Author Topic: Soldering Iron Advice in Australia  (Read 1938 times)

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Offline Johnny B Good

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Re: Soldering Iron Advice in Australia
« Reply #25 on: October 02, 2019, 12:44:28 am »
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BTW, if you've ever wondered about just how compact and how close the heating element is to the business end of a T12 tip but couldn't afford the luxury of a high resolution thermal imaging camera to find out, there's a simple way to visualise this if you can afford to sacrifice a T12 tip - just power it directly off a 24v supply and examine the yellow to bright orange glow with the MK I eyeball. If you're not too keen on wasting a T12 tip like this, you can just take a look at the following video to satisfy prurient curiosity.  :)
Yeah, that's about what I figured. The heater/sensor is obviously at the back of the tip, not anywhere closer to the tip than in any other iron. And you can see on this fatty tip, the temp drop largely happens within the last 5mm of the point. This is in free air. On a heatsink, you would watch that contrast increase, the tip going darker. This is what we live with with all modern soldering irons. A T12 iron can live with this and still work as well as the "obsolete" 888 tech. But mine exhibit additional sag beyond this.

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As my free admission that I would probably have been less impressed if I'd been able to monitor the actual tip temperature whilst applying it to the two pence coin I was using as a 'difficult' test joint, I was acknowledging the fact that it was a less than perfectly scientific test. Nevertheless, it was still a useful test to see how the controller would respond to such thermal loading on a BC3 tip.
You should not be impressed at all, IMO. When you put the iron on a 2 pence coin, the duty cycle increases, and you think this is impressive?

 What impressed me was that it actually did what it was supposed to do, specifically that part where it limits the overshoot (a quite modest 10 deg C) upon removal of the tip from the heat sapping effects of my test joint but then I'm easily pleased after some sixty years' worth of soldering experience with basic soldering irons no more sophisticated than a 25W Antex. :)
 

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Whilst we may both have an understanding of the thermal gradient issues at a basic level in such a temperature control system (sensor sandwiched somewhere along this temperature gradient between the heat source and the heatsink - hopefully in this case, nearer to the heatsink than to the heat source) we both admit to a lack of detailed knowledge of the processes taking place within these T12 tips and the difficulties this presents to the PID control algorithm in maintaining a reasonable semblance of tip temperature accuracy during soldering operations.
To heck with PID. I just want to see the T12 iron that works as well as the 888. I know full well how I would do it. I would correct the sensor coupling error/sag, and then i'd make it work by thermostatic control with nothing else fancy.* I don't know what's going on inside of a microcontroller or how "they" actually do it. That's why test. The clones I have do not achieve this.

 Unless I'm very much mistaken, those Hakko 888's (or at least the 888D) employ some form of PID control to compensate for the limitations of a basic thermostatic control mechanism. Having googled for Hakko's own advertising copy on the discontinued FX-888 and the FX-888D and the FX-951 which fails to mention the use of PID control (which they're more or less obliged to use with a composite T12/T15 tip), I'm forced to conclude that I am very much mistaken after all in regard to the FX-888 at any rate (and probably the 888D as well). :(

 Although the replaceable heater elements in the 888 system include a temperature sensor (thermocouple?) wired separately from the heater circuit, it obviously is no better placed between the tip end and the heater element than in the combined cartridge T12/T15 tips used by the FX-951 stations.

 I'm guessing Hakko must have decided they might as well combine the TC and heater circuit into one simple series arrangement and use a more sophisticated PID based controller to separate out the functions and provide an improved control algorithm for their 'next generation' of soldering station.

 Even in a system with the heater and TC on separate circuits, a PID algorithm can provide better control over a basic proportional control of the heater to hold the sensed temperature at a constant value as I presume to have been the case with the obsolete FX-888 system (with the 888D probably being the same but with a micro-controller added on to accept keyed in settings and to generate a digitally displayed temperature read out).

 If Hakko went to the trouble of patenting the system embodied in the FX-951 (which coincidentally, expired exactly a week ago), there's obviously merit in the use of PID control of soldering iron tip temperature. If it there had been any practical way to improve sensor to tip coupling, I'm sure Hakko (and others) would have done so rather than resort to a sophisticated PID control algorithm to overcome this issue. TBH, I'm not at all sure how you can correct the sensor coupling/sag without using some form of PID algorithm.
 

