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[TK]

I have 7 SYL-2352 in my brewbox.  Some of the controllers will rapidly cycle thru 3 temperatures (example: 50F, 48F, 54F, repeat) over a second or two.  I have done a LOT of debugging, here are my observations so far:

1) A wet RTD, installed in a metal brew kettle is MOST likely to experience the problem.
2) A wet RTD dangled into a metal brew kettle (i.e no metal contact) is less likely to experience the problem
3) A dry RTD, dangled in air (i.e. no metal contact) is never a problem, this tells me the RTD and Cable are OK.
4)  HOWEVER, moving RTD and cable between controllers can make the problem more/less likely in scenarios 1 & 2.
               Example:  CableA/ControllerA-OK     CableB/ControllerB-OK
                                CableA/Controller B-OK    CableB/ControllerA-Faulty

I have a sensor similar to PT100S and this is most susceptible sensor of them all.  Touch it to liquid in the brew kettle or insert it into a thermowell and it immediately goes faulty.  There is no shielding on this style sensor- a clue.  2nd clue, I put heat shrink over the exposed metal, viola - no problem in the thermowell (i.e the sensor is electrically isolated from the pot)

I am an electrical engineer and know just enough to be dangerous.  This sure smells like a grounding problem. 

The XLR and 3pin RTD (I believe) have 4th connection specifically for ground.  It does not seem that the braided shield is connected on EITHER end.  While this is better than nothing:
       connected on one end would a) improve shielding
       connected on both ends would a) Improve shielding  b)establish a ground between the two devices and remove a possible ground loop.

I am about to dive into another round of experiments.  Before I do, I would like to get Auber's expert opinion on this.  Am I barking up the right tree??   Suggestions??

[Kkane]

It looks like your controller is picking up EMI or RF noise from your sensor, which may cause your reading issue. The simple solution you can try is to enable the digital filter in your controller. You can change FILT parameter to 5 or 6 and see if any better. 
If you like to do some troubleshooting, please make sure your probe is inside of the water. The response time in water is much faster than the air.

Since your probe is installed on your kettle, please make sure your kettle is properly grounded.

Yes, XLR connector has a separate pin for grounding purpose. You can make a modification and connect the braiding of your cable to the grounding pin in XLR connector and see if it helps. 3-pin RTD doesn't have it. If you still like to ground its braiding, you may change your connector to 4-pin RTD, then use the 4th pin as grounding.

[TK]

I assume the fastest and most robust test is to connect my brew box 240v supply ground (ie chassis ground) to the pot(s) via a jumper cable  (think automotive battery jumper cable).

[Kkane]

I don't know why you want to connect your brew box ground to your pot together. But you need to ground your control box and ground your pot properly.

Again, use FILT will most likely fix your issue.

[TK]

Increasing FILT does appear to have fixed the issue.  THANK YOU