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screen printing => Equipment => DIY - From master engineered marvels to cobbled together jury-rigged or Jerry-built junk! => Topic started by: Horizongfx on August 10, 2018, 11:56:41 AM
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O.k. Here's the scenario after converting my dryer to digital temperature controller from the old SCR/ Triac PWM style temperature controller.
No matter where I put the Thermocouple, it will hold at a steady temp when Unloaded (no shirts on the belt) and then when I load shirts on the belt the PV value climbs rather quickly then eventually levels back out maybe after two dozen or so shirts go through, but when the PV value rises obviously it shuts off the power to the elements and there is a time when some shirts do not get up to cure temperature !
I have installed 2 different PID's one is an Inkbird and the one in there now is a Berme Rex C-100. It is normal to get these kind of fluctuations with this type of control system ? I know the calrod type elements are slow to respond and that could be part of the problem. But I have tried every variable possible and still cant get it to run at a steady state Loaded and unloaded.
I have also used 3 different Type k thermo couples in different locations within the dryer above the heating elements, below the heating elements, touching the heating elements etc. etc. I also also autotuned the Controller many, many times with both an empty belt and a loaded belt.
what am I missing ? are these low cost PID's just garbage ? dryer has 36" belt, 6 foot of heat 3 feet of in-feed and 3 feet of out-feed. BTw I'm using to two 40 amp Solid state relays two elements per relay, there relays are turning on and off as they should when the controller tells them to do so, I'm not a rookie at this but dialing this thing in is sure making me feel like I am.
Please help ! :'(
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Call brown.
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Winston?
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PV should drop when cool mass is introduced to the chamber.
Are your thermocouple leads reversed?
The fact that it's reaching set temp at some point sort of precludes this possibility,
but stranger things have happened.
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PV should drop when cool mass is introduced to the chamber.
Are your thermocouple leads reversed?
The fact that it's reaching set temp at some point sort of precludes this possibility,
but stranger things have happened.
No, PV value always rises, Thermocouple leads are not reversed, thanks.
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a solution might be to load a bunch of scrap shirts and let the system settle in before drying the printed garments.
here's my guess on what's going on:
If you are running the autotune with shirts on or off the belt, the controller is learning how to manage the heat (how soon it needs to turn on or off the heating elements) under those conditions. When you start loading the shirts, the conditions change and it does not know how to compensate for it. If you tried to autotune with shirts on and off, it might give you better results. . . or it might just get confused! Loading the blanks first, is probably the easiest solution.
pierre
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I think I may have figured it out, swapped out one of the two SSR's and it seems to be behaving better now, I used two different brand SSR's with two different amp ratings one was a 40 amp and one was a 50 amp, not sure the amp rating mattered all that much, but the difference in brand or type may have, who knows... :o Auto-tuning again now, so we shall see, thanks for the feedback guys !
:D