micrologix and temperature control

we use fuji process temperature controllers on our equipment and looking at possibly replacing them and controlling temperature with the plc and temperature card. What would be the pros or cons? Thanks

plc pro:
you can make a menu of diffrent settings for all.
all values on one screen
all settings on one button.

plc con:
if something wrong no backup plan.

you can replace the old controllers with new ones pretty cheap.
(i have a box with used ones)

Are you an equipment manufacturer?

An end user with a production machine?

What's wrong with the Fuji performance now?

What improvements warrant making the change?

This was asked once before I believe, and having standalone controllers does not disallow centralization of parameters. The main difference for me is performance versus panel space. And weigh in: increase in engineering hours and total number of stocked parts.

I like the little Fuji's I have dealt with. If you offload the control including PID to a separate controller that is doing nothing else, it can perform better, but that performance might be complete overkill.

Later on I will look for that old thread perhaps two to three years ago, a nearly identical opening question...

Paul

This has come up again in a meeting with our Director. He is now convinced it can be done cheaper with the plc. Have never done this with the plc but since that is what he now is wanting then i will need to study it.
We have hundreds of machines with the Fuji controllers and they work great but he recently had a meeting with a machine manufacturer that we was looking at to build a machine for us that uses the Siemens plc (we use mostly Allen Bradley) and he told our director he could do it cheaper with the Siemens.
I would say yes to that after as mentioned above all of the extra engineering time has been done. The problem i see with it is that most of the technicians in the plants that work on our equipment do not know anything about plc's and if something is not working right with the temperature all they now have to do is either replace the heaters,temperature sensor or last resort pop a new controller in. If it is controlled by the plc and they replace the above components and still not working then what. All of these plants are overseas. Well enough ranting. Would anyone have a sample program using a micrologixs they might would share?
Thanks

I am always wary of the word "cheaper," because for most people it means "lower initial cost." Even then, I'm skeptical that a PLC could be cheaper than a stand-alone controller. I'm familiar with the Fujis and they're fairly low-cost and easy to use. Analog I/O is not cheap. Neither is programming time. It really sounds like whoever did the cost comparison did a "component cost only" estimation. The problem with this is that it assumes everybody works for free and time is worthless. I honestly cannot think of a situation where a PLC could be cheaper for temperature control (for a single loop) than a controller. Maybe if there were several loops being controlled and you were looking at half a dozen or more controllers, then it might be worth it.

The problem i see with it is that most of the technicians in the plants that work on our equipment do not know anything about plc's and if something is not working right with the temperature all they now have to do is either replace the heaters,temperature sensor or last resort pop a new controller in.

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This is the kicker right here. Introducing a PLC to people who know nothing about them when the previous control method worked just fine is just asking for trouble. People sometimes get this idea that PLCs are this magical fix-all for any process, and that having one automatically makes everything better. That's just not true. Sometimes, it's better to have a stand-alone controller.

Sometimes, it's better to have relay-logic panel. Things to consider: how much does downtime cost and how much more of it are you going to have now that problems can't be fixed in-house? How much is it going to cost to have a service technician drive out to fix a PLC fault?

We have hundreds of machines with the Fuji controllers and they work great but he recently had a meeting with a machine manufacturer that we was looking at to build a machine for us that uses the Siemens plc (we use mostly Allen Bradley) and he told our director he could do it cheaper with the Siemens.

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Sounds like your director was bamboozled. Again, this is only looking at the sticker price of the machine and not the total cost of ownership.

All they now have to do is either replace the heaters,temperature sensor or last resort pop a new controller in. If it is controlled by the plc and they replace the above components and still not working, then what? All of these plants are overseas.

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Keep the stand-alone controllers unless someone is prepared for a big cost in time for retraining your technicians.

Would anyone have a sample program using a Micrologix that they might would share?

