to relate to the OP it is my question as to what are the drawbacks to me eliminating a RIMS tube and placing a RTD and heating element in my MLT? Obviously use a pump to recirculate and a PID controller to maintain correct temperatures.
An element directly in the mash will likely scorch the grain and give you some bad flavors.
In a RIMS set up I have concerns that the temperature of the mash in the MLT may not be accurate due to the fact that the RTD is located in the RIMS tube. Wouldn't it make more sense to put the RTD in the MLT?
RIMS (or HERMS with probe at output of the coil) are monitoring and maintaining the temp of the wort that is going back into the top of your MLT. If you keep that return at your set temp, and you keep circulating, the whole of the mash will be at the set temp with some minor variation.
When I first built my HERMS, I wanted to see how accurate things were, so I put two thermometers in the MLT. One was a digital probe in a thermowell near the top of the grain bed. The other was a glass thermometer that I put directly into the mash and pushed it down so that the tip was sitting on the false bottom in the MLT.
And, of course, there was also the temp readout from the probe at the return to the MLT as a third reference.
During my mash, I checked all three thermometers every 10 minutes or so to see how things looked.
The largest difference I ever saw between the three thermometers was 1*F. That satisfied my curiosity about whether my probe location was getting the job done.
In general, you want the probe near, but AFTER, the heat source so that you don't overshoot. For RIMS, this is the RIMS heater output. For HERMS, this is either the HERMS coil output or directly in the MLT.
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