Thermocouple wire length question, Rinny

[LoneGunman]

Rinny or anyone who's familiar with thermocouples, any idea if the length of the thermocouple wire is matched to the thermocouple? I'm just finishing up my powder coating oven, I'm using a PID controller and a thermocouple to control the heating elements. The thermocouple comes with 36" leads, any problem rolling up the excess or can I just shorten the leads?

 

[rinny_tin_tin]

Rinny or anyone who's familiar with thermocouples, any idea if the length of the thermocouple wire is matched to the thermocouple? I'm just finishing up my powder coating oven, I'm using a PID controller and a thermocouple to control the heating elements. The thermocouple comes with 36" leads, any problem rolling up the excess or can I just shorten the leads?

Normally, you can cut the leads w/o a problem and calib (zero/span), etc is done at the acquisition controller. Lead problems mostly come into play when they are *too* long - and when unshielded. However, please don't take my word for it - check with the tc oem....However, you can (and most people do) roll em up and tuck them away.

Best

 

[LoneGunman]

Thank you. I do a lot of control wiring at work but nothing like this, from what I've read a thermocouple with a PID controller is supposed to be a lot more accurate than a standard oven type thermostat.

My next project is using a little more advanced PID to control a kiln I'm going to use to try some color case hardening. The more advanced one has programmable ramp up, down and hold temps, the one I'm using now just controls the temperature.

 

[rinny_tin_tin]

Thank you. I do a lot of control wiring at work but nothing like this, from what I've read a thermocouple with a PID controller is supposed to be a lot more accurate than a standard oven type thermostat.

My next project is using a little more advanced PID to control a kiln I'm going to use to try some color case hardening. The more advanced one has programmable ramp up, down and hold temps, the one I'm using now just controls the temperature.

Yes - PIDs are extremely useful accurate in process controls. I don't think I ever saw one used before for an ordinary oven - but then, I really don't know much bout powder coating processes. However, and you probably already know this, the thermocouple is your weakest link, or - your accuracy/precision is only as good as your thermo-couple -- how fast she equilibrates, how well she holds her settings, etc. Your second weakest link will be your operators, or in this case - your heating elements, and how fast they respond to PID control. Your precision will ultimately vary based on the size of the item your are heating - or the (modified) 3-bears rule. Too small - overcook, too big - undercook, and mama's bed is just right. So that means that there will be a sweet-spot size where the oven will perform the best. But play with it - I'm sure you will have fun. You may also want to peruse the Omega.com site for their solutions, in particular, their software driven hardware solutions - that are pretty cheap, very tailorable, and very fast to get up and running.

Good Luck

 

[larry4406]

I'm just finishing up my powder coating oven....

Now you have done it. We expect full disclosure of this project including pictures, performance, etc. Inquiring minds want to know.

 

[LoneGunman]

Now you have done it. We expect full disclosure of this project including pictures, performance, etc. Inquiring minds want to know.

I really didn't take any pics of the construction, it's basically just a large oven I converted from a food service heated holding cabinet. Many people make their ovens, they have some interesting builds, I found this heated holding cabinet for $100, it's all stainless and has nice heavy well sealed doors. The doors seem to be the biggest problem with homemade powder coating ovens. So I took the easy way out and bought the heated holding cabinet just for the cabinet, the controls and heaters were removed.

I used a central heating element for my heat, the PID controller as mentioned above and added a circulating fan to attempt to keep the temps somewhat even. The most challenging part for most people would probably be the controls, that's my line of work so it was easy.

I'll take some pics when I'm done, I still need to figure out some sort of rail system to hold large heavy parts and I still need to figure out a system to hand small parts.