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Because the MicroLogix PLCs use essentially the same RSLogix500 software as the SLCs, then any temperature-control program written in RSLogix500 will be a good example. I have plenty of those. Do you want the entire *.RSS program. or a PDF print-out, or what would be most useful (maybe only the ladder file that has a temperature control routine)?

I would consider the Fugi controllers simple to set up and use, and the AB no so simple. Purpose built temp controllers always seem to do the job a little better and a lot easier than PLC's in my mind, altho I've used PLC's for temp control on machines with extra room in the PLC and not so much room for the temp controllers. I wouldn't consider the PLC temp control route to be cheaper, especially if you're using Allen Bradley stuff.

Lancie1 said:

Keep the stand-alone controllers unless someone is prepared for a big cost in time for retraining your technicians.

Because the MicroLogix PLCs use essentially the same RSLogix500 software as the SLCs, then any temperature-control program written in RSLogix500 will be a good example. I have plenty of those. Do you want the entire *.RSS program. or a PDF print-out, or what would be most useful (maybe only the ladder file that has a temperature control routine)?

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I mostly for the last few machines (projects) have used the micrologix 1400 plc and Emerson HMI (Actually a Redlion but doing a lot of projects with the Unidrive servo and the Emerson HMI has the necessary drives that makes it easier to communicate directly to the unidrive). I have RSLogix 500 only. if you could share a *RSS file that would be great. I have found that sample programs work the best to help get you started.
I briefly looked at the thermocouple input card and we have the J type thermocouples. At this moment not exactly sure how to set everything up but i would assume that the input card would give a range of something like 0-16383 if set up for PID and the temperature range for example was 32-900 degrees F, then 32 would equal 0 and 900 would equal 16383. Then use those values in a PID to control a output. Thanks for any advice, it is greatly appreciated

I would assume that the input card would give a range of something like 0-16383 if set up for PID and the temperature range for example was 32-900 degrees F, then 32 would equal 0 and 900 would equal 16383.

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If you use a type J thermocouple connected to a temperature transmitter which is then connected to a standard analog input module, then your assumptions are close.

If instead you use the AB Thermocouple Input module, the Type J temperature range is -346 to 1400 degrees F. When you set up the module correctly, you can read the temperature directly with no other scaling being necessary.

Here is an example RSLogix program that should have everything you could have ever wanted to see as far as temperature control.

Go into the downloads->misc section. There is a file there called hotrod. It was written back in 2005 I think for Ron Beaufort's hotrod system which was a soldering iron with a temperature probe on it. The hotrod program simulates the hotrod and then controls it.

Lancie1 said:

If you use a type J thermocouple connected to a temperature transmitter which is then connected to a standard analog input module, then your assumptions are close.

If instead you use the AB Thermocouple Input module, the Type J temperature range is -346 to 1400 degrees F. When you set up the module correctly, you can read the temperature directly with no other scaling being necessary.

Here is an example RSLogix program that should have everything you could have ever wanted to see as far as temperature control.

Click to expand...

Thanks a lot, tired and ready to get out of here and head home. will download it tomorrow and look at the hotrod sample tomorrow. "when you set the module correctly you can read the temperature directly with no other scaling being necessary" 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. I know i have asked too many questions but with all the cut backs and getting rid of folks without this site i would be up a creek without a paddle at times.

I don't remember exactly what the scale factor is, but i believe the raw value you get from a thermocouple card is the actually temperaturex10. For example, if you are reading something that is 100.5 degrees, you get a value of "1005".

For controlling that value, i would select a range that i know the process will fall within (say 50 - 100 degrees), and set up a SCP to scale up the value to 0 - 16383. Your setpoint will have to be scaled up by the same amount also. You then can scale your output to whatever you need to control your heaters.

maybe this would help

this is a 40ft by 50 ft 8ft tall oven in the program above look at the pid this should give you an idea how to do it. the oven uses a modutrol type controller on the burnner with tc input and analog output. the nice thing about using a plc is its easy to trend and tune!