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Entry  Sun Jan 14 16:52:53 2018, Craig, DailyProgress, TempCtrl, High Current Draw for Vaccan Temp Control Causing Nonlinear Voltage Spikes 20180114_CTNLab_TempControlSpikes_6hours.png
    Reply  Sun Jan 14 20:40:26 2018, awade, DailyProgress, TempCtrl, High Current Draw for Vaccan Temp Control Causing Nonlinear Voltage Spikes 
       Reply  Mon Jan 15 21:35:14 2018, Craig, DailyProgress, TempCtrl, High Current Draw for Vaccan Temp Control Causing Nonlinear Voltage Spikes 
          Reply  Tue Jan 16 10:57:50 2018, Craig, DailyProgress, TempCtrl, High Current Draw for Vaccan Temp Control Causing Nonlinear Voltage Spikes 20180116_OvernightVaccanReheat.png
             Reply  Tue Jan 16 19:10:29 2018, awade, Craig, DailyProgress, TempCtrl, Debugging vac can heater circuit: heat, oscillations, leaking current. 20180115_HeaterCircuit.pdf2018-01-16_19.08.57.jpg
                Reply  Wed Jan 17 23:40:15 2018, awade, Craig, DailyProgress, TempCtrl, Debugging vac can heater circuit issues: oscillations everywhere 2018-01-17_21.20.58.jpg
                   Reply  Mon Jan 22 20:30:11 2018, Craig, awade, DailyProgress, TempCtrl, Debugging vac can heater circuit issues: oscillations everywhere CTN-Lab-Heater-Circuit.pdf
                      Reply  Tue Aug 20 11:19:35 2019, anchal, DailyProgress, TempCtrl, Vac Can Heater Circuit repaired CircuitCloseup.jpgBoxOverview.jpg
                         Reply  Wed Aug 21 16:17:47 2019, anchal, DailyProgress, TempCtrl, Leave the Heater Circuit Alone! 
          Reply  Tue Feb 27 14:17:13 2018, Aaron, DailyProgress, TempCtrl, High Current Draw for Vaccan Temp Control Causing Nonlinear Voltage Spikes 
             Reply  Wed Feb 28 10:20:40 2018, awade, DailyProgress, TempCtrl, Heater and temperaure sensors in cryo lab GroundingDoGroundingDont.jpg
Message ID: 2109     Entry time: Wed Feb 28 10:20:40 2018     In reply to: 2108
Author: awade 
Type: DailyProgress 
Category: TempCtrl 
Subject: Heater and temperaure sensors in cryo lab 

You should check a few things.  Get a 200-300 MHz oscilloscope with a probe and look to see if the circuit has any oscillations.  This should be your first reaction to many problems: looking a little wider than the audio band can often reveal important problems that people miss. We found that the heating elements had some unexpected impedance that made our feed back unstable to the MOSFET at very high frequencies.  The solution there is to put some capacitors over the heater to dampen and maybe in some other places too. We found that very high frequency oscillations actually coupled back to the temperature sensing circuit.  You may want to check to see if you can see any pickup in your temperature sensing here circuit too.

Another thing.  From what I remember of your circuit you are transmitting the signal referenced to a common ground (rather than floated differential signal).  If you're heater is loading up a bunch of current at the table end of a common ground this will generates a potential drop between the power supply/rack and the 0 volt reference of the circuit at the table (see Ohm's law). There is a good table on the American wire gauge wiki page that gives standard resistance for different gauge wires, you can calculated expected potential difference generated by your heater circuit current from this.  Check you grounding situation.  Are you pinning one ADC pin to ground on the Acromag (maybe you shouldn't)? Are you using appropriately chunky wire to establish ground at the table? Are you committing the cardinal sin of having two or more separate paths to ground from the table? Take some time early in your experiment to ensure your grounding network is topologically like a tree rather than a fungal Mycorrhizal network. See attached figure for reference.

A source of wisdom on grounding that rana recommends is Morrison, R. (1998), Grounding and shielding techniques (4th edition), New York: Wiley (link). Craig and I have borrowed out two of the copies, any edition will do so maybe get one that is physically on the shelf or, even better, there is an electronic copy.

 

 

 

Quote:

I think I'm seeing a similar problem that y'all were when I use my heater circuit (which is I believe the same as your heater circuit, it's the one Kira and Kevin are using at the 40m). Our temperature readout circuits might be slightly different.

Basically when I have the heater on the board as my readout op amps, I get up to a few tenths of a volt jump in my temperature readout; however, even after moving this circuit to a different board and using a separate power supply, I'm getting about a millivolt shift. This is not good for <1K control. I'm also well within the limits of my power supplies, have voltage regulatorsbefore the OP amps, etc... I will try swapping out the OP amp as you did, but thought it was a pretty weird problem.

 

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