has function block programming and autotuner. Do all of your PID using the PIDE function block. Do NOT use the PID block that is available in ladder as it is a differant function and so not have the autotuner. The auto tuner is easy to use and gets good results. I used it on a water treatment plant doing flow, level and pressure control and it worked everytime.

IF you need further help let me know. Where in the world are you? I am in Australia.

If you spent much time on this board you'll know that there are quite a few PLC's on the market now that will do very good PID control without going to the expense of a "traditional" DCS type controller. The line between DCS and PLC is very blurred these days.

Allen Bradley Control Logix is very popular and as mentioned make sure you use PIDE not PID blocks.

We are system integrators and use ABB Compact Products for this type of project where cost is important. The AC700 and AC800 range will do exactly what you want quite well. We can get a standard PID control loop programmed in these controllers in a matter of minutes.

I think you might find that a PAC requires a little more programming than you really want to do to get a PID loop working

my 2C


Here is a BOM for what you need from Opto 22.

1x SNAP-PAC-R2 (cpu)
1x SNAP-PAC-RCK16 (rack/chassis)
1x SNAP-AIV-32 (32 channel analog input module)
8x SNAP-AOV-25 (2 Channel analog output module)

With this layout you can configure 96-pid loops and run the system on any Win2000, XP, Vista machine.

The best part is that the control software and SCADA/HMI is included. You can download it without a password or even registering to the site.,,,0,3&system=snappac&

A video is also available that shows you how to configure the full featured HMI/SCADA:

If you email your contact info I could have a friend of mine loan you some opto gear to try out the hardware. Where in NZ are you?