Originally Posted by acidrain
Did you guys mean at the return port? That is the generally accepted place to put it.
You are recirculating from the kettle output to a port through the lid of the kettle, correct? That is what I mean by "kettle output." As I said, it probably won't make much of a difference either way, and it would be easy enough to move the tee if you want to change it over. Check temps at both places with a handheld thermometer, check various locations in the mash, and see which probe location best represents the mash temp.
With the heating element low in the kettle, the temp at the kettle output should read higher than that at the lid, because of heat loss through the tubing. You can insulate the tubing to reduce the heat loss. That said, heat in the kettle rises, so the top of the mash will likely also be hotter than at the return through the lid. If you can recirculate fast enough (this depends upon how fast the bag will drain and can be impeded by the basket), the temps should be fairly uniform throughout.
Once you find the probe location most representative of the mash temp, you can always adjust your setpoint a bit to compensate if you must.