Soldering iron temperature variation/differences

[GregDunn]

I just got one of the cheap FG-100 tip measurement clones and it seems to work fine.  Before this I had a type K thermocouple with a portable DMM designed for it.  Both give reasonably close readings to each other (say 25F or so), but the interesting thing is that both my ancient Ungar 9000 and my new Hakko FX-951 read way hotter than the display indicates.  Given that both thermocouple devices say so (and are pretty repeatable), I'm inclined to trust them as being close enough to accurate to make this a real situation.

Now understand, I don't give a **** what the temperature is to the nearest degree.  I am curious, however - is this normal?  The Ungar runs about 80-100F higher than the display (yes, it is calibrated according to the manual) and the Hakko about 70F higher.  They're using small and similar new spade tips, and I carefully (non-abrasively) cleaned the Ungar heating element when I got the new tip, to make sure thermal contact was good.  I just want the displays to give me a ballpark indication so that I can be sure I'm not overheating the tips - obviously, they'll get adjusted based on application.  I'm just surprised that there was ~100F difference in temperature vs. the displays; that's not trivial.

[sn4k3]

One thing about FG-100 is the measure limit, after some uses the sensor goes bad and need to be replaced. It work very well when a new sensor is used, but after some measurements the result is not reliable.
To make sure about the real temperature you should use other equimenet as reference, other iron or something that you know the real temperature before hand so you can compare

[GregDunn]

Well, I started out with a fresh sensor and measured <10 times total; all the measurements were consistent.  As mentioned, they also matched up pretty well with my existing type K thermocouple  (though there was a consistent offset).  Unless I've overlooked something, I have no reason not to believe what I've measured.  I'm just a little surprised that both an old and a relatively new iron both have such a huge difference between the display and the actual.

[KL27x]

is it your first 951?

The interface is clunky, and I imagine some people can accidentally change calibration when trying to change the set temp.

I'd be curious what happens when you do a factory reset. If it significantly improves it, I would suspect user error. Maybe not yours, if the iron has ever been used by anyone else. At any rate, you can calibrate the station to w/e you want, although it will vary a bit, tip to tip. And there may be some offsets in the overall range.

So.... if you found yourself limited by the 840F max set temp, you could turn it up to 11, if you wanted. I guess your iron is already calibrated to the Spinal Tap standard.

I have tested several irons. 4x 888's and a couple of T12 irons. All my hakko stuff was within maybe  +-15 C, or say 30F, depending on the tip (and most of that was due to variation between handpieces when swapped around). One of the clones was maybe 30C higher than the displayed set temp. I guess that's pretty close to 50F. The Bakon clone was actually pretty close, IIRC. 10C over, tops. This is more impressive because the manual states something to this effect. To expect the actual temp to be 10C higher than the set temp, and it was pretty much spot on.

[GregDunn]

No, I don't think I have reset the unit.  It was indeed refurbished, so that's something to try.  I haven't owned one before - I got this one for an excellent price (about 1/2 list) from a Hakko dealer because I wanted an official unit instead of a clone, as well as post sales support.    Except for minor signs of use on the case, it's just about mint; I disassembled it for a good look.

I spent a lot of time playing with the UI and I believe I am adjusting both set temp and offset values correctly; I know it's easy to hit the wrong button and change the other value, but if anything I think the problem may lie in something left over from its prior life.  I'll check and report.

[GregDunn]

OK, I definitely had the offset and settings as intended.  So I went ahead and reset the iron, which necessitated setting the offsets again anyway.  This time, the difference was a little closer - about 30F and still consistent.  I'm going to use that for the offset and call it good here.