Dave wrote: > I feel that a simple "Bang Bang" (?) controller is not going to give you what > you seek. > To get truly accurate and stable temperature control, you will almost > certainly need a full "PID" controller, with some sort of variable > control of the heating element.
Not a bad idea, AND that is the normal way to do it. BUT Not so true and not really necessary. For what it is worth What I use is a modified "Electronic Temperature Controller for Heat Mat" One of many examples on Ebay is Item number:260519976777. By changing the value of the internal resistor and or putting a RC in series with it, You can set the hysteresis level to anything you want in both time and temperature.. I use 0.02 deg and 30 seconds. It drives up to 10 amps at the line voltage by way of its internal relay. Its sensor is a sealed unit on a long wire that can be place most anywhere. I've had no problem cycling a low wattage light bulb on and off at about a one min rate to hold temp variation to better than 0.01 deg. It makes a nice Tbolt temp controller, if you don't want to use LadyHeaters built in controller. More info on request ws ******************** ************************* Dave wrote: I know, I know, I should use God's units as revealed by the French, but it was easier in this case to follow the instructions as printed by the Chinese... All is true. A bang-bang is probably OK if the thermal first order filter is long enough? Don Dave Baxter > Hmmm. Another two digests missing..... > > > Hi... > > I feel that a simple "Bang Bang" (?) controller is not going to give you > what you seek. > > To get truly accurate and stable temperature control, you will almost > certainly need a full "PID" controller, with some sort of variable > control of the heating element. "Phase control" (EMI is fun) or "Burst > Fire" (can make lights flicker with big heaters) if powered from the > utility AC feed. DC of course is another option. But you will also > need to "Measure" the temperature in one form or another, not just > having a comparator (or two with dead band) and simple switching. > > With heating (and cooling) systems, there are significant time lag's > between applying the heating/cooling stimulus, and the sensor seeing > that change (let alone whatever you are trying to stabilise.) Those > time constants can be a real pain in the but, resulting in long settling > times if you don't want considerable over/undershoot, but with a "Good" > controller, you should easily get within a couple degree of what you ask > for. With a big thermal mass, probably 1'F is doable, but it'll take > time to settle. > > Any sudden changes due to external (or internal) conditions though, > could again "kick" it off kilter. (Clasical PID servo system theory > etc) > > I used to work on GC-MS systems (Finnigan MAT) where there are multiple > controlled heating systems, the GC oven being the most capable > controller. CPU controlled full PID type, controlling what was > effectively a fan assisted oven. I learnt a lot, as to what you can > (and cant!) do with temperature controls. > > I have also seen small systems (metal block heating) using power > transistors as the heating elements, with a "Type K" thermocouple, or > Platinum probe used (depending on the application and temperature range) > as the sensor, all bonded to the work piece. > > Anyway, what's all this degree F nonsense? SI units, 'C (or 'k for the > purists, or is that 'K?) is surely the way to go, like the rest of the > world. > > Have Fun. > > Dave B. > G0WBX. > Tin Hat and fire extinguisher ready... :)) > > > --------------Original Message---------------- > > Message: 4 > Date: Mon, 15 Mar 2010 18:42:19 -0700 > From: jimlux <jimlux at earthlink.net> > Subject: Re: [time-nuts] enclosure temperature controllers > To: Discussion of precise time and frequency measurement > <time-nuts at febo.com> > Message-ID: <4B9EE1FB.4080007 at earthlink.net> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > Don Latham wrote: >> hello the group: >> I've just installed a new "mercury-free" thermostat in my shop. I >> looked the thing over and realized it has everything needed to control > >> a "constant temperature" enclosure. There's a diode used as temp >> sensor,easy to remote with two wires, a place to put two AA batteries, > >> a pot to adjust the set temperature, all needed circuitry for a >> bang-bang controller with 1deg F hysteresis, uses a latching relay so >> the batteries last a long time, a low battery indicator, and an easily > >> backengineered circuit board, and a low price. There is provision for >> external power as well. The one I bought is a rite-temp model 6005; >> distributed by home despot. And it's relatively cheap, about 20 >> devalued rasbuckniks. All that's required is whatever needed for a >> heater and its power supply. Unfortunately, not for 110 volts but I >> didn't look at the relay to get the capability; that may be a lawyer > problem rather than a capacity problem. >> Don >> _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
