How do I control furnace temps (ramp and soak)? What hardware do I need?

[Gerry S]

Please help me~~~~

I use Labview version 8.2 and Compact Field Point.  I currently have a small Lindberg/Blue furnace (120V, 6.8A, 8KW) that has a mounted Lindberg/Blue UP150 programmable controller.  The temperature control is not currently connected to my PC (and that's a pain). 

I would like to replace the present furnace controller with labview control through Compact Field Point.  I need to create a ramp and soak program in labview.  My

program must be able to:

Soak at 300C for 30 min

ramp to 650C

soak at 650C for 15 min

ramp to 700C

soak at 700C for 10 min

cool to 300C

repeat the above steps as many times as desired.   

I am familar with labview but have never controlled any furnace temps.  I have figured out that I will need the PID control toolkit.  But I'm totally stumped about the hardware I will need.  I have searched everywhere but can't find an explanation.  I have Compact Field Point and the furnace.  What hardware goes inbetween?  Just what hardware does the PID toolkit (PID VI's) send a signal to?  It seems to me the PID would read a thermocouple and then send a signal to some sort of current regulator that sends a varying current to the furnace.  Am I way off?  How do I set this up.  Can anyone recommend a good book or web site that explains how to set up furnace control using labview?   

I really appreciate your help.  I'm at the end of my road without it.  Thanks alot. 

-Gerry Szachara

Chemist

BASF Catalysts LLC

[Jaime Rodriguez]

Your application does not seem too difficult to achieve with the hardware you have described. The LabVIEW PID toolkit is simply a set of VIs that include the algorithms necessary for PID controls, autotunig, Fuzzy Logic, etc. With the Compact Fieldpoint unit you would be acquiring the temperature with thermocouples, or whatever other sensors, and then controlling the ouput to the heater with the PID VIs serving as input to a PWM module for Cfp, where that would be connected to a relay which would then switch the heater on / off according to the Duty Cycle you would specify in your LabVIEW code.

How many temperature sensors would you be using??? How many output channels would you need?

[Dennis_Knutson]

According to this, the controller has an option for RS-485 communication and you would not need to replace the controller with your own hardware and software PID. I've written a few programs for chambers (not with the UP150 though) and the communication is usually pretty straight forward.

[Gerry S]

Message Edited by GerrySzach on 11-10-2006 09:45 AM

Message Edited by GerrySzach on 11-10-2006 09:45 AM

[Gerry S]

I'm beginning to get a glimmer of hope here!  Thank you for helping me out. 

Jaime, I will only be reading one type K thermocouple sensor  that is inside the tube furnace.  The furnace is a single zone furnace with only one coil, so I guess I only need one output channel.   What type of relay do I use between the PWM and the furnace?  A solid state relay?  Or a mechanical relay?   The furnace operates on 120V AC input.  Am I going to wire the 120V through the relay and directly to the coils?  

Thanks Jaime.

Gerry

[Gerry S]

Dennis, it seems like using the RS485 would be easier, if I understood how to perform the communication.  I have thus far only used labview for data acquisition.  Now I trying to control.  I have figured out how to use relays easily enough.  But I haven't figured out at all how to perform instrument communication.  I'm trying to learn though.  I'm going through some online tutorials, but I will probably need more than that.  How straightforward is it?  I'm starting at Zero as far as instrument control...parity, baud rate, bits, etc.  Would it be difficult to learn how to control the UP150 using labview? 

Thanks againg guys. 

-Gerry

[Dennis_Knutson]

Have you looked at the programming manual? It appears that you can use what they call PC Link or Modbus. It seems that PC Link is normal serial communication and it's a matter of formatting the commands correctly. That means sending and receiving hex and the correct control codes. You send strings with a VISA Write but you can write click on a string control/constant and select Hex Display or '\' Code Display. The functions Byte Array to String and String to Byte Array are also very useful. The communication would be done with regular VISA Writes and Reads. There are shipping examples of serial communication. Modbus is a bit more complex and is not something I've done. NI does have a free Modbus Library and there have been numerous postings on the subject. You might also try to do a search for the term 'temperature chamber' to see what shows up.

[Ben]

I have written a driver for one of those. Unfortunatley I can not give them away free.

Funny, it was for another catalyst lab.

If you do your own take care about how you interpret the step times returned when you query the unit. It reports back in the corrently configured time interval (seconds/minutes) while on the other hand only accepts the step times in seconds (?).

This gave me the weird problem of the temperature profile would increase by a factor of 60 if I just read, modified and re-wrote ONLY if the unit was set for minutes!

Have fun!

Ben

PS If you want to purchase my code "As-Is" e-mail me off list.

Message Edited by Ben on 11-10-2006 11:49 AM

[Conseils]

If you can, use a solid state relay as this will be the most reliable and noise free solution to switching. Switching 8kW loads with a relay can lead to arcing of the contacts after a while (and other issues), this is bad news for computers. For an 8kW device you will need to mount the device on some form of heatsink / dissapation surface. Solid state relays normally use an opto-isolated coupling which can usually be powered in the range 3 to 24v. This is connected to the control output of your selected controller.

For control of this sort I personally I prefer a dedicated controller, I use a PC for data logging, program management and monitoring. This is for reliability more than anything else, an NI controller won't come with integrated display and controls to set the device and the foot print in the panel is considerably larger. They also take an age to boot in comparison. You should also consider that you could get an electrical engineer to fit a standard controller with suitable solid state relay etc. and that will help you meet any health and safety requirements easily and quickly! Don't forget than any modifications will need to meet local regulatory requirements such as CE and thus circuit diagrams must normally be produced etc.

If I have the choice of selecting a controller, I like the Eurotherm range of temperature controllers, they are available with varying options just like the controller mentioned in the thread. There are drivers available in this forum and the NI web site for the devices.

http://www.eurotherm.com/
There is also OPC support and the diagnostic software available from Eurotherm is good.

But if a device has a specific manufacturers controller on it I might select one from the same family. Often I look around the plant / factory and see what models are in use. Using a model / type that already in use makes it easy for support in the factory and reduces support calls!

Hope these thoughts help out.