On Fri, 2011-02-18 at 20:27 -0500, cogoman wrote: ... snip > I imagine a setup where three 500 watt halogen bulbs in series > (giving maybe 250 watts worth of heat, and a lifetime that will outlive > me) are nestled in an aluminum plate.
Why not: http://www.amazon.com/Whirlpool-Electric-Heating-Element-279838/dp/B001DHLGOS and: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CC1082-ND > One of those glass bead > thermistors (see Re: [Emc-users] Multiplexers) senses the surface > temperature on the side opposite the heating elements. It should be > simple to set up EMC2 to accurately set that temperature quickly with > proper PID values. Now I sandwich my block of aluminum between this > heat source, and a plate underneath it with another thermistor. I set > the temperature of the top block to be 10 degrees hotter than I want, > assuming the center of my object is halfway between the temperature of > the top plate, and the temperature of the bottom plate. > > When the bottom plate gets to 9 degrees short of the temperature I > want, I start to back the temperature of the top plate down, with the > intention of having them meet in the middle. When the temperature > difference between top plate and bottom plate is about 1 degree, I could > have the PC buzz a speaker, letting me know I can make a measurement. Why not put a temperature sensor on the workpiece and have EMC2 tell you when it comes up to temperature? > The nesting of PID loops occurs because the temperature of the top > plate becomes the commanded temperature for my block of aluminum, and > the temperature of the bottom plate becomes my actual temperature for > the inside PID loop. > > Since the temperature control doesn't need sub second speeds, any old > PC, even one still using the on-board video should be fast enough for > this purpose, You don't even need EMC2's realtime, but since it's already there, it may be harder to try to remove it. > unless we read temperature using the game card method. A > fast thread can discharge a capacitor to ground, then release it and > start counting. A comparator will change state when the voltage passes > that of the thermistor. Then EMC2 takes that integer value, looks it up > in a table, and passes on the temperature in degrees C to the PID loop. There are many ways to get analog into EMC2. It's hard to tell which is the best way. I used this: http://www.wallacecompany.com/machine_shop/EMC2/serial_adc/ This can be used for your (single) PID (slow PWM to heating element) and alarm trip points. > * What I need help with is how to implement this. I can picture > setting the target temperature using G-code, perhaps setting it up as a > very slow spindle that needs to come up to speed, but that sounds too > kludgey. I suspect that a separate GUI program tied into HAL might be a > more appropriate way to do this. I am also wondering if classic ladder > would be appropriate. Any ideas?* I vote for a pyVCP or one of the newer VCP's. A DRO could be an example: http://www.wallacecompany.com/machine_shop/EMC2/serial_adc/ > I think temperature control is one area that if we set up some good > instructions to make it easy on a beginner, or perhaps even set up some > temperature configurations in the drop down list of sample machines, we > might get some users outside of the CNC arena. Agreed. > As I wrote that, I thought about the wiki page on stepper motors > (guilt, guilt) that I have in the works. It's fairly far along, so > maybe I should post it, and tweak it as others read, and point out > anything that's unclear. One of my techniques is to post really awful content so that others might feel compelled to contribute. I would vote for posting whatever you have and fix it as you go. I see a lot of good new content in the making on the wiki while looking for other things. It would be nice to have a mail list that automatically posts new content, but this doesn't exist, so if you post a message when you make the new page or edits, it might help to get contributions. The user map indicates that there are over 1200 people registered on linuxcnc, but I see the same old 20 or 30 people active on the list and forum. If we get more people posting, I might not have to be the only one that's always right. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ The ultimate all-in-one performance toolkit: Intel(R) Parallel Studio XE: Pinpoint memory and threading errors before they happen. Find and fix more than 250 security defects in the development cycle. Locate bottlenecks in serial and parallel code that limit performance. http://p.sf.net/sfu/intel-dev2devfeb _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
