Hi all.

novice in old type relay controls and such am trying to gather the correct data i/o in order to change over to a plc that will act as a total controler of the entire proccess. which plc will be best? I corrently have a machine running with koyo. any advice?

thanks
Hanan

 

Try looking at Unitronics OPLC line.

Regards
Mickey Moore
[email protected]

 

hanan: The best plc for your project depends on a few things. What type of inputs will be going to the plc.
ac inputs,dc inputs or a combination.
Next what type of outputs.
ac,dc or combbination.
After you know that infomation then you need to
check on space in the enclosure for the plc and
if there is a problem with heat.
If the enclosure gets to hot the plc might not function properly.
Get a accurate count of inputs and what kind
and outputs what kind.
Ones you have this info you can find the best plc for your project.

 

Hi Hanan,
Depending exactly on the magnitude of the project, you'll probably need a PLC that can handle PID-controls (most newer PLCs has that feature); if it's only a "local" reactor, which is not to be connected in any form of communication, a PLC might not be the solution.

Apart from your power relay (solid state, thyristor etc.) you could use a simple external PID-controller; with an analog SP from a PLC (via analog output or comms.) the external controller would take care of the control-loop. If you need a ramp control, that can be created in the PLC using FPD (for increased accuracy).

The OMRON CJ1 series have some PID-modules; all you have to connect is the appropriate TC/PT & output (digital).

CJ1W-TC002 (4 controllers TC)
CJ1W-TC004 (2 controllers TC + alarm)
CJ1W-TC102 (4 controllers PT)
CJ1W-TC104 (2 controllers PT + alarm)

I've build such a controller using an analog output as a SP, but unfortunately I used a non-self tuning controller (it was an experiment). If you DO use this model, make sure to use a controller that has self-tuning, as it will save you the time it takes to manually enter all the PID-variables!

-Peter

 

Hi Hanan
The easiest way to control an oven is with an off-the-shelf temperature controller. You can get very fancy ones that do temperature profiles and some digital I/O as well. They are dead easy to install and set up and generally cheaper than a PLC solution. They also have the advantage of a built-in operator display.

Some brands are Eurotherm, Yokogawa or for a low cost model Shimaden.

Apart from the complexity of the wiring and programming of a PLC, you also would require a separate user interface.

Jamie
[email protected]

 

There is no "best" PLC.

I suggest sticking with what you already know how to use.

Bob Peterson

 

Thanks Jamie.
I could not agree with you more.
Staying with off the shelf components seems the right way.
The twist to this is the need to modulate various components after the initial process is done.
Example: I need a stage temp. Rise like 2hr at 135 tops. Than loop to higher temp. I need to control Rh that will open a damper motor or a shower valve at set point. I need to reach to 205 after that (damper closed). To condition that in relation to Rh interpolation. I also need to operate the power intermitted plus the damper in order to avoid condensation after the process is done. Mainly reached 205 for 10 min.
I thought just hooking a timer that will start the blower with a on off t/d but since the product behaves differently in the oven you can't predict when it will reach the set temp.
Your comment
> The easiest way to control an oven is with an off-the-shelf temperature controller. You can get very fancy ones that do temperature profiles and some digital I/O as well. They are dead easy to install and set up and generally cheaper than a PLC solution. They also have the advantage of a built-in operator display.
>
> Some brands are Eurotherm, Yokogawa or for a low cost model Shimaden.
>
> Apart from the complexity of the wiring and programming of a PLC, you also would require a separate user interface.
>
> Jamie
> [email protected]

 

Yes I did for 12 years after left an engineering job to start this enterprise. This got me behind. It's time for progress wouldn't you agree?

There is no "best" PLC.

 

Thanks Peter.
Most informative.
one of my machines got old analog processors (not pid). I guess I could hook the plc to the some of the siglas like relays on offs to start a count up or down there.

 

Hi Hanan:

The importance of your application is not the automation of the smoker oven itself. All PLC and control manufacturers offer you a specific product to perform the task. Wouldn´t be nice to record the temperature? Or to monitor and control your Oven through EXCEL?

Please visit http://www.lt-automation.com

Orlando Charria
[email protected]

 

Hanan,

I have programmed a plc for a client doing something similar, it had a rotating set of grills in it which the plc controlled the rate of
rotation based on the temperature. Hotter meant faster so as not to burn the food.

As Orlando points out, monitoring and logging of the cooking temperature also helps prove to the health department that you are cooking food at
or above the required temps.

The plc had an attached touchscreen which gave access to the menus, batches if you were making cookies, so that when you put raw meat in the
cooker, you then entered what rack you put it on and what type of meat it was. When it had been in the cooker long enough the panel produced an audible alarm with info on what rack to empty.

Jeff