You have a clone you are pleased with. You have spent many hours playing with it and modifying it. You have a tip temp tester, FG100 style, I believe? You just need to buy some spare thermistor sensors for it and wire one to your temp tester with flywires. (The third connection where the two metal wires are twisted together is only to hold the sensor in place; it does not need to connect to anything. It's dead weight; the thermistor wires make connection inside the solder-wettable crimp block). Then you could do an actual meaningful test with the real temperatures. You have time to write text walls to rival mine  >:D, so you would think you have time and inclination to do this test. If we had some standardized heat sink, we could share/compare notes. Say some size of double sided copper clad with 1 oz copper and standard 0.064" thickness.

 I like your thinking (and you're right about my spending the time I should be using to get on with my GPSDO project, instead of writing these massive missives - sorry but I'm still waiting to take delivery of a Mustool G600 microscope:- AJR Syndrome, a Red Dwarf reference ). That's just the sort of cost saving that appeals to my sense of 'cheapness'. :)

 I do have a clone FG-100 and since I took delivery of a pack of ten TCs a week or so back, I can well afford to repurpose one to this task. I also have some single sided copper clad board that I'd bought about 8 or 9 months ago from an Ebay seller when I was considering the option of building my GPSDO project "Dead Bug" style but I've no idea what weight of copper, nor the composition of the base.

 I'll have to check my purchase history to see whether any of this had been mentioned (in view of its intended use, I hadn't been concerned about these particulars at the time). I can probably identify the base material by sight and smell (drill a test hole or two) and, from a thickness measurement, work out the weight of the base material and subtract it from total weight to calculate the copper (oz per sq foot is it?).

 Before I do that however, I'll repurpose a TC to perform an initial test with my two pence piece and let you know before we decide on whether we both possess matching copper clad board and how much of it to sacrifice. I think I may also have some very old stock of copper clad board tucked away somewhere which might help to create a matching test board if the new board is too cheap to match what you have to hand.
 

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Where we seem to differ is over the need for a 17 bit ADC used in the Pace controllers versus the 12 bit ADC's built into these cheap Chinese STM32 controllers. Whilst I can see the benefit of the extra 0.02 deg C resolution in detecting temperature trends quicker to reduce the effects of lag in preempting variations in heatsinking effect at the soldering iron tip, I have my doubts as to whether such small temperature changes can be picked out from the noise fast enough to be useful in this endeavour but, of course, I'm no expert in the technology of sensing such small temperature changes in the context of a soldering iron environment.
As do I; I don't suspect it is a cake walk. But if this is the case, the Pace ADS uses a 17bit ADC purely for show. And all T12 irons are pretty sucky at temp regulation and have significant sag, as do my clones. I would bet this isn't the case; I doubt Pace uses 17 bit ADC unless they managed to get an actual performance gain out of it.

*Well, if you could accurately measure the sensor error, you could do better than just correct for it. You could "boost" the set temp above and beyond in accordance with the amount of correction done, because the sensor error will be proportional to thermal load. And base to tip gradient is also proportional to thermal load. So if your readings can be accurate enough, and the station can identify the tip that is on there, it could actually attempt to compensate for base-tip sag and perform better than a traditional iron. This makes me more intrigued to try the PACE ADS.

 Well, I'm sure this is exactly what the PID control algorithm is doing its best achieve in the FX-951 as well as in all these Chinese STM32 based soldering stations. The TC is a very low impedance voltage source with just the 8 ohms of heater wire in series to spoil this perfection.

 Even so, an 8 ohm signal source is a very low impedance compared to the more typical 600 to 10KR impedances we usually associate with low level audio signals. Since I doubt we need to worry about signals higher than 100Hz or so in this case, the use of an extra 4 or 5 bits of resolution might actually be a practical proposition after all in spite of my reservations over possible noise pollution. As I said, I don't have any expertise in this particular field so I could be 'over-thinking' this issue of noise. Instincts can sometimes be misleading.

 However, even with less than perfect performance over control of the tip temperatures in these cheap Chinese soldering stations, they're still a vast improvement over my previous experience with simple plug into the wall socket soldering irons (did I mention I was easily pleased :)).

JBG
 


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