AB plc to control temperature

[Guest Guest_rock]

I am new to the AB line of PLC's. Have a question that I hope someone could help with. I am looking into using a Micrologics 1500 plc and try to figure out how to use it to control temperature in a heater. I am wanting to connect 2 Thermocouples into the PLC and with the use of a small display, be able to select the temperature in the heat chamber by taking the value from both Thermocouples and average them to control a set point that you select from the display. Could someone post a example of how to do this? At the moment, do not know how to accomplish this. A sample connection diagram using two thermocouples and a sample plc program would be very helpful. I have learned quite a bit from just referencing this forum in the last few weeks. I had considered using a Omron plc, but leaning more to the AB Line. Thanks rock

[Sleepy Wombat 27]

Guest rock,,why do u say you are new to AB when there are a number of previous postings ?? I don't think Jay will be too happy.... Why ? Tried online editing for the Micrologix ? Opp's lack there of ... Sorry but that is my pet hate of the Micrologix series... <> Personnally i would stick in a dedicated TC card for the CQM/CJ1 series...

[Guest JorgeR]

Guest_rock, What are you trying to do? There are afew diffrent ways to do this, depending upon what your accuracy must be. Are you trying to keep a room at a comfortable 72 degrees F, accuratly roast a turkey in a convection oven, hold molten plastic in an even melt, or what? Jorge

[Guest Guest_rock]

Well My previous post where about questions that I had about the ab line before we actually recieved any of the new equipment, still not arrive yet. Suppose to arrive in house this week. Was trying to figure out how to do some things in theory that had been throwed at me by upper management about what would possibly have to be done to the equipment. Been told we was going to have to possibly add this, do this etc., but not exactly sure what yet. I have had the micrologics software now for about 5 weeks and still trying to learn my way around all the shortcuts etc., while still trying to take care of all the other items that have been assigned, so that is why I reference this site, there is usually someone out there who at some point or another been faced with something similiar. So, to answer your question, I consider only a few months exposure to a certain line of a controller as sorta new. Also, as far as using a omron over a ab or ab over a omron, omron would always be my first choice. But upper management, (vp of engineering, etc. ) reads all the great things about ab, without knowing anything about anything, if you know what i mean, and says we will use ab. Even told machine vendor to use all ab line, without even knowing if we had software, etc., but that is way it is. So, that is what you look into. By the way, sleepy, thanks for all of your post, been very helpful.

[Guest Guest_rock]

What we will be doing as a prototype, is building a heat chamber with forms that have garments pulled over them will be going through. At the moment, after the last brainstorming meeting I attended, this chamber would be about 20 feet in length, variable speed control to pull the forms through, etc. The forms will pass through this chamber at a certain speed, and the average temperature inside the chamber will be 400 degrees. We are looking at mounting thermocouples , evenly spaced at four different locations inside the chamber, and using the average value from them to control a forced air blower, blowing across electric heat strips to circulate the air inside the chamber. The fabric on the forms, which is a patented type fabric, when kept at a certain temp for a certain period, molds itself to a certain shape. The theroy is having multiple forms, loaded automatically with a robotic arm (which i am controlling with festo servo's) move through the chamber at a certain speed to give the amount of time necessary from entry to exit, to allow the fabric to set to shape.

[Ken Moore 23]

I may be able to give you a hand, but I have a question. How will the temperature be controlled? By changing the speed of the blower, or by turning the heating elements on and off? Ken

[Guest Guest_rock]

Thanks for reply. The heat will be controlled by controlling a heating element. We have discussed controlling the blower based on the temp, but after some experiments, the fabric would set better, if the blower and air flow was a constant speed.

[Ken Moore 23]

Will the control of the heating element be on/off or will it be varible? Do you need to turn the heating element on and off using a discrete output, or can you control it proportionally, using an analog output? Ken

[kcor 1]

At the moment, plan on using on/off control.

[Guest merlin]

You will want to use a time proportional control PID loop to control your oven . I have 4 that I take care of (SLC503 controlled) and they will hold temp within a couple degrees with open ends and exhaust blowers. There is a great example of this in the AB slc book or if you want I can set you up with some code. Merlin

[Guest Guest_rock]

Thanks could you post the code, at the moment, trying to set up a pick and place robotic arm with 6 festo servo drives.

[Beryl 0]

The time proportional code mentioned earlier works well. However, this thread looks like it would work very well with less code. If you use it let us know how it works.

[Guest Guest_rock]

thanks for input I guess i was hoping that someone who has actually did a project such as this would post a example.

[Guest technogumbo]

My 2-cents worth...in building a PLC-based control system, one should start with making a list of the I/O. So far, sounds like you will have 2 TC inputs (since your target setpoint is 400F, you will probably use a Type-J TC?) and 1 discrete output (120V or 24VDC?). Also, take into consideration future I/O needed (I always figure 20% free I/O for those points that design engineers or customers want to add before you walk away from the startup). Once you have all of your I/O count, then it is time to figure out what PLC to use. There are 3 Micrologix 1500 base units (#1764-24AWA for twelve 120VAC inputs and twelve relay outputs) (#1764-24BWA for twelve 24VDC inputs and twelve relay outputs) (#1764-28BXB for sixteen 24VDC inputs and six DC FET plus six relay outputs). You might notice that there is not a base unit with analog or thermocouple inputs, so you will have to add a analog input module (#1769-IT6 is a six thermocouple input module).