NTC temperature control

[Boobo-oobo]

Hi, I have a CP1L plc and a NQ3 touch screen, and need to make a program that controls the temperature of heating plates. The temp. of the plate is around 180 degrees C, and i was planing to use a NTC reisistor to measure the temp. My question is, is it possible to make such a ladder program that will control that using a NTC resistor, and could someone give me some directions to how to make such a program, cause i have little knowledge about this kind of thing, I know how to make simple ladder programs, but this is a bit more complex. Can the plc directly measure the analog value of the temp with the NTC resistor, or it needs some kind of an device to do that? Dont know if you need any more info. about all this . . . Thanks, Marko.

[pfort]

My advice would be to use a thermocouple and a temperature controler. There is no analog input on CP1L. NTC, as far as i know, are not very good for that application.

[Boobo-oobo]

Could you explain that a bit further? How would I exactly do that? To explain a bit more, i need to enter a temp. on the screen (like 180C) and the PLC has to get to that temp, and keep it that way. Are there any good examples of that?

[pfort]

Do you have a PLC anyway on that project or do you plan to use it only for this?

[Boobo-oobo]

The PLC is only for the temp. regulation. I have to make it so that he reads the temp. and heats the plates accordingly. The program would go like this, you enter the temp you want, PLC reads current temp, then if the plates are cold, heats it up to the temp, and keeps that temp. Now my problem is how to read the temp.

[pfort]

You need a temperature controler (not a PLC). It read the temperature, dislay it, and control your heating device (SSR...) There is an example: https://www.omron247.com/Industrial-Automation/Store/OmronProductDetailView?productId=61447&langId=-1&storeId=10051&catalogId=10051&parent_category_rn=12312

[Boobo-oobo]

I understand that there are those kind of controlers, but here they are quite expensive. And i want avoid buying those controlers, and use what i have, the PLC and the touch screen. Are you saying that this kind of temp. control is hard to do with the PLC?

[Jay Anthony]

A temperature controller for this kind of application would be $100-$150. I doubt you can buy a PLC for this amount.

[Boobo-oobo]

Maybe true, but i need to control more than one plate, i think its about ~10 of them. And i would like to solve this by putting one PLC that i already have, then buying 1000$+ of new gear. So, how can i do such a thing with my plc?

[pfort]

Maybe it is cheaper to buy 10 controlers than add expansions to a PLC to control 10 zones. What is this PLC? Edited February 14, 2011 by pfort

[BITS N BYTES]

Is is absolutely essential to get feedback on the actual temperature of the plate? If NOT then a simple [albeit crude] method is to use the PWM outputs to control the ON/OFF time of a solid state relay that switches power to your heater. The CP1L only has two outputs configurable for PWM. For additional heater controls one can create your own PWM pattern on standard outputs using high speed timers [make sure you use transistor type because of frequent switching]. It all really depends on the type of heater you are using. My 2 cents.

[Boobo-oobo]

Yes, i have to get the temp. reading. So this method doesn't cut it . . . I dont mean to be rude or anything, but i didnt ask what else could i use to solve this. I need to use the touchscreen and the PLC for this. Now, i can sell the one that i got, and buy a different one if necessary. So, as i understand it now, i would need to get a plc that has analog inputs, is there a plc that has 8 or more analog inputs? Or i need to buy expansions? Lets start with what would be a good PLC for this job. And thanks for the help so far, if any more info. is needed just ask . . .

[pfort]

Sorry, just wanted to suggest what seemed a better solution. That is one of the goals of this kind of forum. Your CP1L is great for that...just add 2 temperature sensor unit (CP1W-TS002). They have 4 thermocouple input each.

[Boobo-oobo]

NP, but i need to do this with a PLC. So, i buy those sensor units, and connect them to my PLC. What type of data about the temp do i get from the unit? Do i get lets say a integer/float value of the temp, and write it in the memory?

[pfort]

I dont remember if it is Integer or BCD, but there is no need for scaling. If you want it Float you will have to convert it.

[PdL]

There is something that would answer your questions. It's called a manual. CP1L Operation Manual @ MrPLC.com CP1L documentation

[BITS N BYTES]

The CP1L series is restricted to only 1 expansion unit for 14 and 20 I/O models and 3 expansion units for the30, 40 & 60 I/O units. You will not be able to get a combination of Analogue I/O Expansion units to satisfy your "I thinks its about 10 of them". If you switch to a CP1H XA model with built-in analogue [2 In/2Out] you can attain a maximum of 10 In and 10 Out analogue. RTFM

[Jay Anthony]

Oh, that they would RTFM!

[pfort]

I thought that 30, 40 and 60 I/O CP1L allowed 3 expansion units even if they need 4 words each, as for the TS002. I never found any mention of limitation in term of number of total words for theses expansions. If it is the case it allow 12 thermocouples input. If not i would appreciate if someone would indicate me where i can find it in documentations. CP1H allow 7 expansion or a maximum of 15 words, wich mean that it allow 14 thermocouples inputs. (3x TS002 (12 words)+ 1x TS001 (2 words)) Edited February 17, 2011 by pfort

[BITS N BYTES]

He RTFM! Your statement is correct, however your first post said you were using a CP1L and appeared to suggest you needed an Analog Input and Output for each heating plate. You now have the manual and have changed to a CP1H. How do you plan to control the heaters?

[pfort]