micrologix and temperature control

[bce123]

I think i got it this time this is an histroical view so the current temp and setpoint displayed is while the oven is off

 

[Lancie1]

Could you give a little detail? Hopefully i will understand a little more tomorrow but if the input card gives me a raw value for the temperature range, would you not have to scale that in the plc to represent the full temperature range?

No, no scaling necessary IF you use the Thermocouple/mV input module. That is one of the advantages of using the Thermocouple input module. You simply configure the module one time to tell it what type of TC (of the 10 available), whether you want C or F degrees, whole degrees or degrees and tenths, and a few other parameters (failure mode and so on), and then its output count reads degrees DDDD (or DDDD.d depending on your selection) temperature directly. What there is is what you get.

On the other hand, if you use a standard analog current or voltage input module, you will have to scale the counts to represent a temperature range.

 

[irondesk40]

Thanks alot. .

 

[irondesk40]

Just ordered the thermocouple card. Was not exactly cheap. Cost was $434. 4 of the Fuji modules cost me $692.

Problem we running into is our Director is being told by equipment manufacturer they can get Siemens for around $200. Difference is they probably buy a large quantity and I only purchase items as projects come up.

I still like stand alone controllers better even though it looks like it is pretty straight forward to do it with a plc. Mainly because i know in the field the techs we have have to have help just figuring out how to hook up a sensor. They have no clue about plcs etc. Actually getting ready to get on a plane this weekend and go to Brazil for 3 weeks and install some equipment we shipped over a few months ago because they can not get any of it to run.
Well at least it gets me a trip to Brazil.

Thanks to everyone for some direction.

 

[Lancie1]

...our Director is being told by equipment manufacturer they can get Siemens for around $200.

That is the old "bait and switch" routine in another form. Suck him in, then let him know that $200 was only the processing fee to bring in the Siemens expert - the Siemens PLC with all auxiliary equipment and programming will be an additional $10000.

Get it in writing with a complete list of all items to be supplied, with the total cost. Then you will have something to compare to your known Fuji costs. The only way you can break the PLC system cost down into cost per temperature point is to add up the total PLC cost, including the PLC CPU, rack, I/O modules, software, cables, programming, and the installation & wiring labor, then divide that by the number of temperature loops. Now you can compare that cost/point to one of your $692 Fuji temperature controllers. I doubt if it would be $200 per temp loop, or $692, but more like $1000 to $1500 per temperature point. Still that is an apples-to-oranges comparison. The reasons to use a PLC consist of other advantages.

 

[maxketcham]

If I were you and wanting to go to PLC temperature control, and already have AB PLC experience, I would not allow a rep to bring Siemens into you shop, stay with what you already know, it's cheaper.

 

[irondesk40]

thanks to everyone for input on this.
i had to make a emergency trip to one of our plants in Brazil for the last 3 weeks and just not getting back into the office and looking at this again.
I actually can get the fuji controllers for $175 each but still being asked to look at doing it with a plc.
At least i have been able to order a allen bradley input card for a micrologixs 1400 in order to test.
I have read the post and looked at the sample programs and thanks to your post I have a lot better understanding.
The only thing that concerns me about this is that with the fuji controllers we can control the temperature plus or minus only a couple of degrees and the only way i can see doing that with the plc is by using a pid loop to control a 4-20ma output to a solid state relay that has a 4-20ma input.
We use Carlo Gavazzi Solid State Relays and they carry a singele phase relay that uses a 4-20ma input.
Any thoughts or advice? Thanks