Official Luthiers Forum!

what is PID?

Here is another thread http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=19892

Fred

_________________
Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

PID stands for Proportional, Integral, and Derivative. A PID controller is used to control how changes are made to an output based on feedback from an input. For a bending machine you would be making changes to the voltage (the output) based on feedback from the temperature sensor (the input).

Proportional looks at how far you are away from you setpoint and makes changes based on that. So if you are near your setpoint, it makes small changes to the electrical output. If you are way away from your temperature setpoint, it makes large changes to the eletrical output trying to get the measured temperature up to the setpoint.

Integral looks out how long you've been away from you setpoint and makes changes based on that. You could be way away from your target but only for a short time and the Integral would only make small changes to the output. The longer you are away from your target, the bigger the changes the Integral makes to the electrical output.

Derivative looks at how fast the input is changing and makes corrections based on the rate of change. This is typically only needed for systems that change quickly like positioning a robot arm or reactively changing belt speeds. Temperature typically doesn't change at a rate fast enough to use derivative.......but if you did and the rate of temperature cahnge was slowly creeping up toward the target it would contribute little to the electrical output. If the rate of temperature change was rapidly increasing, the Derivative would make an immediate change to slow down the electrical output.

With all this said, PID control is probably overkill for a heating blanket controller. Seems toggling the blanket on and off would work fine......shutoff when the target is reached and turn the blanket back on when you are a few degrees below target.

_________________
Formerly known as Adaboy.......

Search online for home roasting coffee. A lot of PID stuff there. People take old hot air popcorn poppers and use PID control. Check it out.

_________________
Randy Muth
RS Muth Guitars Website
RS Muth Guitars Blog
Facebook Fan Page

As said above the PID is overkill, if you get a digital controller you need to get one with an on off control mode. A PID must react to the circumstances presented to it and be tuned to the dynamics of the load being controlled but we don't need this. For what we are doing a simple on/off will keep the temperature within a couple degrees + or - of the set point and is easy to set up. For a timer a simple bathroom type timer is better than trying to get a controller that includes this feature. Search Ebay there are lots available for a low price.

Fred

_________________
Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

I haven't used one yet, but router speed controllers are suppose to work very well.

_________________
Randy Muth
RS Muth Guitars Website
RS Muth Guitars Blog
Facebook Fan Page

The good ones work well...I made the mistake of buying my first ones from a company that rhymes with, "Marbor Greight" and they lasted less than 10 seconds...

_________________
http://www.presnallguitars.com

Probably one of the most important things I made when I decided to start building was the fox style bender using a blanket controled by a pid. I have yet to break a side and have bent cutaways and bindings as well and I attribute this to having a controlled heating device taking all guesswork out of heating the wood, that and all the help I have gotten here...mine is a simple setup The pid and the SSR I got off of ebay for around 50 bucks, the timer is a 10 bucks at a big box store, thermocouple wire with ends twisted together, ala Fred's advise, makes the process real simple

_________________
MK5acoustics.com

I just built a bender with both a PID temp controller and a digital timer, programmed for a 5 min countdown. I'll take some pictures of it tomorrow when I go over to the shop and post them. It's overkill, yes, but I'm a research scientist and we love our gadgets!!

I put together a PID controller a while ago. It works fairly well and isn't too complicated. The only part that I am not crazy about is finding a thermocouple that works well with the setup. What are others using?

_________________
Brad
Avon, OH

Actually a thermocouple is just the contact between the thermocouple wires used, type K, J etc one can be created by twisting the bare ends together. We use to make our own for the radient heat zones in the plant paint ovens, twisted ends crimped into a ring connector then screwed to the wall. I made one from the couple that came with my controller that was way too big to put between the blanket and slats, just cut off the end stripped and twisted the wires. I worked great but I fell into a long 1/8" diameter couple that is easy to use. There are also some thinner ones but the 1/8th is fine.

Fred

_________________
Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

Still a PID controller is used just in on/off control mode, same box just not using its full functions. I have used miner for 3 years now and love it. Probably $50 invested in it. I used the spreed controller method once and thought I would ad proper control as that is part of what I did for a living for 36 years.

Fred

_________________
Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

I'd love to see a tutorial for the visual guys like me.