Rotordamper Aux. TC board with two probe jacks, blower and servo connections


 
I don't think its normal. If i take the thermocouple in between my fingers and squeeze the junction point, Its stable as it can be. But, soon as it is in air, it will read from 72.1-72.9 and it wont stay on any one point for more then a second. It will make the graph look like saw teeth.

But, as long as they read correctly in boiling water and they don't fluctuate more then a degree, i think they will be ok, as they still have a accuracy of +-2° or so.
 
John, does the fluctuation increase over time? I have this problem with my on board TC. Starts with a degree or so then increaseincreases over the hours to as much as 4 degrees. I know your TC amp is on the satellite board just wondering if there is a cool root cause?
 
I know mine does NOT do this, my TC is quite stable, even when run over a 50FT CAT5 cable... If the temp is stable my TC registers rock solid, in fact, here is a short video of my TC Pit Probe showing how stable it is....
 
Yeah I think the stability is greatly influenced by the 12V supply. Some are great and have almost no noise and some are really wonky and can cause the temperature to vary quite a bit on its own. I'm going to try some things on v5.0 to reduce that but I also tried than in v4.2.0 and it was a miserable failure.
 
I've got a boat load of 12VDC power supplies here, I will try to get around to testing TC stability on a few of them to compare... Right now I am using a giant old school transformer type PS, not a modern light weight switching mode PS that is more common today, I seem to have better results from the old school PS if I recall properly....
 
I'm in Nairobi for another wee but will try a transformer type psu and also a 12v sla battery to see if this helps. Makes sense that a cheap switching supply could give grief. Thanks for the advice Bryan and Ralph.
 
Ron Webb said:
I'm in Nairobi for another wee but will try a transformer type psu and also a 12v sla battery to see if this helps. Makes sense that a cheap switching supply could give grief. Thanks for the advice Bryan and Ralph.
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Yeah, definitely try a better adapter. But, if you a re seeing a rise of 4° over a period of time and you know the temp has not changed then you may have another issue.

Put the tc in boiling water and it should read close to 212° and be pretty stable, as long as you dont leave it touching the bottom of the pan.

How's Nairobi? I have been to Mombasa. Its somewhat a dirty but beautiful place to visit. Would like to go back there sometime.
 
The probes all read accurately in boiling water and ice/water so calibration is ok. Nairobi is in the 90s (30°C) and clear blue skies again today. Traffic is horrendous - 4th worst city form Commuter Pain according to the IBM Index. Very quiet out on the golf course though!
 
I guess like the song goes.... "the waiting is the hardest part"....
I've got an order in with OSHPark for a batch of the RDTCv3 boards (that's got a ring to it, maybe 3rd time is the charm!), they say the panel has been sent out for fabrication but I'm not exactly sure when they will be done and in my hands. Meanwhile I've put in a hefty order with Digikey for the parts to build these up. Gotta love Digikey... Ordered at 6:18PM and my package was actually scanned at the PO at 9:37PM that same day, so that stuff will be here by the weekend...
 
Bryan Mayland said:
Yeah I think the stability is greatly influenced by the 12V supply. Some are great and have almost no noise and some are really wonky and can cause the temperature to vary quite a bit on its own. I'm going to try some things on v5.0 to reduce that but I also tried than in v4.2.0 and it was a miserable failure.
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Why don't you back up and try to do something to tame the +12V a bit? Right now +12V on the HM is whatever the wallwart says it is. Without a load most wall warts read way high, as they are loaded it drops. So maybe regulate the 12V supply which feeds everything to clean up the whole thing from the root?
 
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It isn't so much the 12V line because we switching convert that down to 5V then linearly convert that to 3.3V which becomes the reference voltage. That should be a pretty good start, the issue comes in when there's a grounding problem or something. Ground loops are a definite problem and that can be seen when touching the probe shields barefoot with a terrible power supply. I am not sure what the good supplies do that makes it that much better the v5.0.0 has two sides with two separate grounds. They are sourced through an inductor and grounded through a ferrite. I am anxious to see how that performs. I'm really still trying to find the right way to isolate the circuitry so hopefully this is a step in the right direction.

I'd hate to think I need to include a 1:1 transformer on the input. Do they make tiny versions of those to supply just 3.3V and less than 50mA?
 
Just noticed that OSHPark got my RDTCv3 boards back today and shipped out to me. So I guess I will have them Tuesday, 'cause I think Monday is a holiday of some sort? At any rate, I should have one together early next week...
 
Speaking of which, the only part im mossing atm, is the 1m resistor.

Can i use another resistor, say 1k, to test with or do i really need the 1m resistor.
 
Actually you can use just about anything, my prototype offset circuit didn't have it at all. I found the range of adjustment to be way beyond what was needed, so I added that resistor to reduce the range of adjustment, which will also make finer adjustment possible.
So bridge over it, or use the largest SMD resistor you have.... It's a simple voltage divider, the trim pot is 1M, so a 1M resistor in series would cut the voltage on the trim pot in half, 500k would make it 2/3 etc...
The TC bottoms out around 37 if I recall, something around that. So if you tune the TC ref up 70F (and offset -70) it should measure down to -33F.... It doesn't take much offset voltage to achieve 70 degrees. The circuit without the extra resistor is capable of offsetting the TC hundreds of degrees, way more than needed to measure temps on planet earth! LOL
 
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Maybe i can used the 402smd 1m resistor,i got by accident, somehow. But, that thing is as big as the period at the of this post, lol...........,well actually, this big •
 
Anything will work, from 0 Ohm (shorted out=jumpered) to a couple Meg... the closer to 1M the better, cause I think about half the range I am getting on the first circuit would be about ideal...
 
I just made a quick check of the 3.3v regulator, opamp, and the trimmer, and they all are the correct size. So, thats good. I may not get to it tonight, its movie night with the wife:(
 
I received Version3 yesterday and soldered one up late last night. It was definitely a challenge to solder, especially the trimmer and I found out that the middle pin on the probe jacks is actually pin3 not pin2. So, when you plug in the probe it will display a temp just as you put it in and when it clicks in it does not work. As it is now I would need to put a small jumper wire between the two pins and the jacks work fine. Although I had some problems getting the TC to work, I believe the circuit to be good and my soldering not so good, as after fooling around and replacing the .01 cap and resoldering the TC amp, I was able to get it to work and I could adjust the temp with the trimmer. I can't do any more testing at the moment as the 4 Atmega chips I have, none of them are working correctly and the only one that I have that works, I cant communicate with it(could be my HM too, I guess). Im waiting on 10 Atmega chips I ordered.

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This looks like some amazing progress is the servo header going to be on the board? Maybe I'm not seeing it...
 
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