Need everyones help on a PID problem

[Arcs_n_Sparks]

Okay, uninsulated junction. Are you keeping it from touching stuff? I assume you are, but was trying to figure out if you have a ground loop that is driving you crazy. Running out of ideas.....   :(

Arcs_n_Sparks

[Wildcat]

The wire is flexable where I can just lightly loop it onto one of the racks.  The exposed tip does not touch anything.  I might be wrong but I really think it is the Maverick or its probe that is the problem.  Once I get another thermometer I should be able to determine whether it is the Maverick or the PID that is changing (with the assumption that one of them will stay consistant with the 3rd thermometer).

[pensrock]

Mike,
  The +-.2 degrees C is most likely from the max of the thermocouple not the operating temperature. I do not think you can use a 200 degree setpoint to measure the calibration. I may be wrong but normally it is measured at the high limit of the thermocouple. If it is a type K it could be 1800 to 2200 degrees F. Still this is not something to be too concerned about. I'm just trying to figure out why he sees the temp differance if he uses the offset and matches the control to the Mav.
  If the manual says the offset is 'Pb' then I guess it is so. Sounds very odd to me but I have not used an Auber instrument so I cannot say. Most instruments we use have a setting in the input section not the tuning section that says something like, 'off' or 'ofset' or 'ost' well you get the idea.
  Arcs has  a good idea of a possible ground loop.

[Wildcat]

Is it difficult to explain "ground loop"?  I am new to this electronic stuff.  I know a little about electricity.  Is it essentially allowing a break in the flow of current or a decrease in the flow of current, thereby giving false readings?

[Arcs_n_Sparks]

Wildcat,

Basically, you follow the electrons, and keep them moving where they belong. The worst example of a ground loop problem is if you are holding a tool that has the hot side contacting the case, you grab it, and are connected to ground somehow (standing in water or holding something that is grounded). Electrons start flowing through you with a bad outcome. That is how GFIs protect you: making sure the electrons flowing out match those flowing back.

The potential problem here is more subtle. Very small currents and voltages in the TC wiring loop. If the end contacts ground, some electrons flow back to the instrument (since it is grounded in some fashion) in a way not anticipated, and disrupt the measurement.

[Wildcat]

Thanks.  I think I understand that.  Unless there is a break in this new wire, I do not think that is the problem since the end was not touching anything.

[pensrock]

Wildcat,
  If you get an actual break in the t/c wire it should read as high as the instrument will read, sometimes just a series of bars will be on the screen. If a t/c is shorted, both wires touching one another, it should read about ambient temperature. Arcs did not mean that one of the wires was actually broken but if the + side of the extention wire or t/c is rubbed through and touching a ground or some other odd thing, it can cause weird things to happen. You have a new t/c and if I read right it is an ungrounded t/c, so I doubt it is the problem. But it could have something else to do with how the PID, smoker or where you plug it in is grounded. The millivolt signal that is produced by a thermocouple is very small and can be influenced by any number of things.

Arcs,
  Beverage.... beverage... beverage...
   Now that I got your attention, is there a place on the Auber instrument to ground it? From looking at the wiring diagram on olds site I did not see a ground run to the instrument. All the temperature controllers we use require a separate ground run to the instrument.
   I'm also wondering if he has a good ground from his receptacle. My last bit of thinking for the day is.... he may want to run a ground wire to the negative side of the thermocouple at the instrument, I do not know if it would help but it should not hurt to try.
   This is an odd problem to try to figure out without being there to look at things for yourself. Now its time for me to partake in a beverage.
pensrock

[Wildcat]

Thanks for all the info pensrock.  I think the house wiring is fine.  The PID is plugged into a GFI plug.  The BS runs off of the PID.  Iceman built the PID for me.  The PID is reflecting that it is maintaining the set temp within a couple of degrees so it appears to be working fine.

I just ordered the MTC along with a 113-159 probe and 113-041 from ThermoWorks.  Once it gets here and I get the time and adequate weather to do another smoke (hopefully next week) I will do a cold and hot test on it and then I should be able to figure out if it is the Maverick that is acting up or the PID/BS.

[Arcs_n_Sparks]

Arcs,
  Beverage.... beverage... beverage...
   Now that I got your attention, is there a place on the Auber instrument to ground it?

Don't have the Auber, so cannot answer. I do, however, have a beverage...   :D

[Wildcat]

Finally got the MTC today.  Did a cold and hot test on it myself.  Off by 0.6F.  This jewel should work fine.  Leaving town for about a week in the RV this weekend so I may not be able to get a smoke in before we go to determine where the problem lies.

[Wildcat]

Finally got around to another smoke (brisket).  Started at 7:30 this morning, it is now 2:25 here locally in Central Time Zone.

It is NOT the Maverick that has been acting up.  I started with the Pb setting on the PID at -10.  After about an hour I had to reset to -18 to match the MT and the Maverick, which were within 1 degree of each other.  I had to do this about every hour or two all day.  At one point is was set at -4.  It is now at -10.

Each time I did this, I found that the PID would cause temp to fluctuate -3 degrees to at + 10 degrees above the 200 set temp.  13 degrees.  I tried doing auto tunes and they sometimes worked.  I also simply unplugged from power and re-plugged.  This would normally fluctuate 3 degrees either side of set temp (6 degrees).  It appears that the PID cannot maintain the variance setting of the Pb.

Any thoughts?

[Mr Walleye]

 ???  ???  ???

That's got me puzzled WildCat! I'm going to have to think about this... I'll let you know if I come up with any thoughts on it.

Mike

[Wildcat]

Another point to ponder.  Could un-plugging the tc from the PID to check with MT and then re-connecting be part of the cause of temp variance?

[Mr Walleye]

Another point to ponder.  Could un-plugging the tc from the PID to check with MT and then re-connecting be part of the cause of temp variance?

I don't really think so unless you were running auto tune at that point but you never know. Did you re-check all your settings after?

So I'm assuming you unplugged the TC off the PID, then plugged it into the MTC? If so, how did these readings compare? (assuming you didn't move the TC location inside the cabinet for this test)

Mike

[Wildcat]

Did not move location.  The tc and Maverick are in the same place.  Yes, I did unplugged the tc from the PID to check with the MT.  I did not do this during auto tune, and I only did so while temp was relatively stable.