Can't Reset Extech SDL200 Quad Temp Logger

[glowitz]

Here's a good one for you Extech fans. My first experience with Extech reminds me why I buy Fluke when I can. But in this case, Extech had the product I needed. Here's my problem: Fresh out of the box, it set up Ok. All 4 channels measured the ambient temperature using Type K thermocouples supplied with the unit. So far so good. Then, I pressed the two "offset buttons" to set an offset adjustment. Works great. But, there seems to be no way to remove the offset. I can't restore the original ambient temp readings. All four channels show an offset of at least 20 degrees from ambient. Even the manual doesn't explain how to revert back. I've tried everything I can think of, including removing the batteries! It remembers the offset! Not sure for how long, but it's probably written into memory somewhere. This is nuts! Anyone out there with an Extech SDL200? Of course, I called support. But it's Friday on a holiday weekend and I need to use this tomorrow for an extended test. I'm hoping that the EEVBlog gurus out there might have some ideas or suggestions. I've got to believe some combination of buttons should reset it, but so far I haven't figured it out. I believe the unit itself is working OK. This really feels like a software bug and it's in a state that I can't seem to shake... Thanks for your help!

[David_AVD]

The manual says:

Thermocouple OFFSET Adjustment
1. Set the desired thermocouple type.
2. Insert a probe to the T1 input jack at the top of the meter.
3. Press and hold both OFFSET buttons (up and down arrow keys) for at least 1.5 seconds to access the OFFSET screen
4. The last measured value is shown on the left side of the LCD; the offset adjusted value is shown on the right.
5. Use the arrow keys to set the desired offset.
6. Press the ENTER button momentarily to store the adjusted offset value and to return to the normal operating mode
7. In the normal mode, the offset value will be applied to all four inputs

That implies you can set it to whatever you want?

[glowitz]

Correct. You can set it to whatever you want. But there is no way to know what the correct "ambient" temperature is anymore because it only shows the adjusted temperature. I'll try to explain. When you insert the thermocouple into slot 1 (before making any adjustments), it shows the ambient temperature reading. Let's say that's 20 Deg C. Ok. Now, you use the up/down arrows to set an offset. In my case, pressed the down arrows until it reads 10 Deg C. Now, when you plug in thermocouples into all 4 ports, all of them read 10 Deg C. However, if you try to restore to the original value (true ambient, without any offset), there is no measurement that shows you what the current true temperature is. So you don't know what to adjust it back to. Is it 20.0? Is it 20.1? 19.8? It seems you'd have to have another system to calibrate against. Basically, at least as far as I can tell, I can't seem to "turn off" the offset because there is no reference anymore to the true current reading. It's very odd -- and certainly not intuitive at all. Does this make sense what I'm trying to explain? The other clue that something is awry is that once it gets into this mode, there's no way to turn off the unit either. Holding the power button does nothing. Only way it to unscrew the back, remove a battery, and reboot after reinserting the battery. I'll try leaving the battery out for longer than a minute to see if something in there resets....but so far, it remembers the random offset that I plugged in. Please note that the display isn't really an "offset" per-se (in absolute terms). It's just subtracting or adding some amount to the ambient reading.

[glowitz]

Let me add some additional clarity to my last post, because the values I picked as examples (20 deg and 10 deg) could lead to ambiguity...so I'll pick a different example.

1) Insert probe into slot 1 (before any adjustments)
2) The display shows 20.0 degrees ambient (example for illustration).
3) Enter the "offset mode" by pressing down the two keys
4) The left display shows 20.0 degrees (actual) and the right display also shows 20.0 degrees. They call this an "offset" reading, but it's not really an offset in absolute terms. It's the same measurement as the last ambient reading. This is important...
5) Ok, now, lets say I want to introduce an offset of 3 degrees lower. I press the down arrow keys which adjust the so-called offset reading --- and it goes from 20.0 to 17.0.
6) So, at this point, the left display shows 20.0 (current ambient) and the right display shows 17.0, which represents a -3 degree offset (not a 17 degree offset).
7) Now I press "Enter" and I plug in all the other thermocouples (4 in total).
All four displays now read approximately 17 degrees (not 20 degrees) as a result of introducing effectively a -3 degree offset.
9) That would all be ok...but now there is no way to get back to where you started. You've lost the reference to the current actual temperature....because the "offset"display isn't really just an offset from zero.
10) So, I try to get back to square 1 --- and I enter the "offset" mode again. But the left display doesn't show the ambient, it still shows 17 degrees -- and the right display shows 17 degrees. So how do I know what the current ambient is anymore? Yes, in this case I may remember that it was 3 degrees adjusted. But the temperature has changed in the meantime....and there seems to be no way to get back to square 1 where the input simply reads the current temperature without any arbitrary offset applied.

Hopefully this explains it better. It seems right now the only way to fix this is to adjust the offset to match the current ambient temperature as measured by another (separate) accurate temperature sensor (like my other Fluke meter)..

It really seems like they got the definition of offset wrong. To me, an offset should start at zero (meaning no offset is being applied). If I adjust it up 3, then I know I'm +3 above whatever the real temp is. But that's not how this seems to work. The offset is really a new temp reading. Very strange. I'm willing to accept there is something I'm doing wrong -- but the manual doesn't say how to eliminate the offset per-se and I can't seem to do it unless I have an absolute reference somewhere else. It seems as a result that I've lost the full calibration of this meter because the offset is something arbitrary that I was just playing with --- and I don't remember exactly where the ambient was at the time -- I'm probably back to within a couple of degrees -- but that's silly. Hopefully this additional detail helps if anyone has experience with this particular meter... thanks again!

[David_AVD]

Sounds screwy.  Offset should be a +/- figure surely.   

[glowitz]

Yeah, screwy is being nice :-). I can't believe that the Extech engineers wouldn't have tested or understood this. I think this meter has been out for a while -- and I haven't found much online about it. I'm sure others have come across a similar issue, you'd think. I'll keep fiddling. Meanwhile, if you or anyone else some some good ideas, I'm all ears. Thanks for your contributions. Meanwhile, I think I just need to recalibrate it myself. I just did a quick test to check freezing and boiling -- and I've dialed it back in within a degree or so.