temperature control?!? 1

[tzuny]

Hi all, I'm new in PLC and i want to know if a PLC is the right thing to use in my application. I'm trying to control a steam boiler. I'm reading the outside temperature and i want to run the boiler using those readings( example: for 40 deg outside run the boiler one hour every 4 hours; for 20 deg outside run the boiler one hour every 3 hours; for 0 deg outside run non-stop. thanx for any help

 

[ADMIRALKEN]

Assuming you already have existing controls in place to run the boiler, and the PLC will just close a "run" contact. Then this would be a simple application for a PLC.

 

[itsmoked]

And a good solution to that. As long as it has nothing to do with function of the boilers as mentioned by ADMIRALKEN.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[tzuny]

thank you for the help, but now the problem is whitch PLC will do the work. what kind of I/O cards to use? I'm trying to buy something from ebay, just in case i'll destroy it. i don't want to sped more then 2-3 hundred $.thank's again.

 

[danw2]

Two major considerations:
- cost of programming software.
- communications port
- required programming accessories (cable)

Find out what software program will be necessary to program any specific brand and model PLC (PLC have model lines, just like automobiles) and what the software costs. That will be a major differentiator between brands and models.

Which communications port does the PLC CPU use to get its program from the development software in the PC? serial COM port? ethernet?
Does your PC have that port (most laptops nowadays do not have a serial port)?

Some brand comm ports/protocols are notorius for not coping with USB-to-serial adapters. But ethernet communications is frequently an upgrade situation.

Some PLCs use serial cables that are not stright through or null modem cables. What's it cost for a programming cable?

From what I've heard, I'd start with Automation Direct, a mail order/web PLC supplier. (I've never used it, but reports are generally favorable). You can probably buy A-D new components, with a warranty and telephone support for the cost of many used items on eBay.

Dan

 

[itsmoked]

I second everything danw2 said.

You really need to first figure out what inputs the boilers need and what you are going to use for the temperature. Also the number of these points. Keep in mind you will want some idiot light stuff for showing which boilers are being commanded on and any panel switches you might want for enabling or disabling boilers.

Essentially you should create a working block diagram with all inputs, and outputs and your power source. Once you have that you can find The Correct PLC.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[richs]

Here's a pretty good one that might just do your job. You
might need some external relays to handle higher current.

One of the other members of this group had passed this along
in a different thread on this same board.

I haven't used it, but at first blush, it looks like it might
do your job for you. And the price seems right.

I am not affiliated with the company, just passing along some
information from another person in the group.

http://www.factorymation.net/

and look for the product reference to:

Programmable Logic Relays

cheers,

Rich S.

 

[Skogsgurra]

Yes, these "programmable relays" are, in fact, very competent little PLCs. The TECO SG2 sold by FactoryAutomation is available under under labels, too.

The analogue inputs are only for 0 - 10 V, so you need a temperature transducer with that kind of output. The resolution is 10 bits (0.1 percent) and the accuracy is quite good. Simple NTC+resistor combinations have been used for temperature measurements with good result.

SW is easy and there is even a simulation mode and a monitoring mode. Both are very handy and the whole thing is a good introduction to PLC. Price is way below what you are willing to pay. And that's usually not a problem.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Skogsgurra]

"under OTHER labels"

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...